The authors would like to thank Michael Pankey, Chris Butler, and the WVSOM staff for their assistance in the animal care and data collection.

All procedures described in the present study followed the Guide for the Care and Use of Laboratory Animals, 8th Edition. The experimental design was approved by the Office of Research and Sponsored Programs (ORSP) under the Institutional Animal Care and Use Committee (IACUC) 2019-5 at the West Virginia School of Osteopathic Medicine. Refer to the Table of Materials and Table 1 for additional details about all the materials used in this protocol. A general outline of the protocol timeline is displayed in Figure 1.
1. Experimental design
<ol>
	<li>Use 40 female, 21 day old Sprague-Dawley rats from a commercial source (see Table of Materials).</li>
	<li>Use proper protective equipment when handling the animals in accordance with the IACUC guidelines. These safety measures include, but are not limited to, wearing single-use sterile gloves, a lab coat, shoe covers, etc.</li>
	<li>Weigh each animal, and calculate the mean and standard error of the mean to ensure that the groups do not differ in weight. If the groups differ, match the groups for body weight by redistributing the heavier individuals into the lighter groups and the lighter individuals into the heavier groups.</li>
	<li>Randomly divide the animals into four groups: control (CON, n = 10), control diet/exercise-trained (TRN, n = 10), high-fat diet/control (HFD, n = 10), and high-fat diet/exercise-trained (HFD/TRN, n = 10).</li>
	<li>House the rats in individual cages (one animal per cage) in a controlled environment (12 h light/dark cycles, 21 &#176;C &#177; 2 &#176;C, 60% &#177; 10% humidity), and wean all the rats to a control diet of commercially bought laboratory chow (see Table of Materials) for a 1 week acclimatization period. Supply each cage with enrichment devices (shelter, gnawables, and nesting material). 
	NOTE: The CON diet consists of commercially bought laboratory chow (see Table of Materials and Table 1 for additional details) with 10% kcal from fat (3.82 kcal/g).</li>
	<li>Allow for ad libitum access to food and water throughout the experiment.</li>
	<li>Following the 1 week acclimatization period, begin the 8 week diet period by supplying the HFD and HFD/TRN groups with HFD chow. The HFD chow (see Table of Materials and Table 1 for additional details) consists of 45% kcal from fat (4.7 kcal/g), representing the macronutrient breakdown found in a typical Western diet. Ensure all animals continue to have ad libitum access to food and water.
	<ol>
		<li>At the beginning of each week, weigh out and record the mass of chow given to each animal. Use 140 g of chow to feed each animal for a full week.</li>
		<li>To weigh the chow, place a weigh boat on a precision electronic digital scale (see Table of Materials), and tare the scale by pressing the &#34;tare&#34; button. Place 140 g of chow in the weigh boat, and record the weight (g) from the scale. This is the &#34;before&#34; weight.</li>
		<li>Place the chow into the feed trough in each individual animal&#39;s housing cage.</li>
		<li>If an animal starts to run low on chow, weigh an additional allotment (20 g for each remaining day), and add that chow to the food tray. Record how much additional chow is given to each animal. Weight may need to be added on top of the food in the hopper to allow greater ease of consumption if the animals are struggling to consume the pellets (as evidenced by rounded pellets in the hopper).</li>
	</ol>
	</li>
	<li>At the end of each week, weigh the remaining chow for each animal. Every animal should have leftover chow to ensure they were able to eat ad libitum. Using the same scale, record the food remaining. This is the &#34;after&#34; weight.</li>
	<li>Subtract the &#34;after&#34; weight from the &#34;before weight&#34; for each individual animal to record the food intake (g) per week.</li>
	<li>Following the 8 weeks diet induction period, begin the HIIT training protocol for rats in TRN and HFD/TRN. This consists of an 8 week HIIT regimen with training sessions every week on Monday, Tuesday, Thursday, and Friday (see &#34;HIIT Training Protocol&#34; below) between 08:00 A.M. and 10:00 A.M. Ensure all animals have ad libitum access to their assigned experimental diets throughout the protocol. 
	NOTE: There is no standardization of the protocol between the groups, as this protocol is designed to maximize the performance of each cohort, and each cohort may differ (due to phenotypes induced by diet).</li>
	<li>Euthanize the rats 48 h after their last exercise session via vital tissue harvest following anesthesia induction using inhaled isoflurane (5%).
	<ol>
		<li>Begin by making sure there is adequate oxygen and isoflurane in the system to induce anesthesia. Open the oxygen tank by turning the main valve (typically on top of the tank) counterclockwise. There may or may not be a regulator valve that needs to be opened on the oxygen tank as well, depending on the size of the oxygen tank. Additionally, check that the exhaust tubing is properly secured and that the collection canister is not overweight.</li>
		<li>Weigh the canister before use, and note the date and weight on the side of the canister. Check to make sure the stopcock is open to the induction chamber and the stopcock to the nose cone is closed.</li>
		<li>To induce anesthesia, place the animal in the induction chamber, and seal the chamber by securing the lock devices. Set the isoflurane to 5% by depressing the safety lock and turning the dial counterclockwise.</li>
		<li>Next, turn the dial at the base of the oxygen flowmeter counterclockwise until the meter reads between 1.5-2 L/min.</li>
		<li>After 1-2 min, when the animal is no longer conscious, turn off the isoflurane by rotating the dial clockwise while depressing the safety lock. Flush the induction chamber with oxygen by pressing the oxygen release valve for 3-5 s. Unlock the induction chamber, and remove the unconscious animal.</li>
		<li>Place the unconscious animal on its back, and secure a nose cone to deliver further anesthesia. Open the stopcock for facemask delivery, and close the stopcock for the induction chamber. Deliver 5% isoflurane with 100% oxygen for anesthesia via the facemask until pedal reflexes are absent.
		<ol>
			<li>Check the pedal reflexes by applying a pinching pressure to the toes of the anesthetized animal and looking for a reflex response.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Sacrifice the animal according to IACUC-approved methods (which may vary by study), and carefully dissect out the target tissues for measurement and further analysis (subcutaneous adipose tissue, perirenal adipose tissue, skeletal muscle, liver, gonads, and heart). Depending on the IACUC protocols, euthanasia can be completed by decapitation with a guillotine or by vital tissue (heart) harvest.
	<ol>
		<li>To collect the heart, make an incision below the ribs and through the diaphragm.
		<ol>
			<li>Locate the heart, and cut the vasculature (aorta, vena cava, pulmonary artery, pulmonary vein) with surgical scissors. Grab the heart with forceps, and cut any connective tissue to release the heart. Working quickly, rinse the heart with saline solution, dab off the excess fluid with gauze, and record the weight. If needed, separate the left ventricle, right ventricle, and septum with surgical scissors, and weigh them individually.</li>
			<li>Place the heart tissue samples in a cryovial, and flash-freeze in liquid nitrogen.</li>
		</ol>
		</li>
		<li>Next, make a longitudinal incision down the abdomen with a scalpel and two lateral incisions from the umbilical region to the lateral side of the animal to allow for access to the abdominal organs.
		<ol>
			<li>Using forceps and surgical scissors, remove any organs of interest. 
			NOTE: For this study, the liver, visceral (abdominal) adipose tissue, pancreas, and gastrocnemius were collected. The abdominal adipose tissue was removed in one or two large sections by gently trimming the connective tissue around the organs and body cavity wall. The subcutaneous fat was not collected, similar to previous methods22.</li>
			<li>For the organs, after removal, place them in a clean weigh boat on a tared scale. Record the weight (g), and place the samples in cryovials for flash-freezing.</li>
		</ol>
		</li>
		<li>For the gastrocnemius, make two incisions down the lateral sides of the lower leg and one horizontally across the Achilles tendon.
		<ol>
			<li>Cut or tear the connective tissue connecting the skin to the musculature to expose the gastrocnemius. Cut the Achilles tendon with surgical scissors as close to the muscle as possible, and grab the gastrocnemius with forceps.</li>
			<li>Follow the gastrocnemius to the upper connection point, and make a similar cut to free the muscle.</li>
			<li>Weigh the sample on a clean, tared weigh boat, place in a cryovial, and flash-freeze in liquid nitrogen.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Immediately place any other collected tissue samples in cryovials, flash-freeze in liquid nitrogen, and store at &#8722;80 &#176;C. These tissues can be saved for future laboratory analyses such as PCR, western blot, or other methods according to the research goals.</li>
</ol>
2. HIIT training protocol
<ol>
	<li>To begin a training session, turn on the treadmill (see Table of Materials) by flipping the power switch on the back of the control unit.</li>
	<li>Adjust the treadmill shock to 0.00 mA by turning the dial on the control unit counterclockwise until the monitor reads 0.00 mA.</li>
	<li>Set the inclination of the treadmill to 5.0% by loosening the locking nut on the bottom of the treadmill and setting the incline to the first notch. Retighten the locking nut to secure the treadmill incline in this position.</li>
	<li>Supporting the animal&#8217;s body with one hand, gently grasp the base of the tail with the other hand and&#160;place the animal&#160;in an individual lane on the treadmill.</li>
	<li>Repeat the process until all five individual lanes on the treadmill are occupied by a rat from the same cohort.</li>
	<li>Adjust the treadmill speed to 45&#160;cm/s by rotating the speed dial clockwise until the monitor reads 45&#160;cm/s. Press the Stop/Run button to start the treadmill, and allow it to run for 5 min. Press the Stop/Run button again to stop the treadmill after 5 min. No electric shock is used during this time. 
	NOTE: The animals may need encouragement with stiff bristle brushes to stay off the shock grid during the earlier stages of the protocol to facilitate their learning of how to use the treadmill.</li>
	<li>At the end of the 5 min, allow a 2 min rest before beginning the training period. Turn the dial on the control unit clockwise until the monitor reads the corresponding starting velocity of the training bout. Use an initial running speed for the first session of 55 cm/s. For the first sprint of each new training day, use a starting speed that is 4 cm/s slower than the highest speed achieved the prior day.
	<ol>
		<li>Start the treadmill by pressing the Start button, have the animals run until the monitor reads 1:00 (1 min), and then stop the treadmill by pressing the Stop/Run button again.</li>
		<li>Agitate the animals with brushes to encourage forward motion if the animal reaches the shock grid (located at the rear of the treadmill). If any animal per training group fails to respond to the brushes more than twice per training bout, turn on the shock grid to 2.0 mA for the remainder of the session.</li>
	</ol>
	</li>
	<li>After the sprint, let the animals rest for 2 min. At the end of the 2 min rest, begin the next sprint by starting the treadmill by pressing the Stop/Run button on the control unit. The details regarding the treadmill speed are defined below.
	<ol>
		<li>Increase the speed by 4 cm/s for the following sprint interval from the previous speed used if all the five animals within a cohort complete the sprint interval without needing motivation (encouragement with a stiff bristle brush or touching the shock grid more than five times) for a full 1 min sprint interval. The speed is increased by turning the speed knob on the control unit clockwise.</li>
		<li>Use the same interval speed as the previous sprint interval if the brushes are used to encourage running or if any animal touches the shock grid more than five times in a single 1 min sprint.</li>
		<li>Reduce the speed for the following interval by 4 cm/s if an animal struggles excessively during a sprint interval (more than 20 s of accumulated time on the shock grid). 
		NOTE: In our experience, 100% of the animals were able to complete the required running. Nevertheless, animals may need to be removed from the study at the investigator&#8217;s discretion if they demonstrate an unwillingness to run or experience excessive shocks.</li>
		<li>Record the speed and distance run for each bout.</li>
	</ol>
	</li>
	<li>Repeat the process for a total of 10 HIIT training bouts each training day. Each training bout consists of 1 min of high-intensity running followed by 2 min of rest.</li>
	<li>At the end of the training session, remove each animal from the treadmill, and place it in its individual cage.</li>
	<li>For every new day of training, the initial running speed for the first bout begins at 4 cm/s slower than the fastest speed obtained in the prior day&#39;s workout, with a minimum speed of 55 cm/s.</li>
</ol>
3. Statistical analysis
<ol>
	<li>Report the morphometrics and other outcome measures as means and standard errors.</li>
	<li>Determine the differences between the groups in an analysis software (see Table of Materials) using a mixed-effects model allowing for multiple comparisons. 
	NOTE: &#352;id&#225;k correction was implemented to account for multiple comparisons. A repeated-measures model was implemented when appropriate. Significant differences were determined by p &#60; 0.05.</li>
</ol>

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The authors declare that there are no conflicts of interest regarding the publication of this paper.

This protocol provides an effective method for examining the effects of HIIT on several health markers in a diet-induced obesity model. The procedure draws from previous studies to allow for a more time-efficient method of examining multiple outcome variables, such as exercise training variables, appetite regulation markers, and invasive analyses of body composition3,7,8,18,23,24. The diet content, duration, and exercise intervention protocol were consistent with prior publications23,24. In this study, commercially available laboratory chow was purchased (see Table of Materials). The laboratory chow for the high-fat and control diets contained the same amount of protein and micronutrients. The carbohydrate and fat content of the diets were modified to provide a safe method of inducing obesity in the experimental group (see Table 1).
The 8 week obesity induction period used in the present study was modeled based on previous research showing significant changes in weight following the provision of commercial laboratory chow consisting of 45% kcal from fat (4.7 kcal/g), which represents the macronutrient breakdown found in the typical western diet23. Additionally, prior studies have demonstrated the effectiveness of an 8 week HIIT protocol on influencing food intake7,8, adipose profiles18,23, and muscle gain18.&#160;The results of the protocol described in this study were consistent with previous studies reporting that HIIT impacts appetite regulation, as well as compositional changes in adiposity and muscle mass.
A benefit of this protocol is that it maximizes the intensity of the exercise training in the animals and maintains maximum effort throughout the protocol. As the animals continuously learn how to use the treadmill proficiently and make fitness gains, the speed of the treadmill is increased accordingly relative to their performance. Furthermore, the use of the 5.0% inclination allows for the animals to reach maximum intensity in each session and throughout the protocol more quickly than would be accomplished without using inclination. As a result, the exercise performance is maximized for each workout and for the duration of the protocol.
During the study, one animal was unable to complete the experimental protocol due to illness, resulting in n = 39 animals completing the study, with only n = 9 rats in the HFD cohort. This protocol was initially designed to assess changes in cytokine profiles in response to exercise and diet, and the power analysis resulted greater than 90% power to identify a difference (p &#60; 0.05) in the primary target cytokine (irisin). Future studies using this model should rely on unique power analyses to determine appropriate sample sizes.
This study was primarily designed to examine the physiologic outcomes of HIIT in a rodent model of diet-induced obesity and to maximize the intensity of exercise. This protocol was able to demonstrate variation in ADG and adiposity in response to diet and HIIT (Figure 6 and Figure 7). Future studies could specifically identify endocrine, myokine, and adipokine responses to HIIT. The elucidation of these mechanisms may prove beneficial in the treatment and prevention of obesity and its comorbidities.
This study also demonstrated the impact of diet and HIIT on feed intake. The results indicated that when the animals consumed a high-fat diet, the trained animals consumed more calories than the non-trained animals. In contrast, when the animals ate the control diet, the trained animals consumed less calories than the non-trained animals, demonstrating different appetite regulation responses depending on the composition of the diet. Therefore, strategies for weight loss that utilize HIIT may be less effective for those that simultaneously consume a high-fat diet, as they may be more likely to consume excess calories. In contrast, balanced macronutrient intake during HIIT may promote low calorie intake and, therefore, facilitate weight loss. This model can facilitate research efforts to develop a deeper understanding of the mechanisms behind energy balance and efforts to develop effective weight loss strategies.
Finally, this protocol demonstrated variation in cardiac tissue among the cohorts, reflecting adaptational changes in the body composition in response to diet and exercise training. These data suggest that obesity induction followed by HIIT may predispose individuals to myocardial hypertrophy without any accompanied alterations in hepatic size. Future analyses to determine the mechanisms behind these findings could be useful for investigating myocardial hypertrophy and the metabolic connections between obesity, HIIT, and cardiovascular disease.
The protocol described in this study has several limitations. First, the treadmill used in this study had five lanes, which allowed for five rats to be run at a single time. While this manner of executing the protocol was efficient, it was difficult for a single researcher to attend to each of the animals at once. There were occasions when it was difficult for the treadmill attendant to divide their attention among the multiple animals needing stimulation with bristle brushes. In the future, ensuring that more research personnel are available to assist with the training protocols will be a priority. Additionally, the five-lane treadmill model does not have the capability to measure gas exchange, and, therefore, the aerobic/anaerobic metabolism of the animals during the protocol could not be assessed. The company that provided the rodent treadmill (see Table of Materials) does offer a treadmill with the capability to measure gas exchange, but it is a single-lane treadmill and, therefore, would require significantly greater time and effort. That effort may be worthwhile, however, for investigators who need to measure or control for specific outcomes of indirect calorimetry. Additionally, there is very little evidence available regarding how the shock grid may impact exercise performance, which should be considered when interpreting the results from this model. Lastly, the exercise protocol described in this study was designed with young female Sprague-Dawley rats. Previous studies have shown sexually dimorphic effects, especially regarding HIIT and appetite regulation3,7.&#160;Although similar outcomes are anticipated, this protocol did not test animals of different species, ages, sexes, or health outcomes.
In comparison to prior models, this protocol demonstrates a more time-efficient method to evaluate a range of outcome variables. For instance, this protocol was able to identify interactions between HIIT and appetite regulation in a protocol that involved four training sessions per week for 8 weeks, in comparison to prior studies that involved five training sessions per week for 8 weeks24 or even 12 weeks of training8.&#160;Additionally, this study design allowed for the analysis of a variety of health markers, such as exercise data, markers of appetite regulation, and body composition. These markers, as well as the heart adaptations to exercise training, represent promising means of evaluating the training adaptations of the cardiovascular system as well. Measures of endothelial function, muscle fiber type composition, and cardiac myocyte hypertrophy could easily be added to further the understanding of these exercise-induced adaptations. Further, this protocol included performance-based escalations in intensity. This design allowed for the maximization of the training outcomes and ensured that the rats did not adapt to the exercise environment and approach a moderate-intensity continuous training model toward the end of the intervention. This is demonstrated in Figure 2; specifically, the sprint speeds of these animals were more than double the speeds achieved in previous publications, which went on to demonstrate many cardiovascular, skeletal muscle, and thermoregulatory adaptations consistent with HIIT interventions25.

Obesity and comorbid conditions, such as cardiovascular diseases, metabolic diseases, and cancer, continue to be some of the most serious, costly, and preventable of all health outcomes. Currently, over one-third of adults in the United States and more than 1.6 billion adults worldwide are classified as obese according to their body mass index (BMI; defined as weight in kilograms divided by the square of height in meters)1.&#160;Obesity as a disease results from a genetic predisposition, environmental exposures, and a breakdown in the normal mechanisms regulating energy intake and energy expenditure2. As the human and financial costs of the obesity epidemic continue to rise, there has been an intensified focus on trying to understand the mechanisms involved in energy balance and the effects of diet and exercise in combating metabolic disease.
Previous studies have demonstrated that exposure to highly palatable, energy-dense diets stimulates overeating in rat models3.&#160;Ad libitum access to highly palatable diets drives excessive weight gain as a result of increased caloric intake4. Studies have also shown that exercise can modulate appetite and improve the sensitivity of satiety signaling in obese individuals5. It is theorized that this recovery of the sensitivity of satiety signaling with exercise is partially mediated through the impact of exercise training on the reactivity of the central and peripheral tissues to leptin, a key adipocyte-derived regulatory hormone that suppresses appetite and stimulates energy expenditure5. While these studies have investigated a variety of exercise protocols, there is no clear consensus on which intervention is superior6,7. There is some evidence to suggest that high-intensity interval training (HIIT), which involves repeated bursts of strenuous exercise interwoven with intervals of recovery, may improve appetite regulation more than other forms of exercise, such as moderate-intensity continuous exercise training (MICT), vigorous-intensity continuous training, or voluntary physical activity8. However, there are gaps in knowledge surrounding the intersectionality of high-intensity interval training, diet, and appetite regulation.
Previous studies have also demonstrated that exercise is a powerful mediator of inactivity-related comorbidities, particularly from the perspective of alterations in muscle and adipose tissue9,10,11. It is hypothesized that these compositional changes lead to the promotion of an anti-inflammatory state that may be responsible for the amelioration of disease risk seen with exercise12. Myokines, which are cytokines, other small proteins, and proteoglycan peptides released from skeletal muscle during muscular contractions have been posited as moderating the anti-inflammatory outcomes associated with physical activity. In contrast, adipokines, cell-signaling molecules produced by adipose tissue, have been shown to primarily play a more deleterious role and contribute to the promotion of an inflammatory state13,14,15,16.&#160;While there is significant evidence demonstrating that the compositional alterations seen with MICT promote positive health outcomes, less work has been done to evaluate the potential benefits of HIIT17,18.
Finally, cardiovascular disease is well-established as the leading cause of morbidity in humans and is highly correlated with obesity, diet, and physical activity1.&#160;This protocol provides an efficient way in which to train rodents for the evaluation of the effects of cardiovascular training on numerous systems. In particular, cardiac hypertrophy is a marked adaptation that occurs with cardiovascular exercise. This hypertrophy allows for more robust cardiac contractions and delivery of blood and oxygen to the exercising tissues. Previous research suggests that high-intensity exercise is more likely to induce cardiac hypertrophy than moderate-intensity exercise19.
This protocol helps fill the gaps in the literature by providing an approach for examining the effects of HIIT on appetite regulation, compositional changes (thus, myokine and adipokine changes), and cardiovascular adaptations in a murine model of diet-induced obesity. Further, the performance-based increases in intensity maximize the training outcomes and ensure that animals are not adapting to the exercise training and approaching a moderate intensity later in the training protocol.
The overall goal of this method is to maximize the exercise effort and identify phenotypic changes in Sprague-Dawley rats in response to HIIT, diet-induced obesity, and the interaction of these stimuli. This protocol is unique compared to other techniques due to its ability to maximize the effort throughout the training period, even with increases in the skill and fitness levels of the rats. It also allows for the simultaneous analysis of exercise and obesity, rather than solely focusing on one or the other. Specifically, this study intended to test the following hypotheses. (1) Exercise speeds may increase throughout the training, and the distance covered by rats in the TRN group may be larger than in the HFD/TRN group20. (2) The average weekly caloric intake of the trained rats may be greater than controls, and this may be evident within each diet cohort21. (3) The average daily gain in mass may be greater in control rats than exercised rats, and control rats may have higher fat mass at sacrifice21. (4) The mass of the heart and liver may be larger in the HFD/TRN rats versus the TRN rats19.

<table><tbody><tr><td>Commercial laboratory chow for control diet</td><td>Research Diets Inc., New Brunswick, NJ</td><td>D12450H</td><td></td></tr><tr><td>Commercial laboratory chow for high-fat diet</td><td>Research Diets Inc., New Brunswick, NJ</td><td>D12451</td><td></td></tr><tr><td>GraphPad Prism software</td><td>GraphPad Software Inc., San Diego, CA</td><td></td><td></td></tr><tr><td>Precision Electronic Digital Scale</td><td>Ohaus Corporation, Pine Brook, NJ</td><td>V11P30</td><td></td></tr><tr><td>Rodent treadmill</td><td>Panlab, Barcelona, Spain</td><td></td><td></td></tr><tr><td>Sprague Dawley rats</td><td>Charles River, Durham, NC</td><td></td><td></td></tr><tr><td>Table top anesthesia machine</td><td>VetEquip Inc., Livermore, CA</td><td>V0557</td><td></td></tr></tbody></table>

a chronic high-intensity interval training and diet-induced obesity model to maximize exercise effort and induce physiologic changes in rats

Compared to continuous-moderate or low-intensity training, high-intensity interval training (HIIT) is a more time-efficient alternative method that results in similar physiologic benefits. This paper presents a HIIT protocol that can be used to assess various health markers in a Sprague-Dawley rat model of diet-induced obesity. Female Sprague Dawley rats aged 21 days old were randomly assigned to the following groups: control (CON, n = 10), exercise-trained (TRN, n = 10), high-fat diet (HFD, n = 10), and high-fat diet/exercise training (HFD/TRN, n = 10). The control diets consisted of commercial laboratory chow with 10% kilocalories (kcal) from fat (3.82 kcal/g), and the high-fat diets (HFD) consisted of 45% kcal from fat (4.7 kcal/g). The animals had ad libitum access to their assigned diet throughout the study. After an 8 week diet induction period, the exercise cohorts completed four HIIT sessions per week for 8 weeks. Each HIIT session consisted of 10 intervals of 1 min sprints/2 min rest using a rodent treadmill with a motor-driven belt. After the 8 weeks of training, the animals were sacrificed for tissue collection. The results revealed no differences in the distance run between the TRN and HFD/TRN groups, and the training speed steadily increased over the duration of the study, with a final running speed of 115 cm/s and 111 cm/s for the TRN and HFD/TRN groups, respectively. The weekly caloric intake was decreased (p &#60; 0.05) in the TRN group relative to the CON group but increased (p &#60; 0.05) in the HFD/TRN group relative to the HFD group. Lastly, the animals on the HFD had greater (p &#60; 0.05) adiposity, and the trained animals had reduced (p &#60; 0.05) adiposity relative to controls. This protocol demonstrates an efficient method to evaluate the effects of HIIT on various physiologic outcomes in a diet-induced obesity model.

Figure 2 demonstrates that the training performance increased over the duration of the protocol. The final running speeds of the TRN and HFD/TRN groups were 115 cm/s and 111 cm/s respectively. The total running distance did not differ between differ between the TRN and HFD/TRN groups (Figure 3).
The average weekly feed intake for the animals on the control diet was higher (p &#60; 0.0001) than for those on the high-fat diet (103 g/week &#177; 1.0 g/week vs. 91 g/week &#177; 1.0 g/week, respectively). The average weekly feed intake was also greater (p &#60; 0.001) in trained groups than the non-trained groups (98 g/week &#177; 1.3 g/week vs. 92.2 g/week &#177; 1.0 g/week, respectively). When looking at the interactions, the CON versus TRN groups did not differ from each other but had greater (p &#60; 0.05) weekly intake than the HFD/TRN group, which ate more (p &#60; 0.05) than the HFD group (Figure 4). When translating feed intake to kcal intake, the animals on the high-fat diet had a higher (p &#60; 0.0001) caloric intake than those on the control diet (430 kcal/week &#177; 4.6 kcal/week vs. 396 kcal/week &#177; 3.7 kcal/week, respectively). This resulted in differences (p &#60; 0.05) in the weekly caloric intake among all four groups, with the HFD/TRN group showing the greatest weekly caloric intake, followed by the HFD, CON, and TRN groups sequentially (Figure 5).
Body weight did not differ between groups until week 8 of the feeding period, when the HFD and HFD/TRN groups reached a greater (p &#60; 0.05) mass than the CON and TRN groups (293 g &#177; 10.1 g and 298 g &#177; 13.1 g vs. 270 g &#177; 8.6 g and 264 g &#177; 6.8 g, respectively). The HFD and HFD/TRN groups remained heavier (p &#60; 0.05) than the CON and TRN groups for the remainder of the study (reaching 332 g &#177; 14.4 g, 347 g &#177; 16.3 g, 304 g &#177; 10.3 g, and 304 g &#177; 10.1 g for the HFD, HFD/TRN, CON, and TRN groups, respectively). The average daily gain (ADG) was greater (p &#60; 0.05) in the trained versus non-trained animals over the exercise portion of the study (0.8 g/day &#177; 0.11 g/day vs. 0.5 g/day &#177; 0.09 g/day, respectively), and there were no differences in ADG between the CON versus HFD groups over this period. Together, this resulted in greater (p &#60; 0.05) ADG in the HFD/TRN group than in the HFD group and no differences between the CON and TRN groups (Figure 6) over the training period. However, the 8 week training period did not induce a difference in weight between the HFD/TRN and HFD groups (347 g &#177; 16.3 g vs. 331.5 g &#177; 14.4 g, respectively).
After the completion of the training protocol, the tissue retrieval revealed that animals on the HFD had greater (p &#60; 0.05) visceral adiposity than the CON group (25 g &#177; 2.1 g vs. 19 g &#177; 1.5 g, respectively), and the exercise-trained animals had reduced (p &#60; 0.05) visceral adiposity relative to the control animals (21 g &#177; 2.4 g vs. 25 g &#177; 2.1 g, respectively). The HFD group had a greater (p &#60; 0.05) visceral adiposity than the TRN and HFD/TRN groups (Figure 7). The heart mass was greater in the HFD/TRN group than in the CON, TRN, and HFD groups (p &#60; 0.05; 1.3 g &#177; 0.2 g vs. 1.1 g &#177; 0.1 g, 1.1 g &#177; 0.1 g, and 1.0 g &#177; 0.1 g, respectively). There were no differences observed in the liver mass among the groups. No differences were identified in the mass of any other organs or tissues.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/64447/64447fig01.jpg" /> 
Figure 1: Study protocol timeline by animal age in days. <a href="https://www.jove.com/files/ftp_upload/64447/64447fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/64447/64447fig02.jpg" /> 
Figure 2: HIIT speed throughout the training protocol for the TRN and HFD/TRN animals by session. HIIT was performed on four different days every week for 8 weeks, resulting in 32 training sessions. The mean data per workout are presented. <a href="https://www.jove.com/files/ftp_upload/64447/64447fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/64447/64447fig03.jpg" /> 
Figure 3: Average distance covered per sprint in the TRN and HFD/TRN groups throughout the training protocol. HIIT was performed on four different days every week for 8 weeks, resulting in 32 training sessions. The data are presented as mean &#177; SEM. <a href="https://www.jove.com/files/ftp_upload/64447/64447fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/64447/64447fig04.jpg" /> 
Figure 4: Average weekly feed intake of the CON, TRN, HFD, and HFD/TRN cohorts. Data are presented as mean &#177; standard error of the mean (SEM). a,b,cMeans with different letters differ (p &#60; 0.05). <a href="https://www.jove.com/files/ftp_upload/64447/64447fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/64447/64447fig05.jpg" /> 
Figure 5: Weekly caloric intake of the CON, TRN, HFD, and HFD/TRN cohorts. Data are presented as mean &#177; SEM. a,b,c,dMeans with different letters differ (p &#60; 0.05). <a href="https://www.jove.com/files/ftp_upload/64447/64447fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/64447/64447fig06.jpg" /> 
Figure 6: Average daily weight gain in the CON, TRN, HFD, and HFD/TRN cohorts. Data are presented as mean &#177; SEM. a,bGroups with different letters differ (p &#60; 0.05). <a href="https://www.jove.com/files/ftp_upload/64447/64447fig06large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/64447/64447fig07.jpg" /> 
Figure 7: Average visceral fat mass at necropsy. Data are presented as mean &#177; SEM. a,bGroups with different letters differ (p &#60; 0.05). <a href="https://www.jove.com/files/ftp_upload/64447/64447fig07large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Table 1: Compositions of the diets used in the protocol. <a href="https://www.jove.com/files/ftp_upload/64447/Table 1.xlsx" target="_blank">Please click here to download this Table.</a>

Watch this Scientific Journal Video about A Chronic High-Intensity Interval Training and Diet-Induced Obesity Model to Maximize Exercise Effort and Induce Physiologic Changes in Rats at JoVE.com

A Chronic High-Intensity Interval Training and Diet-Induced Obesity Model to Maximize Exercise Effort and Induce Physiologic Changes in Rats

This paper presents the morphometric responses and training performance outcomes of a high-intensity interval training (HIIT) protocol in a Sprague-Dawley rat model of diet-induced obesity. The purpose of this protocol was to maximize exercise intensity and determine the physiologic responses to HIIT in lean and obese rats.

Compared to continuous-moderate or low-intensity training, high-intensity interval training (HIIT) is a more time-efficient alternative method that ...

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749 Views.  West Virginia School of Osteopathic Medicine. This paper presents the morphometric responses and training performance outcomes of a high-intensity interval training (HIIT) protocol in a Sprague-Dawley rat model of diet-induced obesity. The purpose of this protocol was to maximize exercise intensity and determine the physiologic responses to HIIT in lean and obese rats.

Video: A Chronic High-Intensity Interval Training and Diet-Induced Obesity Model to Maximize Exercise Effort and Induce Physiologic Changes in Rats

Fat Preference: A Novel Model of Eating Behavior in Rats

Obesity is a growing problem in the United States of America, with more than a third of the population classified as obese. One factor contributing to this multifactorial disorder is the consumption of a high fat diet, a behavior that has been shown to increase both caloric intake and body fat content. However, the elements regulating preference for high fat food over other foods remain understudied.
To overcome this deficit, a model to quickly and easily test changes in the preference for dietary fat was developed. The Fat Preference model presents rats with a series of choices between foods with differing fat content. Like humans, rats have a natural bias toward consuming high fat food, making the rat model ideal for translational studies. Changes in preference can be ascribed to the effect of either genetic differences or pharmacological interventions. This model allows for the exploration of determinates of fat preference and screening pharmacotherapeutic agents that influence acquisition of obesity.

Dietary fat content influences both energy intake and body fat composition in mammals. By examining rats&#8217; preference for high fat food in a series of choice experiments, it is possible to test genetic differences and pharmacological interventions on their preference for high fat food.

Obesity is a growing problem in the United States of America, with more than a third of the population classified as obese. One factor contributing to ...

Behavior

Getting to Compliance in Forced Exercise in Rodents: A Critical Standard to Evaluate Exercise Impact in Aging-related Disorders and Disease

There is a major increase in the awareness of the positive impact of exercise on improving several disease states with neurobiological basis; these include improving cognitive function and physical performance. As a result, there is an increase in the number of animal studies employing exercise. It is argued that one intrinsic value of forced exercise is that the investigator has control over the factors that can influence the impact of exercise on behavioral outcomes, notably exercise frequency, duration, and intensity of the exercise regimen. However, compliance in forced exercise regimens may be an issue, particularly if potential confounds of employing foot-shock are to be avoided. It is also important to consider that since most cognitive and locomotor impairments strike in the aged individual, determining impact of exercise on these impairments should consider using aged rodents with a highest possible level of compliance to ensure minimal need for test subjects. Here, the pertinent steps and considerations necessary to achieve nearly 100% compliance to treadmill exercise in an aged rodent model will be presented and discussed. Notwithstanding the particular exercise regimen being employed by the investigator, our protocol should be of use to investigators that are particularly interested in the potential impact of forced exercise on aging-related impairments, including aging-related Parkinsonism and Parkinson&#8217;s disease.

Exercise may alleviate behavioral impairments associated with neurodegenerative diseases. Studies of the mechanisms underlying exercise-mediated effects have increased in disease models, but the neurobiological background accompanying these diseases, specifically aging, is likely not considered. Here, we illustrate measures to increase the likelihood of a successful exercise paradigm in aged rats.

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A Model of Chronic Nutrient Infusion in the Rat

Chronic exposure to excessive levels of nutrients is postulated to affect the function of several organs and tissues and to contribute to the development of the many complications associated with obesity and the metabolic syndrome, including type 2 diabetes. To study the mechanisms by which excessive levels of glucose and fatty acids affect the pancreatic beta-cell and the secretion of insulin, we have established a chronic nutrient infusion model in the rat. The procedure consists of catheterizing the right jugular vein and left carotid artery under general anesthesia; allowing a 7-day recuperation period; connecting the catheters to the pumps using a swivel and counterweight system that enables the animal to move freely in the cage; and infusing glucose and/or Intralipid (a soybean oil emulsion which generates a mixture of approximately 80% unsaturated/20% saturated fatty acids when infused with heparin) for 72 hr. This model offers several advantages, including the possibility to finely modulate the target levels of circulating glucose and fatty acids; the option to co-infuse pharmacological compounds; and the relatively short time frame as opposed to dietary models. It can be used to examine the mechanisms of nutrient-induced dysfunction in a variety of organs and to test the effectiveness of drugs in this context.

A protocol for chronic infusions of glucose and Intralipid in rats is described. This model can be used to study the impact of nutrient excess on organ function and physiological parameters.

Chronic exposure to excessive levels of nutrients is postulated to  affect the function of several organs and tissues and to contribute to the  ...

Medicine

Supramaximal Intensity Hypoxic Exercise and Vascular Function Assessment in Mice

Exercise training is an important strategy for maintaining health and preventing many chronic diseases. It is the first line of treatment recommended by international guidelines for patients suffering from cardiovascular diseases, more specifically, lower extremity artery diseases, where the patients' walking capacity is considerably altered, affecting their quality of life. 
Traditionally, both low continuous exercise and interval training have been used. Recently, supramaximal training has also been shown to improve athletes' performances via vascular adaptations, amongst other mechanisms. The combination of this type of training with hypoxia could bring an additional and/or synergic effect, which could be of interest for certain pathologies. Here, we describe how to perform supramaximal intensity training sessions in hypoxia on healthy mice at 150% of their maximal speed, using a motorized treadmill and a hypoxic box. We also show how to dissect the mouse in order to retrieve organs of interest, particularly the pulmonary artery, the abdominal aorta, and the iliac artery. Finally, we show how to perform ex vivo vascular function assessment on the retrieved vessels, using isometric tension studies.

High-intensity training in hypoxia is a protocol that has been proven to induce vascular adaptations potentially beneficial in some patients and to improve athletes&#39; repeated sprint ability. Here, we test the feasibility of training mice using that protocol and identify those vascular adaptations using ex vivo vascular function assessment.

Exercise training is an important strategy for maintaining health and preventing many chronic diseases. It is the first line of treatment recommended by ...

Short Session High Intensity Interval Training and Treadmill Assessment in Aged Mice

High intensity interval training (HIIT) is emerging as a therapeutic approach to prevent, delay, or ameliorate frailty. In particular short session HIIT, with regimens less than or equal to 10 min is of particular interest as several human studies feature routines as short as a few minutes a couple times a week. However, there is a paucity of animal studies that model the impacts of short session HIIT. Here, we describe a methodology for an individually tailored and progressive short session HIIT regimen of 10 min given 3 days a week for aged mice using an inclined treadmill. Our methodology also includes protocols for treadmill assessment. Mice are initially acclimatized to the treadmill and then given baseline flat and uphill treadmill assessments. Exercise sessions begin with a 3 min warm-up, then three intervals of 1 min at a fast pace, followed by 1 min at an active recovery pace. Following these intervals, the mice are given a final segment that starts at the fast pace and accelerates for 1 min. The HIIT protocol is individually tailored as the speed and intensity for each mouse are determined based upon initial anaerobic assessment scores. Additionally, we detail the conditions for increasing or decreasing the intensity for individual mice depending on performance. Finally, intensity is increased for all mice every two weeks. We previously reported in this protocol enhanced physical performance in aged male mice and here show it also increases treadmill performance in aged female mice. Advantages of our protocol include low administration time (about 15 min per 6 mice, 3 days a week), strategy for individualizing for mice to better model prescribed exercise, and a modular design that allows for the addition or removal of the number and length of intervals to titrate exercise benefits.

Short session (&#8804;10 min) high intensity interval training (HIIT) is emerging as an alternative to longer exercise modalities, yet the shorter variants are rarely modeled in animal studies. Here, we describe a 10 min, 3 day a week, uphill treadmill HIIT protocol that enhances physical performance in male and female aged mice.

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Ascending Aortic Constriction in Rats for Creation of Pressure Overload Cardiac Hypertrophy Model

Ascending aortic constriction is the most common and successful surgical model for creating pressure overload induced cardiac hypertrophy and heart failure. Here, we describe a detailed surgical procedure for creating pressure overload and cardiac hypertrophy in rats by constriction of the ascending aorta using a small metallic clip. After anesthesia, the trachea is intubated by inserting a cannula through a half way incision made between two cartilage rings of trachea. Then a skin incision is made at the level of the second intercostal space on the left chest wall and muscle layers are cleared to locate the ascending portion of aorta. The ascending aorta is constricted to 50&#8211;60% of its original diameter by application of a small sized titanium clip. Following aortic constriction, the second and third ribs are approximated with prolene sutures. The tracheal cannula is removed once spontaneous breathing was re-established. The animal is allowed to recover on the heating pad by gradually lowering anesthesia. The intensity of pressure overload created by constriction of the ascending aorta is determined by recording the pressure gradient using trans-thoracic two dimensional Doppler-echocardiography. Overall this protocol is useful to study the remodeling events and contractile properties of the heart during the gradual onset and progression from compensated cardiac hypertrophy to heart failure stage.

We describe a stepwise procedure for creating pressure overload and left ventricular hypertrophy in Wistar rats by constriction of the ascending aorta using a small metallic clip. This model is extensively used for studying remodeling changes during cardiac hypertrophy and for identifying and evaluating strategies for regression of such changes.

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Intraperitoneal Glucose Tolerance Test, Measurement of Lung Function, and Fixation of the Lung to Study the Impact of Obesity and Impaired Metabolism on Pulmonary Outcomes

Obesity and respiratory disorders are major health problems. Obesity is becoming an emerging epidemic with an expected number of over 1 billion obese individuals worldwide by 2030, thus representing a growing socioeconomic burden. Simultaneously, obesity-related comorbidities, including diabetes as well as heart and chronic lung diseases, are continuously on the rise. Although obesity has been associated with increased risk for asthma exacerbations, worsening of respiratory symptoms, and poor control, the functional role of obesity and perturbed metabolism in the pathogenesis of chronic lung disease is often underestimated, and underlying molecular mechanisms remain elusive. This article aims to present methods to assess the effect of obesity on metabolism, as well as lung structure and function. Here, we describe three techniques for mice studies: (1) assessment of intraperitoneal glucose tolerance (ipGTT) to analyze the effect of obesity on glucose metabolism; (2) measurement of airway resistance (Res) and respiratory system compliance (Cdyn) to analyze the effect of obesity on lung function; and (3) preparation and fixation of the lung for subsequent quantitative histological assessment. Obesity-related lung diseases are probably multifactorial, stemming from systemic inflammatory and metabolic dysregulation that potentially adversely influence lung function and the response to therapy. Therefore, a standardized methodology to study molecular mechanisms and the effect of novel treatments is essential.

The incidence of obesity is rising and increases the risk of chronic lung diseases. To establish the underlying mechanisms and preventive strategies, well-defined animal models are needed. Here, we provide three methods (glucose-tolerance-test, body plethysmography, and lung fixation) to study the effect of obesity on pulmonary outcomes in mice.

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Palatable Western-style Cafeteria Diet as a Reliable Method for Modeling Diet-induced Obesity in Rodents

Obesity is rapidly increasing in incidence in developed and developing countries and is known to induce or exacerbate many diseases.&#160;The health burden of obesity and its comorbid conditions highlight the need for better understanding of its pathogenesis, yet ethical constraints limit studies in humans. To this end externally valid models of obesity in laboratory animals are essential for the understanding of being overweight and obesity.&#160;While many species have been used to model the range of changes that accompany obesity in humans, rodents are most commonly used. Our laboratory has developed a western-style cafeteria diet that consistently leads to considerable weight gain and markers of metabolic disease in rodents. The diet exposes rodents to a variety of highly palatable foods to induce hyperphagia, modeling the modern western food environment. This diet rapidly induces weight gain and body fat accumulation in rats allowing for the study of effects of overeating and obesity. While the cafeteria diet may not provide the same control over macronutrient and micronutrient profile as purified high-fat or high-fat, high-sugar diets, the cafeteria diet typically induces a more severe metabolic phenotype than that observed with purified diets and is more in line with metabolic disturbances observed in the overweight and obese human population.

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Obesity is rapidly increasing in incidence in developed and developing countries and is known to induce or exacerbate many diseases.&#160;The health ...

A Rat Model of Pressure Overload Induced Moderate Remodeling and Systolic Dysfunction as Opposed to Overt Systolic Heart Failure

In response to an injury, such as myocardial infarction, prolonged hypertension or a cardiotoxic agent, the heart initially adapts through the activation of signal transduction pathways, to counteract, in the short-term, for the cardiac myocyte loss and or the increase in wall stress. However, prolonged activation of these pathways becomes detrimental leading to the initiation and propagation of cardiac remodeling leading to changes in left ventricular geometry and increases in left ventricular volumes; a phenotype seen in patients with systolic heart failure (HF). Here, we describe the creation of a rat model of pressure overload induced moderate remodeling and early systolic dysfunction (MOD) by ascending aortic banding (AAB) via a vascular clip with an internal area of 2 mm2. The surgery is performed in 200 g Sprague-Dawley rats. The MOD HF phenotype develops at 8-12 weeks after AAB and is characterized noninvasively by means of echocardiography. Previous work suggests the activation of signal transduction pathways and altered gene expression and post-translational modification of proteins in the MOD HF phenotype that mimic those seen in human systolic HF; therefore, making the MOD HF phenotype a suitable model for translational research to identify and test potential therapeutic anti-remodeling targets in HF. The advantages of the MOD HF phenotype compared to the overt systolic HF phenotype is that it allows for the identification of molecular targets involved in the early remodeling process and the early application of therapeutic interventions. The limitation of the MOD HF phenotype is that it may not mimic the spectrum of diseases leading to systolic HF in human. Moreover, it is a challenging phenotype to create, as the AAB surgery is associated with high mortality and failure rates with only 20% of operated rats developing the desired HF phenotype.

We describe the creation of a rat model of pressure overload induced moderate remodeling and early systolic dysfunction where signal transduction pathways involved in the initiation of the remodeling process are activated. This animal model will aid in identifying molecular targets for applying early therapeutic anti-remodeling strategies for heart failure.

In response to an injury, such as myocardial infarction, prolonged hypertension or a cardiotoxic agent, the heart initially adapts through the activation ...

Accumulated High-intensity Interval Training Protocol: A New Approach to Study Health Markers in Wistar Rats

High-Intensity Interval Training (HIIT) and accumulated exercises are two time-efficient programs to improve health in humans and animal models. However, to date, there are no studies on whether HIIT performed in an accumulated fashion is as effective as a traditional HIIT performed with single daily sessions in improving health markers. This paper presents the effects of a new HIIT protocol, called accumulated HIIT, on body weight gain, maximal oxygen consumption (VO2max), and cardiac hypertrophy in young Wistar rats. 
Sixty-day-old male Wistar rats were assigned to three groups: untrained (UN; n = 16), HIIT performed with single daily sessions (1-HIIT; n = 16), and HIIT performed with three daily sessions (3-HIIT; n = 16). Body weight and VO2max were recorded before and after the training period. The VO2max measurements were taken using a metabolic analyzer at the maximal running velocity (Vmax). The training was performed for both HIIT groups five days per week over eight weeks with the same weekly progression of the exercise intensity (85-100% Vmax). The 1-HIIT group performed single daily sessions (6 bouts of 1 min interspersed with 1 min of passive recovery). The 3-HIIT group performed three daily sessions (2 bouts of 1 min interspersed with 1 min of passive recovery with an interval of 4 h between bouts). After the last VO2max test, the rats were euthanized, and their hearts were harvested and weighed.
The results showed that 3-HIIT had similar beneficial effects to 1-HIIT in preventing body weight gain, improving VO2max, and inducing cardiac hypertrophy. These findings reveal for the first time the efficacy of an accumulated HIIT protocol on the health markers of young Wistar rats. This new HIIT protocol may be more feasible than traditional HIIT protocols as exercise can be split into very short sessions throughout a day in this new approach.

Here, we present accumulated high-intensity interval training (HIIT) protocols, which may be a more feasible and time-efficient strategy than traditional HIIT protocols.

High-Intensity Interval Training (HIIT) and accumulated exercises are two time-efficient programs to improve health in humans and animal models. However, ...