Name: muscle imbalances: testing and training functional eccentric hamstring strength in athletic populations
Uploaded: 2018-05-01T15:00:00
Description: Watch this Scientific Journal Video about Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations at JoVE.com

The authors would like to thankfully acknowledge all of the subjects in the study. Funding sources A research grant from the Czech Science Foundation GACR NO. 16-13750S, PRIMUS/17/MED/5 and UNCE 032 project.

The presented protocol follows the guidelines of human research ethics committee at Charles University, Faculty of Physical Education in Sport and has been previously approved as part of research.
1. Familiarize All Subjects Before Isokinetic Testing by Following Steps
<ol>
	<li>Ensure that the subjects have not had any recent musculoskeletal injuries or pain in the lower limbs in the previous 6 months. If a subject reports recent knee pain, or has knee pain during testing, exclude the subje...

The first critical step in the aforementioned protocol is the athlete&#39;s familiarization, especially for the eccentric tests. Subjects may have to be familiarized two or three times to ensure reliable data during such isokinetic testing. Furthermore, it may be a good idea to re-familiarize subjects if testing sessions are more than two months apart. The second critical step is properly setting up the athlete in the dynamometer, ensuring that the knee axis is in-line with the axis of the dynamometer; it is also importa...

The relationship between knee flexor and extensor strength has been identified as an important parameter in assessing a person&#39;s risk of incurring a lower limb injury1. Specifically, there is an increased probability of hamstring injury when ipsilateral or bilateral imbalances in hamstring strength are present when compared to quadricep strength2. Therefore, many sport scientists and practitioners test knee flexor and extensor strength to determine whether an athlete is at risk of incurring a hamstring injury. However, various testing methods are used that do not allow for direct comparisons to be made between methods (e.g., different contraction speeds, different muscle actions, and field testing vs. laboratory testing)3,4,5,6,7,8,9. Although different testing methods provide different bits of valuable information regarding strength levels, the methodological approach for thigh muscle isokinetic strength testing should be unified to enable comparisons across individuals, populations, and time.
Although the evaluation of ipsilateral imbalances between knee flexors and extensors have been often described using the conventional concentric hamstring to concentric quadriceps ratio (H/QCONV)10,11, co-activation of the knee flexors and extensors is known to occur during all movements and takes place through opposing contraction modes. To explain, the knee extensors are primarily involved in propulsion during jumping and running, whereas the knee flexors primarily stabilize the knee during landing and running by decelerating the lower limb and counteracting the rapid and forceful concentric contractions of the extensors. As most movements in sports require simultaneous concentric knee extension and eccentric knee flexion, a relative strength comparison between the two would be appropriate. Therefore, eccentric knee flexor strength relative to concentric knee extensor strength is commonly tested and is known as the &#34;functional ratio&#34; (H/QFUNC)12.
Compared to the H/QCONV ratio where values can range from 0.43 to 0.9012, the H/QFUNC ratio can range from 0.4 to 1.413, indicating that data from different protocols should not be compared to each other. Although maximal concentric torque decreases as concentric speed increases14,15,16, eccentric torque is greater than concentric torque as speed increases16,17. As such, the H/QFUNC ratio can approach a value of 1.0 as the speed of testing contraction increases13,18. Since most sport movements occur at high velocities, knee extensor and flexor strength testing are likely more ecologically valid at higher speeds. Therefore, such strength testing protocols should include progressively increased speeds in a stepwise progression.
If isokinetic testing reveals a large discrepancy between eccentric hamstring and concentric quadricep strength, the discrepancy should be narrowed through training. For this purpose, decreasing knee extensor strength should never compensate for weak knee flexors at the expense of a more favorable H/QFUNC ratios, especially in sporting environments. The other option would be to progressively and intensively increase knee flexor strength so that the hamstrings become stronger, especially in relation to the quadriceps, at higher speeds. Therefore, if isokinetic testing reveals some degree of hamstring weakness, a training intervention will likely be necessary to increase hamstring strength, especially during eccentric muscle actions. As with all training interventions, follow-up testing should be performed to determine the efficacy of the eccentrically-focused hamstring strength training program, and further adjustments may need to be made. The objective of this paper is to describe how to test isokinetic functional eccentric hamstring strength, reveal potential hamstring weakness, and suggest how to resolve a functional hamstring weakness.

<table>
	<tbody>
		<tr>
			<td>HumacNorm</td>
			<td>CSMI, Stoughton, MA, USA</td>
			<td>021-54412236 (model 502140)</td>
			<td>Standard Dynamometr</td>
		</tr>
		<tr>
			<td>SoftwareHumac 2015</td>
			<td>Computer Sports Medicine Inc. Stoughton, MA, USA</td>
			<td>Version155</td>
			<td>Software for dynamometr</td>
		</tr>
	</tbody>
</table>

muscle imbalances: testing and training functional eccentric hamstring strength in athletic populations

Many hamstring injuries that occur during physical activity occur while the muscles are lengthening, during eccentric hamstring muscle actions. Opposite of these eccentric hamstring actions are concentric quadriceps actions, where the larger and likely stronger quadriceps straighten the knee. Therefore, to stabilize the lower limbs during movement, the hamstrings must eccentrically combat against the strong knee-straightening torque of the quadriceps. As such, eccentric hamstring strength expressed relative to concentric quadricep strength is commonly referred to as the &#34;functional ratio&#34; as most movements in sports require simultaneous concentric knee extension and eccentric knee flexion. To increase the strength, resiliency, and functional performance of the hamstrings, it is necessary to test and train the hamstrings at different eccentric speeds. The main purpose of this work is to provide instructions for measuring and interpreting eccentric hamstring strength. Techniques for measuring the functional ratio using isokinetic dynamometry are provided and sample data will be compared. Additionally, we briefly describe how to address hamstring strength deficiencies or unilateral strength differences using exercises that specifically focus on increasing eccentric hamstring strength.

The examples below show the differences between young elite soccer athletes (age 15.4 &#177; 0.5 years, body mass 62.7 &#177; 8.2 kg, height 175 &#177; 9.1, training experience more than 8 years) performing eccentric hamstring training (EHT, n = 18) and without EHT (n = 15) for 12 weeks (Figure 3). The group performing EHT included this exercise two times per week, while the group without EHT performed core training and a general lower limb program instead. B...

Watch this Scientific Journal Video about Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations at JoVE.com

Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations

The hamstrings are a group of muscles that are sometimes problematic for athletes, resulting in soft tissue injury in the lower limbs. To prevent such injuries, functional training of the hamstrings requires intensive eccentric contractions. Additionally, hamstring function should be tested in relation to quadricep function at different contraction speeds.

Many hamstring injuries that occur during physical activity occur while the muscles are lengthening, during eccentric hamstring muscle actions. Opposite ...

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