Name: using a split-belt treadmill to evaluate generalization of human locomotor adaptation
Uploaded: 2017-08-23T12:30:00
Description: Watch this Scientific Journal Video about Using a Split-belt Treadmill to Evaluate Generalization of Human Locomotor Adaptation at JoVE.com

This work has been funded by an American Heart Association Scientist Development Grant (#12SDG12200001) to E. Vasudevan. R. Hamzey's current affiliation is Department of Mechanical Engineering, Boston University, Boston, MA, USA. E. Kirk's current affiliation is the MGH Institute of Health Professions Department of Physical Therapy.

All procedures have been approved by the Institutional Review Board at Stony Brook University.
1. Experimental Set-up
Note: Refer to Supplementary File 1-Definitions for definitions of common terms used in split-belt treadmill experiments.
<ol>
	<li>Screen all participants for prior experience with the split-belt treadmill. 
	NOTE: People have been shown to readapt faster to the split-belt treadmill following a prior exposure to it<sup class=...

Numerous studies have now shown that people adapt gait coordination on a split-belt treadmill in order to restore symmetry in interlimb coordination parameters like step length and double support duration. When natural walking conditions are restored following split-belt walking, participants continue using the adapted gait pattern, leading to after-effects that have to be unlearned in order to return to normal walking coordination. Researchers primarily use adaptation rate and after-effect amplitude to quantify the abil...

A split-belt treadmill has two belts that can drive each leg at a different speed or in a different direction. This device was first used over 45 years ago as a tool to study coordination between the legs (i.e., interlimb coordination) during walking1. This, and other early studies primarily used cats as an experimental model1,2,3, but insects were also studied4. The first investigations of split-belt locomotion in human infants and adults were published in 1987 and 1994, respectively5,6. These initial studies in both human and non-human animals mostly investigated short-term (i.e., immediate) adjustments in interlimb coordination to preserve stability and forward progression when the legs are driven at different speeds. A 1995 study noted that longer periods (several minutes) of split-belt walking impaired the ability of human adults to accurately perceive treadmill belt speed and make adjustments to equalize speeds on each side. This suggests that the sensorimotor mapping of walking had been recalibrated7. However, it was not until 2005 that the first detailed kinematic report of human motor adaptation over 10 minutes of split-belt treadmill walking was published8.
Motor adaptation refers to an error-driven process during which sensorimotor mappings of well-learned movements are adjusted in response to a new, predictable demand9. It is a form of motor learning that occurs over an extended practice period (minutes to hours) and results in after-effects, which are changes in the movement pattern when the demand is removed and/or conditions return to normal. For example, walking on split-belts initially causes people to walk with asymmetric interlimb coordination, resembling a limp. Over several minutes of split-belt walking, people adapt their walking coordination so that their gait becomes more symmetric. When the two belts subsequently return to the same speed (i.e. tied-belts), thus restoring normal walking conditions, people demonstrate after-effects by walking with asymmetric coordination. These after-effects must be actively de-adapted or unlearned over several minutes of tied-belt walking before normal walking coordination is restored8.
Following the 2005 Reisman et al.8 kinematic analysis of split belt walking in humans, use of the split-belt treadmill in published research has increased approximately ten-fold compared to the previous decade. Why is the split-belt treadmill becoming more popular as an experimental tool? Split-belt ambulation is clearly a laboratory task &#8211; the closest real-world analog is turning or walking in a tight circle, but the split-belt treadmill induces a much more extreme version of turning, with one leg being driven two- to four-times faster than the other. The fact that the split-belt treadmill is a highly unusual walking task offers several advantages for studying locomotor learning. First, it is novel for most people regardless of age and independent of walking experience; it is easy to screen experimental participants for novelty of split-belt walking. Second, the split-belt treadmill induces sizeable changes in interlimb coordination that are not quickly resolved. The relatively slow rates of adaptation and de-adaptation permit us to study how different training interventions can alter these rates without approaching a ceiling. Third, the kinematic8,10, kinetic11,12,13,14, electromyographic6,15,16, and perceptual7,17,18,19 modifications that occur with split-belt treadmill adaptation have been well-studied, as has the neural control of this task20,21,22. In other words, adaptations to the split-belt treadmill have been documented and replicated by several different groups, making this a well-characterized locomotor learning task.
Over the past ten years, several studies have demonstrated the task- and context-specific nature of split-belt adaptation. After-effects following split-belt adaptation are significantly reduced in amplitude if they are tested under different conditions from the training condition. For example, after-effects are smaller if the person is moved to a different environment (e.g., over ground walking23), performs a different locomotor task (e.g., backward walking or running13,24), or even walks at a speed that differs from the speed of the slower belt during adaptation25. Efforts to establish parameters governing the generalization of locomotor adaptation are ongoing.
The objective of this paper is to describe a protocol for using the split-belt treadmill to investigate human locomotor adaptation and generalization of the adapted pattern to other walking contexts (i.e., different walking speeds and environments). While the protocol described here is most directly derived from that used in Hamzey et al.25 (Figure 1a), it should be noted that this protocol was informed by a number of studies that preceded it8,23,24,26,27,28. The method was originally developed to test the hypothesis that maintaining constancy in walking speed between the treadmill and over ground environments would improve generalization of split-belt walking across these different environments25. In the protocol section below, we give instructions on how to replicate this version of the split-belt treadmill method, with notes that indicate how certain protocol steps may be modified to for different method purposes.

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		<tr height="220">
			<td height="220" style="height:220px;width:216px;">Split-belt treadmill</td>
			<td style="width:71px;">Woodway</td>
			<td style="width:119px;"></td>
			<td style="width:591px;">The WOODWAY SPLIT-BELT is an advanced gate measurement and analysis tool used for synchronous or asynchronous running/walking. With its unique and innovative dual belt system, the &#34;SPLIT-BELT,&#34; provides infinitely variable speed control of each leg independently. Used for gait rehab, the gas-assisted, fully adjusted handrail options provide more room for therapists and patients.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Codamotion CX1</td>
			<td>Charmwood Dynamics, Ltd, Leicestershire, UK</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

using a split-belt treadmill to evaluate generalization of human locomotor adaptation

Understanding the mechanisms underlying locomotor learning helps researchers and clinicians optimize gait retraining as part of motor rehabilitation. However, studying human locomotor learning can be challenging. During infancy and childhood, the neuromuscular system is quite immature, and it is unlikely that locomotor learning during early stages of development is governed by the same mechanisms as in adulthood. By the time humans reach maturity, they are so proficient at walking that it is difficult to come up with a sufficiently novel task to study de novo locomotor learning. The split-belt treadmill, which has two belts that can drive each leg at a different speed, enables the study of both short- (i.e., immediate) and long-term (i.e., over minutes-days; a form of motor learning) gait modifications in response to a novel change in the walking environment. Individuals can easily be screened for previous exposure to the split-belt treadmill, thus ensuring that all experimental participants have no (or equivalent) prior experience. This paper describes a typical split-belt treadmill adaptation protocol that incorporates testing methods to quantify locomotor learning and generalization of this learning to other walking contexts. A discussion of important considerations for designing split-belt treadmill experiments follows, including factors like treadmill belt speeds, rest breaks, and distractors. Additionally, potential but understudied confounding variables (e.g., arm movements, prior experience) are considered in the discussion.

Walking on a split-belt treadmill initially causes large asymmetries in interlimb coordination. Over a period of 10 - 15 min, symmetry in many of these measures is gradually restored. Detailed descriptions of how kinematic walking parameters change over the course of split-belt treadmill adaptation have been published elsewhere8,10. This paper focuses on two measures of interlimb coordination: ste...

Watch this Scientific Journal Video about Using a Split-belt Treadmill to Evaluate Generalization of Human Locomotor Adaptation at JoVE.com

Using a Split-belt Treadmill to Evaluate Generalization of Human Locomotor Adaptation

We describe a protocol for investigating human locomotor adaptation using the split-belt treadmill, which has two belts that can drive each leg at a different speed. We specifically focus on a paradigm designed to test the generalization of adapted locomotor patterns to different walking contexts (e.g., gait speeds, walking environments).

Understanding the mechanisms underlying locomotor learning helps researchers and clinicians optimize gait retraining as part of motor rehabilitation. ...

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