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

Summary

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).

Abstract

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.

Introduction

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 model^1,2,3, but insects were also studied⁴. The first investigations of split-belt locomotion in human infants and adults were published in 1987 and 1994, respectively^5,

Protocol

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.

1. 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^29,30. The timescale over which people "forget" the split-belt treadmill is not presently know....

Results

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 elsewhere^8,10. This paper focuses on two measures of interlimb coordination: ste.......

Discussion

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.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Split-belt treadmill	Woodway
Codamotion CX1	Charmwood Dynamics, Ltd, Leicestershire, UK