The effect of treadmill speed and gradient on equine hindlimb muscle activity.

REASONS FOR PERFORMING STUDY: Locomotion requires successful negotiation of different terrains, but we currently know little of how the musculoskeletal system adapts to cope with positive and negative slopes.

OBJECTIVE

To compare the effects of treadmill speed and gradient on equine hindlimb muscle mean electromyographic (EMG) intensity.

METHODS

Surface EMG recorded the activity of gluteus medius (GM), biceps femoris (BF), vastus lateralis (VL), gastrocnemius lateralis (GL) and extensor digitorum longus (EDL) in 6 horses at walk (1.4-1.6 m/s) and trot (2.6-3 m/s) on 3 different treadmill gradients (0, 10% and -10%). Significant differences in mean EMG intensity and kinematic data were determined using Friedman and Wilcoxon signed rank tests (P < 0.05).

RESULTS

Increasing velocity increased the mean EMG intensity of GM, BF and GL regardless of gradient. Treadmill incline increased the mean EMG intensity for all muscles at the walk and that of GM at trot. Treadmill decline reduced the mean EMG intensity of GM at both the walk and the trot and that of BF at the walk, but not the trot. The mean EMG intensity of EDL, VL and GL remained similar at both gaits when compared to the horizontal.

CONCLUSIONS

The hip retractors are the primary muscles responsible for powering equine locomotion in response to increasing workload.

POTENTIAL RELEVANCE: A better understanding of the effects of speed and gradient on the functional activity of the horses' locomotor muscles will enable the development of more effective training programmes pre- and post injury.