A comparison of equine hindlimb muscle activation and joint motion between forward and backward walking

Backward walking (BW) is commonly employed as a physiotherapeutic exercise for horses based on anecdotal evidence for improving hindlimb strength, coordination, and range of motion. However, limited scientific evidence supports these assumed benefits. This study aimed to measure and compare equine hindlimb muscle activity and movement during BW and forward walking (FW). Three-dimensional kinematic and surface electromyography (sEMG) data were synchronously collected from unilateral (left) hindlimb and hip extensor (biceps femoris and gluteus medius) and flexor (tensor fasciae latae) muscles of ten horses during FW and BW. Normalised average rectified value (ARV), peak amplitude (PA), and muscle activity duration were calculated from sEMG data. Spatiotemporal and angular parameters were calculated from kinematic data. Wilcoxon signed rank tests or paired t-tests assessed differences between FW and BW. Compared to FW, significant (p<0.001) increases in hip extensor and decreases in hip flexor muscle ARV and PA were observed during BW. Muscle activity duration was significantly (p<0.001) longer for biceps femoris, and shorter for gluteus medius and tensor fasciae latae during BW. Hindlimb pro/retraction and sagittal plane hip and stifle joint movement cycles were time-reversed between BW and FW. Hindlimb joints were significantly less flexed and extended (p<0.001) during BW, except for peak stifle and hock flexion during swing, and MTPJ extension during stance, which were significantly greater (p<0.001) during BW. Findings support BW as a physiotherapeutic exercise to target increased hip extensor activity during weightbearing and to facilitate increased stifle and hock joint flexion during non-weightbearing phases of the gait cycle. • Horses significantly modify hindlimb muscle activity and movement in backward walk. • Biceps femoris and gluteus medius activity increases in backward vs. forward walk. • Tensor fascia latae activity decreases during backward compared to forward walking. • Greater stifle and hock joint flexion occur during backward walking swing phase. • Backward walk targets increased hip extensor activity and stifle and hock flexion.