Human–Horse Neuromuscular Coordination Across Sequential Conditions During Physical Therapy Utilizing Equine Movement in Parkinson’s Disease

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This exploratory, single-session, repeated-measures study characterized human and equine trunk muscle activity and human–horse EMG covariation during physical therapy utilizing equine movement in individuals with Parkinson’s disease (PD). Nine individuals with PD and three horses completed pre-session quiet sitting (QS Pre), figure-eight riding (F8), stop-and-go riding (SNG), and post-session quiet sitting (QS Post). Bilateral surface EMG was recorded from three human and four equine trunk muscles. All analyses were exploratory and examined four outcomes: normalized EMG amplitude, zero-lag human–horse correlation, lagged human–horse correlation, and human–horse EMG-EMG coherence. Human normalized EMG amplitude did not differ across QS Pre, F8, and SNG. Equine amplitude was greater during F8 than QS Pre (difference 9.43 percentage points, 95% CI [4.27, 14.59]). SNG also showed greater amplitude than QS Pre (5.30 percentage points, 95% CI [0.32, 10.27]), although this difference was not statistically significant in the participant-level sensitivity analysis. F8 exceeded SNG in the direct comparison (4.43 percentage points, 95% CI [1.44, 7.41]) but not in the adjusted three-condition comparison. Zero-lag correlations were generally close to zero; SNG exceeded F8 by only 0.0056 Fisher’s z units (95% CI [0.0004, 0.0107]) in the direct comparison, but this difference was not statistically significant in the adjusted three-condition comparison. When temporal offsets of ±300 ms were permitted, lagged correlation strength was greater during F8 than QS Pre (difference 0.013, 95% CI [0.003, 0.024]) and during SNG than QS Pre (0.011, 95% CI [0.001, 0.021]), with no difference between riding conditions. Median wavelet coherence was greater during QS Pre than F8 (difference 0.016, 95% CI [0.013, 0.018]) or SNG (0.013, 95% CI [0.011, 0.015]), while SNG exceeded F8 overall (0.003, 95% CI [0.002, 0.004]). Simultaneous human and equine EMG was feasible during the sequential mounted conditions, but the observed signal properties differed across outcomes. Because the conditions were administered in a fixed sequence, their individual effects could not be distinguished from order-related influences. These exploratory findings require confirmation in larger studies with counterbalanced task orders, controlled gait characteristics, and relevant clinical outcomes.