The effect of full-limb flexion tests on static and dynamic muscle activity and locomotion asymmetry in owner-sound horses.
Authors: Jonkhart Marijke, Serra Bragança Filipe M, Smit Ineke H, Brommer Harold, Suskens Jozef J M
Journal: Equine veterinary journal
Summary
# Editorial Summary Flexion tests remain a cornerstone of equine lameness and pre-purchase examinations, yet their underlying mechanisms have received limited scientific scrutiny. Jonkhart and colleagues used surface electromyography to measure muscle activity in 16 warmblood horses across ten muscles (five in the forelimb region, five in the hindlimb), with inertial measurement units simultaneously capturing kinematic asymmetry during 60-second full-limb flexions followed by trot-ups. Contrary to the assumption that sustained flexion might alter neuromuscular recruitment patterns, the researchers found no significant changes in normalised muscle activity in either region during or immediately after flexion; however, pelvic displacement increased by approximately 8 mm in the vertical plane during suspension of the flexed limb (p ≤ 0.004), suggesting a subtle biomechanical compensation rather than muscular inhibition. These findings suggest that any response observed during clinical flexion tests may reflect proprioceptive or pain-mediated effects rather than straightforward neuromuscular fatigue, and they raise questions about the clinical utility of flexion tests in detecting underlying pathology—particularly since no muscle activation changes preceded the observable gait alterations. Whilst the study's limitation to full-limb tests only restricts direct application to distal or carpal/tarsal flexions commonly used in practice, the lack of standardised flexion force and the absence of neuromuscular effects warrant reconsideration of what flexion tests actually measure in sound horses and whether response variability during clinical assessment reflects true pathology or normal biomechanical noise.
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Practical Takeaways
- •Full-limb flexion tests do not appear to trigger measurable changes in muscle activation patterns, questioning their mechanism for detecting underlying locomotor issues
- •Flexion tests produce temporary kinematic changes (increased pelvic displacement) but these are not accompanied by detectable neuromuscular responses, suggesting caution in interpreting clinical responses
- •The variable clinical response to flexion tests observed in practice may not be explained by direct neuromuscular effects, warranting re-evaluation of their diagnostic value in lameness work-ups
Key Findings
- •No significant differences in normalised muscle activity observed in fore- or hindlimb muscles during flexion tests or subsequent trotting compared to baseline
- •Pelvic vertical displacement increased during suspension phase of ipsilateral limb after both left (8.4 mm, p=0.002) and right (8.1 mm, p=0.004) hindlimb flexion tests
- •Full-limb flexion tests did not affect equine neuromuscular functioning in the muscles investigated using surface electromyography