Passive Stretching and Explosive Jumps Acutely Reduce Spinal Reflex Excitability and Alter Sit-To-Stand Biomechanics in Active Adults

Objectives: To investigate the acute effects of passive stretching and explosive effort countermovement jumps on spinal reflex excitability and sit-to-stand electromyography patterns and vertical stiffness, in active adults. Methods: A randomised within-participant crossover design was utilised, with 10 males and 10 females completing two separate sessions, each involving three sets of 60-seconds passive stretching (PS) and five sets of 20 explosive effort (EE) countermovement jumps (100 total); measures taken pre-intervention, post-PS and post-EE. Results: Spinal reflex excitability decreased in both post-PS and post-EE conditions (p < 0.001) compared to pre-condition measures, with no sex effect (p = 0.115). A condition × sex interaction revealed lower spinal reflex excitability in females post-EE (p = 0.002) compared to males. Biomechanically, sit-to-stand vertical stiffness increased in both post-PS and post-EE conditions (p < 0.001) compared to pre-condition, and electromyography patterns were influenced by both condition and sex (p ≤ 0.047). Conclusions: Our findings provide insight into the neurophysiological–biomechanical link warranting further investigation as a potential mechanism contributing to the known sex-based differences in lower limb injury risk, informing our understanding of movement control, rehabilitation, and injury prevention strategies.