Within-session dose-response and between-session carry-over effects of eccentric contractions versus static stretches on range of motion and muscle-tendon mechanics

Purpose: Eccentric resistance training produces substantial increases in maximum joint range of motion (ROM), highlighting its potential as an alternative to static stretching. However, little is known about the short-term effects or associated mechanisms. Therefore, this study compared within-session responses and between-session carry-over effects of eccentric contractions and static stretching in 18 healthy human volunteers. Methods: Using a counterbalanced crossover design, participants completed four sessions across two conditions: Eccentric contractions (EC1, EC2) and static stretching (SS1, SS¬2), with 48-72 h between sessions. EC comprised 5 sets of 10×3-s isokinetic eccentric contractions while SS comprised 5 sets of 30-s static stretches (total time under tension = 150 s). Dorsiflexion ROM and passive plantarflexor torque were recorded before and after each set, and maximal isometric plantarflexor torque, active Achilles tendon stiffness, and passive gastrocnemius medialis stiffness were measured pre- and post-intervention. Results: Significant within-session increases in ROM (2.2-6.0°) and reductions in muscle-tendon unit (MTU) stiffness (2.7-7.3%) and muscle stiffness (8.4%) occurred after both EC1 and SS1. However, only EC1 improved stretch tolerance (30.7%) and decreased Achilles tendon stiffness (12.0%). Comparable between-session carry-over effects occurred after two sessions of stretches and contractions in pre-intervention ROM (5.9°, collapsed data), stretch tolerance (38.0%), and MTU stiffness (41.7%). Conclusion: Eccentric contractions produced more than twice the acute ROM increase and greater changes in stiffness and stretch tolerance than static stretching. The significant carry-over effects after two sessions indicate also indicate a more potent stimulus for increasing ROM, with important implications for clinical practice and exercise prescription.