Unilateral hamstrings static stretching can impair the affected and contralateral knee extension force but improve unilateral drop jump height.

Purpose: Prolonged static stretching (SS) in isolation (no dynamic warm-up) can impair muscle performance. There are conflicting reports whether impairments are present in antagonist and contralateral muscles. The objective of this study was to assess the effect of unilateral hamstrings SS on ipsilateral stretched and contralateral limbs' strength and jump power.

Methods: The SS (four repetitions of 30-s) and control sessions involved unilateral testing of the stretched leg and contralateral leg for knee extension (KE) maximum voluntary isometric contraction (MVIC) force and electromyography (EMG), drop jump (DJ) height and contact time at 1-min post-stretching.

Results: There were significant KE MVIC force impairments for both the SS (p = 0.006, d = 0.3, - 8.1%) and contralateral (p = 0.02, d = 0.20, - 4.2%) leg. With normalized data, there was a near-significant (p = 0.1), small magnitude (d = 0.29), greater force impairment with the ipsilateral (93.0 ± 12.8% of pre-test) versus the contralateral (96.2 ± 9.1% of pre-test) KE MVIC force. DJ height significantly improved for the stretched leg (p = 0.03, d = 0.18, + 9.2%) with near-significant, improvements for the contralateral leg (p = 0.06, d = 0.22, + 12.1%). For the stretched leg, DJ contact time was significantly (p = 0.04, d = 0.18, + 3.4%) prolonged, but there was no significant change with the contralateral leg.

Conclusions: Unilateral hamstrings SS induced strength deficits in the ipsilateral and contralateral knee extension MVIC and a prolongation of the stretched leg DJ contact period. In anticipation of maximal force outputs, prolonged SS in isolation (no dynamic warm-up included) can have negative consequences on antagonist and contralateral muscle performance.