Neuromuscular versus Mechanical Stretch-induced Changes in Contralateral versus Ipsilateral Muscle

Purpose: Whether or not the homologous contralateral muscle (CM) undergoes stretch-induced force

reduction as the stretched muscle (SM) is still unclear. The neuromuscular and mechanical factors underlying the force reduction in CM and

SM were investigated. Methods: Twenty-one participants underwent unilateral knee extensors passive stretching. In both CM and SM, before,

immediately after (POST), 5 (POST5), and 10min (POST10) after passive stretching,maximumvoluntary contraction (MVC), peak force

(pF), and voluntary activation (VA) were measured. DuringMVC, the electromyographic and mechanomyographic root mean square (EMG

RMS and MMG RMS, respectively) was calculated in rectus femoris, vastus lateralis, and vastus medialis, together with M-wave. The total

electromechanical delay (EMD), divided in time delay (Δt) EMG-MMG and Δt MMG-F was calculated. Results: In CM at POST, the decrease

in MVC (−11%; 95% confidence interval [CI], −13 to −9; effect size [ES], −2.27) was accompanied by a fall in VA (−7%; 95% CI,

−9 to −4; ES, −2.29), EMG RMS (range, −22% to −11%; ES, −3.92 to −2.25), MMG RMS (range, −10% to −8%; ES, −0.52 to −0.39)

and an increase in Δt EMG-MMG (≈+10%; ES, 0.73 to 0.93). All changes returned to baseline at POST5. In SM, decrease in MVC

(−19%; 95% CI, −24 to −18; ES, −3.08), pF (−25%; 95% CI, −28 to −22; ES, −4.90), VA (−10%; 95% CI, −11 to −9; ES, −5.71), EMG

RMS (≈−33%; ES, −5.23 to −3.22) and rise in MMG RMS (range, +25% to +32%; ES, 4.21 to 4.98) and EMD (≈+28%; ES, 1.59 to

1.77) were observed at POST and persisted at POST10. No change in M-wave occurred. Conclusions: The contralateral central motor drive

stretch-induced inhibition seems to account for the force reduction in CM. In SM, both central inhibition and mechanical factors concurred.