There is no difference between two and five minutes of static stretching training and detraining on gastrocnemius medialis muscle thickness, pennation angle and fascicle length

BACKGROUND: Skeletal muscle’s architecture can undergo temporary or permanent adaptations when subjected to chronic passive loading, such as during passive static stretching (PSS). AIM: We evaluated the effects of a 6-week PSS program, with two and five minutes of duration, on the architecture of the Gastrocnemius Medialis (GM) muscle. In addition, we determined the inter-analyzer reliability of the GM’s muscle architecture images analysis process. METHOD: 30 healthy adults participated in this study. Participants were divided into three groups: Control Group (CG), 2-minutes of PSS (G2) and 5-minutes of PSS (G5). Plantar flexors’ PSS was applied three times a week for 6 weeks. Participants were assessed before intervention, after intervention, and two weeks post detraining. GM’s muscle thickness (MT), pennation angle (PA) and fascicle length (FL) were measured with an ultrasound system by an experienced evaluator. All images were analyzed by two independent analyzers, using the Image-J software. RESULTS: No significant effects were identified (p>0.05) of the PSS program on muscle architecture parameters. No architectural changes were observed following the detraining period. GM’s MT results presented excellent reliability, while good reliability was found for the FL measures. For PA, good reliability was only observed for the post-intervention moment. On the pre-intervention and follow-up moments, the intraclass correlation coefficients values were moderate. CONCLUSION: A 6-week PSS program did not generate adaptations on GM’s muscle architecture parameters in healthy subjects, independent of the stretching duration. Muscle architecture parameters are reliable when analyzed by different analyzers following clinical interventions.