There is No Difference Between Two and Five Minutes of Static Stretching on Gastrocnemius Medialis Muscle Architecture

Abstract Background Skeletal muscle’s architecture can undergo temporary or permanent adaptations when subjected to chronic passive loading, such as during passive static stretching (PSS). Aims We evaluated the effects of a 6-week PSS program, with two and five minutes of duration, on the Gastrocnemius Medialis (GM’s) muscle architecture parameters. The second aim of this study was to determine the inter-analyzer reliability of the GM’s muscle architecture images analysis process. Methods 30 healthy adults participated in this study. Plantar flexors’ PSS was applied three times a week for 6 weeks. Participants were divided into three groups: Control Group (CG), 2-minutes of PSS (G2) and 5-minutes of PSS (G5). They were assessed before, after, and two weeks post the intervention. 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 just 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. Registration Number: This study was registered in Brazilian Clinical Trials Registry RBR-5j3h3c on 07/24/2018 (http://www.ensaiosclinicos.gov.br/).