Acute Effects of Different Foam Rolling Protocols on the Plantar Flexors' Musculotendinous Properties in Healthy Individuals

Self-massage is a set of therapeutic technique performed by the individual using instruments such as a foam roller (i.e., foam rolling [FR]). This technique has been used in rehabilitation to recover myofascial dysfunctions and in physical/sports training, to improve performance in functional and sports activities. Possible changes in the muscle's and tendon's mechanical properties may help to explain the FR effects. Although some studies have found a decreased muscle stiffness after FR intervention, other studies have reported no changes in muscle stiffness. Furthermore, a single study investigated the FR effects on the tendon and found no stiffness changes post-intervention. The between-studies methodological procedures heterogeneity, especially the different FR protocols (e.g., pressure-volume) may partially justify conflicting results. However, the dose-response relationship is not clear acutely. Furthermore, body composition also seems to influence the pressure applied to the different tissues during FR. Therefore, the aim of this study is to verify the acute effects of different FR volumes on the plantar flexors' musculotendinous properties in healthy individuals. Twenty healthy subjects (male and female) aged between 18-35 years will perform three different FR conditions: FR90 (3x30s), FR180 (3x60s), and a control condition (CTRL; without the application of any intervention) with a seven-day wash-out period. The weight-bearing during the FR application will be obtained through ground reaction forces, measured through force platform. The Achilles tendon morphological properties (length and cross-sectional area) will be evaluated using ultrasonography. In order to evaluate the mechanical (stiffness, force, and elongation) and material (Young's modulus, stress, and strain) properties, three maximum voluntary isometric contractions (MVIC) will be performed in a plantar flexion ramp in the isokinetic dynamometer with ultrasonography. The tendon force will be corrected by the tibialis anterior coactivation and adjusted by the tendon displacement caused by joint rotation during MVIC. The tendon elongation will be monitored during CMVIC using the ultrasound. The medial gastrocnemius muscle stiffness will be calculated by the variation in a passive dorsiflexion torque (isokinetic dynamometer) and the variation in the muscle length (ultrasound). The adipose tissue's thickness also will be obtained from ultrasound. The skin temperature will be evaluated by a thermographic camera to investigate possible post-intervention changes. The unilateral countermovement jump performance will be evaluated by 2D kinematic data measurements, using a video camera. Assessments will be carried out before and immediately after the FR application in the different conditions. Descriptive statistics (mean, standard deviation, and standard error) will be used to present the results. The normality and sphericity of the data will be evaluated using the Shapiro-Wilk and Mauchly tests, respectively. A two-way ANOVA (condition [FR90, FR180, and CTRL] and moments [pre- and post-intervention]) will be used to compare the results. A post-hoc Bonferroni test will be used to localize possible differences. A Pearson product-moment correlation test (parametric data) or a Spearman correlation test (non-parametric data) will be used to verify the association between the adipose tissue's thickness on the evaluated parameters, classified as none (0.0), weak (0.1-0.3), moderate (0.4-0.6), strong (0.7-0.9), or perfect (1.0). The effect size (Cohen's d) of each condition will be obtained, classified as small effect size (< 0.20); moderate effect size (0.20-0.50); or large effect size (>0.80). Responsiveness to conditions (FR90, FR180, and CTRL) will be determined using the typical error.