Effect Of Slow-speed Vs. Traditional Resistance Training Regimens On Myonuclear Domain And Satellite Cell Content

Abstract

PURPOSE: The purpose of this study was to investigate muscle fiber adaptations in myonuclear domain and satellite cell content in conjunction with varying degrees of fiber hypertrophy following slow-speed vs. "normal-speed“ resistance training protocols. METHODS: Thirty-four healthy adult females (21.1 ± 2.7 yr.) were randomly divided into four groups: slow-speed (SS), traditional strength (TS), traditional muscular endurance (TE), and non-exercising control (C). Workouts, consisting of 3 sets each of 3 exercises (leg press, squat, and knee extension), were performed 2d/wk for the first week and 3d/wk for the remaining 5 weeks. For each training session, the SS group performed 6-10RM (6-10 repetitions maximum) for each set with 10s con and 4s ecc contractions for each repetition. TS and TE performed 6-10RM and 20-30RM, respectively, at "normal“ speed (1-2s/con and ecc contraction). Both TE and SS trained at the same relative intensity (40-60% 1RM), whereas TS trained at 80-85% 1RM. Pre- and post-training vastus lateralis muscle biopsies were analyzed for fiber cross-sectional area (CSA), myonuclear domain and number, NCAM + (anti-neural cell adhesion molecule) satellite cells, and fiber type. RESULTS: 1) As previously reported, the CSA of all major fiber types (I, IIA, and IIX) increased post-training for TS, whereas only the fast fiber types increased in size for SS. No significant change in fiber size was found for either the TE or C groups. 2) Myonuclear domain was significantly larger post-training in TS for all major fiber types, whereas only Type IIA domain increased in SS. There were no changes in myonuclear domain for TE or C. 3) Myonuclear number did not differ significantly from pre- to post-training in any group. 4) Satellite cell content increased post-training for TS in all major fiber types, while only NCAM + nuclei associated with Type IIX and Type IIAX fibers increased in SS. No changes in the satellite cell population were observed for TE or C. CONCLUSIONS: Slow-speed resistance training resulted in a larger degree of fiber hypertrophy, increased myonuclear domain, and stimulus to muscle stem cells compared to training with a similar resistance at a normal speed. However, training at a higher intensity (80-85% 1RM) at normal speed resulted in the greatest overall fiber response for each of these variables.