Early-Phase Satellite Cell and Myonuclear Domain Adaptations to Slow-Speed vs. Traditional Resistance Training Programs.

The purpose of this investigation was to identify adaptations in satellite cell (SC) content and myonuclear domain (MND) after 6-week slow-speed vs. "normal-speed" resistance training programs. Thirty-four untrained females were divided into slow speed (SS), traditional strength (TS), traditional muscular endurance (TE), and nontraining control (C) groups. Three sets each of leg press, squat, and knee extension were performed 2 days per week for the first week and 3 days per week for the following 5 weeks. The SS group performed 6-10 repetition maximum (6-10RM) for each set with 10-second concentric (con) and 4-second eccentric (ecc) contractions for each repetition. Traditional strength and TE performed 6-10RM and 20-30RM, respectively, at "normal" speed (1-2 seconds per con and ecc contractions). Traditional muscular endurance and SS trained at the same intensity (40-60% 1RM), whereas TS trained at 80-85% 1RM. Pretraining and posttraining muscle biopsies were analyzed for fiber cross-sectional area, fiber type, SC content, myonuclear number, and MND. Satellite cell content of type I, IIA, IIAX, and IIX fibers significantly increased in TS. However, SC content of only type IIAX and IIX fibers increased in SS, and there was no change in TE or C. Myonuclear number did not change in any group. Myonuclear domain of type I, IIA, IIAX, and IIX fibers increased in TS, whereas MND of only type IIA fibers increased in SS, and there was no change in TE or C. In conclusion, slow-speed resistance training increased SC content and MND more than training with a similar resistance at normal speed. However, high-intensity normal-speed training produced the greatest degree of fiber adaptation for each variable.