Early-phase muscular adaptations in response to slow-speed versus traditional resistance-training regimens.

Thirty-four untrained women participated in a 6-week program to investigate slow-speed versus "normal" speed resistance-training protocols. Subjects were divided into: slow-speed (SS), normal-speed/traditional-strength (TS), normal-speed/traditional muscular endurance (TE), and non-exercising control (C) groups. Leg press, squats, and knee extensions were performed 2 days/week for the first week and 3 days/week for the remaining 5 weeks (~2 min rest). The SS group performed 6-10 repetitions maximum (6-10RM) for each set with 10 s concentric (con) and 4 s eccentric (ecc) contractions. The TS and TE groups performed sets of 6-10RM and 20-30RM, respectively, at "normal" speed (1-2 s/con and ecc contractions). TE and SS trained at the same relative intensity (~40-60% 1RM), whereas TS trained at ~80-85% 1RM. Pre- and post-training muscle biopsies were analyzed for fiber-type composition, cross-sectional area (CSA), and myosin heavy chain (MHC) content. The percentage of type IIX fibers decreased and IIAX increased in all three training groups. However, only TS showed an increase in percentage of type IIA fibers. CSA of fiber types I, IIA, and IIX increased in TS. In SS, only the CSA of IIA and IIX fibers increased. These changes were supported by MHC data. No significant changes for any parameters were found for the C group. In conclusion, slow-speed strength training induced a greater adaptive response compared to training with a similar resistance at "normal" speed. However, training with a higher intensity at "normal" speed resulted in the greatest overall muscle fiber response in each of the variables assessed.