Neuromuscular responses to three days of velocity-specific isokinetic training

The purpose of this investigation was to examine the effects of 3 days of velocity-specific isokinetic training on peak torque (PT) and the electromyographic (EMG) signal. Thirty adult women were randomly assigned to a slow-velocity training (SVT), fast-velocity training (FVT), or control (CON) group. All subjects performed maximal, concentric, isokinetic leg extension muscle actions at 30 and 270°·s^-1 for the determination of PT on visits 1 (pretest) and 5 (posttest). Electromyographic signals were recorded from the vastus lateralis, rectus femoris, and vastus medialis muscles during each test. The training groups performed 4 sets of 10 maximal repetitions at 30°s·^-1 (SVT group) or 270°·s^-1 (FVT group) on visits 2, 3, and 4. For the SVT group, PT increased from pretest to posttest at 30 and 270°·s^-1. The increase in PT at 30°·s^-1 was greater than at 270°·s ^-1. For the FVT group, PT increased at 270°·s^-1 only. For the CON group, there were no changes in PT at either velocity. There were no pretest to posttest changes in EMG amplitude or mean power frequency (MPF) for any group at any velocity, with the exception of an increase in EMG MPF from the vastus medialis muscle at 270°·s^-1 for the FVT group. The results indicated that 3 sessions of slow velocity (30°·s^-1) isokinetic training resulted in an increase in PT at slow and fast velocities (30 and 270°·s^-1), whereas training at the fast velocity (270°·s^-1) increased PT only at 270°·s^-1. The lack of consistent increases in EMG amplitude or MPF suggested that the training-induced increases in leg extension PT were not caused by increased activation of the superficial muscles of the quadriceps femoris. The important implication for coaches, trainers, and physical therapists is that significant muscular performance gains may be achieved even after very short training periods, but determination of the specific physiological adaptation(s) underlying these performance gains requires further investigation.