Vastus lateralis fatigue alters recruitment of musculus quadriceps femoris in humans

1 Department of Life Sciences (Sports Sciences), The University of Tokyo, Meguro, Tokyo 153-8902, Japan; 2 Department of Exercise Science, The University of Georgia, Athens, Georgia 30602; and Departments of 3 Physiology, 4 Kinesiology, and 5 Radiology, Michigan State University, East Lansing, Michigan 48824 This study tested the hypothesis that fatigue of a single member of musculus quadriceps femoris (QF) would alter use of the other three muscles during knee extension exercise (KEE). Six men performed KEE with the left QF at a load equal to 50% of the 4 × 10 repetitions maximum. Subsequently, electromyostimulation (EMS), intended to stimulate and fatigue the left m. vastus lateralis (VL), was applied for 30 min. Immediately after EMS, subjects repeated the KEE. Transverse relaxation time (T2)-weighted magnetic resonance images were taken before and after each bout of KEE and at 3 and 30 min of EMS to assess use and stimulation, respectively, of the QF. T2 of each of the QF muscles was increased 8-13% after the first KEE. During EMS, T2 increased ( P