P-31-NMR SPECTROSCOPY, RSEMG, AND HISTOCHEMICAL FIBER TYPES OF HUMAN WRIST FLEXOR MUSCLES

The metabolic response to graded rhythmic forearm exercise determined by phosphorus-31 nuclear magnetic resonance (P-31-NMR) spectroscopy was evaluated with respect to recruitment pattern of muscles and to fiber type composition of the nondominant arm in 14 untrained subjects. Rectified smoothed surface electromyography (rsEMG) over finger and wrist flexor muscles increased similarly and progressively at 30, 45, and 60% of maximal exercise intensity. On the basis of the P-31-NMR response pattern during exercise, subjects were separated into three groups: H group (n = 4), with a single high-pH P-i peak; M group (n = 7), with two P-i peaks reflecting two pH components; and L group (n = 3), with a single low-pH P-i peak. The H group demonstrated a faster recovery of P-i and phosphocreatine than the L group (P < 0.05). The M group displayed both types of P-i recovery and an intermediate resynthesis rate of phosphocreatine. The M group had an even distribution of slow- and fast-twitch fibers in the flexor carpi radialis muscle, whereas subjects in the H and L groups possessed a predominance of slow- and fast-twitch fibers, respectively. The results suggest that during rhythmic forearm exercise the interindividual NMR variation in energy metabolism is related closely to fiber type composition of the muscle.