Gr. Hunter et al., Muscle metabolic economy is inversely related to exercise intensity and type II myofiber distribution, MUSCLE NERV, 24(5), 2001, pp. 654-661
It is not known what causes the well-established inverse relationship betwe
en whole-body exercise economy and exercise intensity. The purpose of this
study was to: (1) evaluate muscle exercise economy at 45%, 70%, and maximum
isometric strength using P-31 magnetic resonance spectroscopy (P-31-MRS);
and (2) determine the relationship between percent type II muscle fiber cro
ss-section, whole-body exercise economy, and muscle exercise economy. Subje
cts included 32 premenopausal women. Muscle exercise economy was significan
tly different across the three exercise intensities (28.1 +/- 10,4, 24.8 +/
- 8,2, and 20.2 +/- 7.5 N/cm(2) mmol/L adenosine triphosphate [ATP] for the
45%, 70%, and maximum intensities, respectively). Percent type II muscle a
rea was significantly related to whole-body metabolic economy during activi
ties of daily living (r = -0.68) and P-31-MRS muscle metabolic economy duri
ng isometric plantar flexion (r = -0.53), These data suggest that skeletal
muscle becomes less economical as force production increases, and that thes
e decreases in metabolic economy may be related to increased dependence on
inefficient type II muscle. (C) 2001 John Wiley & Sons, Inc.