european college of sport science

Friday, June 26th, 2009
15:15 - 16:45
Oral presentations
OP-PH02 Physiology 2
MUSCLE METABOLIC DEMAND IN ELECTRICALLY EVOKED MAXIMAL ISOMETRIC CONTRACTIONS OF THE ELBOW
FLEXORS INVESTIGATED BY NEAR-INFRARED SPECTROSCOPY
MUTHALIB, M., JUBEAU, M., MILLET, G.Y., MAFFIULETTI, N.A., NOSAKA, K.
EDITH COWAN UNIVERSITY
INTRODUCTION: Previous studies (1,2) reported that muscle oxidative metabolic demand in isometric contractions induced by electrical
muscle stimulation (EMS) was greater than voluntary isometric contractions (VOL) at the same force level. Our previous study (ECSS-2008)
showed that the metabolic demand of the biceps brachii assessed by near-infrared spectroscopy (NIRS) during EMS (30 Hz) was similar
to VOL, when repeated isometric contractions (1-s contraction, 1-s relaxation) were performed at maximal intensity for VOL and at maximally
tolerable current intensity for EMS. Since higher stimulation frequency (>50 Hz) and contraction duration (>4 s) are often used to
improve strength in EMS training, this study compared EMS (75 Hz) and VOL for changes in biceps brachii muscle oxidative metabolism
during intermittent 4-s maximal isometric contractions.
METHODS: Ten men (23-39 yrs) performed EMS with one arm and VOL with the other arm separated by 2-3 weeks in a counterbalanced
order. EMS and VOL consisted of 50 maximal isometric contractions (4-s contraction, 15-s relaxation) of the elbow flexors at an elbow joint
angle of 160°. For EMS, the biceps brachii and brachioradialis muscles were stimulated at maximal tolerated current (36-64 mA) via
surface electrodes (frequency: 75 Hz, pulse duration: 0.2 ms). Maximal voluntary isometric contraction (MVC) torque was measured
before and after exercise, and torque produced during exercise was recorded. A NIRS probe was placed on the mid-biceps brachii of the
exercise arm and NIRS signals were sampled at 6 Hz using a NIRO200-NIRS system. Changes in muscle oxygenation (TOI), oxygen extraction
(HHb) and blood volume (cHb) over 50 contractions (contraction and relaxation phases) were compared between EMS and VOL
by a two-way repeated measures ANOVA with Bonferoni post-hoc test. Significance was set at P