Effects Of Strength TVaining By Electrostimulation On Skeletal Muscle Oxidative Metabolism

Abstract

Strength training is frequently associated with endurance exercise during training and rehabilitation. The effects of strength training (particularly when obtained by electrostimulation) per se on skeletal muscle oxidative metabolism are not well known. PURPOSE: To evaluate the effects of strength training by electrostimulation on variables of functional evaluation of oxidative metabolism specifically aimed at skeletal muscle. METHODS: Measurements were conducted on 7 young untrained subjects, during incremental cycloergometric exercises up to voluntary exhaustion and 6-min constant-load exercises below and above the gas exchange threshold (GET). Measurements were carried out before (B) and after (A) a strength training period (25 sessions of neuromuscular electrical stimulation of both quadriceps, over 8 weeks), which determined a 24% increase in force during maximal voluntary contraction. Breath-by-breath pulmonary O2 uptake (VO2) and vastus lateralis oxygenation indices by continuous-wave near-infrared spectroscopy (NIRS) were determined. Skeletal muscle O2 extraction was estimated by NIRS on the basis of changes in concentration of deoxygenated hemoglobin + myoglobin (Delta[deoxy(Hb+Mb)]), expressed as a percentage of values obtained during transient limb ischemia. RESULTS: VO2 peak and Delta[deoxy(Hb+Mb)] peak were, respectively, 44.5 ± 3.1 (x ± SE) ml/kg/min in B vs. 47.8 ± 2.2 in A; and 84.2 ± 6.0 % in B vs. 85.4 ± 6.3 in A. GET occurred at 66.6 ± 2.8 % of VO2 peak in B, vs. 67.6 ± 3.5 in A. The time-constant of VO2 kinetics during the transition to constant-load exercise below GET was 34.7 ±6.8 s in B vs. 32.3 ± 4.3 in A. During constant-load exercise above GET slow components of VO2 and Delta[deoxy(Hb+Mb)] kinetics were observed. For VO2, the slow component amplitude, expressed as a percentage of the total response, was 17.8 ± 3.3 % in B, vs. 11.7 ± 2.5 in A. With exception of force, all differences, in A vs. B, were not statistically significant. CONCLUSIONS: In young subjects a strength training program by electrostimulation of the vastus lateralis, capable of significantly increasing muscle force, did not significantly affect VO2 peak and other variables of functional evaluation specifically aimed at skeletal muscle oxidative metabolism.