The Effect Of 4-week Low-intensity Ischemic Training On Quadriceps Size, Performance And Oxygen Availability

Abstract

Low-intensity/high-repetition exercise combined with restricted blood flow has been reported effective for increasing muscle mass and muscle strength. In contrast, ischemic exercise has been also shown to have an opposite effect: enhanced muscle aerobic metabolism and endurance capacity. PURPOSE: To evaluate the effect of ischemic training on quadriceps performance, cross-sectional area (CSA) and O2 availability. METHODS: Ten healthy males trained on a leg-extension machine at loads equal to 15% of maximal voluntary contraction (MVC) force for 16 training sessions. One leg (I-leg) was trained with vascular occlusion induced by cuffs (≥230mmHg), whereas the other leg (C-leg) completed the same training volume without blood flow restrictions. Peak muscle strength was assessed with isometric MVC force, while endurance capacity was evaluated with one control and one ischemic test of repetitive load lifting to volitional failure. Oxygen availability in v. lateralis and activation of rectus f. and v. medialis during the endurance trials were measured with near-infrared spectroscope and surface EMG. Muscle CSA was measured with a series of slices acquired by MRI. All tests and measurements were performed prior to and after training. Differences in means were tested using factorial ANOVA. RESULTS: After training, a 9±2%, 5±1% and 7±1% increase (P<0.05) in CSA of rectus f., v. lateralis and v. medialis was observed in the I-leg, respectively. There was no change in MVC force in either I-leg or C-leg. Number of repetitions during control endurance test with I-leg and C-leg increased (P<0.01) by 63±9% and 36±8%, respectively. Root mean square EMG amplitudes of all muscles remained similar in both leg. The attained plateau of relative decrease in oxy-haemoglobin was reduced (P<0.01) by 15.7±0.4 μmol in I-leg and 6.7±0.4 μmol in C-leg. In contrast, the mean relative increase in total haemoglobin was higher (P<0.01) by 9.3±0.2 μmol in I-leg and 5.4±0.2 μmol in C-leg. The slope of change in both oxy-and deoxy-haemoglobin at the onset of exercise increased (P<0.05) in both legs, but more in I-leg. CONCLUSION: Ischemic training substantially augments endurance capacity of m. quadriceps, which can be attributed mainly to enhanced muscle blood supply and O2 availability. Increased muscle CSA may be an index of ischemia-induced capilarisation.