Relative Contributions Of Muscular Strength, Muscle Size, And Tissue Oxygenation To Isometric Performance Fatigability

Abstract

PURPOSE: Performance fatigability (PF) has been defined as fatigue-induced decline in force. It has been hypothesized that muscle mass and strength may affect the magnitude of PF by limiting oxygenated blood to the muscle during sustained isometric muscle actions. Therefore, the purpose of the present study was to determine the relative contributions of muscular strength, muscle cross-sectional area (mCSA), and the rate of decline in tissue saturation index (TSI%) to PF. METHODS: Fifteen men (± SD: 20.9 ± 1.7 yr) performed a sustained bilateral isometric leg extension muscle action at 45% of maximum voluntary isometric contraction (MVIC) until failure. PF was quantified as the percent decline in force from pretest to posttest MVIC. mCSA was defined as the sum of the right and left vastus lateralis (VL). Muscular strength was defined as pretest MVIC. Near-infrared spectroscopy was used to assess TSI% from the right VL and was log transformed to determine the linear slope coefficient (b) of TSI% vs. Time (every 5%). A paired t-test was used to examine differences between pretest and posttest MVIC. Regression analyses were used to determine the full-model and stepwise linear regression model. RESULTS: The mean (±SD) sum of the VL mCSA was 51.3 ± 8.6 cm2. The pretest MVIC (119.4 ± 17.6 kg) was significantly (p=0.003; d=1.3) greater than the posttest MVIC (96.7 ± 16.9 kg). The mean PF was 17.5 ± 16.5%, and there was a significant (p=0.031), negative b (-0.005 ± 0.003 au) for TSI% vs. Time. The muscular strength standardized ß was 3.25 times and 6.5 times greater than mCSA and TSI% standardized ßs, respectively (Table 1). The stepwise linear regression analysis indicated that only muscular strength was a significant predictor of PF. CONCLUSION: Muscular strength independent of muscle mass and rate of decline in TSI% contributed to PF. There was, however, 59% unexplained variance, so future investigations should examine the contribution of neuromuscular and metabolic responses to PF.