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  • Title: Aerobic fitness, muscle efficiency, and motor unit recruitment during ramp exercise.
    Author: Boone J, Koppo K, Barstow TJ, Bouckaert J.
    Journal: Med Sci Sports Exerc; 2010 Feb; 42(2):402-8. PubMed ID: 19927017.
    Abstract:
    PURPOSE: The purpose of this study was to test whether the higher slope of the oxygen uptake/work rate relationship (DeltaVO2/DeltaW) in aerobically trained subjects compared with less trained counterparts during a ramp protocol is related to changes in muscle fiber activation. METHODS: Ten cyclists and 10 physically active (PA) students performed two ramp exercises (ramp 25 protocol and relative ramp protocol, leading to exhaustion in 12 min) and a step protocol (20-60-100-140-180-220 W). Pulmonary gas exchange was measured, and muscle fiber activity was recorded with surface EMG of the musculus vastus lateralis. V O2 and integrated EMG (iEMG) were described as functions of work rate up to the gas exchange threshold, and linear regression analysis was used to determine the DeltaVO2/DeltaW and the slope of the iEMG/W relationship (DeltaiEMG/DeltaW). RESULTS: The statistical analysis revealed a higher DeltaVO2/DeltaW in cyclists compared with PA students in ramp exercises (ramp 25 = 9.98 +/- 0.51 vs 9.18 +/- 0.59 mL x min(-1) x W(-1); relative ramp = 9.87 +/- 0.30 vs 9.16 +/- 0.33 mL x min(-1) x W(-1) in the cyclists and PA students, respectively; P < 0.05) but not in step exercise (9.97 +/- 0.32 and 9.83 +/- 0.37 mL x min(-1) x W(-1) in cyclists and PA students, respectively; P > 0.05). In addition, cyclists demonstrated a higher DeltaiEMG/DeltaW in ramp exercises (0.96 +/- 0.14% x W(-1) and 0.98 +/- 0.14% x W(-1) in ramp 25 and relative ramp, respectively) compared with step exercise (0.75 +/- 0.12% x W(-1), P < 0.05), whereas in the PA students, DeltaiEMG/DeltaW did not differ between the ramp protocol (0.75 +/- 0.10% x W(-1) and 0.70 +/- 0.12% x W(-1) in ramp 25 and relative ramp, respectively) and the step protocol (0.77 +/- 0.17% x W(-1), P > 0.05). CONCLUSIONS: The present study reveals that trained cyclists demonstrate reduced mechanical efficiency in the ramp protocol and that this phenomenon is associated with an "overactivation" of muscle fibers.
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