Skip Navigation LinksHome > February 2010 - Volume 42 - Issue 2 > Aerobic Fitness, Muscle Efficiency, and Motor Unit Recruitme...
Medicine & Science in Sports & Exercise:
doi: 10.1249/MSS.0b013e3181b0f2e2
Applied Sciences

Aerobic Fitness, Muscle Efficiency, and Motor Unit Recruitment during Ramp Exercise


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Purpose: The purpose of this study was to test whether the higher slope of the oxygen uptake/work rate relationship (ΔV˙O2W) 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 ΔV˙O2W and the slope of the iEMG/W relationship (ΔiEMG/ΔW).

Results: The statistical analysis revealed a higher ΔV˙O2W in cyclists compared with PA students in ramp exercises (ramp 25 = 9.98 ± 0.51 vs 9.18 ± 0.59 mL·min−1·W−1; relative ramp = 9.87 ± 0.30 vs 9.16 ± 0.33 mL·min−1·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·min−1·W−1 in cyclists and PA students, respectively; P > 0.05). In addition, cyclists demonstrated a higher ΔiEMG/ΔW in ramp exercises (0.96 ± 0.14%·W−1 and 0.98 ± 0.14%·W−1 in ramp 25 and relative ramp, respectively) compared with step exercise (0.75 ± 0.12%·W−1, P < 0.05), whereas in the PA students, ΔiEMG/ΔW did not differ between the ramp protocol (0.75 ± 0.10%·W−1 and 0.70 ± 0.12%·W−1 in ramp 25 and relative ramp, respectively) and the step protocol (0.77 ± 0.17%·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.

©2010The American College of Sports Medicine


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