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

BOONE, JAN1,2; KOPPO, KATRIEN3; BARSTOW, THOMAS J.4; BOUCKAERT, JACQUES1,2

Medicine & Science in Sports & Exercise: February 2010 - Volume 42 - Issue 2 - pp 402-408
doi: 10.1249/MSS.0b013e3181b0f2e2
Applied Sciences

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.

1Department of Movement and Sports Sciences, Ghent University, Ghent, BELGIUM; 2Center of Sports Medicine, University Hospital of Ghent, Ghent, BELGIUM; 3Department of Pharmacology, Ghent University, Ghent, BELGIUM; and 4Department of Kinesiology, Kansas State University, Manhattan, KS

Address for correspondence: Jan Boone, Department of Movement and Sports Sciences, Ghent University, Watersportlaan, 2, B-9000 Gent, Belgium; E-mail: Jan.boone@ugent.be.

Submitted for publication January 2009.

Accepted for publication June 2009.

©2010The American College of Sports Medicine