Aerobic fitness, muscle efficiency, and motor unit recruitment during ramp exercise.
OBJECTIVE
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.
Boone
Jan
J
Department of Movement and Sports Sciences, Ghent University, Ghent, Belgium. Jan.boone@ugent.be
Koppo
Katrien
K
Barstow
Thomas J
TJ
Bouckaert
Jacques
J
D000293:Adolescent; D001642:Bicycling / Q000502:physiology; D004576:Electromyography; D005080:Exercise Test / Q000295:instrumentation*; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology; D011999:Recruitment, Neurophysiological / Q000502:physiology*; D055815:Young Adult