Determinants of VO(2) kinetics at high power outputs during a ramp exercise protocol.
OBJECTIVE
To determine the relationship between the additional, nonlinear increase in oxygen uptake (Delta VO(2)) that occurs at high power outputs during a ramp cycle ergometer test, on one hand; and possible explanatory mechanisms of the phenomenon, such as cardiorespiratory work, blood lactate, fitness level, or muscle fiber distribution, on the other.


METHODS
Ten healthy, sedentary young adults (age (mean +/- SEM), 22 +/- 1 yr) were chosen as subjects. A muscle biopsy specimen was taken from the vastus lateralis of the right leg to determine fiber type distribution by immunohistochemical identification of myosin heavy chain (MHC) isoforms. During the ramp tests (power output increases of 5 W every 15-s interval), the ventilatory threshold (VT) and lactate threshold (LT) were measured. We defined Delta VO(2) as the difference between "true" VO(2) values observed at the maximal power output (VO(2)obs) and those expected (VO(2)exp) from the previous linear VO2:power output relationship below the VT.


RESULTS
A nonlinear increase was observed in VO2 (Delta VO(2) = 239 +/- 79 mL x min(-1), P < 0.05 for VO(2)obs vs VO(2)exp), which was significantly correlated with the percentage of type IIX fibers (r = 0.80, P < 0.05). No other correlations were found between Delta VO(2) and possible explanatory mechanisms.


CONCLUSIONS
A greater percentage of type IIX fibers is associated with a higher excess VO(2) at high power outputs (above VT).
Lucía
Alejandro
A
Departamento de Ciencias Morfológicas y Fisiología, Universidad Europea de Madrid, Spain. alejandro.lucia@mrfs.cisa.uem.es
Rivero
José-Luis L
JL
Pérez
Margarita
M
Serrano
Antonio L
AL
Calbet
José A L
JA
Santalla
Alfredo
A
Chicharro
José L
JL
D000328:Adult; D001707:Biopsy, Needle; D005080:Exercise Test; D006801:Humans; D007700:Kinetics; D019344:Lactic Acid / Q000097:blood; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000166:cytology; D018482:Muscle, Skeletal / Q000166:cytology* / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology; D013385:Succinate Dehydrogenase / Q000378:metabolism
D019344:Lactic Acid; D013385:Succinate Dehydrogenase; D018995:Myosin Heavy Chains