The importance of muscle phosphocreatine during intermittent
maximal cycling.
Trump, Mark E., George J. F. Heigenhauser, C. T. Putman, Lawrence L.
Spriet.
Department of Human Biology and Nutritional Sciences, University of
Guelph, Guelph, Ontario, N1G 2W1 and Department of Medicine, McMaster
University, Hamilton, Ontario, L8N 3Z5, CANADA
APStracts 3:0018A, 1996.
To examine the importance of PCr degradation in maintaining power
output during maximal intermittent cycling, seven healthy males
completed three bouts of isokinetic cycling (30 s, 100 rpm) with 4
min of rest between bouts. Following bout 2, blood flow to one leg
was occluded by cuffing the thigh (CUFF) during the rest period to
prevent PCr resynthesis, while the circulation to the other leg was
intact (CONT). The cuff was then removed and bout 3 completed. Muscle
biopsies were sampled from the vastus lateralis of both legs just
prior to and immediately following bout 3. Total work produced by
each leg was similar during bouts 1 (9.3 + 0.5, 9.6 + 0.5 kJ) and 2
(8.1 + 0.4, 8.3 + kJ). Cuffing prevented the resynthesis of PCr as
pre-bout 3 contents were 20.7 +/- 8.4 and 63.0 +/- 3.3 mmol/kg dry
muscle in the CUFF and CONT legs. Cuffing also resulted in
significantly higher muscle levels of lactate, [H+] (287 +/- 26 vs.
217 +/- 15 nM), ADP, AMP and acetyl-CoA prior to bout 3, but had no
effect on other glycolytic intermediates, ATP or acetylcarnitine.
Total work in bout 3 was significantly reduced by 15% in the CUFF leg
(5.8 + 0.4 vs. 6.8 + 0.6 kJ). PCr degradation during bout 3 was 3.1
and 47.5 mmol/kg in the CUFF and CONT legs and lactate accumulation
was minimal in both legs. Changes in all other metabolites during
bout 3 were not different between legs. The results suggest that PCr
contributed 15% of the total ATP provision during the third, 30 s
bout of maximal isokinetic cycling and most was provided during the
initial 15 s. Muscle glycogenolysis contributed minimally to ATP
provision (10-15%) during the third, 30 s bout, suggesting that
aerobic metabolism becomes the dominant source of ATP during this
model of repeated sprinting.
Received 24 August 1995; accepted in final form 27 December 1995.
APS Manuscript Number A928-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96