Abstract
Few studies have focused on the metabolic responses to alternating high- and low-intensity
exercise and, specifically, compared these responses to those seen during constant-load
exercise performed at the same average power output. This study compared muscle metabolic
responses between two patterns of exercise during which the intensity was either constant
and just below critical power (CP) or that oscillated above and below CP. Six trained
males (mean ± SD age 23.6 ± 2.6 y) completed two 30-minute bouts of cycling (alternating
and constant) at an average intensity equal to 90 % of CP. The intensity during alternating
exercise varied between 158 % CP and 73 % CP. Biopsy samples from the vastus lateralis
muscle were taken before (PRE), at the midpoint and end (POST) of exercise and analysed
for glycogen, lactate, PCr and pH. Although these metabolic variables in muscle changed
significantly during both patterns of exercise, there were no significant differences
(p > 0.05) between constant and alternating exercise for glycogen (PRE: 418.8 ± 85
vs. 444.3 ± 70; POST: 220.5 ± 59 vs. 259.5 ± 126 mmol · kg-1 dw), lactate (PRE: 8.5 ± 7.7 vs. 8.5 ± 8.3; POST: 49.9 ± 19.0 vs. 42.6 ± 26.6 mmol
· kg-1 dw), phosphocreatine (PRE: 77.9 ± 11.6 vs. 75.7 ± 16.9; POST: 65.8 ± 12.1 vs. 61.2
± 12.7 mmol · kg-1 dw) or pH (PRE: 6.99 ± 0.12 vs. 6.99 ± 0.08; POST: 6.86 ± 0.13 vs. 6.85 ± 0.06),
respectively. There were also no significant differences in blood lactate responses
to the two patterns of exercise. These data suggest that, when the average power output
is similar, large variations in exercise intensity exert no significant effect on
muscle metabolism.
Key words
Glycogen - phosphocreatine - alternating-intensity exercise - lactate - pH - cycling
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PhD Gary Brickley
Chelsea School Research Centre
University of Brighton
Gaudick Road
Eastbourne
BN20 7SP
United Kingdom
Phone: + 44 12 73 64 37 60
Email: g.brickley@bton.ac.uk