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Cited by 87Sports Performance and TrainingCardiovascular and exercise physiologyMuscle metabolism and nutrition

Metabolic and performance responses to constant-load vs. variable-intensity exercise in trained cyclists

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Palmer, Garry S., Borghouts, Lars B., Noakes, Timothy D., Hawley, John A.·1999·Journal of Applied Physiology
DOI 10.1152/jappl.1999.87.3.1186
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Abstract

We studied glucose oxidation (Glu ox ) and glycogen degradation during 140 min of constant-load [steady-state (SS)] and variable-intensity (VI) cycling of the same average power output, immediately followed by a 20-km performance ride [time trial (TT)]. Six trained cyclists each performed four trials: two experimental bouts (SS and VI) in which muscle biopsies were taken before and after 140 min of exercise for determination of glycogen and periodic acid-Schiff’s staining; and two similar trials without biopsies but incorporating the TT. During two of the experimental rides, subjects ingested a 5 g/100 ml [U- 14 C]glucose solution to determine rates of Glu ox . Values were similar between SS and VI trials: O 2 consumption (3.08 ± 0.02 vs. 3.15 ± 0.03 l/min), energy expenditure (901 ± 40 vs. 904 ± 58 J ⋅ kg −1 ⋅ min −1 ), heart rate (156 ± 1 vs. 160 ± 1 beats/min), and rating of perceived exertion (12.6 ± 0.6 vs. 12.7 ± 0.7). However, the area under the curve for plasma lactate concentration vs. time was significantly greater during VI than SS (29.1 ± 3.9 vs. 24.6 ± 3.7 mM/140 min; P = 0.03). VI resulted in a 49% reduction in total muscle glycogen utilization vs. 65% for SS, while total Glu ox was higher (99.2 ± 5.3 vs. 83.9 ± 5.2 g/140 min; P < 0.05). The number of glycogen-depleted type I muscle fibers at the end of 140 min was 98% after SS but only 59% after VI. Conversely, the number of type II fibers that showed reduced periodic acid-Schiff’s staining was 1% after SS vs. 10% after VI. Despite these metabolic differences, subsequent TT performance was similar (29.14 ± 0.9 vs. 30.5 ± 0.9 min for SS vs. VI). These results indicate that whole body metabolic and cardiovascular responses to 140 min of either SS or VI exercise at the same average intensity are similar, despite differences in skeletal muscle carbohydrate metabolism and recruitment.

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  • Multiple studies comparing continuous versus variable intensity cycling found no differences in total glycogen use, although fiber-type-specific depletion patterns do occur.

    “multiple studies comparing continuous versus variable intensity cycling, which found no differences in total glycogen use, although fi ber-type-speci fi c depletion patterns do occur (54, 76).”

    From Carbohydrate ingestion during prolonged exercise and net skeletal muscle glycogen utilization: A meta-analysis. (2026) · cites this paper as [76]

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Authors
Palmer, G. S., Borghouts, L. B., Noakes, T. D., & Hawley, J. A.
Affiliations
  • Kingston University London (GB)
  • Maastricht University (NL)
  • University of Cape Town (ZA)
  • RMIT Europe (ES)
ORCID
Venue
Journal of Applied Physiology
Publisher
American Physiological Society
Published
1999-09-01
Volume
87
Issue
3
Pages
1186-1196
ISSN
  • 0161-7567 (ISSN-L)
  • 8750-7587
  • 1522-1601
DOI
10.1152/jappl.1999.87.3.1186
OpenAlex
W1925377137
Cited by
87
References
36
Citations by year
2026: 2 · 2025: 3 · 2024: 3 · 2023: 1 · 2022: 1 · 2021: 2 · 2020: 5 · 2019: 4 · 2018: 3 · 2017: 1 · 2016: 1 · 2015: 3 · 2014: 4 · 2013: 4 · 2012: 6
FWCI
2.62
Type
journal article
Language
en
Open access
Licence
other-oa
Locations
  • Journal of Applied Physiology (publishedVersion)
  • PubMed (publishedVersion)
  • Data Archiving and Networked Services (DANS) (submittedVersion, other-oa)
  • Research Repository (Kingston University London) (submittedVersion)
Topics
  • Health Sciences › Medicine › Orthopedics and Sports Medicine › Sports Performance and Training
  • Health Sciences › Medicine › Complementary and alternative medicine › Cardiovascular and exercise physiology
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Muscle metabolism and nutrition
Keywords
constant-load exercise, steady-state exercise, trained cyclists, glucose oxidation, plasma lactate, time trial performance, type I muscle fibers, fast-twitch muscle, exercise metabolism, endurance cycling, energy expenditure, oxygen consumption, rating of perceived exertion, heart rate response, carbohydrate oxidation, glycogen depletion
MeSH terms
Adolescent, Adult, Bicycling, Blood Glucose, Diet, Dietary Carbohydrates, Energy Metabolism, Fats, Glucagon, Heart Rate, Humans, Insulin, Kinetics, Male, Metabolism, Oxygen Consumption, Physical Fitness, Muscle, Skeletal, Muscle Fibers, Skeletal, Cross-Over Studies

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