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Neuromuscular Fatigue and Metabolism during High-Intensity Intermittent Exercise

FIORENZA, MATTEO1,2; HOSTRUP, MORTEN1; GUNNARSSON, THOMAS P.1; SHIRAI, YUSUKE1; SCHENA, FEDERICO2; IAIA, F. MARCELLO3; BANGSBO, JENS1

Medicine & Science in Sports & Exercise: August 2019 - Volume 51 - Issue 8 - p 1642–1652
doi: 10.1249/MSS.0000000000001959
BASIC SCIENCES
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Purpose To examine the degree of neuromuscular fatigue development along with changes in muscle metabolism during two work-matched high-intensity intermittent exercise protocols in trained individuals.

Methods In a randomized, counter-balanced, crossover design, 11 endurance-trained men performed high-intensity intermittent cycle exercise protocols matched for total work and including either multiple short-duration (18 × 5 s; SS) or long-duration (6 × 20 s; LS) sprints. Neuromuscular fatigue was determined by preexercise to postexercise changes in maximal voluntary contraction force, voluntary activation level and contractile properties of the quadriceps muscle. Metabolites and pH were measured in vastus lateralis muscle biopsies taken before and after the first and last sprint of each exercise protocol.

Results Peak power output (11% ± 2% vs 16% ± 8%, P < 0.01), maximal voluntary contraction (10% ± 5% vs 25% ± 6%, P < 0.05), and peak twitch force (34% ± 5% vs 67% ± 5%, P < 0.01) declined to a lesser extent in SS than LS, whereas voluntary activation level decreased similarly in SS and LS (10% ± 2% vs 11% ± 4%). Muscle [phosphocreatine] before the last sprint was 1.5-fold lower in SS than LS (P < 0.001). Preexercise to postexercise intramuscular accumulation of lactate and H+ was twofold and threefold lower, respectively, in SS than LS (P < 0.001), whereas muscle glycogen depletion was similar in SS and LS. Rate of muscle glycolysis was similar in SS and LS during the first sprint, but twofold higher in SS than LS during the last sprint (P < 0.05).

Conclusions These findings indicate that, in endurance-trained individuals, multiple long-sprints induce larger impairments in performance along with greater degrees of peripheral fatigue compared to work-matched multiple short-sprints, with these differences being possibly attributed to more extensive intramuscular accumulation of lactate/H+ and to lower rates of glycolysis during multiple long-sprint exercise.

1Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, DENMARK;

2Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, ITALY; and

3Department of Biomedical Sciences for Health, University of Milan, Milan, ITALY

Address for correspondence: Jens Bangsbo, Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, August Krogh Building, Universitetsparken 13, 2100 KBH Ø, Copenhagen, Denmark; E-mail: jbangsbo@nexs.ku.dk.

Submitted for publication October 2018.

Accepted for publication February 2019.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.acsm-msse.org).

Online date: February 27, 2019

© 2019 American College of Sports Medicine