Environmental heat stress, hyperammonemia and nucleotide metabolism during intermittent exercise

Magni Mohr, Peter Rasmussen, Barry Drust, Bodil Nielsen, Lars Nybo

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29 Citations (Scopus)


This study investigated the influence of environmental heat stress on ammonia (NH3) accumulation
in relation to nucleotide metabolism and fatigue during
intermittent exercise. Eight males performed 40 min of
intermittent exercise (15 s at 306±22 W alternating with
15 s of unloaded cycling) followed by five 15 s all-out
sprints. Control trials were conducted in a 20C environment while heat stress trials were performed at an
ambient temperature of 40C. Muscle biopsies and
venous blood samples were obtained at rest, after 40 min
of exercise and following the maximal sprints. Following
exercise with heat stress, the core and muscle temperatures peaked at 39.5±0.2 and 40.2±0.2C to be 1C
higher (PMean power output during the five maximal sprints was
reduced from 618±12 W in control to 558±14 W
during the heat stress trial (Ptrial, plasma NH3 increased from 31±2 lM at rest to
93±6 at 40 min and 151±15 lM after the maximal
sprints to be 34% higher than control (Pcontrast, plasma K+ and muscle H+ accumulation were
lower (Pstress compared to control, while muscle glycogen, CP,
ATP and IMP levels were similar across trials. In conclusion, altered levels of ‘‘classical peripheral fatiguing
agents’’ does apparently not explain the reduced
capacity for performing repeated sprints following
intermittent exercise in the heat, whereas the augmented
systemic NH3 response may be a factor influencing fatigue during exercise with superimposed heat stress.
Original languageEnglish
Pages (from-to)89-95
Number of pages7
JournalEuropean Journal of Applied Physiology
Issue number1
Publication statusPublished - 2006


  • Sprint performance
  • Fatigue
  • Muscle metabolism
  • Exercise
  • Hyperthermia


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