The effect of pH on fatigue during submaximal isometric contractions of the human calf muscle

Jason C Siegler*, Paul Marshall, Mathias Krogh Poulsen, Niels-Peter Brøchner Nielsen, David Kennedy, Simon Green

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


PURPOSE: This study examined whether changes in pH throughout the physiologic range would have a differential effect on central and peripheral factors associated with fatigue and force production during submaximal lower limb isometric exercise to task failure.

METHODS: Eight males completed three experimental trials [0.2 g kg(-1) ammonia chloride (ACD); 0.3 g kg(-1) calcium carbonate (PLA); or 0.3 g kg(-1) sodium bicarbonate (ALK)], each consisting of submaximal calf contractions at 55% of maximal voluntary contraction (MVC) to task failure. Every minute of the task subjects performed an MVC, coupled with stimulation of the tibial nerve during and immediately post MVC.

RESULTS: Time to task failure was not different between trials (ACD 531 ± 166 s, PLA 592 ± 163 s, ALK 596 ± 150 s; p = 0.31). MVC force in all trials declined 29 % from the start of exercise to the fifth minute (mean decline of 371 ± 26 N; p < 0.001), however was not different between trials (p = 0.21). Fatigue was mediated in all trials by central and peripheral factors, as declines in voluntary activation, V/M-wave in the soleus and the potentiated resting twitch amplitudes were evident throughout the task (p < 0.05). Central fatigue appeared to be muscle specific, as reductions in central drive (V/M-wave and rate of sEMG rise) persisted in the soleus but not the medial gastrocnemius.

CONCLUSIONS: These data suggest that calf fatigue associated with intermittent, isometric contractions to task failure is unaffected by alterations in pH; however, central drive reductions may be muscle specific.

Original languageEnglish
JournalEuropean Journal of Applied Physiology
Issue number3
Pages (from-to)565-577
Publication statusPublished - Mar 2015
Externally publishedYes


  • Fatigue
  • Sodium Bicarbonate
  • Acid-base balance
  • ammonia chloride
  • Ammonia chloride
  • Sodium bicarbonate
  • Acid–base balance


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