Mechanical and metabolic determination of V̇O2 and fatigue during repetitive isometric contractions in situ

Bill T. Ameredes, William F. Brechue, Wendell N. Stainsby

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


Repetitive isometric tetanic contractions (1/s) of the canine gastrocnemius-plantaris muscle were studied either at optimal length (L(o)) or short length (L(s); ~0.9 · L(o)), to determine the effects of initial length on mechanical and metabolic performance in situ. Respective averages of mechanical and metabolic variables were (L(o) vs. L(s), all P < 0.05) passive tension (preload) = 55 vs. 6 g/g, maximal active tetanic tension (P(o)) = 544 vs. 174 (0.38 · P(o)) g/g, maximal blood flow (Q̇) = 2.0 vs. 1.4 ml · min-1 · g-1, and maximal oxygen uptake (V̇O2) = 12 rs. 9 μmol · min-1 · g-1. Tension at L(o) decreased to 0.64 · P(o) over 20 min of repetitive contractions, demonstrating fatigue; there were no significant changes in tension at L(s). In separate muscles contracting at L(o), Q̇ was set to that measured at L(s) (1.1 ml · min-1 · g-1), resulting in decreased V̇O2 (7μmol · min-1 · g-1), and rapid fatigue, to 0.44 · P(o). These data demonstrate that 1) muscles at L(o) have higher Q̇ and V̇O2 values than those at L(s); 2) fatigue occurs at L(o) with high V̇O2, adjusting metabolic demand (tension output) to match supply; and 3) the lack of fatigue at L, with lower tension, Q̇, and V̇O2 suggests adequate matching of metabolic demand, set low by short muscle length, with supply optimized by low preload. These differences in tension and V̇O2 between L(o) and L(s) groups indicate that muscles contracting isometrically at initial lengths shorter than L(o) are working under submaximal conditions.

Original languageEnglish (US)
Pages (from-to)1909-1916
Number of pages8
JournalJournal of Applied Physiology
Issue number6
StatePublished - Jun 1998
Externally publishedYes


  • Blood flow
  • Canine
  • Gastrocnemius muscle
  • Length
  • Oxygen uptake
  • Passive tension
  • Preload

ASJC Scopus subject areas

  • General Medicine


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