Prior heavy knee extension exercise does not affect VO 2 kinetics during subsequent heavy cycling exercise

John R. Thistlethwaite, Benjamin C. Thompson, Joaquin U. Gonzales, Barry W. Scheuermann

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4 Scopus citations


This study examined the magnitude of the oxygen uptake slow component (VO 2 SC) during heavy exercise when preceded by heavy knee extension (KE) exercise. Nine males (26.6 ±1.7 years, ±SE) performed repeated bouts of heavy exercise, each lasting 6 min with 6 min of recovery. Cycling-cycling trials (CYC1, CYC2) involved step transitions to a workrate corresponding to 50% of the difference between peak VO 2 and the lactate threshold (Δ 50%). During bilateral KE-cycling trails (KE, CYC3), KE was performed at an intensity requiring twofold greater muscle activation relative to CYC1 followed by a cycling transition to Δ 50%. VO 2 was measured breath-by-breath and was modeled using three exponentials to determinate the amplitudes (A 2', A 3') and time constants (τ 2, τ 3) of the primary phase and VO 2 SC. Electromyography (EMG) recorded from the vastus lateralis and medialis was averaged and reported relative to maximal voluntary contraction (%MVC). EMG was higher (p < 0.05) during KE (37.6 ±8.1 %MVC) than CYC1 (20.8 ± 1.9 %MVC), CYC2 (21.6 ± 5.7 %MVC) and CYC3 (19.8 ± 6.3 %MVC). The amplitude of the VO 2 SC was lower (p < 0.05) in CYC2 (197 ± 120 ml min -1) and CYC3 (163 ± 51 ml min -1) compared to CYC1 (325 ± 126 ml min -1). No difference in VO 2 SC was observed between CYC2 and CYC3. Although the activation of additional motor units during KE exercise reduced the amplitude of the VO 2 SC, the decrease was similar to that observed following heavy cycling exercise. Thus, the activation of motor units in excess of those required for the activity does not alter the VO 2 response during a subsequent bout of exercise.

Original languageEnglish
Pages (from-to)481-491
Number of pages11
JournalEuropean journal of applied physiology
Issue number4
StatePublished - Mar 2008


  • Knee-extension
  • Muscle activation
  • O cost
  • Prior heavy exercise
  • Time constant


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