The slow component of O2uptake is not accompanied by changes in muscle EMG during repeated bouts of heavy exercise in humans

• DOI: 10.1111/j.1469-7793.2001.0245j.x
• Publication Date: 2004-08-05T11:13:24Z
• Authors: Barry W. Scheuermann; Brian D. Hoelting; M. Larry Noble; Thomas J. Barstow
• Keywords: Work rate; Lactate threshold; Cycle ergometer; Intensity

1 We hypothesized that either the recruitment of additional muscle motor units and/or progressive less efficient fast-twitch fibres was predominant contributor to oxygen 1uptake (V̇ O 2 ) observed during heavy exercise. Using surface electromyographic (EMG) techniques, we compared V̇ response with integrated EMG (iEMG) and mean power frequency (MPF) vastus lateralis repeated bouts moderate (below lactate threshold, <LT) (above >LT) intensity cycle ergometer Seven male subjects (age 29 ± 7 years, ±s.d.) performed three transitions a work rate (WR) corresponding 90 % LT two would elicit 50 difference between peak (i.e. Δ50 %, >LT1 >LT2). 3 The slow component significantly reduced by prior exercise (>LT1, 410 196 ml min−1; >LT2, 230 191 min−1). time constant (τ), amplitude (A) gain (ΔV̇ /ΔWR) primary (phase II) were not affected when three-component, exponential model used describe response. 4 Integrated MPF remained relatively at same level throughout both >LT2 therefore associated component. 5 These data are consistent view increased O2 cost component) performing is coupled increase in ATP requirements already recruited rather than changes pattern versus units. Further, lack speeding kinetics exercise, thought represent initial response, inconsistent delivery being limiting factor