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EMG and Oxygen Uptake Responses During Slow and Fast Ramp Exercise in Humans
Author(s) -
Scheuermann Barry W.,
McConnell Joyce H. Tripse,
Barstow Thomas J.
Publication year - 2002
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/eph8702246
Subject(s) - cycle ergometer , electromyography , lactate threshold , linear regression , vo2 max , root mean square , chemistry , work rate , mathematics , medicine , zoology , blood lactate , cardiology , heart rate , physical medicine and rehabilitation , physics , biology , blood pressure , statistics , quantum mechanics
This study examined the relationship between muscle recruitment patterns using surface electromyography (EMG) and the excess O 2 uptake (ExV̇ O2 ) that accompanies slow (SR, 8 W min −1 ) but not fast (FR, 64 W min −1 ) ramp increases in work rate (WR) during exercise on a cycle ergometer. Nine subjects (2 females) participated in this study (25 ± 2 years, ± S.E.M.). EMG was obtained from the vastus lateralis and medialis and analysed in the time (root mean square, RMS) and frequency (median power frequency, MDPF) domain. Results for each muscle were averaged to provide an overall response and expressed relative to a maximal voluntary contraction (%MVC). ΔV̇ O2 /ΔWR was calculated for exercise below (S 1 ) and above (S 2 ) the lactate threshold (LT) using linear regression. The increase in RMS relative to the increase in WR for exercise below the LT (ΔRMS/ΔWR‐S 1 ) was determined using linear regression. Due to non‐linearities in RMS above the LT, ΔRMS/ΔWR‐S 2 is reported as the difference in RMS (ΔRMS) and the difference in WR (ΔWR) at end‐exercise and the LT. SR was associated with a higher (P < 0.05) ΔV̇ O2 /ΔWR (S 1 , 9.3 ± 0.3 ml min −1 W −1 ; S 2 , 12.5 ± 0.6 ml min −1 W −1 ) than FR (S 1 , 8.5 ± 0.4 ml min −1 W −1 ; S 2 , 7.9 ± 0.4 ml min −1 W −1 ) but a similar ΔRMS/ΔWR‐S 1 (SR, 0.11 ± 0.01% W −1 ; FR, 0.10 ± 0.01% W −1 ). ExV̇ O2 was greater (P < 0.05) in SR (3.6 ± 0.7 l) than FR (‐0.7 ± 0.4 l) but was not associated with a difference in either ΔRMS/ΔWR‐S 2 (SR, 0.14 ± 0.01% W −1 ; FR, 15 ± 0.02% W −1 ) or MDPF (SR, 2.6 ± 5.9%; FR, ‐15.4 ± 4.5%). The close matching between power output and RMS during SR and FR suggests that the ExV̇ O2 of heavy exercise is not associated with the recruitment of additional motor units since ExV̇ O2 was observed during SR only. Compared to the progressive decrease in MDPF observed during FR, the MDPF remained relatively constant during SR suggesting that either (i) there was no appreciable recruitment of the less efficient type II muscle fibres, at least in addition to those recruited initially at the onset of exercise, or (ii) the decrease in MDPF associated with fatigue was offset by the addition of a higher frequency of type II fibres recruited to replace the fatigued motor units.