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Influence of work rate on the determinants of oxygen deficit during short‐term submaximal exercise: implications for clinical research *
Author(s) -
Reybrouck Tony,
Defoor Johan,
Bijnens Bart,
Mertens Luc,
Gewillig Marc
Publication year - 2003
Publication title -
clinical physiology and functional imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.608
H-Index - 67
eISSN - 1475-097X
pISSN - 1475-0961
DOI - 10.1046/j.1475-097x.2003.00468.x
Subject(s) - medicine , work rate , oxygen , treadmill , vo2 max , respiratory exchange ratio , heart rate , physical therapy , steady state (chemistry) , physical exercise , cardiology , blood pressure , chemistry , organic chemistry
Summary Objective: The effect of increasing work rate was studied on the determinants of the oxygen deficit. Methods: Exercise testing was performed on a treadmill and gas exchange was measured on a breath‐by‐breath basis. Eleven healthy subjects, aged 18–25 years, performed three square wave exercise tests of different intensity. Before exercise, gas exchange was measured at rest in the standing position for 3 min, followed by a 6‐min square wave exercise test, randomly assigned at 4, 8 or 12% inclination. Immediately after exercise the recovery gas exchange was determined for 3 min. To calculate oxygen deficit, the oxygen uptake (O 2 ) values at onset of exercise were subtracted from the steady‐state value, the differences were cumulated and expressed as a percentage of the total oxygen cost for the 6‐min exercise. Results: The oxygen deficit increased significantly ( P <0·001) with increasing work rate (6·1 ± 1·4% for 4%, 8·4 ± 2·1% for 8% and 9·4 ± 1·7% at 12% inclination). This resulted from a somewhat slower increase of O 2 at the onset of exercise at the highest work rate, reflected by a significantly higher time constant for O 2 at 8 and 12% (24·6 ± 7·3 s at 8% and 24·1 ± 6·3 s at 12% versus 20·2 ± 8·1 s at 4%). More importantly a significantly higher steady‐state value for O 2 was found at the highest exercise level, compared with the other exercise intensities. Conclusion: The higher oxygen deficit at the highest level of exercise is determined by a slower time constant and a higher asymptote value for O 2 .