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We evaluated the effect of supplemental O2 on energy metabolism of hypoxemic humans by measuring O2 uptake (VO2) kinetics and other cardiorespiratory parameters in nine male chronic obstructive pulmonary disease (COPD) patients and seven age-matched control subjects (on air and on 30% O2) at rest and during moderate cycle ergometer exercise. Heart rate, ventilation, VO2, CO2 output, respiratory exchange ratio, O2 cost of work, and work efficiency were measured with a computerized metabolic cart; O2 deficit and VO2 time courses were calculated. In COPD patients, 30% O2 breathing resulted in 1) reduction of O2 deficit (from 488 +/- 34 ml in air to 398 +/- 27 ml in O2; P < 0.05) and phase 2 VO2 time constant (from 116 +/- 13 s in air to 74 +/- 12 s in O2; P < 0.05); 2) a smaller steady-state increment in CO2 output than in room air (315 +/- 17 ml/min in O2 vs. 358 +/- 27 ml/min in air; P < 0.02), which resulted in a lower exercise respiratory exchange ratio (0.75 +/- 0.02 in O2 vs. 0.80 +/- 0.02 in air; P < 0.02); and 3) reduced steady-state ventilation (22.6 +/- 1.0 l/min in O2 vs. 25.4 +/- 1.1 l/min in air; P < 0.05). In conclusion, 30% O2 breathing accelerated exercise VO2 kinetics in mildly hypoxemic COPD patients. The observed VO2 kinetics improvement with O2 supplementation is consistent with an enhancement of aerobic metabolism in skeletal muscles during moderate exercise.

Federal law prohibits pre-employment physical examination of firefighter recruits, but these workers must perform intense exercise in arduous environments. Components of physical fitness of rookie firefighters (n ϭ 115; 104 men, mean Ϯ SD: age ϭ 28.3 Ϯ 4.3 years; height ϭ 1.76 Ϯ 0.07 m; weight ϭ 83.2 Ϯ 13.9 kg; percent body fat ϭ 17 Ϯ 8%) were measured upon being hired and following a 16-week exercise training program (1 h·d Ϫ1 , 3 d·wk Ϫ1 ) designed to improve physical fitness. Maximum aerobic capacity (V O 2 max) was estimated from submaximal cycle ergometry, body composition from skinfold tests, flexibility from a sit and reach test, strength by hand grip dynamometry, and muscle endurance by a push-up test. The results are as follows (*, p Յ 0.007 vs. pretraining): V O 2 max increased by 28% (35 Ϯ 7 to 45 Ϯ 6* ml·kg Ϫ1 ·min Ϫ1 , 88 Ϯ 20 to 113 Ϯ 17%* of predicted increase); muscle endurance increased (41 Ϯ 13 to 51 Ϯ 14* push-ups); flexibility increased (0.34 Ϯ 0.07 to 0.35 Ϯ 0.07* m); muscle strength tended to increase (102.9 Ϯ 18.7 to 105.4 Ϯ 18.7 kg, p ϭ 0.06); body weight tended to decrease (83.2 Ϯ 13.9 to 82.7 Ϯ 13.2 kg, p ϭ 0.06); lean tissue weight increased (68.8 Ϯ 9.9 to 69.9 Ϯ 9.5* kg); and fat weight decreased (14.6 Ϯ 8.0 to 13.0 Ϯ 7.1* kg). We concluded that aerobic capacity was 20% lower before training than that deemed sufficient for safe performance of fire suppression duties; that training improved aerobic capacity by 28%, decreased fat and increased lean tissue weight, and increased/ tended to increase other components of physical fitness. Prior to initiation of this training program, aerobic capacity of these firefighters was below that deemed appropriate for performing fire suppression duties. Training resulted in a large increase in aerobic capacity, so that the trainees ended the program with an aerobic capacity considered appropriate for fighting fires. It is hoped that the results of this study will encourage those who oversee workers who are responsible for the public's safety to mandate assessment of physical fitness of new hires, with mandatory participation in exercise training for those new hires who are found to possess less than appropriate aerobic capacity.

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