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The following is the abstract of the article discussed in the subsequent letter: Koga, Shunsaku, Tomoyuki Shiojiri, Narihiko Kondo, and Thomas J. Barstow. Effect of increased muscle temperature on oxygen uptake kinetics during exercise. J. Appl. Physiol. 83(4): 1333–1338, 1997.—To test whether increased muscle temperature (Tm) would improve O2 uptake (V˙o 2) kinetics, seven men performed transitions from rest to a moderate work rate [below the estimated lactate threshold (LTest)] and a heavy work rate (V˙o 2 = 50% of the difference between LTest and peakV˙o 2) under conditions of normal Tm (N) and increased Tm (H), produced by wearing hot water-perfused pants before exercise. Quadriceps Tm was significantly higher in H, but rectal temperature was similar for the two conditions. There were no significant differences in the amplitudes of the fast component ofV˙o 2 or in the time constants of the on and off transients for moderate and heavy exercise between the two conditions. The increment inV˙o 2 between the 3rd and 6th min of heavy exercise was slightly but significantly smaller for H than for N. These data suggest that elevated Tm before exercise onset, which would have been expected to increase O2delivery and off-loading to the muscle, had no appreciable effect on the fast exponential component ofV˙o 2 kinetics (invariant time constant). These data further suggest that elevated Tm does not contribute to the slow component ofV˙o 2 during heavy exercise.

Maximal O2 uptake (VO2max) was determined on a bicycle ergometer in chronic hypoxia (CH) and during acute exposure to normoxia (AN) in 50 healthy young men who were born and had lived at 3,600 m altitude (La Paz, Bolivia). VO2max was significantly improved (approximately 8%) by AN. However, the difference in VO2max measured in CH and AN (delta VO2max) was lower than that reported in sea-level natives (SN) who exercised in chronic normoxia and acute hypoxia. It is shown that high-altitude natives (HN) and SN have a similar VO2max in normoxia, but highlanders can attain a greater VO2max when O2 availability is reduced by altitude exposure. In addition, in HN, the higher the subject's VO2max in hypoxia, the smaller his delta VO2max. These results contrast with the data obtained in 14 lowlanders acclimatized to high altitude who showed that their delta VO2max was positively related to their VO2max in hypoxia, as previously reported in SN who exercised in acute hypoxia (A. J. Young, A. Cymerman, and R. L. Burse. Eur. J. Appl. Physiol. Occup. Physiol. 54: 12–15, 1985). Furthermore, arterial O2 saturation of HN behaved differently from acclimatized lowland natives, inasmuch as it fell less during exercise both in CH and AN. HN with high aerobic capacity display a lower exercise ventilation and a reduced arterial saturation, which could explain their inability to improve VO2max with normoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

End tidal O2 and CO2 (PETCO2) pressures, expired volume, blood lactate concentration ([Lab]), and arterial blood O2 saturation [dry breath holds (BHs) only] were assessed in three elite breath-hold divers (ED) before and after deep dives and BH and in nine control subjects (C; BH only). After the dives (depth 40-70 m, duration 88-151 s), end-tidal O2 pressure decreased from approximately 140 Torr to a minimum of 30.6 Torr, PETCO2 increased from approximately 25 Torr to a maximum of 47.0 Torr, and expired volume (BTPS) ranged from 1.32 to 2.86 liters. Pulmonary O2 exchange was 455-1,006 ml. CO2 output approached zero. [Lab] increased from approximately 1.2 mM to at most 6.46 mM. Estimated power output during dives was 513-929 ml O2/min, i.e. approximately 20-30% of maximal O2 consumption. During BH, alveolar PO2 decreased from approximately 130 to less than 30 Torr in ED and from 125 to 45 Torr in C. PETCO2 increased from approximately 30 to approximately 50 Torr in both ED and C. Contrary to C, pulmonary O2 exchange in ED was less than resting O2 consumption, whereas CO2 output approached zero in both groups. [Lab] was unchanged. Arterial blood O2 saturation decreased more in ED than in C. ED are characterized by increased anaerobic metabolism likely due to the existence of a diving reflex.