Gas exchange, blood lactate, and plasma catecholamines during incremental exercise in hypoxia and normoxia

Abstract

The interrelationships among blood lactate (La-) and plasma norepinephrine (NE) and epinephrine (Epi) were studied simultaneously with measures of ventilation (VE) and gas exchange during incremental exercise to exhaustion in nine healthy young men. We wanted to observe whether the tight coupling that exists during normoxic exercise between the concentrations of La- ([La-]) and of both NE and Epi would also be found in hypoxia (inspired O2 fraction = 0.14). In addition, we used recently advocated methods of V slope [CO2 output vs. O2 uptake (VO2)] to select the ventilatory threshold (VT) and log-log transformation of [La-] and VO2 to select the lactate threshold (LT). Peak VO2 was reduced from 4,164 +/- 184 ml/min in normoxia to 3,635 +/- 144 ml/min in hypoxia (P < 0.05). The increase in [La-] was linearly related to the increases in both NE and Epi concentrations in the normoxic and hypoxic tests (r = 0.92-0.96). Estimates of VO2 at VT were significantly greater than those at LT in both normoxia and hypoxia, but these estimates were poorly correlated (r = -0.11-0.46). VT and LT were reduced by hypoxia. Visual interpretation of the VT by examination of VE vs. VO2 and VE/VO2 vs. VO2 did not differ from the LT, but they were less than the VTs by the V-slope method (P < 0.05); yet, all were poorly correlated. The tight coupling between the increase in [La-] and the increase in plasma catecholamines might indicate a common mechanism for the increase or a causative link. VT and LT provided estimates of the general trend in the data, but the poor correlation between them questions the utility of attempting to predict one from the other.

Regulation of V̇o2 kinetics by O2 delivery: insights from acute hypoxia and heavy-intensity priming exercise in young men

“…On the basis of previous findings (17,38), a WR corresponding to ϳ80% of the V O2 at L was expected to still reside in the moderate-intensity domain when performed in Hypo; this was confirmed in the present study by the identical estimated steadystate V O2p values observed in normoxia and hypoxia (without previous Hvy) and, thus, the absence of a V O2p slow component under hypoxic conditions. Thus, after the ramp incremental test and on separate days, subjects completed three repetitions of each of three different exercise protocols (Fig.…”

Effects of Hypoxia on the Onset of Muscle Deoxygenation and the Lactate Threshold

“…These relationships may be explained by our observations, as well as those of others [2,5,6], that under hypoxic conditions the LT occurred at a lower exercise intensity compared to that seen during normoxia. It is generally believed that during hypoxia there is greater sympathetic nervous system activation, which stimulates glycogenolysis and glycolysis, thus contributing to increased lactate accumulation [4,5,7,8].…”

“…Furthermore, when graded exercise is performed under hypoxic conditions, the LT is shifted leftward and occurs at a lower absolute intensity than what is observed under normoxia [2,4,5]. Whether there would be a similar shift in the onset of muscle deoxygenation (OMD) under hypoxia is unknown; thus we have undertaken this study.…”

Metabolic, enzymatic, and transporter responses in human muscle during three consecutive days of exercise and recovery

“…Each participant performed the same amount of work on each of the 3 days of cycling. For each individual, the relative intensity was determined from the relationship between V O2 and power output obtained during a progressive cycle test (41). The progressive cycle test was performed ϳ4 wk prior to the short-term training sessions.…”

“…The V O2peak was assessed during the progressive exercise test to fatigue by a protocol previously used in our laboratory (41). Ventilation and gas exchange were measured continuously through the test by previously published methods (42).…”