Muscle Oxygenation During Hypoxic Exercise in Children and Adults

Abstract

IntroductionWhile hypoxia is known to decrease peak oxygen uptake (V.⁢o2 max) and maximal power output in both adults and children its influence on submaximal exercise cardiorespiratory and, especially, muscle oxygenation responses remains unclear.MethodsEight pre-pubertal boys (age = 8 ± 2 years.; body mass (BM) = 29 ± 7 kg) and seven adult males (age = 39 ± 4 years.; BM = 80 ± 8 kg) underwent graded exercise tests in both normoxic (PiO2 = 134 ± 0.4 mmHg) and hypoxic (PiO2 = 105 ± 0.6 mmHg) condition. Continuous breath-by-breath gas exchange and near infrared spectroscopy measurements, to assess the vastus lateralis oxygenation, were performed during both tests. The gas exchange threshold (GET) and muscle oxygenation thresholds were subsequently determined for both groups in both conditions.ResultsIn both groups, hypoxia did not significantly alter either GET or the corresponding V.⁢o2 at GET. In adults, higher trueV.E levels were observed in hypoxia (45 ± 6 l/min) compared to normoxia (36 ± 6 l/min, p < 0.05) at intensities above GET. In contrast, in children both the hypoxic trueV.E and V.⁢o2 responses were significantly greater than those observed in normoxia only at intensities below GET (p < 0.01 for trueV.E and p < 0.05 for V.⁢o2). Higher exercise-related heart rate (HR) levels in hypoxia, compared to normoxia, were only noted in adults (p < 0.01). Interestingly, hypoxia per se did not influence the muscle oxygenation thresholds during exercise in neither group. However, and in contrast to adults, the children exhibited significantly higher total hemoglobin concentration during hypoxic as compared to normoxic exercise (tHb) at lower exercise intensities (30 and 60 W, p = 0.01).ConclusionThese results suggest that in adults, hypoxia augments exercise ventilation at intensities above GET and might also maintain muscle blood oxygenation via increased HR. On the other hand, children exhibit a greater change of muscle blood perfusion, oxygen uptake as well as ventilation at exercise intensities below GET.

Effects of Pre-Term Birth on the Cardio-Respiratory Responses to Hypoxic Exercise in Children

“…First, the variability in several outcome measures was relatively high, so similarities between groups may be due to a lack of statistical power in those comparisons. However, our previous work in children cohorts [30,31] suggested that this study was sufficiently powered to detect differences in exercise capacity. Furthermore, participants with BPD were excluded from the study which, while allowing an investigation of prematurity per se, may underestimate the effect of pre-term birth in relation to the entire population.…”

Effects of Acute Moderate Hypoxia versus Normoxia on Metabolic and Cardiac Function and Skeletal Muscle Oxygenation during Endurance Exercise at the Same Heart Rate Level

“…Endurance exercise under hypoxia decreases skeletal muscle oxygenation, such as decreased oxhb and StO 2 , and increased dxhb compared with that under normoxia. Skeletal muscle oxygenation during endurance exercise under hypoxia can decrease due to increased skeletal muscle extraction and a reduction in oxygen supply to the skeletal muscle tissue compared with that under normoxia [ 11 , 12 , 13 , 28 ]. Therefore, we examined changes in skeletal muscle oxygenation during endurance exercise at the same relative exercise intensity under hypoxia and normoxia.…”

“…In addition, exercise under hypoxia has been shown to have some adverse effects on skeletal muscle oxygen profiles [ 10 , 11 , 12 , 13 ]. Acute exposure to hypoxia induces systemic hypoxia, which can compromise skeletal muscle oxygenation and subsequently, skeletal muscle ability [ 14 , 15 ].…”

“…Acute exposure to hypoxia induces systemic hypoxia, which can compromise skeletal muscle oxygenation and subsequently, skeletal muscle ability [ 14 , 15 ]. These acute responses of skeletal muscle oxygenation under hypoxia induce attenuated aerobic exercise capacity and VO 2 max, as well as changes in metabolic function [ 9 , 13 ]. Regarding cardiac function, exercise corresponding to the same exercise load under hypoxia induces increased HR and cardiac output (CO) to compensate for the decrease in oxygen delivery and utilization capacities and the activated sympathetic nervous system [ 16 , 17 ].…”

“…The majority of previous studies comparing the acute response during exercise under hypoxia and normoxia examined the changes in various physiological parameters in response to the same load or relative intensity during submaximal exercise and maximal exercise [ 3 , 4 , 5 , 6 , 7 , 8 , 10 , 12 , 13 , 17 , 20 ]. However, studies on metabolic function, skeletal muscle oxygenation, and cardiac function responses during exercise with the same HR level under hypoxia and normoxia are limited [ 21 ].…”