ECSS Paris 2023: CP-PN07
INTRODUCTION: The energetic cost of transport (CoT) follows a U-shaped curve during walking (where the lowest walking CoT defines the economical speed (ES), intersecting with a linear running CoT at the economical transition speed (EOTS). Muscle tissue saturation index (TSI), derived from near-infrared spectroscopy (NIRS), quantifies local oxygenation and may reflect different components of the oxygen transport chain. Environmental factors such as heat and hypoxia are known to influence CoT as well as muscular TSI. The aim of the study was a) to assess the relationship between CoT and muscle TSI during human locomotion under environmental stress and b) to assess the impacts of environmental stress on energetic markers of economy (ES and EOTS). METHODS: Thirteen participants completed four randomized trials in control (CON; FiO2 20.9%, 24 °C, 50% relative humidity [RH]), heat (HOT; FiO2 20.9%, 35 °C, 50% RH), moderate normobaric hypoxia (MH; FiO2 16.8%, simulating ~1800 m altitude, 24 °C, 50% RH), and severe hypoxia (SH; FiO2 13.3%, simulating ~3600 m altitude, 24 °C, 50% RH) conditions. Each trial included eight walking stages (from 2.4 to 7.3 km·h-1) and four running stages (from 7.3 to 9.4 km·h-1). A computerized breath-by-breath system (Quark, Cosmed, Rome, Italy) was used to measure Pulmonary oxygen uptake (VO2) and carbon dioxide output (VCO2) for CoT, while the TSI of the vastus lateralis was continuously recorded using a portable NIRS device (PortaMon, Artinis Medical Systems, Zetten, the Netherlands). RESULTS: Walking and running CoT increased significantly in SH (+8.8 ± 0.95%, P = 0.003 and +6.0 ± 0.6%, P = 0.005, respectively) and in MH (+7.4 ± 0.9%, P = 0.006 and +8.1 ± 0.6%, P = 0.0002, respectively) versus CON. HOT had no significant effect during walking (-1.9 ± 0.9%, P = 0.47), and running (-3.4 ±. 0.6%, P = 0.099) versus CON. TSI in SH significantly decreased during walking (-9.9 ± 10.7%, P = <0.00001) and running (-13.8 ± 12.5%, P = 0.0009), While in MH no difference was observed during walking (-1.5 ± 8.7%, P =0.39) or running (-1.0 ± 9.7%, P =0.75), compared to CON. No significant difference observed in HOT during walking (-0.9 ± 9.1%, P =0.61) and running (-4.1 ±1 1.7%, P =0.27) compared to CON. ES and EOTS did not significantly change under any condition. CONCLUSION: These results suggest that pulmonary gas exchange limitations under SH contribute substantially to increases in CoT and reductions in muscle TSI during locomotion. MH also increases CoT but without a significant impact on TSI, indicating possible compensatory mechanisms or insufficient environmental stress to observe effects. HOT appears not to have any significant impact on either CoT or TSI, possibly due to thermoregulatory adjusments such as increased cardiac output and blood flow redistribution. The lack of change in ES and EOTS suggests that other factors maintain gait transition parameters under environmental stress.
Read CV Hubert WoronieckiECSS Paris 2023: CP-PN07