Heart Rate and Muscular Oxygen Uptake Kinetics of Astronauts Compared to Younger and Elderly Subjects

Abstract

Heart rate (HR) and muscular (VO2musc) exercise oxygen uptake kinetics are indicators of aerobic fitness. PURPOSE: The kinetics of 12 astronauts (AG) participating in International Space Station (ISS) missions ranging from 94 to 190 days were compared with groups of younger (YG) and elderly subjects (EG). The pre/post mission ISS findings are also presented. METHODS: Subjects performed a cardio-respiratory kinetics test with randomized changes in WR between 30 W and 80 W. VO2musc was derived from HR and VO2pulm using the method of Hoffmann et al. (2013). The kinetics of HR and VO2musc are summarized by maximum and respective lag of cross-correlation function (CCFmax, CCFlag). To determine differences between the groups and for the pre/post ISS mission measurements, ANOVA and following Bonferroni-tests were applied. P<=0.05 was regarded as significant. RESULTS: Table 1 gives the results for the different groups (means±SD; *: significant differences between all groups, †: significant differences from the other two groups, #: significant difference between YG and EG). For the pre/post ISS mission comparison, CCFmax(VO2musc) was significantly decreased (-0.06±0.06; P=0.014) while other parameters did not differ. CONCLUSIONS: The HR kinetics of astronauts (AG) more closely resemble the EG than the YG despite differences in VO2peak and age. In contrast, VO2musc kinetics of the AG reflect a level of fitness nearer that of the YG. The change in CCFmax(VO2musc) following ISS flight indicates that future countermeasures training should focus on maintaining muscle-specific aerobic function. Funded by DLR (Deutsches Zentrum für Luft- und Raumfahrt) Germany (FKZ 50WB0726)Table: No title available.