V˙O2 and HR kinetics before and after International Space Station missions

Purpose Heart rate (HR), pulmonary and muscle oxygen uptake ( V ˙ O 2 pulm, V ˙ O 2 musc) kinetics after changes of work rate (WR) indicate regulatory characteristics related to aerobic metabolism. We analysed whether the kinetics of HR, V ˙ O 2 pulm and V ˙ O 2 musc are slowed after missions to the International Space Station (ISS). The changes of the kinetics were correlated with V ˙ O 2 peak data. Methods 10 astronauts [4 females, 6 males, age: 48.0 ± 3.8 years, height: 176 ± 7 cm, mass: 74.5 ± 15.9 kg (mean ± SD)] performed an incremental test to determine V ˙ O 2 peak (before missions on L-110 days, after return on R+1/+10/+36 days), and a cardio-respiratory kinetics test (CRKT) with randomized 30–80 W WR changes to determine HR, V ˙ O 2 pulm and V ˙ O 2 musc kinetics by time-series analysis (L-236/-73, R+6/+21). Kinetics were summarized by maximum and related lag of cross-correlation function (CCF max , CCF lag ) of WR with the analysed parameter. Results Statistically, significant changes were also found for CCF max ( V ˙ O 2 musc) between L-236 and R+6 ( P = 0.010), L-236 and R+21 ( P = 0.030), L-72 and R+6 ( P = 0.043). Between pre-to-post mission change in V ˙ O 2 peak and CCF max (HR), a correlation was shown ( r SP = 0.67, P = 0.017). Conclusion The V ˙ O 2 musc kinetics changes indicate aerobic detraining effects which are present up to 21 days following space flight. The correlations between changes in V ˙ O 2 peak and HR kinetics illustrate the key role of cardiovascular regulation in V ˙ O 2 peak. The addition of CRKT to ISS flight is recommended to obtain information regarding the potential muscular and cardiovascular deconditioning. This allows a reduction in the frequency of higher intensity testing during flight.