(V) over dotO2 and HR kinetics before and after International Space Station missions

Heart rate (HR), pulmonary and muscle oxygen uptake (O(2)pulm, O(2)musc) kinetics after changes of work rate (WR) indicate regulatory characteristics related to aerobic metabolism. We analysed whether the kinetics of HR, O(2)pulm and O(2)musc are slowed after missions to the International Space Station (ISS). The changes of the kinetics were correlated with O(2)peak data. 10 astronauts [4 females, 6 males, age: 48.0 +/- A 3.8 years, height: 176 +/- A 7 cm, mass: 74.5 +/- A 15.9 kg (mean +/- A SD)] performed an incremental test to determine 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, O(2)pulm and 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 (CCFmax, CCFlag) of WR with the analysed parameter. Statistically, significant changes were also found for CCFmax(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 O(2)peak and CCFmax(HR), a correlation was shown (r (SP) = 0.67, P = 0.017). The O(2)musc kinetics changes indicate aerobic detraining effects which are present up to 21 days following space flight. The correlations between changes in O(2)peak and HR kinetics illustrate the key role of cardiovascular regulation in 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.