Biological Rhythms 48 Hour Experiment: Flight Engineer (FE)-5 Parmitano configured and donned an Actiwatch, attached electrodes to his chest, and will wear the Digital Walk Holter Electrocardiogram (ECG) for JAXA’s 48 hour Biological Rhythms experiment. This study examines the circadian variation of astronaut’s cardiac autonomic function during space flight. The research is expected to provide …