BackgroundTo counteract microgravity (µG)-induced adaptation, European Space Agency (ESA) astronauts on long-duration missions (LDMs) to the International Space Station (ISS) perform a daily physical exercise countermeasure program. Since the first ESA crewmember completed an LDM in 2006, the ESA countermeasure program has strived to provide efficient protection against decreases in body mass, muscle strength, bone mass, and aerobic capacity within the operational constraints of the ISS environment and the changing availability of on-board exercise devices. The purpose of this paper is to provide a description of ESA’s individualised approach to in-flight exercise countermeasures and an up-to-date picture of how exercise is used to counteract physiological changes resulting from µG-induced adaptation. Changes in the absolute workload for resistive exercise, treadmill running and cycle ergometry throughout ESA’s eight LDMs are also presented, and aspects of pre-flight physical preparation and post-flight reconditioning outlined.ResultsWith the introduction of the advanced resistive exercise device (ARED) in 2009, the relative contribution of resistance exercise to total in-flight exercise increased (33–46 %), whilst treadmill running (42–33 %) and cycle ergometry (26–20 %) decreased. All eight ESA crewmembers increased their in-flight absolute workload during their LDMs for resistance exercise and treadmill running (running speed and vertical loading through the harness), while cycle ergometer workload was unchanged across missions.ConclusionIncreased or unchanged absolute exercise workloads in-flight would appear contradictory to typical post-flight reductions in muscle mass and strength, and cardiovascular capacity following LDMs. However, increased absolute in-flight workloads are not directly linked to changes in exercise capacity as they likely also reflect the planned, conservative loading early in the mission to allow adaption to µG exercise, including personal comfort issues with novel exercise hardware (e.g. the treadmill harness). Inconsistency in hardware and individualised support concepts across time limit the comparability of results from different crewmembers, and questions regarding the difference between cycling and running in µG versus identical exercise here on Earth, and other factors that might influence in-flight exercise performance, still require further investigation.

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The purpose of this study was to 1) evaluate the baroreflex (BR) modulation of the sinus node during isometric exercise in humans by analyzing the variations in pulse interval (PI) in response to beat-by-beat spontaneous changes in systolic arterial pressure (SAP), thus avoiding external intervention to alter arterial pressure (AP); and to 2) evaluate the specific influence of muscle chemoreflex on the SAP-PI relationship. Sixteen healthy males were studied during rest, handgrip at 30% of maximum voluntary contraction [isometric handgrip (IHG)], post-IHG arrested forearm circulation (AFC), and recovery. AP and PI were measured continuously and noninvasively. A BR response was defined by series of at least three consecutive beats in which SAP and PI of the following beat either increased or decreased in a linear fashion. In nine subjects, forearm (FVR) and calf vascular resistances (CVR) were determined. Mean slope (by linear regression) of SAP-PI sequences did not significantly differ between rest, IHG, and AFC (14.1 +/- 2.0, 12.2 +/- 1.6, and 13.2 +/- 1.4 ms/mmHg, respectively), i.e., BR sensitivity was unchanged. IHG resulted in a rightward shift of the regression line relating SAP to PI. The shift was maintained during AFC, when PI returned to control and AP fell slightly but remained significantly elevated. CVR, which did not change during IHG, significantly increased during AFC, whereas FVR increased during both IHG and AFC, but not significantly. The data indicate that arterial BR is "reset" to a higher operating point during isometric exercise. Muscle chemoreflex appears to be partially involved in this modification.(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of the present study was to compare arterial pressure (AP) and heart rate (HR) responses to submaximal isokinetic, isotonic and isometric exercises currently employed in physical rehabilitation therapy in terms of both magnitude and time-course. To this aim AP and HR were continuously and noninvasively measured in ten healthy subjects performing isokinetic, isotonic and isometric exercises at the same relative intensity. Isokinetic and isotonic exercises consisted of 30 knee extension/flexion repetitions at 40% of maximal effort. Isokinetic speed was set at 180 degrees s(-1). Isometric exercise consisted of a 60-s knee extension at 40% maximal voluntary contraction. The AP showed a rapid and marked increase from the onset of all types of exercise progressing throughout the exercises. Peak systolic (SAP) and diastolic (DAP) arterial pressure were 190.7 (SEM 8.9) and 121.6 (SEM 7.8) mmHg during isokinetic and 197.6 (SEM 11.2) and 128.3 (SEM 7.7) mmHg during isotonic exercise, respectively. During isometric exercise peak SAP and DAP were 168.1 (SEM 6.3) and 102.1 (SEM 3.7) mmHg, respectively [both lower compared to isokinetic and isotonic exercise (P < 0.05)]. The HR rose abruptly and after five isokinetic and isotonic repetitions it had already increased by about 30 beats min(-1), continuing to rise throughout the exercises. The HR response to isometric exercise was significantly less (P < 0.05) at all times. An immediate fall in AP, undershooting resting levels, was observed at the cessation of all types of exercise, being more marked after isokinetic and isotonic exercise. These results indicate that submaximal exercise of a dynamic type induces greater AP responses than intensity-matched isometric exercise and that even submaximal endurance-type rehabilitation exercise yields an elevated functional stress on the cardiovascular system which could precipitate hazardous events particularly in subjects with unrecognized cardiac diseases.

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