Leveraging Spaceflight to Advance Cardiovascular Research on Earth.

The direct (eg, radiation, microgravity) and indirect (eg, lifestyle perturbations) effects of spaceflight extend across multiple systems resulting in whole-organism cardiovascular deconditioning. For over 50 years, National Aeronautics and Space Administration has continually enhanced a countermeasures program designed to characterize and offset the adverse cardiovascular consequences of spaceflight. In this review, we provide a historical overview of research evaluating the effects of spaceflight on cardiovascular health in astronauts and outline mechanisms underpinning spaceflight-related cardiovascular alterations. We also discuss how spaceflight could be leveraged for aging, industry, and model systems such as human induced pluripotent stem cell-derived cardiomyocytes, organoid, and organ-on-a-chip technologies. Finally, we outline the increasing opportunities for scientists and clinicians to engage in cardiovascular research in space and on Earth.

Teleguided self-ultrasound scanning for longitudinal monitoring of muscle mass during spaceflight.

Loss of muscle mass is a major concern for long duration spaceflight. However, due to the need for specialized equipment, muscle size has only been assessed before and after spaceflight where ~20% loss is observed. Here, we demonstrate the utility of teleguided self-ultrasound scanning (Tele-SUS) to accurately monitor leg muscle size in astronauts during spaceflight. Over an average of 168 ± 57 days of spaceflight, 74 Tele-SUS sessions were performed. There were no significant differences between panoramic ultrasound images obtained by astronauts seven days prior to landing and expert sonographer after flight or between change in muscle size assessed by ultrasound and magnetic resonance imaging. These findings extend the current capabilities of ultrasound imaging to allow self-monitoring of muscle size with remote guidance.

Novel Computerized Method for Automated Determination of Ventilatory Threshold and Respiratory Compensation Point.

Introduction: The ventilatory threshold (named as VT1) and the respiratory compensation point (named as VT2) describe prominent changes of metabolic demand and exercise intensity domains during an incremental exercise test. Methods: A novel computerized method based on the optimization method was developed for automatically determining VT1 and VT2 from expired air during a progressive maximal exercise test. A total of 109 peak cycle tests were performed by members of the US astronaut corps (74 males and 35 females). We compared the automatically determined VT1 and VT2 values against the visual subjective and independent analyses of three trained evaluators. We also characterized VT1 and VT2 and the respective absolute and relative work rates and distinguished differences between sexes. Results: The automated compared to the visual subjective values were analyzed for differences with t test, for agreement with Bland-Altman plots, and for equivalence with a two one-sided test approach. The results showed that the automated and visual subjective methods were statistically equivalent, and the proposed approach reliably determined VT1 and VT2 values. Females had lower absolute O2 uptake, work rate, and ventilation, and relative O2 uptake at VT1 and VT2 compared to men (p ≤ 0.04). VT1 and VT2 occurred at a greater relative percentage of their peak VO2 for females (67 and 88%) compared to males (55 and 74%; main effect for sex: p < 0.001). Overall, VT1 occurred at 58% of peak VO2, and VT2 occurred at 79% of peak VO2 (p < 0.0001). Conclusion: Improvements in determining of VT1 and VT2 by automated analysis are time efficient, valid, and comparable to subjective visual analysis and may provide valuable information in research and clinical practice as well as identifying exercise intensity domains of crewmembers in space.

Disuse-Induced Muscle Loss and Rehabilitation: The National Aeronautics and Space Administration Bed Rest Study.

OBJECTIVES: The time course and magnitude of atrophic remodeling and the effects of an acute rehabilitation program on muscle atrophy are unclear. We sought to characterize bed rest-induced leg muscle atrophy and evaluate the safety and efficacy of an acute rehabilitation program. DESIGN: Prespecified analysis of a randomized controlled trial. SETTING: Single-center urban hospital. PATIENTS: Adults (24-55 yr) randomized to 70 days of sedentary bed rest. INTERVENTIONS: The 11-day post-bed rest rehabilitation program consisted of low intensity exercise and progressed to increased aerobic exercise duration, plyometric exercises, and higher intensity resistance exercise. MEASUREMENTS AND MAIN RESULTS: Upper (rectus femoris, vastus lateralis, quadriceps, hamstrings, adductors) and lower leg (medial gastrocnemius, lateral gastrocnemius, and soleus) MRI scans were obtained once before, nine times during, and three times after bed rest to assess muscle cross-sectional area. The magnitude and rate of muscle atrophy and recovery were determined for each muscle. Nine participants completed 70 days of sedentary bed rest and an 11-day rehabilitation program. A total of 11,588 muscle cross-sectional area images were quantified. Across all muscles except the rectus femoris (no change), there was a linear decline during bed rest, with the highest atrophic rate occurring in the soleus (-0.33%/d). Following rehabilitation, there was rapid recovery in all muscles; however, the quadriceps (-3.74 cm2; 95% CI, -7.36 to -0.12; p = 0.04), hamstrings (-2.30 cm2; 95% CI, -4.07 to -0.54; p = 0.01), medial gastrocnemius (-0.62 cm2; 95% CI, -1.10 to -0.14; p = 0.01), and soleus (-1.85 cm2; 95% CI, -2.90 to -0.81; p < 0.01) remained significantly lower than baseline. CONCLUSIONS: Bed rest results in upper and lower leg muscle atrophy in a linear pattern, and an 11-day rehabilitation program was safe and effective in initiating a rapid trajectory of muscle recovery. These findings provide important information regarding the design and refinement of rehabilitation programs following bed rest.

High intensity training during spaceflight: results from the NASA Sprint Study.

Historically, International Space Station (ISS) exercise countermeasures have not fully protected astronauts' musculoskeletal and cardiorespiratory fitness. Although these losses have been reduced on more recent missions, decreasing the time required to perform in-flight exercise would permit reallocation of that time to other tasks. To evaluate the effectiveness of a new training prescription, ISS crewmembers performed either the high intensity/lower volume integrated Sprint resistance (3 d wk-1) and aerobic (interval and continuous workouts, each 3 d wk-1 in alternating fashion) exercise program (n = 9: 8M/1F, 48 ± 7 y, 178 ± 5 cm, 77.7 ± 12.0 kg) or the standard ISS countermeasure consisting of daily resistance and aerobic exercise (n = 17: 14M/3F, 46 ± 6 y, 176 ± 6 cm, 80.6 ± 10.5 kg) during long-duration spaceflight. Bone mineral density (dual energy X-ray absorptiometry (DXA)), muscle strength (isokinetic dynamometry), muscle function (cone agility test), and cardiorespiratory fitness (VO2peak) were assessed pre- and postflight. Mixed-effects modeling was used to analyze dependent measures with alpha set at P < 0.05. After spaceflight, femoral neck bone mineral density (-1.7%), knee extensor peak torque (-5.8%), cone agility test time (+7.4%), and VO2peak (-6.1%) were decreased in both groups (simple main effects of time, all P < 0.05) with a few group × time interaction effects detected for which Sprint experienced either attenuated or no loss compared to control. Although physiologic outcomes were not appreciably different between the two exercise programs, to conserve time and optimally prepare crewmembers for the performance of physically demanding mission tasks, high intensity/lower volume training should be an indispensable component of spaceflight exercise countermeasure prescriptions.

Exercise and Testosterone Countermeasures to Mitigate Metabolic Changes during Bed Rest.

BACKGROUND/OBJECTIVES: Exercise is a front-line countermeasure used to maintain astronaut health during long-duration spaceflight; however, reductions in metabolic health still occur. Accordingly, we evaluated serial changes in metabolic parameters in a spaceflight analog and evaluated the efficacy of exercise with or without the addition of low-dose testosterone treatment on mitigating adverse metabolic changes. SUBJECTS/METHODS: Healthy young (<55 years) men were randomly assigned to one of three groups during 70-days of strict, diet controlled, 6° head-down bed rest: Control (CON, n=9), exercise plus testosterone countermeasure (TEX, n=8), or exercise countermeasure plus placebo (PEX, n=9). Basal metabolic rate (BMR), glucose tolerance, and insulin sensitivity were measured before, during, and after bed rest. Exercise energy expenditure and excess post-exercise oxygen consumption were measured in TEX and PEX subjects during bed rest. RESULTS: Leptin decreased during bed rest (Pre to BR+0 changed from 6.9 ± 5.1, 5.8 ± 4.2, and 4.7 ± 4.1 to 7.9 ±3.6, 6.5 ± 4.6, and 4.1 ±3.0 ug• L-1 for CON, PEX, and TEX respectively). Bed rest induced a decrease in BMR (Pre to BR57 changed from 1655 ± 212, 1629 ± 108, and 1706 ± 146 to 1476 ± 166, 1668 ± 142, and 1603 ± 132 kcal • day-1 ± 95%CI for CON, PEX, and TEX respectively). Similarly, bed rest negatively affected glucose metabolism assessed by 2hr OGTT glucose (Pre to BR66 changed from 6.29 ± 0.72, 5.13 ± 0.72, and 5.87 ± 0.73 to 6.62 ± 0.72, 5.83 ± 0.72, and 7.08 ± 0.72 mmol • L-1 ± 95%CI). Reambulation following bed rest positively affected glucose tolerance in CON (2hr OGTT glucose at BR+12: 5.3 ± 0.72, 6.42 ± 0.73, and 6.04 ± 0.73 mmol • L-1 ± 95%CI). Testosterone protected against bed rest induced insulin resistance (HOMA-IR from Pre to BR+66 changed from 1.74 ± 0.54, 1.18 ± 0.55, and 1.45 ± 0.56 to 2.24 ± 0.56, 1.47 ± 0.54, and 1.07 ± 0.54). CONCLUSION: This study confirmed that inactivity during 70 days of head-down bed rest adversely affects metabolic health. The daily exercise countermeasures were beneficial but not completely protective of bed rest induced decrements in metabolic health. Supplementary countermeasures such as testosterone may provide additional benefits not provided by exercise alone.

Countermeasures-based Improvements in Stress, Immune System Dysregulation and Latent Herpesvirus Reactivation onboard the International Space Station - Relevance for Deep Space Missions and Terrestrial Medicine.

The International Space Station (ISS) has continued to evolve from an operational perspective and multiple studies have monitored both stress and the immune system of ISS astronauts. Alterations were ascribed to a potentially synergistic array of factors, including microgravity, radiation, psychological stress, and circadian misalignment. Comparing similar data across 12 years of ISS construction and operations, we report that immunity, stress, and the reactivation of latent herpesviruses have all improved in ISS astronauts. Major physiological improvements seem to have initiated approximately 2012, a period coinciding with improvements onboard ISS including cargo delivery and resupply frequency, personal communication, exercise equipment and protocols, food quality and variety, nutritional supplementation, and schedule management. We conclude that spaceflight associated immune dysregulation has been positively influenced by operational improvements and biomedical countermeasures onboard ISS. Although an operational challenge, agencies should therefore incorporate, within vehicle design limitations, these dietary, operational, and stress-relieving countermeasures into deep space mission planning. Specific countermeasures that have benefited astronauts could serve as a therapy augment for terrestrial acquired immunodeficiency patients.

Bridging the gap between military prolonged field care monitoring and exploration spaceflight: the compensatory reserve.

The concept of prolonged field care (PFC), or medical care applied beyond doctrinal planning timelines, is the top priority capability gap across the US Army. PFC is the idea that combat medics must be prepared to provide medical care to serious casualties in the field without the support of robust medical infrastructure or resources in the event of delayed medical evacuation. With limited resources, significant distances to travel before definitive care, and an inability to evacuate in a timely fashion, medical care during exploration spaceflight constitutes the ultimate example PFC. One of the main capability gaps for PFC in both military and spaceflight settings is the need for technologies for individualized monitoring of a patient's physiological status. A monitoring capability known as the compensatory reserve measurement (CRM) meets such a requirement. CRM is a small, portable, wearable technology that uses a machine learning and feature extraction-based algorithm to assess real-time changes in hundreds of specific features of arterial waveforms. Future development and advancement of CRM still faces engineering challenges to develop ruggedized wearable sensors that can measure waveforms for determining CRM from multiple sites on the body and account for less than optimal conditions (sweat, water, dirt, blood, movement, etc.). We show here the utility of a military wearable technology, CRM, which can be translated to space exploration.

The Behavioral Biology of Teams: Multidisciplinary Contributions to Social Dynamics in Isolated, Confined, and Extreme Environments.

Teams in isolated, confined, and extreme (ICE) environments face many risks to behavioral health, social dynamics, and team performance. Complex long-duration ICE operational settings such as spaceflight and military deployments are largely closed systems with tightly coupled components, often operating as autonomous microsocieties within isolated ecosystems. As such, all components of the system are presumed to interact and can positively or negatively influence team dynamics through direct or indirect pathways. However, modern team science frameworks rarely consider inputs to the team system from outside the social and behavioral sciences and rarely incorporate biological factors despite the brain and associated neurobiological systems as the nexus of input from the environment and necessary substrate for emergent team dynamics and performance. Here, we provide a high-level overview of several key neurobiological systems relevant to social dynamics. We then describe several key components of ICE systems that can interact with and on neurobiological systems as individual-level inputs influencing social dynamics over the team life cycle-specifically food and nutrition, exercise and physical activity, sleep/wake/work rhythms, and habitat design and layout. Finally, we identify opportunities and strategic considerations for multidisciplinary research and development. Our overarching goal is to encourage multidisciplinary expansion of team science through (1) prospective horizontal integration of variables outside the current bounds of team science as significant inputs to closed ICE team systems and (2) bidirectional vertical integration of biology as the necessary inputs and mediators of individual and team behavioral health and performance. Prospective efforts to account for the behavioral biology of teams in ICE settings through an integrated organizational neuroscience approach will enable the field of team science to better understand and support teams who work, live, serve, and explore in extreme environments.

Exercise effects on bed rest-induced brain changes.

PURPOSE: Spaceflight negatively affects sensorimotor behavior; exercise mitigates some of these effects. Head down tilt bed rest (HDBR) induces body unloading and fluid shifts, and is often used to investigate spaceflight effects. Here, we examined whether exercise mitigates effects of 70 days HDBR on the brain and if fitness and brain changes with HDBR are related. METHODS: HDBR subjects were randomized to no-exercise (n = 5) or traditional aerobic and resistance exercise (n = 5). Additionally, a flywheel exercise group was included (n = 8). Exercise protocols for exercise groups were similar in intensity, therefore these groups were pooled in statistical analyses. Pre and post-HDBR MRI (structure and structural/functional connectivity) and physical fitness measures (lower body strength, muscle cross sectional area, VO2 max, body composition) were collected. Voxel-wise permutation analyses were used to test group differences in brain changes, and their associations with fitness changes. RESULTS: Comparisons of exercisers to controls revealed that exercise led to smaller fitness deterioration with HDBR but did not affect brain volume or connectivity. Group comparisons showed that exercise modulated post-HDBR recovery of brain connectivity in somatosensory regions. Posthoc analysis showed that this was related to functional connectivity decrease with HDBR in non-exercisers but not in exercisers. Correlational analyses between fitness and brain changes showed that fitness decreases were associated with functional connectivity and volumetric increases (all r >.74), potentially reflecting compensation. Modest brain changes or even decreases in connectivity and volume were observed in subjects who maintained or showed small fitness gains. These results did not survive Bonferroni correction, but can be considered meaningful because of the large effect sizes. CONCLUSION: Exercise performed during HDBR mitigates declines in fitness and strength. Associations between fitness and brain connectivity and volume changes, although unadjusted for multiple comparisons in this small sample, suggest that supine exercise reduces compensatory HDBR-induced brain changes.

Exercise Training Mitigates Multisystem Deconditioning during Bed Rest.

INTRODUCTION: This study investigated the safety and effectiveness of a new integrated aerobic and resistance exercise training prescription (SPRINT) using two different sets of exercise equipment: a suite of large International Space Station-like exercise equipment similar to what is found on the International Space Station and a single device with aerobic and resistance exercise capability in the spaceflight analog of bed rest (BR). METHODS: Subjects (n = 34) completed 70 d of 6° head down tilt BR: 9 were randomized to remain sedentary (CONT), 9 to exercise training using traditional equipment (EX), 8 to exercise using traditional equipment and low-dose testosterone supplementation (ExT), and 8 to exercise using a combined resistance and aerobic flywheel device. Peak aerobic capacity, ventilatory threshold, cardiac morphology and function (echocardiography), muscle mass (magnetic resonance imaging) and strength/power (isokinetic, leg press, and vertical jump), and bone health (bone mineral density, blood and urine bone markers) were assessed before and after BR. RESULTS: The SPRINT protocol mitigated BR-induced muscle and cardiac deconditioning regardless of the exercise device used. Molecular markers of bone did not change in the CONT or EX groups. Peak aerobic capacity was maintained from pre- to post-BR in all exercise groups similarly, whereas significant declines were observed in the CONT group (~10%). Significant interaction effects between the CONT group and all EX groups were observed for muscle performance including leg press total work, isokinetic upper and lower leg strength, vertical jump power, and maximal jump height as well as muscle size. CONCLUSIONS: This is the first trial to evaluate multisystem deconditioning and the role of an integrated exercise countermeasure. These findings have important implications for the design and implementation of exercise-based countermeasures on future long-duration spaceflight missions.

Overview of the NASA 70-day Bed Rest Study.

PURPOSE: The purpose of this article was to provide an overview of the National Aeronautics and Space Administration (NASA) 70-day Bed Rest Study. The integrated complement of investigations and the standardized bed rest environment that served as the platform for this study complement are described. Outcomes of the studies will not be presented here but will be reported in separate publications. METHODS: A set of studies running in an integrated fashion along the entire period (pre-, in-, and post-bed rest) and using the same subjects is referred in this article as "the campaign" or "complement." NASA selected eight individual studies to participate in the 70-d bed rest campaign. These studies were integrated to increase efficiency in the utilization of resources and to share common measures among the investigations. In addition to the individual studies addressing specific aims, a battery of standardized measures was included. Standard measures target a wide range of physiologic systems and represent some of the testing routinely done on astronauts. Bed rest subjects underwent rigorous medical and psychological screening. Standardized conditions included 70 d of bed rest in a 6° head-down tilt position. Subjects' vital signs, body weight, and fluid intake and output were measured daily. A standardized diet was provided to ensure consistent nutritional intake across subjects. Exercising subjects were prescribed individualized aerobic and resistance training 6 d·wk performed in a horizontal body position. Subjects in the testosterone supplementation countermeasure group received testosterone enanthate injections at 2-wk intervals during bed rest. CONCLUSION: Long-duration head-down tilt bed rest provided a suitable platform for examining physiologic effects of spaceflight and testing countermeasures in a ground-based model. Integrating studies into a complement is an effective way to support multiple investigations while minimizing the number of subjects to answer many research questions.

Efficacy of Exercise and Testosterone to Mitigate Atrophic Cardiovascular Remodeling.

PURPOSE: Early and consistent evaluation of cardiac morphology and function throughout an atrophic stimulus is critically important for the design and optimization of interventions. This randomized controlled trial was designed 1) to characterize the time course of unloading-induced morphofunctional remodeling and 2) to examine the effects of exercise with and without low-dose testosterone supplementation on cardiac biomarker, structural, and functional parameters during unloading. METHODS: Twenty-six subjects completed 70 d of head-down tilt bed rest (BR): 9 were randomized to exercise training (Ex), 8 to EX and low-dose testosterone (ExT), and 9 remained sedentary (CONT). Exercise consisted of high-intensity, continuous, and resistance exercise. Cardiac morphology (left ventricular mass [LVM]) and mechanics (longitudinal, radial, and circumferential strain and twist), cardiovascular biomarkers, and cardiorespiratory fitness (V˙O2peak) were assessed before, during, and after BR. RESULTS: Sedentary BR resulted in a progressive decline in LVM, longitudinal, radial, and circumferential strain in CONT, whereas Ex and ExT mitigated decreases in LVM and function. Twist was increased throughout BR in sedentary BR, whereas after an initial increase at BR7, there were no further changes in twist in Ex and ExT. HDL cholesterol was significantly decreased in all groups compared with pre-BR (P < 0.007). There were no significant changes in other cardiovascular biomarkers. Change in twist was significantly related to change in V˙O2max (R = 0.68, P < 0.01). CONCLUSION: An integrated approach with evaluation of cardiac morphology, mechanics, V˙O2peak, and biomarkers provides extensive phenotyping of cardiovascular atrophic remodeling. Exercise training and exercise training with low-dose testosterone supplementation abrogates atrophic remodeling.

Panoramic ultrasound: a novel and valid tool for monitoring change in muscle mass.

BACKGROUND: The strong link between reduced muscle mass and morbidity and mortality highlights the urgent need for simple techniques that can monitor change in skeletal muscle cross-sectional area (CSA). Our objective was to examine the validity of panoramic ultrasound to detect change in quadriceps and gastrocnemius size in comparison with magnetic resonance imaging (MRI) in subjects randomized to 70 days of bed rest (BR) with or without exercise. METHODS: Panoramic ultrasound and MRI images of the quadriceps and gastrocnemius muscles were acquired on the right leg of 27 subjects (26 male, 1 female; age: 34.6 ± 7.8 years; body mass: 77.5 ± 10.0 kg; body mass index: 24.2 ± 2.8 kg/m2 ; height: 179.1 ± 6.9 cm) before (BR-6), during (BR3, 7, 11, 15, 22, 29, 36, 53, 69), and after (BR+3, +6, +10) BR. Validity of panoramic ultrasound to detect change in muscle CSA was assessed by Bland-Altman plots, Lin's concordance correlation coefficient (CCC), sensitivity, specificity, positive predictive value, and negative predictive value. RESULTS: Six hundred ninety-eight panoramic ultrasound CSA and 698 MRI CSA measurements were assessed. Concordance between ultrasound and MRI was excellent in the quadriceps (CCC: 0.78; P < 0.0001), whereas there was poor concordance in the gastrocnemius (CCC: 0.37; P < 0.0006). Compared with MRI, panoramic ultrasound demonstrated high accuracy in detecting quadriceps atrophy and hypertrophy (sensitivity: 73.7%; specificity: 74.2%) and gastrocnemius atrophy (sensitivity: 83.1%) and low accuracy in detecting gastrocnemius hypertrophy (specificity: 33.0%). CONCLUSIONS: Panoramic ultrasound imaging is a valid tool for monitoring quadriceps muscle atrophy and hypertrophy and for detecting gastrocnemius atrophy.

Blood Flow Restricted Exercise Compared to High Load Resistance Exercise During Unloading.

BACKGROUND: Bed rest studies have shown that high load (HL) resistance training can mitigate the loss of muscle size and strength during musculoskeletal unloading; however, not all individuals are able to perform HL resistance exercise. Blood flow restricted (BFR) resistance exercise may be a novel way to prevent maladaptation to unloading without requiring HL exercise equipment. This study evaluated the muscular training adaptations to HL and BFR resistance training during unilateral lower limb suspension (ULLS), a human limb unloading model. ULLS allows for evaluation of exercise training in both weight-bearing and nonweight-bearing legs within the same individual. METHODS: There were 13 participants who completed 25 d of ULLS and were counterbalanced to: 1) HL, N = 6; or 2) BFR, N = 7, training groups. During ULLS, HL and BFR performed unilateral leg press and heel raise exercise (3 d/wk). RESULTS: In weight-bearing legs, both HL and BFR increased knee extensor muscle cross-sectional area (CSA) and strength. In nonweight-bearing legs, knee extensor CSA and strength increased only in HL and decreased with BFR. CONCLUSION: HL and BFR resistance exercise were both effective exercise programs for the weight-bearing leg. However, BFR exercise was not as effective as HL resistance exercise in the nonweight-bearing leg. These data show that exercise that improved muscle CSA and strength in ambulatory weight-bearing conditions was not sufficient to maintain muscle function during unloading. For the preservation of muscle CSA and strength, BFR exercise should be considered an adjunct but not a primary exercise countermeasure for future space missions. Hackney KJ, Downs ME, Ploutz-Snyder L. Blood flow restricted exercise compared to high load resistance exercise during unloading. Aerosp Med Hum Perform. 2016; 87(8):688-696.

The Astronaut-Athlete: Optimizing Human Performance in Space.

It is well known that long-duration spaceflight results in deconditioning of neuromuscular and cardiovascular systems, leading to a decline in physical fitness. On reloading in gravitational environments, reduced fitness (e.g., aerobic capacity, muscular strength, and endurance) could impair human performance, mission success, and crew safety. The level of fitness necessary for the performance of routine and off-nominal terrestrial mission tasks remains an unanswered and pressing question for scientists and flight physicians. To mitigate fitness loss during spaceflight, resistance and aerobic exercise are the most effective countermeasure available to astronauts. Currently, 2.5 h·d, 6-7 d·wk is allotted in crew schedules for exercise to be performed on highly specialized hardware on the International Space Station (ISS). Exercise hardware provides up to 273 kg of loading capability for resistance exercise, treadmill speeds between 0.44 and 5.5 m·s, and cycle workloads from 0 and 350 W. Compared to ISS missions, future missions beyond low earth orbit will likely be accomplished with less vehicle volume and power allocated for exercise hardware. Concomitant factors, such as diet and age, will also affect the physiologic responses to exercise training (e.g., anabolic resistance) in the space environment. Research into the potential optimization of exercise countermeasures through use of dietary supplementation, and pharmaceuticals may assist in reducing physiological deconditioning during long-duration spaceflight and have the potential to enhance performance of occupationally related astronaut tasks (e.g., extravehicular activity, habitat construction, equipment repairs, planetary exploration, and emergency response).

Exercise as potential countermeasure for the effects of 70 days of bed rest on cognitive and sensorimotor performance.

BACKGROUND: Spaceflight has been associated with changes in gait and balance; it is unclear whether it affects cognition. Head down tilt bed rest (HDBR) is a microgravity analog that mimics cephalad fluid shifts and body unloading. In consideration of astronaut's health and mission success, we investigated the effects of HDBR on cognition and sensorimotor function. Furthermore, we investigated if exercise mitigates any cognitive and sensorimotor sequelae of spaceflight. METHOD: We conducted a 70-day six-degree HDBR study in 10 male subjects who were randomly assigned to a HDBR supine exercise or a HDBR control group. Cognitive measures (i.e., processing speed, manual dexterity, psychomotor speed, visual dependency, and 2D and 3D mental rotation) and sensorimotor performance (functional mobility (FMT) and balance performance) were collected at 12 and 8 days pre-HDBR, at 7, 50, and 70 days in HDBR, and at 8 and 12 days post-HDBR. Exercise comprised resistance training, and continuous and high-intensity interval aerobic exercise. We also repeatedly assessed an outside-of-bed rest control group to examine metric stability. RESULTS: Small practice effects were observed in the control group for some tasks; these were taken into account when analyzing effects of HDBR. No significant effects of HDBR on cognition were observed, although visual dependency during HDBR remained stable in HDBR controls whereas it decreased in HDBR exercise subjects. Furthermore, HDBR was associated with loss of FMT and standing balance performance, which were almost fully recovered 12 days post-HDBR. Aerobic and resistance exercise partially mitigated the effects of HDBR on FMT and accelerated the recovery time course post-HDBR. DISCUSSION: HDBR did not significantly affect cognitive performance but did adversely affect FMT and standing balance performance. Exercise had some protective effects on the deterioration and recovery of FMT.

The metabolic cost of an integrated exercise program performed during 14 days of bed rest.

BACKGROUND: Exercise countermeasures designed to mitigate muscle atrophy during long-duration spaceflight may not be as effective if crewmembers are in negative energy balance (energy output > energy input). This study determined the energy cost of supine exercise (resistance, interval, aerobic) during the spaceflight analogue of bed rest. METHODS: Nine subjects (eight men and one woman; 34.5 +/- 8.2 yr) completed 14 d of bed rest and concomitant exercise countermeasures. Body mass and basal metabolic rate (BMR) were assessed before and during bed rest. Exercise energy expenditure was measured during and immediately after [excess post-exercise oxygen consumption (EPOC)] each of five different exercise protocols (30-s, 2-min, and 4-min intervals, continuous aerobic, and a variety of resistance exercises) during bed rest. RESULTS: On days when resistance and continuous aerobic exercise were performed daily, energy expenditure was significantly greater (2879 +/- 280 kcal) than 2-min (2390 +/- 237 kcal), 30-s (2501 +/- 264 kcal), or 4-min (2546 +/- 264 kcal) exercise. There were no significant differences in BMR (pre-bed rest: 1649 +/- 216 kcal; week 1: 1632 +/- 174 kcal; week 2:1657 +/- 176 kcal) or body mass (pre-bed rest: 75.2 +/- 10.1 kg; post-bed rest: 75.2 +/- 9.6 kg). DISCUSSION: These findings highlight the importance of energy balance for long-duration crewmembers completing a high-intensity exercise program with multiple exercise sessions daily.

Peak exercise oxygen uptake during and following long-duration spaceflight.

This investigation was designed to measure aerobic capacity (V̇o2peak) during and after long-duration International Space Station (ISS) missions. Astronauts (9 males, 5 females: 49 ± 5 yr, 77.2 ± 15.1 kg, 40.6 ± 6.4 ml·kg(-1)·min(-1) [mean ± SD]) performed peak cycle tests ∼90 days before flight, 15 days after launch, every ∼30 days in-flight, and on recovery days 1 (R + 1), R + 10, and R + 30. Expired metabolic gas fractions, ventilation, and heart rate (HR) were measured. Data were analyzed using mixed-model linear regression. The main findings of this study were that V̇o2peak decreased early in-flight (∼17%) then gradually increased during flight but never returned to preflight levels. V̇o2peak was lower on R + 1 and R + 10 than preflight but recovered by R + 30. Peak HR was not different from preflight at any time during or following flight. A sustained decrease in V̇o2peak during and/or early postflight was not a universal finding in this study, since seven astronauts were able to attain their preflight V̇o2peak levels either at some time during flight or on R + 1. Four of these astronauts performed in-flight exercise at higher intensities compared with those who experienced a decline in V̇o2peak, and three had low aerobic capacities before flight. These data indicate that, while V̇o2peak may be difficult to maintain during long-duration ISS missions, aerobic deconditioning is not an inevitable consequence of long-duration spaceflight.