INTRODUCTION: Long-duration spaceflight results in musculoskeletal, cardiorespiratory, and sensorimotor deconditioning. Historically, exercise has been used as a countermeasure to mitigate these deleterious effects that occur as a consequence of microgravity exposures. The International Space Station (ISS) exercise community describes their approaches, biomedical surveillance, and lessons learned in the development of exercise countermeasure modalities and prescriptions for maintaining health and performance among station crews. This report is focused on the first 10 yr of ISS defined as Expeditions 1–25 and includes only crewmembers with missions > 30 d on ISS for all 5 partner agencies (United States, Russia, Europe, Japan, and Canada). All 72 cosmonauts and astronauts participated in the ISS exercise countermeasures program. This Supplement presents a series of papers that provide an overview of the first decade of ISS exercise from a multidisciplinary, multinational perspective to evaluate the initial countermeasure program and record its operational limitations and challenges. In addition, we provide results from standardized medical evaluations before, during, and after each mission. Information presented in this context is intended to describe baseline conditions of the ISS exercise program. This paper offers an introduction to the subsequent series of manuscripts.Hayes J. The first decade of ISS exercise: lessons learned on Expeditions 1–25. Aerosp Med Hum Perform. 2015; 86(12, Suppl.):A1–A6.

The hardware systems necessary to support exercise countermeasures to the deconditioning associated with microgravity exposure have evolved and improved significantly during the first decade of the International Space Station (ISS), resulting in both new types of hardware and enhanced performance capabilities for initial hardware items. The original suite of countermeasure hardware supported the first crews to arrive on the ISS and the improved countermeasure system delivered in later missions continues to serve the astronauts today with increased efficacy. Due to aggressive hardware development schedules and constrained budgets, the initial approach was to identify existing spaceflight-certified exercise countermeasure equipment, when available, and modify it for use on the ISS. Program management encouraged the use of commercial-off-the-shelf (COTS) hardware, or hardware previously developed (heritage hardware) for the Space Shuttle Program. However, in many cases the resultant hardware did not meet the additional requirements necessary to support crew health maintenance during long-duration missions (3 to 12 mo) and anticipated future utilization activities in support of biomedical research. Hardware development was further complicated by performance requirements that were not fully defined at the outset and tended to evolve over the course of design and fabrication. Modifications, ranging from simple to extensive, were necessary to meet these evolving requirements in each case where heritage hardware was proposed. Heritage hardware was anticipated to be inherently reliable without the need for extensive ground testing, due to its prior positive history during operational spaceflight utilization. As a result, developmental budgets were typically insufficient and schedules were too constrained to permit long-term evaluation of dedicated ground-test units ("fleet leader" type testing) to identify reliability issues when applied to long-duration use. In most cases, the exercise unit with the most operational history was the unit installed on the ISS.Korth DW. Exercise countermeasure hardware evolution on ISS: the first decade. Aerosp Med Hum Perform. 2015; 86(12, Suppl.):A7–A13.

INTRODUCTION: Physical training has been conducted on the International Space Station (ISS) for the past 10 yr as a countermeasure to physiological deconditioning during spaceflight. Each member space agency has developed its own approach to creating and implementing physical training protocols for their astronauts. We have divided physical training into three distinct phases (preflight, in-flight, and postflight) and provided a description of each phase with its constraints and limitations. We also discuss how each member agency (NASA, ESA, CSA, and JAXA) prescribed physical training for their crewmembers during the first 10 yr of ISS operations. It is important to understand the operational environment, the agency responsible for the physical training program, and the constraints and limitations associated with spaceflight to accurately design and implement exercise training or interpret the exercise data collected on ISS. As exploration missions move forward, resolving agency differences in physical training programs will become important to maximizing the effectiveness of exercise as a countermeasure and minimizing any mission impacts.Loehr JA, Guilliams ME, Petersen N, Hirsch N, Kawashima S, Ohshima H. Physical training for long-duration spaceflight. Aerosp Med Hum Perform. 2015; 86(12, Suppl.):A14–A23.

INTRODUCTION: The system of countermeasures for the adverse effects of microgravity developed in the USSR supported the successful implementation of long-duration spaceflight (LDS) programs on the Salyut and Mir orbital stations and was subsequently adapted for flights on the International Space Station (ISS). From 2000 through 2010, crews completed 26 ISS flight increments ranging in duration from 140 to 216 d, with the participation of 27 Russian cosmonauts. These flights have made it possible to more precisely determine a crewmember’s level of conditioning, better assess the advantages and disadvantages of training processes, and determine prospects for future developments.Koslovskaya IB, Yarmanova EN, Yegorov AD, Stepantsov VI, Fomina EV, Tomilovaskaya ES. Russian countermeasure systems for adverse effects of microgravity on long-duration ISS flights. Aerosp Med Hum Perform. 2015; 86(12, Suppl.):A24–A31.

INTRODUCTION: Countermeasures to prevent or partially offset the negative physiologic changes that are caused by the effects of microgravity play an important role in supporting the performance of crewmembers in flight and their safe return to Earth. Research conducted in Russia on the orbital stations Salyut and Mir, as well as simulation experiments on the ground, have demonstrated that changes that occur during extended spaceflight in various physiologic systems can be prevented or significantly decreased by using countermeasures. Hardware and techniques used on the ISS have been substantially improved to reflect the experience of previous extended missions on Russian orbital stations. Countermeasures used during early ISS missions consisted of the U.S. treadmill (TVIS), cycle ergometer (ВБ-3), a set of resistance bands, a postural muscle loading suit (Penguin-3), electrical stimulator (Tonus-3), compression thigh cuffs (Braslet-М), a lower body negative pressure (LBNP) suit (Chibis), a lower body g-loading suit (Kentavr), and water/salt supplements. These countermeasures are described in this article.Yarmonova EN, Kozlovskaya IB, Khimoroda NN, Fomina EV. Evolution of Russian microgravity countermeasures. Aerosp Med Hum Perform. 2015; 86(12, Suppl.):A32–A37.

INTRODUCTION: The measurement of bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) is the Medical Assessment Test used at the NASA Johnson Space Center to evaluate whether prolonged exposure to spaceflight increases the risk for premature osteoporosis in International Space Station (ISS) astronauts. The DXA scans of crewmembers’ BMD during the first decade of the ISS existence showed precipitous declines in BMD for the hip and spine after the typical 6-mo missions. However, a concern exists that skeletal integrity cannot be sufficiently assessed solely by DXA measurement of BMD. Consequently, use of relatively new research technologies is being proposed to NASA for risk surveillance and to enhance long-term management of skeletal health in long-duration astronauts.Sibonga JD, Spector ER, Johnston SL, Tarver WJ. Evaluating bone loss in ISS astronauts. Aerosp Med Hum Perform. 2015; 86(12, Suppl.):A38–A44.

INTRODUCTION: Postflight postural ataxia reflects both the control strategies adopted for movement in microgravity and the direct effects of deconditioning. Computerized dynamic posturography (CDP) has been used during the first decade of the International Space Station (ISS) expeditions to quantify the initial postflight decrements and recovery of postural stability.METHODS: The CDP data were obtained on 37 crewmembers as part of their pre- and postflight medical examinations. Sensory organization tests evaluated the ability to make effective use of (or suppress inappropriate) visual, vestibular, and somatosensory information for balance control. This report focuses on eyes closed conditions with either a fixed or sway-referenced base of support, with the head erect or during pitch-head tilts (± 20° at 0.33 Hz). Equilibrium scores were derived from peak-to-peak anterior-posterior sway. Motor-control tests were also used to evaluate a crewmember’s ability to automatically recover from unexpected support-surface perturbations.RESULTS: The standard Romberg condition was the least sensitive. Dynamic head tilts led to increased incidence of falls and revealed significantly longer recovery than head-erect conditions. Improvements in postflight postural performance during the later expeditions may be attributable to higher preflight baselines and/or advanced exercise capabilities aboard the ISS.CONCLUSIONS: The diagnostic assessment of postural instability is more pronounced during unstable-support conditions requiring active head movements. In addition to supporting return-to-duty decisions by flight surgeons, the CDP provides a standardized sensorimotor measure that can be used to evaluate the effectiveness of countermeasures designed to either minimize deconditioning on orbit or promote reconditioning upon return to Earth.Wood SJ, Paloski WH, Clark JB. Assessing sensorimotor function following ISS with computerized dynamic posturography. Aerosp Med Hum Perform. 2015; 86(12, Suppl.):A45–A53.

INTRODUCTION: Cardiovascular deconditioning apparently progresses with flight duration, resulting in a greater incidence of orthostatic intolerance following long-duration missions. Therefore, we anticipated that the proportion of astronauts who could not complete an orthostatic tilt test (OTT) would be higher on landing day and the number of days to recover greater after International Space Station (ISS) than after Space Shuttle missions.METHODS: There were 20 ISS and 65 Shuttle astronauts who participated in 10-min 80° head-up tilt tests 10 d before launch, on landing day (R+0), and 3 d after landing (R+3). Fisher’s Exact Test was used to compare the ability of ISS and Shuttle astronauts to complete the OTT. Cox regression was used to identify cardiovascular parameters associated with OTT completion and mixed model analysis was used to compare the change and recovery rates between groups.RESULTS: The proportion of astronauts who completed the OTT on R+0 (2 of 6) was less in ISS than in Shuttle astronauts (52 of 65). On R+3, 13 of 15 and 19 of 19 of the ISS and Shuttle astronauts, respectively, completed the OTT. An index comprised of stroke volume and diastolic blood pressure provided a good prediction of OTT completion and was altered by spaceflight similarly for both astronaut groups, but recovery was slower in ISS than in Shuttle astronauts.CONCLUSIONS: The proportion of ISS astronauts who could not complete the OTT on R+0 was greater and the recovery rate slower after ISS compared to Shuttle missions. Thus, mission planners and crew surgeons should anticipate the need to tailor scheduled activities and level of medical support to accommodate protracted recovery after long-duration microgravity exposures.Lee SMC, Feiveson AH, Stein S, Stenger MB, Platts SH. Orthostatic intolerance after ISS and Space Shuttle missions. Aerosp Med Hum Perform. 2015; 86(12, Suppl.):A54–A67.

INTRODUCTION: Long-duration spaceflight results in a loss of muscle strength that poses both operational and medical risks, particularly during emergency egress, upon return to Earth, and during future extraterrestrial exploration. Isokinetic testing of the knee, ankle, and trunk quantifies movement-specific strength changes following spaceflight and offers insight into the effectiveness of in-flight exercise countermeasures.METHODS: We retrospectively evaluated changes in isokinetic strength for 37 ISS crewmembers (Expeditions 1–25) following 163 ± 38 d (mean ± SD) of spaceflight. Gender, in-flight resistance exercise hardware, and preflight strength were examined as potential modifiers of spaceflight-induced strength changes.RESULTS: Mean isokinetic strength declined 8–17% following spaceflight. One month after return to Earth, strength had improved, but small deficits of 1–9% persisted. Spaceflight-induced strength losses were not different between men and women. Mean strength losses were as much as 7% less in crewmembers who flew after the Advanced Resistive Exercise Device (ARED) replaced the interim Resistive Exercise Device (iRED) as the primary in-flight resistance exercise hardware, although these differences were not statistically significant. Absolute and relative preflight strength were moderately correlated (r = −0.47 and −0.54, respectively) with postflight strength changes.DISCUSSION: In-flight resistance exercise did not prevent decreased isokinetic strength after long-duration spaceflight. However, continued utilization of ARED, a more robust resistance exercise device providing higher loads than iRED, may result in greater benefits as exercise prescriptions are optimized. With reconditioning upon return to Earth, strength is largely recovered within 30 d.English KL, Lee SMC, Loehr JA, Ploutz-Snyder RJ, Ploutz-Snyder LL. Isokinetic strength changes following long-duration spaceflight on the ISS. Aerosp Med Human Perform. 2015; 86(12, Suppl.):A68–A77.

INTRODUCTION: Aerobic deconditioning may occur during International Space Station (ISS) flights. This paper documents findings from exercise testing conducted before, during, and after ISS expeditions.METHODS: There were 30 male and 7 female astronauts on ISS missions (48 to 219 d, mean 163 d) who performed cycle exercise protocols consisting of 5-min stages eliciting 25%, 50%, and 75% peak oxygen uptake (Vo_2peak). Tests were conducted 30 to 90 d before missions, on flight day 15 and every 30 flight days thereafter, and on recovery (R) days +5 and +30. During pre- and postflight tests, heart rate (HR) and metabolic gas exchange were measured. During flight, extrapolation of the HR and Vo₂ relationship to preflight-measured peak HR provided an estimate of Vo_2peak, referred to as the aerobic capacity index (ACI).RESULTS: HR during each exercise stage was elevated (P < 0.05) and oxygen pulse was reduced (P < 0.05) on R+5 compared to preflight; however, no other metabolic gas analysis values significantly changed. Compared to preflight, the ACI declined (P < 0.001) on R+5, but recovered to levels greater than preflight by R+30 (P = 0.008). During flight, ACI decreased below preflight values, but increased with mission duration (P < 0.001).CONCLUSIONS: Aerobic deconditioning likely occurs initially during flight, but ACI recovers toward preflight levels as flight duration increases, presumably due to performance of exercise countermeasures. Elevated HR and lowered oxygen pulse on R+5 likely results from some combination of relative hypovolemia, lowered cardiac stroke volume, reduced cardiac distensibility, and anemia, but recovery occurs by R+30.Moore AD Jr, Lynn PA, Feiveson AH. The first 10 years of aerobic exercise responses to long-duration ISS flights. Aerosp Med Hum Perform. 2015; 86(12, Suppl.):A78–A86.

INTRODUCTION: Long-duration spaceflight missions lead to the loss of muscle strength and endurance. Significant reduction in muscle function can be hazardous when returning from spaceflight. To document these losses, NASA developed medical requirements that include measures of functional strength and endurance. Results from this Functional Fitness Test (FFT) battery are also used to evaluate the effectiveness of in-flight exercise countermeasures. The purpose of this paper is to document results from the FFT and correlate this information with performance of in-flight exercise on board the International Space Station.METHODS: The FFT evaluates muscular strength and endurance, flexibility, and agility and includes the following eight measures: sit and reach, cone agility, push-ups, pull-ups, sliding crunches, bench press, leg press, and hand grip dynamometry. Pre- to postflight functional fitness measurements were analyzed using dependent t-tests and correlation analyses were used to evaluate the relationship between functional fitness measurements and in-flight exercise workouts.RESULTS: Significant differences were noted postspaceflight with the sit and reach, cone agility, leg press, and hand grip measurements while other test scores were not significantly altered. The relationships between functional fitness and in-flight exercise measurements showed minimal to moderate correlations for most in-flight exercise training variables. DISCUSSION: The change in FFT results can be partially explained by in-flight exercise performance. Although there are losses documented in the FFT results, it is important to realize that the crewmembers are successfully performing activities of daily living and are considered functional for normal activities upon return to Earth.Laughlin MS, Guilliams ME, Nieschwitz BA, Hoellen D. Functional fitness testing results following long-duration ISS missions. Aerosp Med Hum Perform. 2015; 86 (12, Suppl.):A87–A91.

INTRODUCTION: The first decade of the International Space Station Program (ISS) yielded a wealth of knowledge regarding the health and performance of crewmembers living in microgravity for extended periods of time. The exercise countermeasures hardware suite evolved during the last decade to provide enhanced capabilities that were previously unavailable to support human spaceflight, resulting in attenuation of cardiovascular, muscle, and bone deconditioning. The ability to protect crew and complete mission tasks in the autonomous exploration environment will be a critical component of any decision to proceed with manned exploration initiatives.The next decade of ISS habitation promises to be a period of great scientific utilization that will yield both the tools and technologies required to safely explore the solar system. Leading countermeasure candidates for exploration class missions must be studied methodically on ISS over the next decade to ensure protocols and systems are highly efficient, effective, and validated. Lessons learned from the ISS experience to date are being applied to the future, and international cooperation enables us to maximize this exceptional research laboratory.Loerch LH. Exercise countermeasures on ISS: summary and future directions. Aerosp Med Hum Perform. 2015; 86 (12, Suppl.):A92–A93.