Exercise as a Countermeasure to Microgravity-Induced Deconditioning

Kim, Ji-Seok; Moon, Hyo Youl; Ji-Seok Kim; Hyo Youl Moon

doi:10.15857/ksep.2025.00430

Exerc Sci > Volume 34(3); 2025 > Article

Kim and Moon: Exercise as a Countermeasure to Microgravity-Induced Deconditioning

Review Article

Exerc Sci.. 2025; 34(3): 231-240.

Published online: Aug 28, 2025

DOI: https://doi.org/10.15857/ksep.2025.00430

Exercise as a Countermeasure to Microgravity-Induced Deconditioning

Ji-Seok Kim PhD^1,²

, Hyo Youl Moon PhD^3,^4,

¹Department of Physical Education, Gyeongsang National University, Jinju, Korea

²Research Institute of Pharmaceutical Sciences, Gyeongsang National University, Jinju, Korea

³Department of Physical Education, Seoul National University, Seoul, Korea

⁴Learning Sciences Research Institute, Seoul National University, Seoul, Korea

Corresponding author: Hyo Youl Moon Tel +82-2-880-7802 Fax +82-2-872-2867 E-mail skyman19@snu.ac.kr

*Grant/Fund Support: This work was supported by grants from the National Research Foundation of Korea (NRF) funded by the Korean government (MSIT) (No. RS-2022-NR070859 and RS-2022-NR075830), the Research Resurgence under the Glocal University 30 Project at Gyeongsang National University in 2024, and the Learning Sciences Research Institute at Seoul National University.

Received Jul 4, 2025 Revised Jul 25, 2025 Accepted Jul 30, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

PURPOSE

This study aimed to comprehensively evaluate the physiological challenges posed by microgravity on the neuromuscular and cardiovascular systems of astronauts and to assess exercise-based countermeasures designed to mitigate these effects during long-duration spaceflight.

METHODS

We conducted a structured review of over 70 peer-reviewed studies on spaceflight missions, ground-based analogs, and exercise intervention trials. Findings related to musculoskeletal atrophy, cardiovascular deconditioning, and neurovestibular adaptations were analyzed, with special emphasis on the efficacy of resistance, aerobic, and sensorimotor training regimens, as well as wearable technologies and physiological monitoring strategies used on the International Space Station.

RESULTS

Microgravity induced significant muscle atrophy, bone mineral loss, cardiovascular fluid shift, autonomic dysregulation, and sensorimotor deficits. Resistance training using devices such as ARED has been shown to attenuate muscle and bone loss, whereas aerobic training with equipment such as CEVIS helped preserve VO2peak. Sensorimotor exercises improved postflight postural stability. Wearable monitoring systems facilitated real-time health data tracking, allowing personalized adjustments to exercise protocols.

CONCLUSIONS

Exercise is the most effective and multifaceted countermeasure against microgravity-induced deconditioning. Future countermeasure strategies should integrate individualized exercise regimens with real-time physiological monitoring, artificial intelligence-supported prediction, and adaptive systems to optimize astronaut health during prolonged missions, particularly beyond the low Earth orbit.

Keywords: Microgravity, Exercise countermeasures, Musculoskeletal atrophy, Cardiovascular deconditioning, Spaceflight adaptation

INTRODUCTION

As human space exploration advances and extended missions become increasingly feasible, understanding the physiological and psychological effects of the space environment has become essential [1]. In particular, microgravity presents a unique and potent stressor that disrupts homeostasis and induces systemic adaptations, many of which can compromise astronaut health and mission performance [2]. The transition from Earth's gravity to microgravity triggers a cascade of acute and chronic physiological changes, including fluid redistribution, altered neuromuscular activity, and sensory recalibration [3]. These adaptations, while necessary for survival in space, can lead to long-term impairments upon return to Earth [4].

Prolonged exposure to microgravity has been associated with muscle atrophy, bone demineralization, cardiovascular deconditioning, immune suppression, and neurovestibular dysfunction [4]. These changes not only reduce operational performance but also pose serious risks to astronaut safety. Furthermore, psychological stressors such as isolation, confinement, and disrupted circadian rhythms compound the physiological burden, highlighting the need for comprehensive health management strategies [5].

Among available countermeasures, regular exercise remains the most effective intervention for preserving physiological function in space [6]. Decades of research and operational experience have led to the development of structured exercise programs that target musculoskeletal, cardiovascular, and neurological systems [7,8]. These programs are continuously refined to maximize efficacy under microgravity conditions, with evidence supporting their role in mitigating physical deterioration and promoting mental well-being [5,8]. As space missions extend in duration and complexity, optimizing exercise protocols will be critical to safe-guarding astronaut health and ensuring the success of long-term human spaceflight.

This review aims to systematically address three key questions: (1) What are the neuromuscular and cardiovascular adaptations to microgravity? (2) How effective are current exercise-based countermeasures in space? (3) What future directions are necessary to optimize personalized countermeasures for deep space missions?

MATERIALS AND METHODS

This study was conducted to collect current scientific knowledge on the physiological adaptations to microgravity and the effectiveness of exercise-based countermeasures during spaceflight, with particular emphasis on neuromuscular and cardiovascular deconditioning. To achieve this, a comprehensive literature search was performed using four major electronic databases such as PubMed, Scopus, Web of Science, and the NASA Technical Reports Server (NTRS), covering publications from 1990 to 2025. Both peer-reviewed journal articles and technical reports from space agencies were included. Search terms included combinations of the following keywords: “ microgravity”, “ spaceflight”, “ exercise countermeasures”, “ muscle atrophy”, “ cardiovascular deconditioning”, “ ARED (Advanced Resistive Exercise Device)”, “ VO2max (maximal oxygen uptake)”, “ sensorimotor training”, and “ astronaut rehabilitation”. Relevant studies were selected for their focus on the physiological effects of microgravity and the role of exercise interventions in mitigating spaceflight-induced deconditioning. Inclusion criteria encompassed peer-reviewed articles and official technical reports published in English between 1990 and 2025 that focused on physiological deconditioning in microgravity and exercise countermeasures. Both human and animal studies were considered. Exclusion criteria included studies lacking em-pirical data or relevance to space analog environments.

RESULTS

1. Neuromusculoskeletal adaptation to microgravity: from fiber-type specific atrophy to neuroplastic reorganization

Prolonged exposure to the microgravity environment of spaceflight fundamentally challenges human homeostasis by removing the constant gravitational loading experienced on Earth. This unique perturbation disrupts the mechanical stresses, sensory feedback loops, and neuromuscular integration patterns that are essential for maintaining physiological integrity, thereby precipitating a systemic deconditioning cascade. This process most prominently and profoundly affects the musculoskeletal and nervous systems, initiating a complex series of adaptations across molecular, cellular, and systemic levels [9]. The absence of ground reaction forces and impact loads, in particular, serves as a primary driver for the degradation observed across these interconnected systems [9].

Within the musculoskeletal system, a primary and visually evident consequence of microgravity exposure is site-specific muscle deconditioning. A distinct inferior-to-superior gradient of atrophy is consistently observed, with the greatest loss of muscle mass occurring in the antigravity musculature of the lower limbs and lumbar spine, such as the quadriceps, soleus, and paraspinal muscles [10,11]. Conversely, muscles of the upper limbs, which are often utilized for in-situ locomotion and task manipulation within the spacecraft, may exhibit a degree of functional preservation or even hypertrophy.

This structural decline in muscle mass has direct functional consequences, leading to a significant degradation of contractile performance [12]. A hallmark of spaceflight adaptation is a marked reduction in maximal isometric force, a decline that mirrors the pattern of atrophy with the greatest impact on antigravity muscles. This loss of force generation is attributed not only to the reduced size of individual muscle fibers but also to a concurrent decrease in specific force— the intrinsic force-pro-ducing capacity per unit of cross-sectional area [13]. At the single-fiber level, biopsies from astronauts have confirmed a reduction in peak force, demonstrating that the functional deficit permeates to the most fundamental level of muscle structure [14].

Interestingly, the musculoskeletal system initiates a compensatory adaptation to mitigate the loss of force and preserve muscle power, a critical measure of overall performance. In response to diminished force capacity, single muscle fibers, particularly within the soleus and gastrocnemius, exhibit a notable increase in their maximum unloaded shortening velocity [15]. This phenomenon allows the muscle to maintain power output (Power=Force×Velocity) despite a significant reduction in the force component [16]. This adaptation toward a faster contractile profile is a consistent finding across both human and rodent studies, indicating a fundamental principle of muscle plasticity in response to unloading [17].

Underpinning these dynamic changes in contractile function is a profound alteration in cellular and molecular properties, beginning with fi-ber-type specificity. Histological analyses consistently reveal that slow-twitch (Type I) muscle fibers, which are responsible for sustained postural maintenance on Earth, are preferentially susceptible to atrophic changes due to the chronic reduction in their activation demand [18,19]. This shift is directly linked to the observed increases in contraction and relaxation speeds, which are attributed to a molecular remodeling of the sarcoplasmic reticulum's calcium-handling machinery. Specifically, evidence points to a shift toward faster-acting sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) isoforms, enabling more rapid release and reuptake of intracellular calcium and thus facilitating a faster twitch profile [16,20].

This slow-to-fast phenotypic transition extends to the core metabolic identity of the muscle. The chronic disuse of postural, slow-twitch domi-nant muscles triggers a systemic shift in their bioenergetic profile, moving away from a reliance on aerobic fatty acid oxidation and toward increased dependence on glycolysis [21]. This metabolic reprogramming is driven by both the phenotypic fiber-type transition and a significant downregulation of key mitochondrial enzymes essential for beta-oxidation [22]. This finding is corroborated by human bed rest studies, which serve as a ground-based analog for spaceflight and similarly show a reduction in whole-body dietary fat oxidation, reflecting a diminished metabolic capacity of endurance-oriented muscle fibers [23].

Rodent models offer a powerful paradigm for understanding the molecular basis of this differential susceptibility. The slow-twitch postural Soleus (SOL) muscle exhibits extreme vulnerability to microgravity, ex-periencing a cross-sectional area (CSA) reduction of as much as 35% and a pronounced shift away from Type I Myosin Heavy Chain (MHC) protein expression [24]. In stark contrast, the fast-twitch Extensor Digito-rum Longus (EDL) remains remarkably resilient. This divergence is ex-plained at the genetic level; global gene expression analyses show the SOL undergoes massive transcriptional reprogramming (∼680 differen-tially expressed genes), while the EDL shows minimal changes (∼72 genes) and appears to activate protective, stress-related pathways [24,25]. This indicates the deconditioning of the SOL is systemic, involving ex-tensive changes in protein balance, mitochondrial function, and calcium signaling pathways [26].

Crucially, muscle deconditioning does not occur in isolation but is in-tricately linked with skeletal degradation. The unloading of weight-bearing bones, such as the tibia, femur, and lumbar vertebrae, leads to a significant loss of bone mineral density (BMD) [27,28]. Trabecular bone, with its high metabolic turnover rate, is particularly susceptible to resorption compared to cortical bone [29]. Furthermore, a vicious cycle can emerge, as the atrophy of adjacent musculature can exacerbate skeletal weakening by reducing mechanical loads at tendinous entheses, poten-tially compromising the integrity of the entire tendon-bone junction [30].

Concurrently, the nervous system, as the master controller, initiates its own profound adaptive responses. The initial disruption of vestibular in-puts often leads to space adaptation syndrome, characterized by spatial disorientation and motion sickness [31]. Over time, this gives way to a deeper neuroplasticity, with functional neuroimaging confirming exten-sive cortical reorganization within vestibular, somatosensory, and motor networks as the brain compensates for the altered sensory landscape [32]. This reorganization, however, leads to a diminished reliance on proprioceptive feedback and impaired sensory integration, resulting in motor control deficits that necessitate greater cognitive oversight for task execution [33].

These functional adaptations are underpinned by neuroplasticity at the cellular and molecular levels. Evidence from animal models and human studies, including the landmark NASA Twins Study, indicates structural remodeling of dendritic spines and significant shifts in the expression of neurotrophic factors and synaptic signaling molecules [34]. Collectively, these findings illustrate that physiological adaptation to microgravity is a deeply integrated, multifactorial process. The consequences span structural, functional, and molecular domains across multiple biological systems, underscoring the critical need for developing robust, multisystem countermeasures to preserve astronaut health and performance during the forthcoming era of long-duration space missions.

2. Cardiovascular challenges in microgravity: from fluid shift to functional decline

Exposure to spaceflight-associated microgravity elicits a complex cascade of physiological adaptations, particularly within the cardiovascular system. While these adaptations are essential for sustaining homeostasis in a weightless environment, they culminate in a significant cardiovascular deconditioning syndrome upon return to Earth [35]. The primary clinical manifestation of this deconditioning is orthostatic intolerance, characterized by symptoms such as syncope, a diminished capacity for exercise, and an elevated resting heart rate [36]. The etiology of this syndrome is multifactorial, stemming from the fundamental cephalad redistribution of body fluids and the subsequent autonomic nervous system dysregulation, systemic fluid volume alterations, and vascular remodeling that ensue [4].

The principal catalyst for this cascade of cardiovascular adaptation is the hemodynamic fluid shift that occurs upon entry into a microgravity environment [37]. On Earth, the body's fluid distribution is governed by a hydrostatic pressure gradient, which results in higher pressure in the lower extremities and lower pressure at the level of the head relative to the heart [38]. The abrogation of this gradient in weightlessness causes a rapid translocation of blood and interstitial fluid from the lower body toward the thorax and head [39]. This acute increase in central blood volume serves as the primary stimulus that disrupts the established ho-meostatic set-points of baroreceptors, the endocrine system, and the nervous system, thereby initiating a series of profound physiological adjustments [40]. One of the most immediate consequences of the cephalad fluid shift is a pronounced dysfunction of the baroreflex system. This critical reflex is responsible for maintaining blood pressure homeostasis by coordinating cardiac and vascular function in response to postural changes [41]. In microgravity, persistent stimulation of central baroreceptors leads to a blunting of baroreflex sensitivity [42]. This maladaptation is characterized by an augmentation of sympathetic outflow and a concomitant reduction in parasympathetic control of the heart [43]. The resulting autonomic imbalance significantly impairs the body's ability to mount an effective cardiovascular response to orthostatic challenges, representing a direct mechanistic link to the orthostatic intolerance experienced by astronauts postflight [44]. While rodent models provide valuable insights, the extrapolation to humans must be made with caution due to differences in upright posture, cardiovascular control mechanisms, and vascular compliance.

Long-term regulation of fluid volume is also significantly altered by the microgravity environment. The centrally-shifted fluid volume is in-terpreted by the body as a state of hypervolemia, triggering a hormonal cascade to reduce total body fluid [45]. This response involves the increased secretion of atrial natriuretic peptide (ANP), which promotes di-uresis, and the suppression of the renin-angiotensin-aldosterone system (RAAS), which normally conserves fluid. The resulting decrease in plas-ma volume, coupled with a reduction in red blood cell production and increased hemolysis, leads to a decline in total red blood cell mass [46]. This systemic fluid loss reduces cardiac preload and stroke volume, further compromising cardiovascular function and exacerbating orthostatic intolerance upon return to Earth [47].

Cardiovascular deconditioning extends beyond functional control systems to encompass structural and functional remodeling of the vas-culature itself [35]. Altered hemodynamic forces, including changes in blood flow-induced shear stress and pressure-related circumferential stress, provoke endothelial dysfunction [48]. Studies have documented increased arterial stiffness and a thickening of the carotid intima-media in astronauts during long-duration missions [49]. Furthermore, microgravity appears to promote a pro-inflammatory state within the endo-thelium, evidenced by the increased expression of adhesion molecules such as VCAM-1. These vascular adaptations contribute to the overall decline in cardiovascular health and performance [49,50].

A particularly critical complication that has gained recent attention is the risk of venous stasis and thrombosis. Strikingly, studies in healthy astronauts have revealed stagnant or even retrograde blood flow within the internal jugular vein (IJV), with at least one documented case of an occlusive thrombus [51]. This phenomenon suggests that stasis of blood flow, potential hypercoagulability, and endothelial injury may occur during spaceflight [52]. It is hypothesized that altered transmural pres-sures across the compliant IJV increase flow resistance, leading to stasis. This finding has identified venous thromboembolism as a previously underappreciated yet serious risk for long-duration space missions [51].

These macroscopic physiological changes are underpinned by complex cellular and molecular mechanisms. At the cellular level, endothelial cells exhibit adaptive responses, including the upregulation of nitric ox-ide synthase (NOS) and heat shock proteins such as HSP70, which may confer protection and promote cell survival [53]. Insights from animal models have highlighted the protective role of specific transcription factors, such as Nrf2, which appears to mitigate vascular inflammation and thrombotic risk [54]. Investigation of these molecular pathways is crucial for understanding the fundamental biology of cardiovascular deconditioning and for identifying potential targets for novel countermeasures.

In conclusion, the physiological adaptation of the human cardiovascular system to microgravity is a multifaceted process, initiated by a cephalad fluid shift that triggers widespread changes in autonomic, endocrine, and vascular function [38]. While these adaptations enable survival in space, they result in a significant deconditioning syndrome that poses considerable health risks upon return to a gravitational environment, including orthostatic intolerance and a potential for thrombosis [55].

3. Exercise-based countermeasures

1) Resistance exercise

Numerous studies aboard the International Space Station (ISS) have demonstrated that resistance exercise is highly effective in preserving muscle mass and strength [56]. Space stations use specialized equipment like ARED for resistance training [57]. The ARED system represents a significant advancement in space exercise equipment, providing variable resistance through a flywheel system that simulates earth-like loading conditions. This equipment allows for a wide range of exercises targeting different muscle groups [58]. Notably, ARED has demonstrated superior effectiveness in preserving muscle mass and strength compared to previ-ous exercise hardware [57,59].

Experimental findings from spaceflight and analog models showed more comprehensive description in terms of optimal resistance exercise protocols for space. Research on astronauts aboard the ISS for six months showed that high-intensity resistance training was effective in preserving muscle mass and strength [59]. The protocol used in that study, performed 3-4 times per week, was instrumental in sustaining a significant portion of pre-flight muscle condition [60]. Regarding exercise volume, findings suggest that commonly recommended parameters, such as 3 sets of 8-12 repetitions per exercise with 2-3 minutes of rest between sets, can help optimize muscle stimulation [60]. Furthermore, it has been suggested that splitting the total weekly volume into more fre-quent sessions (4-5 sessions) may reduce musculoskeletal stress compared to fewer sessions [60,61]. Current evidence, derived from both in-flight studies and terrestrial analogs, supports the use of moderate to high intensity loads, typically ranging from 70% to 85% of one-repetition maximum (1RM), to effectively preserve muscle mass, strength, and bone mineral density during long-duration missions. In terms of training frequency, astronauts are generally prescribed three to five sessions per week, which strikes a balance between maximizing physiological adaptation and minimizing cumulative fatigue or overuse injuries (Table 1). This frequency allows for sufficient mechanical loading to counteract disuse, while accommodating the operational constraints of life aboard the ISS. The duration of each resistance training session typically spans 30 to 60 minutes, depending on mission schedules and available equipment. This time frame is sufficient to complete multi-joint, compound exercises targeting major muscle groups, using devices such as the Advanced Resistive Exercise Device (ARED). Additionally, compound exercises that target multiple muscle groups are known to be more effective in maintaining functional strength than isolation exercises [8,40]. These findings provide a scientific basis for developing increasingly sophisticat-ed exercise programs that maximize the benefits of resistance training while minimizing the risks associated with exercising in microgravity.

Table 1.

Exercise protocols for spaceflight

Exercise mode	Frequency	Intensity	Duration per session	Devices/Protocols	Ref.
Resistance training	3-6 times/week	70-85% 1RM, progressive overload	30-60 min	ARED (Advanced Resistive Exercise Device), flywheel devices	[56], [57], [65]
Aerobic training	4-7 times/week	60-85% HRmax or RPE 12-15, interval and steady state	30-60 min	CEVIS (Cycle Ergometer with Vibration Isolation), T2 treadmill	[59], [62], [66]
Balance/sensorimotor training	3-4 times/week	Moderate challenge level with progression based on stability	20-30 min	Balance board, unstable platforms, virtual reality-based tasks	[58], [68], [69]

2) Aerobic exercise

Aerobic exercise is essential for maintaining cardiovascular function and promoting overall health [57]. The implementation of aerobic exercise programs in space has evolved to address the unique challenges of the microgravity environment. Space stations use treadmills and cycle ergometers for aerobic training [62]. These systems allow for effective aerobic training while minimizing the impact on the space station structure.

Spaceflight research has uncovered expanded discussion concerning the benefits of different aerobic exercise protocols in space. Studies investigating various aspects of exercise prescription have shown that five to six sessions per week, 30-60 minutes per day of high-intensity interval training (HIIT) is successful at preserving pre-flight aerobic capacity, with one study reporting that VO2peak was well-maintained following long-duration spaceflight [9,59,62]. Regarding exercise hardware, the Cycle Ergometer with Vibration Isolation and Stabilization (CEVIS) has been noted as being more effective for maintaining VO2max compared to traditional treadmill exercise due to its capacity to facilitate higher intensity workouts [63]. In terms of exercise prescription, protocols involving continuous moderate-intensity aerobic exercise are recommended for providing adequate cardiovascular stimulation. For instance, daily sessions of 30 minutes at an intensity of 60-80% of VO2max have been proposed as a protocol (Table 1) [64]. Frequency analysis from ground-based analogs further indicates that daily aerobic exercise sessions are more beneficial at mitigating cardiovascular deconditioning than sessions performed only a few times per week (Table 1) [65,66]. Moreover, in a context analogous to that of resistance training, a combined approach of aerobic and resistance training has been shown to yield superior outcomes in terms of maintaining overall physical fitness, encom-passing cardiovascular, strength, and bone parameters, in comparison to either mode performed in isolation [67]. These findings contribute to the refinement of exercise protocols that enhance physiological benefits, es-pecially cardiorespiratory endurance, while mitigating the adverse effects of space flight.

3) Balance and coordination exercise

Exercises aimed at maintaining balance and coordination are critical for enhancing astronauts’ operational performance [68,69]. These include posture stabilization and functional movement tasks that should be performed regularly throughout the mission [70]. The growing duration and complexity of space missions have increased the importance of structured balance and coordination training.

Microgravity presents unique challenges to postural control, as the absence of gravitational cues demands novel strategies for movement and stability. This environment requires the development of new strategies for maintaining posture and performing movements. Training programs must address both the immediate effects of microgravity exposure and the long-term adaptations that occur during spaceflight.

Recent studies on neurovestibular adaptation have identified effective training protocols for addressing balance and coordination deficits, particularly those encountered upon re-entry into Earth's gravity [68]. To address this, postflight rehabilitation programs have been developed, focusing on sensorimotor training to promote the recovery of locomotor function. For instance, training protocols incorporating diverse balance and walking tasks help astronauts relearn motor patterns and regain mobility during postflight recovery [58]. Adapting the central nervous system to microgravity is complex. Effective countermeasures involve progressively challenging sensory–motor tasks to support re-adaptation. Despite variations in quantitative outcomes, evidence supports the effectiveness of structured sensorimotor training in restoring postural stability after long-duration missions [71]. The results are informing the design of advanced training protocols focused on optimizing recovery and enhancing astronaut safety following space missions.

4) Exercise prescription and program

Successful exercise programs also require personalized prescriptions and systematic monitoring. Exercise prescriptions considering astronauts’ individual characteristics and mission requirements are important, with regular evaluation and program adjustment being necessary. The process of developing and implementing exercise programs in space involves multiple considerations. Individual factors such as fitness level, medical history, and mission requirements must be carefully considered.

Studies investigating various aspects of program development emphasize that individualized exercise prescriptions, tailored based on pre-flight assessments and in-flight adaptations, are critical for optimizing astronaut health [57]. The exercise regimens aboard the ISS are a corner-stone of countermeasures, integrating both aerobic and high-load resistance training to mitigate the physiological deconditioning of the musculoskeletal and cardiovascular systems. While specific training ratios are not standardized, a comprehensive program combining various exercise modalities is demonstrably necessary to protect astronauts from the multisystem deconditioning induced by long-duration spaceflight [60]. Recent efforts to personalize exercise protocols include the integration of biomarker-based monitoring such as heart rate variability (HRV), cortisol, muscle oxygen saturation (SmO₂), and electromyographic fatigue index. These parameters are increasingly used to dynamically adjust workloads during space missions. Ongoing advancements based on these findings are enabling the creation of more precise and safer training regimens for astronauts.

4. Physiological monitoring and functional assessment strategies during and after long duration space mission

Functional performance evaluation related to actual task performance is also important. Balance ability, coordination, and endurance are assessed, reflecting astronauts’ actual task performance capabilities. The evaluation of functional performance in space involves multiple aspects of physical capability. Regular monitoring of multiple performance parameters is necessary to evaluate the effectiveness of exercise programs [67,69,72]. Additionally, the interpretation of performance data must consider the challenges of the space environment.

Recent research has provided more expanded evidence on functional performance assessment methods in space. A comprehensive understanding of the effects of spaceflight on musculoskeletal health, derived from systematic reviews and meta-analyses, highlights the need for robust and accurate assessment protocols [72]. The physical training programs for long-duration spaceflight depend heavily on data from these assessments to monitor astronaut health and appropriately adjust exercise countermeasures [57]. Postflight rehabilitation is typically structured in three phases: early (within 1 week), intermediate (2–6 weeks), and long-term (6–12 months). Recent protocols include robotic gait re-training, proprioceptive feedback enhancement, and vestibular recalibration programs. These are increasingly supported by virtual reality and AI-assisted recovery tools.

Current operational procedures involve a suite of functional performance tests to evaluate the efficacy of in-flight exercise regimens. For instance, objective measurements of skeletal muscle characteristics and iso-kinetic strength are utilized to track physiological changes after months in microgravity, providing crucial data on the effectiveness of intervention [60]. While the integration of advanced sensor technology and real-time data analysis is a goal for future missions, current approaches rely on established methods to periodically evaluate performance [61]. Recent technological advances have enabled the incorporation of wearable, real-time monitoring devices aboard the ISS. One such example is the Bio-Monitor system developed by the Canadian Space Agency (CSA), which consists of a smart shirt equipped with embedded sensors capable of continuously measuring heart rate, respiration, and temperature during daily activities, including exercise [9]. Similarly, the European Space Agency's Thermo-Mini system has been utilized to capture real-time thermal responses during and after exercise sessions, aiding in the understanding of metabolic and circulatory adaptation in microgravity. They emphasize that multi-layered performance assessment is vital for informing precision-based interventions that protect astronaut well-being throughout the mission cycle.

DISCUSSION AND CONCLUSION

This review clearly shows that microgravity causes complex changes in the human body, affecting many systems from how our cells work to how we move and perform tasks. To deal with these challenges, space programs have developed exercise-based countermeasures that combine resistance training, aerobic exercise, and balance or coordination training. These programs are more effective when they are personalized for each astronaut and regularly adjusted based on health data and performance tests.

So far, this approach has worked well in Low Earth Orbit missions, such as those on the International Space Station. However, future missions to deep space will be much longer and more difficult. Communi-cation delays, fewer medical resources, and greater health risks mean we need a new approach.

In the future, we must move from simply reacting to problems to pre-dicting and preventing them before they happen. This will require combining wearable health sensors, genetic and biological data over time, and artificial intelligence. These tools will help us track each astronaut's health more closely and design better, more timely interventions.

Psychological stressors such as isolation, confinement, and sleep disruption significantly affect astronaut mental health. Exercise is known to increase brain-derived neurotrophic factor (BDNF) and endorphin levels, improving mood and reducing anxiety. Aerobic exercise in particular has been linked to improved executive function and circadian rhythm regulation in analog environments like aerospace and Antarctica.

Developing such smart and self-guided health systems will be essential for keeping astronauts safe, healthy, and ready for the long missions ahead.

Notes

ACKNOWLEDGMENTS

This work was supported by grants from the National Research Foundation of Korea (NRF) funded by the Korean government (MSIT) (No. RS-2022-NR070859 and RS-2022-NR075830), the Research Resurgence under the Glocal University 30 Project at Gyeongsang National University in 2024, and the Learning Sciences Research Institute at Seoul National University.

CONFLICT OF INTEREST

We declare that we did not receive any financial or other support from any organization in writing this paper, and that I have no relation-ships that could have influenced the paper.

AUTHOR CONTRIBUTIONS

Conceptualization: JS Kim; Data curation: JS Kim, HY Moon; Funding acquisition: JS Kim, HY Moon; Methodology: JS Kim, HY Moon; Writing - original draft: JS Kim; Writing - review & editing: HY Moon.

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