The question of the composition of exercise protocols for use by astronauts in microgravity is unresolved. Based on our knowledge of physical working requirements for astronauts during intra- and extravehicular activity and on the findings from bed-rest studies that utilized exercise training as a countermeasure for the reduction of aerobic power, deterioration of muscular strength and endurance, decrements in mood and cognitive performance, and possibly for bone loss, two exercise protocols are proposed. One assumes that, during microgravity, astronaut exercise physiological functions should be maintained at 100% of ground-based levels; the other assumes that maximal aerobic power in flight can be reduced by 10% of the ground-based level. A recommended prescription for in-flight prevention or partial suppression of calcium (bone) loss cannot be written until further research findings are obtained that elucidate the site, the magnitude, and the mechanism of the changes. Hopefully these proposed exercise prescriptions will stimulate further research and discussion resulting in even more efficient protocols that will help ensure the optimal health and well-being of our astronauts.

Although various exercise paradigms have been tested, none has completely prevented muscle atrophy during non-weight bearing. Because loaded eccentric contractions occur during normal daily activity but are absent during non-weight bearing, this investigation tested whether eccentric resistance training could prevent soleus muscle atrophy during non-weight bearing. Adult female rats were randomly assigned to either weight bearing +/- intramuscular electrodes or non-weight bearing +/- intramuscular electrodes groups. Electrically stimulated maximal eccentric contractions (4 sets of 6 repetitions at approximately 0.2 fiber lengths/s, 128 degrees range of motion) were performed on anesthetized animals at 48-h intervals during the 10-day experiment. Non-weight bearing significantly reduced soleus muscle wet weight (28–31%) and noncollagenous protein content (30–31%) compared with controls. Eccentric exercise training during non-weight bearing attenuated but did not prevent the loss of soleus muscle wet weight and noncollagenous protein by 77 and 44%, respectively. The potential of eccentric exercise training as an effective and highly efficient counter-measure to non-weight-bearing atrophy is demonstrated in the 44% attenuation of soleus muscle noncollagenous protein loss by eccentric exercise during only 0.035% of the total non-weight-bearing time period.

Designing methods for musculoskeletal conditioning in weightlessness. There is an immediate need to find methods to combat the skeletal muscle deconditioning that occurs in microgravity. Important features to be considered for any ergometer or exercise method to be used as a countermeasure against musculoskeletal deconditioning in space include heavy muscular loading of the postural muscles of the lower limbs and that eccentric and concentric muscle activations can be performed. Those are major requirements to produce optimal gains in strength and muscle mass at 1-g and probably to counteract muscle atrophy and strength loss in microgravity. Resistance exercise with a strength-ergometer, using the fly-wheel principle was carried out at a low oxygen cost and required no external power supply. We have developed a resistance training system employing this ergometer so that force and power production easily can be monitored and calibrated. It is suggested that the features of this ergometer meet the presented requirements for use during long-term space missions. Published in The Physiologist (1992)

and function than is microgravity. Certainly exercise regimens and hardware will be required, not only for countering muscle atrophy but for the reasons Even before humans began to venture into space, serious and reasonable concerns were expressed about exposure of humans to the microgravity of space due to the potential systemic effects on terrestrially evolved life-forms adapted to Earth gravity. Unloading of skeletal muscle, both on Earth via bed-rest experiments and during spaceflight, result in remodeling of muscle (atrophic response). As a r With respect to endurance, a majority of the decrease in the total quadriceps work occurred on R+0. This likely reflects significant loss in the first third of the exercise bout (−11%). The declines in peak torque at the faster endurance test velocities are consistent with changes seen at the slower angular velocity used during the strength tests. Torque for the quadriceps at 75° per second was 15% less than preflight values but for the hamstrings was 12% less than the preflight mean at 60° per second. Endurance data showed little difference between preflight and R+7 tests, suggesting that crewmembers had returned to baseline by 1 week after landing. Additionally, subjects who did exercise during flight compared to those who did not had significantly greater (p < 0.05) losses within 5 hours of landing in concentric strength of the back, concentric and eccentric strength of the quadriceps (30° per second), and eccentric strength of the hamstrings, relative to the respective preflight values (data not shown here). According to Greenisen et al., non-exercisers also had significantly less concentric strength of the quadriceps at 75° per second and lower total work extension, work first-third flexion, and work last-third extension, immediately after landing, than before flight. The conclusions reached by the investigators were that the data indicate that muscles are less able to maintain endurance and resist fatigue after spaceflight, and that exercise may avert decrements in these aspects of endurance. Conversely, crewmembers who exercised during flight had greater losses in trunk muscles strength as measured at landing than did the non-exercising group (figure 6-7). However, preflight strength in trunk flexion and extension was substantially greater in the exercising group than in the non-exercising group. Apparently treadmill exercise did not prevent decrements in trunk strength after 9 to 11 days of spaceflight, and the investigators proffered the explanation that preservation of muscle function may be limited only to those muscles that are effectively used as part of the exercise regimen. The… In this section, only the historical highlights of some highly…

Neuromuscular aspects in development of exercise countermeasures. Based on the results generated from experiments conducted by our investigators, it is clear that prolonged exposure to microgravity environments can induce ultrastructural abnormalities and atrophy of muscle and impair muscle function, especially upon return to terrestrial gravity. It is also apparent that ground-base models can be effectively used to study these changes. This provides a less expensive and more controlled laboratory condition in order to conduct experiments. The use of animal models must be more closely examined. In the case of muscle adaptations to microgravity, the data from flight experiments which have used rodents might suggest the use of exercise with characteristics contrary to those which would be most appropriate to defend against atrophy and dysfunction in human muscle. Although many spaceflight experiments may be limited to the use of animal models, the results of the studies reviewed in this paper emphasize the importance of using human models in order to provide the most accurate interpretation of data for the development of exercise countermeasures for spaceflight.

The percent change in calf compliance after bed rest was significantly correlated with changes in calf muscle compartment CSA (r = 0.72, P less than 0.05). The increased leg compliance observed after exposure to simulated microgravity can be partially explained by reduced muscle compartment. Countermeasures designed to minimize muscle atrophy in the lower extremities may be effective in ameliorating increased venous compliance and orthostatic intolerance after spaceflight. Published in Journal of applied physiology (Bethesda, Md. : 1985) (1989)

This review evaluates BFRT as a novel countermeasure against multisystem deconditioning (muscle atrophy, bone loss, cardiovascular impairment) during long-duration space missions. BFRT combines low-load exercise with vascular occlusion, mimicking high-intensity benefits while reducing equipment needs. We synthesize evidence for BFRT's efficacy in microgravity analogs, discusses implementation challenges (equipment adaptation, safety protocols, sex-specific responses), and highlight its potential as a space-efficient adjunct to current exercise regimens, informing future mission planning.