Over the next decades, men will return the Moon, build a new space station, and extend human explorations to Mars: the bravest exploration framework since the Apollo Era. Joint projects by international and national space agencies (e.g., ESA & NASA) and by rising private companies have been launched. Space exploration and all related fields are no more just a matter for few insiders, but it is becoming a worldwide interest. Can man physiologically cope with this exploration challenge? We know from the Apollo missions that man can land on the Moon, ‘walk’ around, collect some rocks, and be back “Home” in a relatively short time. It is much more challenging for them to be back on Earth and ‘walk’ into daily life after 3-12 months on the ISS. And what about a 7-9month one-way flight to Mars? The physiological changes that astronauts will face affect the whole body, all systems with distinct targets and timing. This symposium aims to describe how micro/hypo-gravity affects human neuromuscular system, motor control and locomotion with a ‘micro to macro’ approach, focusing on the potential physiological mechanisms that lay behind maladaptation to disuse. The most important biological and physiological challenges of space flight will be discussed, as well as the main disuse/hypo-gravity models utilized on earth for research. Lastly, each talk will try to provide new perspectives for successful exercise countermeasures to long-term hypo-gravity and disuse exposure.
ECSS Paris 2023: IS-PN02
Human locomotion evolved and has been tuned over the year to cope with Earth gravity. This evolution ended up with walking as the preferred gait for everyday activities; whereas, when more speed is needed, running is the gait of choice. When the first astronauts landed on the Moon, they faced for the first time a lower gravity (almost 1/6 of Earth) and they adopted also (and mostly) other two gaits: skipping (the gallop for bipedal) and hopping (the gait of kangaroos). In the beginning it was thought that this shift was driven by mechanical and balance constrains, however we showed that the metabolic energy required to perform those bouncing gaits was greatly reduced in hypo-gravity, much more than in walking and running (Pavei et al. 2015). This decreased metabolic demand was parallel to a decreased mechanical work performed by the muscle-tendon system while locomoting in hypo-gravity, where not only a decreased in potential energy but also a reduced work to swing the limbs occurred. The reduced gravity decreased the locomotion efficiency, thus from a whole-body perspective it seems that the spring that usually helps muscles in the bouncing gaits was less compressed and hence less able to store and release elastic energy. This is probably given by the evolution that tuned the muscle-skeletal unit to the 1g level and it is not as effective in low gravity conditions. In this respect, the lowered metabolic demand could be even lowered whether the spring could be adjusted to the new hypo-gravity level, and this is likely to be obtained with external aids, such as passive (or active) tools. From bed-rest studies, a decrease in maximal aerobic power is reported. However, the impact of this decrease on exercise with low mechanical (and metabolic) demand, e.g. locomotion, has not well addressed yet, and those few studies reported no differences in metabolic power. Hence, we could say that locomotion could still be feasible from a cardio-metabolic point of view. On the other hand, in order to locomote muscles have to generate the needed amount of force and work, which should be coupled by tendons activity. Muscles and tendons are known to incur a great impairment post bed-rest or microgravity permanence, the muscle-tendon system could possibly be able to maintain a walking gait, but maybe could not a bouncing gait. Another problem regards the posture and balance necessary to locomote, both seem to be impaired after a permanence in microgravity, making potentially difficult an independent locomotion. Unfortunately, there are no studies that can answer now “could astronauts move after a one-way flight to Mars?”. We think that if astronauts will not follow an intensive program of countermeasures aims to use their limbs once out of the shuttle, it would be unlike that the lower metabolic demand of locomotion could help!
Read CV Gaspare PaveiECSS Paris 2023: IS-PN02
Since Yuri Gagarin’s pioneering flight in 1961, numerous missions of varying length and on a range of platforms have explored space and its effects on the human body. To maximize the benefits of future Mars and moon missions, extravehicular activities in low-gravity environments will be essential during human exploration. In sustained missions (Artemis 2), crewmembers are required to move from a defective rover to a safe location over distances of up to 12 km. A simple fall due to muscle weakness or lack of locomotor control could result in injuries or spacesuit damage that could be life-threatening. Ultrasonic visualization of muscle fascicle and tendon (SEE) behavior during locomotion has demonstrated the importance of the storage and release of elastic energy by the Achilles tendon in running and walking, and that the plantar flexor muscles modulate their behavior depending on gait type, speed, and external loading. Despite the relevance of this topic to both space travel and rehabilitation, only a few studies have examined the behavior of muscles and tendons in simulated or real hypergravity. The shorter peak SEE length observed during running in simulated 0.7 g may be the result of lower muscular forces acting on the SEE (Richter et al., 2021a). The longer fascicles observed during running in simulated (0.7 g) hypogravity may result in an increased strain on the z-disks, which in turn may be beneficial for muscle mass preservation. Decreasing g-level from 1 g to simulated Martian and lunar gravity resulted in hypogravity-induced alterations in SEE length, and contractile behavior that persisted between simulated running on the moon and Mars (Richter et al., 2021b). This should be taken into account when evaluating exercise prescriptions and the transferability of locomotion practiced in lunar gravity to Martian gravity. Monti et al. (2021) assessed fascicle behavior during the locomotor-like task—drop jump—during a parabolic flight. Upon landing, gastrocnemius medialis fascicles showed lengthening in all gravity levels below and above 1 g and quasi-isometric fascicle behavior in 1 g. Such behavior was potentially due to the lower level of muscle pre-activation (Waldvogel et al., 2021), implying a modulation of the muscle’s mode of operation toward a damping function. Thus, existing studies have demonstrated that the consequences of locomotion in hypogravity are not limited to a mere reduction in mechanical loading but also to an altered contractile behavior, which could affect the muscle’s work capacity upon return to daily activities in a 1 g environment and may require specific attention for adequate countermeasures and during the rehabilitation phase. Monti, E., et al. (2021). Frontiers in Physiology, 12, 714655. Richter, C., et al. (2021a) Npj Microgravity, 7(1), 1–8. Richter, C., et al. (2021b) Scientific Reports, 11(1), 22555 Waldvogel, J., et al. (2021) Frontiers in Physiology, 12, 614060.
Read CV Kirsten AlbrachtECSS Paris 2023: IS-PN02
It is likely that space explorations will become more common very soon, considering how much effort is being put in by national space agencies and private companies. Man on the Moon part II or space hotels, like the “Voyager Station” idea don’t seem to be just a dream anymore. However, one “dark side of the Moon” is that astronauts experience a dramatic loss of muscle mass following exposure to hypo-gravity and muscle disuse. This is accompanied by even bigger decrease in muscle strength and power, development of insulin resistance and detrimental metabolic and mitochondrial dysfunctions. Lower limbs muscles, and especially the anti-gravity muscles (such as the plantar flexors and the knee extensors), undergo significant wasting (~20% of fibre atrophy after 6 months of space flight for the triceps surae) (Rittweger 2018), despite the astronauts perform daily intense physical exercise that instead, on earth, would lead to muscle hypertrophic responses. Thus, even if muscle atrophy and weakness have been object of research since the 1990s, we still do not fully grasp the mechanisms regulating this dramatic muscle wasting and the strategies that are in place to counteract such atrophic process (in flight or post flight) are still not enough. Of course, the small sample size of astronauts involved in these studies, the different durations of each mission, the type of adherence of exercise programs in flight, have makes things a bit more complicated (Narici & de Boer 2011). Nevertheless, studies employing simulated micro/hypo-gravity on earth through the means of bed rest or limb suspension/casting models have provided useful data on muscle disuse and unloading not only important for space flight missions, but also of extreme interest for bed-ridden patients in hospital settings. Lately, our laboratory has focused on muscle disuse and the study of the causes of muscle weakness, from muscle morphological adaptations (Franchi et al. MSSE 2022) and the instability of the neuromuscular junction occurring after short-term bed rest and limb suspension (Monti et al. 2021; Sarto et al. 2022), to the study of single fibre proteomics to identify the molecular remodelling of muscle unloading (Murgia et al. 2022). With a short journey from whole muscle to molecular adaptations to disuse conditions, this presentation aims to unravel some of the nueromuscular responses to unloading in space flight and with simulated micro-gravity conditions, trying to answer a simple question: “Can we really get to Mars and have a walk?”. Moreover, new unpublished data (at the present time) regarding specific exercise countermeasures after a period of muscle unloading will be presented, with the aim to spark a discussion between sports scientists, exercise physiologists, and biomechanics experts, on what could be the best exercise strategies to counteract disuse atrophy.
Read CV Martino FranchiECSS Paris 2023: IS-PN02