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The international partnership of space agencies has agreed to proceed forward to the Moon sustainably. Activities on the Lunar surface (0.16 g) will allow crewmembers to advance the exploration skills needed when expanding human presence to Mars (0.38 g). Whilst data from actual hypogravity activities are limited to the Apollo missions, simulation studies have indicated that ground reaction forces, mechanical work, muscle activation, and joint angles decrease with declining gravity level. However, these alterations in locomotion biomechanics do not necessarily scale to the gravity level, the reduction in gastrocnemius medialis activation even appears to level off around 0.2 g, while muscle activation pattern remains similar. Thus, it is difficult to predict whether gastrocnemius medialis contractile behavior during running on Moon will basically be the same as on Mars. Therefore, this study investigated lower limb joint kinematics and gastrocnemius medialis behavior during running at 1 g, simulated Martian gravity, and simulated Lunar gravity on the vertical treadmill facility. The results indicate that hypogravity-induced alterations in joint kinematics and contractile behavior still persist between simulated running on the Moon and Mars. This contrasts with the concept of a ceiling effect and should be carefully considered when evaluating exercise prescriptions and the transferability of locomotion practiced in Lunar gravity to Martian gravity.
Stretch-shortening type actions are characterized by lengthening of the pre-activated muscle-tendon unit (MTU) in the eccentric phase immediately followed by muscle shortening. Under 1 g, pre-activity before and muscle activity after ground contact, scale muscle stiffness, which is crucial for the recoil properties of the MTU in the subsequent push-off. This study aimed to examine the neuro-mechanical coupling of the stretch-shortening cycle in response to gravity levels ranging from 0.1 to 2 g. During parabolic flights, 17 subjects performed drop jumps while electromyography (EMG) of the lower limb muscles was combined with ultrasound images of the gastrocnemius medialis, 2D kinematics and kinetics to depict changes in energy management and performance. Neuro-mechanical coupling in 1 g was characterized by high magnitudes of pre-activity and eccentric muscle activity allowing an isometric muscle behavior during ground contact. EMG during pre-activity and the concentric phase systematically increased from 0.1 to 1 g. Below 1 g the EMG in the eccentric phase was diminished, leading to muscle lengthening and reduced MTU stretches. Kinetic energy at take-off and performance were decreased compared to 1 g. Above 1 g, reduced EMG in the eccentric phase was accompanied by large MTU and muscle stretch, increased joint flexion amplitudes, energy loss and reduced performance. The energy outcome function established by linear mixed model reveals that the central nervous system regulates the extensor muscles phase- and load-specifically. In conclusion, neuro-mechanical coupling appears to be optimized in 1 g. Below 1 g, the energy outcome is compromised by reduced muscle stiffness. Above 1 g, loading progressively induces muscle lengthening, thus facilitating energy dissipation.
Astronauts exposed to microgravity experience physiological deconditioning, especially systems sensitive to force loading such as the musculoskeletal system. In order to attenuate these adverse effects, current ISS crew members perform a daily physical exercise countermeasure program, including treadmill running. However, the maximum vertical loading applied is usually not more than 70-80% of body weight (BW). As the triceps surae is one of the muscles most affected by immobilization but at the same time contributes significantly to vertical support and horizontal propulsion of the human body, it is important to examine the behaviour of its fascicles and tendon under unloading conditions to get a deeper understanding of what might cause the wasting and loss of function. Therefore, the aim of this study was to determine fascicle, tendon and muscle-tendon-unit (MTU) length of the gastrocnemius medialis muscle (GM) during running at 0.38g (Martian gravity), 0.7g (70% BW) and 1g.
Sehnen übernehmen im menschlichen Körper die Kraftübertragung zwischen Muskel und Knochen, als auch die Energiespeicherung und -freisetzung. Bisherige Studien zeigen, dass sich Sehnen entsprechend ihren Belastungen anpassen, d.h. Personen, die höhere Muskelkräfte generieren können, weisen in der Regel eine höhere Sehnensteifigkeit auf. Die Steifigkeit der Sehne ist im Wesentlichen durch ihren Querschnitt und ihre Materialeigenschaften determiniert.
High accelerations in the bobsleigh push phase are crucial for high bob velocities and therefore short final race times.For that, leg extensor muscles have to produce high mechanical power at the hip, knee, and ankle to propel the athlete’s body and the sled forward. In order to modify training and to enhance performance, the understanding of joint function is essential for coaches and athletes.
