[Synergy-2]
The elucidation of muscle synergy mechanism during space flight

RESEARCH OVERVIEW

• During long-duration spaceflight, skeletal muscle (such as the soleus) is known to atrophy, and many astronauts have difficulty walking just after return to the Earth. There is a lot of data related to the muscle atrophy of astronauts, however the final mechanism of the muscle weakness during spaceflight is still unclear. Therefore, it is necessary to evaluate the re-adaptation process during astronauts' walk post-return in a comprehensive and systematic fashion.
• In The Elucidation of Muscle Synergy Mechanism During Spaceflight (Synergy-2) investigation, useful data related to re-adaptation of attitude control after return from long-duration spaceflight is obtained. The results of this investigation can help researchers better resolve the mechanisms related to re-adaptation during walking just after return to Earth, and also contribute to the development of an effective rehabilitation program in clinical fields.
• The advantage of this investigation is the whole evaluation from analyzing muscle synergies (combination of muscles usages) quantitatively and we will clarify the essence of motor control. These results will provide the basic information to better understand the training program or rehabilitation not only for astronauts but also for clinical patients.

DESCRIPTION

Astronauts live aboard the International Space Station (ISS) for a long period of time; therefore, the development of astronaut health care technologies is very important. It is vital to gain a better understanding of the effects of the space environment on the human body, such as microgravity and radiation, to develop countermeasures against the adverse effects experienced by astronauts who live in space for long periods of time. During long-duration flights, the physiological effects on astronauts include muscle atrophy and bone calcium loss. Greenleaf et al. reported that astronauts lose their aerobic power and muscle strength, and experience deterioration in mood and psychological state (J. Appl. Physiol. 67, 2191-2204, 1989). Specifically, during long-duration flights, the skeletal muscles, such as the soleus, are known to atrophy and many astronauts have difficulty walking just after the return to Earth. There is much data related to the muscle atrophy of astronauts; however, the mechanism of how the muscle weakens during spaceflight is still unclear. Therefore, the purpose of The Elucidation of Muscle Synergy Mechanism During Spaceflight (Synergy-2) investigation is to further study the re-adaptation of the attitude control of skeletal muscles after return from long-duration spaceflight.

The Synergy-2 investigation assesses the condition of ISS crew members who have lived in space for a long period of time and compares the muscle activity patterns in the lower limb muscles (soleus, gastrocnemius, tibialis anterior, peroneus longus, vastus lateralis, rectus femoris, biceps femoris, and gluteus medius muscles) before and after flight. The goal is to better understand sway balancing, in order to clarify the physiological problems that affect the skeletal muscle and somatosensory system because of long-term spaceflight, and obtain basic data for resolving these problems. In this study for crew members before flight and for a period of 6 to 2 months after return to Earth, the (electromyography (EMG) of the muscles are measured over time in (1) standing, (2) step task, (3) walking, and (4) straddling task. To clarify the physiological problems that affect the skeletal muscle and somatosensory system, the research team evaluates muscle synergies (combination of muscles usages) quantitatively to evaluate the essence of motor control. These results contribute to the improvement of postflight rehabilitation methods.

SPACE APPLICATIONS

Results of this investigation could support development of more effective training and rehabilitation programs to help counter the effects of changes in skeletal muscle and the somatosensory system experienced by astronauts.

EARTH APPLICATIONS

This investigation also could contribute to improving rehabilitation for patients on Earth who experience prolonged bed rest or injuries such as to the anterior cruciate ligament, and for training to counteract the effects of aging.

OPERATIONAL REQUIREMENTS AND PROTOCOLS

For Synergy-2, measurements are taken before and after a crew member’s long-duration stay in orbit aboard the ISS. The measurement times occur once preflight (once during the 1 to 6 months leading up to launch), and 6 times postflight (twice over at least a 2-day interval within the first week after return, once about 1 month later, once about 3 months later, about 6 months later, and about 12 months later), for 7 measurement times. Thus, 7 rounds of data acquisition are to be obtained from a single subject, between the 6 months leading up to the launch, and the 12 months following the return. About 60 minutes is required for each measurement session.

Protocol

1. EMG electrodes are attached to the subject’s lower limbs. Motion-capture markers are attached to various sites on the body. The subject also completes a questionnaire (time required: 10 minutes).
2. Subjects are moved onto a force plate and a body sway while upright is measured (time required: 5 minutes).
3. Then, while still standing on the force plate, subjects shift their center of gravity toward a direction, and then return to the original upright state. This activity is repeated until the subject has moved in 12 different directions for evaluation. EMG measurements are taken while these tasks are being performed (time required: 20 minutes).
4. Subjects walk 4 or 5 times in a straight line of about 10 meters. Subjects straddle a virtual obstacle on the walking path during walking. During walking, EMG is measured (time required: 20 minutes).
5. After completion of the measurements, the electrodes and motion-capture markers are removed (time required: 5 minutes).

TERADA Masahiro [Kyoto University]