Muscle Tone in Space: Myotones experiment on the ISS (ILSRA-2014-0015)

The effects of microgravity on the musculoskeletal system after spaceflight have received much attention. This is when the muscles, particularly the postural muscles (which keep us upright against gravity on Earth), become smaller and weaker due to unloading. The tone of a resting muscle is affected by tissue called fascia, as well as the tissue within the muscle itself and these shape the human resting muscle tone (HRMT) system. Changes in the HRMT system and the effects on function due to microgravity have yet to be studied directly. Basic biomechanical properties of skeletal muscle, such as tone and stiffness, are assessed on Earth using subjective clinical scales, which involve moving a person's arm or leg and making a judgement on how the movement feels. More sophisticated laboratory-based equipment can provide accurate measurements but is non-portable and expensive, so a more practical and affordable way of assessing muscle outside the laboratory is needed. The MyotonPRO device offers a hand-held, user-friendly and non-invasive measurement method to test key biomechanical parameters of the superficial skeletal muscles, tendons and other soft biological tissues. The device has a probe which gives a gentle mechanical tap to the skin, causing the tissues beneath it to vibrate (oscillate). These oscillations are recorded by the device and measurements of the oscillations are calculated automatically to give instant recordings of parameters that represent tone, stiffness, elasticity etc. This project aims to monitor muscle health of crew members by non-invasive, objective measurement of biomechanical properties of muscles pre-, in- and postflight. The two technologies used are Myoton and ultrasound imaging of musculoskeletal tissues. Ultrasound images will be used to measure muscle thickness to see how this changes over time, from preflight to inflight and postflight periods. Recordings using the MyotonPRO will be taken at 10 measurement points over key muscles and tendons in 12 crewmembers pre-exercise and, if crew time allows, also post-exercise, before, during and after spaceflight. Ultrasound scans will also be taken at the same measurement points to monitor changes in local tissue structures (skin, fascia, tendon, muscle). In addition, blood samples will be taken pre- in and postflight to analyse connective tissue turn-over enzymes (e.g., MMPs). Pre and postflight, routine muscle physiology (surface electromyography, strength tests) will be performed on two muscles of the lower leg (gastrocenemius in the calf, anterior tibialis), followed by magnetic resonance imaging (MRI) to complement structural/biomechanical with functional data. Testing with the MyotonPRO may enable effective monitoring of crewmembers' muscular system status during their stay on the ISS (resting periods, mission duties, countermeasures application, extravehicular activities) as well as monitoring pre and postflight recovery from prolonged missions. This non-invasive, easy-to-use, and cost effective technology will help to: i) increase our understanding of the mechanisms behind the loss of muscle mass and strength that occurs in space; ii) achieve objective assessment of muscle to track the time course of changes throughout a mission; iii) monitor effects of exercise programmes (countermeasure) in future missions; and iv) gain new data sets to complement the subjective clinical scales routinely used on Earth. The potential impact of this work is to provide a non-invasive means of indicating which muscles need to be targeted in personalised exercise programmes for astronauts to minimise loss of muscle during spaceflight and enable rapid recovery postflight. This research is intended to provide lessons for rehabilitation of patients on Earth who have restricted mobility from neurological (e.g. Stroke, Parkinson's disease) and musculoskeletal (arthritis, back pain) conditions, and in healthy ageing and dementia.