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Abstract

During space sojourns, astronauts experience musculoskeletal deconditioning caused by the lack of gravity. The adaptation of the musculoskeletal system to inactivity and unloading of the weight-bearing limbs may be countered by daily exercise. However, current exercise devices and strategies employed on the International Space Station (ISS) do not appear to be optimal. As a consequence, a new potential countermeasure has been proposed by the European Space Agency. This exercise countermeasure combines resistive exercise on a Short-Arm Human Centrifuge (SAHC) and whole-body vibration (WBV). This thesis investigated some key aspects of this exercise countermeasure. Additionally, the combined effects of centrifugation and WBV on muscular structure and function were investigated.
These objectives were achieved in a series of four studies:
Study 1: Comparison of joint kinematics between upright front squat exercise and horizontal squat exercise performed on a short arm human centrifugation. This study compared the kinematics of squat exercise conducted on the SAHC with upright squat exercise. In both conditions the exercise was conducted under two loading conditions: (g and 1.25g at the centre of mass (CoM). Twelve health young males participated in this repeated measures study.
Study 2: The effects of exercise on acute muscular activation: resistance exercise vs whole-body vibration resistance exercise.
Using magnetic resonance imaging, this study evaluated muscle activation in the thigh and calf muscles following body weight squat (resistance) exercise performed without and with WBV. Fifteen healthy young males participated in this repeated measures study.
Study 3: Whole-body vibration transmission during resistance vibration exercise
This study compared vibration transmission while performing URVE and AGRVE. Fifteen male participants were assigned to the URVE (N=7) and AGRVE (N=8) groups.
Study 4: Muscular adaptations following a 2-weeks artificial gravity resistance vibration exercise.
This study compared the muscle structure and performance adaptations after 2-weeks of daily resistance vibration exercise (RVE) performed under three conditions: a) URVE: upright RVE, b) HRVE: horizontal RVE conducted on a bespoke exercise device, and c) AGRVE: supine exercise conducted on the SAHC establishing a head-to-foot gravitational vector (i.e., artificial gravity, AG). Twenty-four healthy young male participants were assigned to the three exercise groups.
The main findings of these studies are that:
1) A two-axis cradle allows hips movement which is crucial to maintain muscular activity of those muscles involved into keeping a straight posture and which are the most affected during space exploration. New users cannot replicate their squat movement on the centrifuge, resulting in a diminished range of motion (ROM). However, participants do improve the movement efficacy already within a single session.
2) MRI can be effectively used to measure muscular activity. Vibrations do not promote any additional benefit on muscular water content and metabolite accumulation, which is the main physiological responses after exercise.
3) Vibration transmission is dampened by lower limbs in both URVE and AGRVE. In the latter, vibration transmission is further dampened compared to URVE due to technical factors which could have absorbed part of the vibration stimulus.
4) AGRVE resulted to be a feasible exercise and can be performed by new users. Exercising in AGRVE resulted to be more effective compared to two control exercises in short-term muscular adaptation.