| Summary: | Prolonged spinal unloading in microgravity has been associated with stature elongation and increased risk of intervertebral disc (IVD) herniation, particularly in the lumbar spine. Novel countermeasures to reintroduce axial loading in space are therefore required. This PhD aimed to evaluate the impact of a novel axial loading countermeasure upon stature, spinal structure and functionality, both when static and during motion, utilising a microgravity analogue. Five studies were conducted using novel ‘hyper-buoyancy flotation’ (HBF) as the microgravity analogue, enabling accessible ‘unloading’ for the evaluation of the European Space Agency’s ‘SkinSuit’ (Mk VI) which imparts low-level axial loading (~20% bodyweight). Chapter 3 evaluated HBF’s ability to induce stature elongation. Two groups underwent 4h (n=14) or 8h (n=14) HBF, resulting in a stature elongation (2.1cm), which was greater than that reported in comparable analogues. Chapter 4 (n=9) demonstrated that Mk VI SkinSuit wear attenuated stature (1.7±0.5cm vs. 2.1±0.4cm) and partial lumbar (L1-L3) IVD expansion following 8h HBF, whilst Chapter 5 (n=6) found that SkinSuit loading reduced stature elongation and lumbar length (L1-S1:17.8±1.0 vs. 18.1±0.8cm), presumably through a combination of minor IVD compression and an increase in lumbar lordosis, after 8h HBF. Chapters 6 and 7 evaluated the effects of 4h SkinSuit reloading following 8h unloading. In Chapter 6 (n=8), immediate effects of SkinSuit reloading were observed on stature and in several lumbar IVDs measured using ultrasound (0.2-1.0mm reduction: L2- S1 IVDs). In Chapter 7 (n=8), it was found using quantitative fluoroscopy, that SkinSuit reloading resulted in minor reductions in intervertebral restraint during passive flexion and in reductions in lumbar IVD height (L3/4:-0.44mm and L4/5:- 0.34mm) measured using MRI. These pilot studies suggest that HBF holds promise as a microgravity analogue. The SkinSuit imparted low-level axial loading that consistently attenuated stature. Minor IVD compression was observed which may have led to small attenuations in intervertebral restraint during flexion. Further testing in space and with analogues is recommended, to determine the effectiveness of cumulative wear at mitigating spinal deconditioning.
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