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The effect of axial body loading – via the "SkinSuit" – on human movement. 

Student thesis: Doctoral ThesisDoctor of Philosophy

Bodyweight (BW) loading has been shown to increase metabolic cost and neuromuscular activity during locomotion. The Mk VI ‘SkinSuit’ – initially developed as a spaceflight countermeasure – provides axial body loading (ABL) intended to be equivalent to 20% ‘BW’ via vertical elastic-material in a manner analogous to Earth’s gravity (1Gz). Thus, the aims of this thesis were to determine the influence of additional 0.2Gz ABL on physiological and biomechanical responses during exercise in ≤1Gz. Two main protocol paradigms were adopted, which evaluated the effect of additional 0.2Gz ABL during: 1) incremental exercise to voluntary exhaustion in normal gravity (thus ~1.2Gz) vs. without ABL (1Gz) and 2) simulated 0.8Gz and 0.16Gz vs. a matched equivalent during submaximal exercise. Cardiorespiratory variables and maximal aerobic capacity (V̇ O2Max) were unchanged between 1.2Gz vs. 1Gz during cycling and running, though time to exhaustion was reduced with both (by 13% and 10%, respectively; p<0.05). A steeper breathing rate (BR)/minute ventilation (V̇ E) slope evidenced during running at 1.2Gz (p=0.044), indicative of a more rapid, shallow breathing pattern, may have contributed to this. Performing both exercises in 1.2Gz did not induce differences in electromyographic (EMG) root mean square (RMS) amplitude or median frequency (MDF) in any lower-limb muscle, though lengthened Gastrocnemius Lateralis (GL; cycling) and Soleus (SOL; running) duration (p<0.05). Both the removal (BW suspension) and addition (ABL) of 0.2Gz to 1Gz elicited reductions in ventilatory variables vs. 1Gz during submaximal running (p<0.01) whereas EMG RMS amplitude was unchanged. Although EMG RMS amplitude was reduced in all muscles in 0.16Gz compared to 1Gz, these were not reinstated to levels equivalent to those elicited during a matched trial (MATCHED) when running with 0.2Gz ABL (016SS). GM duration was significantly greater during 016SS vs. 0.16Gz and equivalent to MATCHED. Provision of 0.2Gz ABL in addition to ≤1Gz does not induce cardiorespiratory responses or muscle activity levels equivalent to 20% BW loading, presumably due to the absence of centre of mass displacement. However, the significant effect of additional ABL on muscle activity patterns during both cycling and running in ≤1Gz, particularly in the plantarflexors, suggests strategic modulation of locomotor control governed by the central nervous system. Unloading of 0.2Gz during high or low portions of the gravity spectrum was not potent enough to reduce the activation requirement of lower-limb muscles, making “reloading” opportunities inconceivable; thus, the optimal dose of ABL is yet to be determined.
Original languageEnglish
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Award date2018

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