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The effect of axial body loading on lower limb neuromuscular activity during static and dynamic exercise

Research output: Chapter in Book/Report/Conference proceedingMeeting abstract

Julia Attias, Jonathan Scott, Katya Mileva, Thais Russomano, David Andrew Green

Original languageEnglish
Title of host publicationJoint Life Science Meeting ‘Life in Space for Life on Earth’
PublishedJun 2016
Event14th European Life Sciences Symposium 37th Annual International Gravitational Physiology Meeting - Toulouse, France
Duration: 5 Jun 201610 Jun 2016

Conference

Conference14th European Life Sciences Symposium 37th Annual International Gravitational Physiology Meeting
CountryFrance
CityToulouse
Period5/06/201610/06/2016

King's Authors

Abstract

Introduction: The Gravity-Loading Countermeasure ‘SkinSuit’ (GLCS) has been devised to comfortably compress the body axially in a graded manner analogous to Earth’s gravitational force. We have demonstrated that wearing a Mk VI GLCS (that provides ~0.2Gz) induces >10% lower work product during maximal aerobic exercise without change in Oxygen consumption compared to loose fitting clothes (GYM). Thus, we sought to determine the effect of axial body loading induced by the GLCS upon lower limb neuromuscular activity during maximal voluntary isometric contractions (MVIC) and incremental cycling exercise. Methods: In two separate counterbalanced sessions, eight male subjects (29.6±5.6 yrs; 177.1±6.8 cm and 74.2±7.1 kg) performed - in a random order - single-leg MVICs in knee flexion and extension in addition to ankle plantar- and dorsi-flexion on an Isokinetic Dynamometer prior to completing a cycle ergometer maximal oxygen uptake (VO2max) test (Bruce protocol) wearing either a custom-fabricated Mk VI GLCS or GYM. Surface electromyography (EMG) activity of the right Vastus Lateralis (VL), Biceps Femoris (BF), Tibialis Anterior (TA), and Lateral Gastrocnemius (GL) were recorded continuously throughout the sessions. The Root Mean Square (RMS) amplitude, total area and duration of muscle EMG activity, as well as the Median Frequency (MDF) of the EMG power spectral density were calculated for each revolution. EMG parameters were normalised to the respective mean values at 50W cycling and compared between the conditions (ATTIRE) and across the workloads (WORKLOAD) with a two-way repeated measures ANOVA. Maximal torque and EMG data computed from the MVICs were compared between the conditions using paired t-tests. Results: EMG activation levels and the torque during MVICs were not significantly different between conditions. During cycling, EMG RMS and total area increased with WORKLOAD independent of ATTIRE for all muscles. VL MDF increased and GL decreased with increasing WORKLOAD with no effect of ATTIRE. EMG activity duration increased with WORKLOAD in VL, BF and TA independent of ATTIRE. GL EMG activity was prolonged in GLCS vs. GYM. The GLCS induced subject-specific shifting of EMG onset-offset timing which became more apparent as workload increased to VO2max. Conclusion: Addition of GLCS-induced ~0.2G axial body loading does not affect muscle function during isometric maximal contractions and has minimal effects on the workload-related increments in EMG activation levels during incremental cycling. Although the overall EMG duration within the cycling revolution was unchanged, subject-specific shifting of muscle activation suggests an effect of axial loading upon lower limb neuromuscular control despite the biomechanical constraints of cycling. Therefore investigation of the effect of additional axial loading upon neuromuscular function during locomotion - where there is the requirement to control centre-of-body mass - is warranted.

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