The effects of hypoxia on motor output during a 60 minute lower limb cycling protocol

Sullivan, Kathleen Margaret (2013) The effects of hypoxia on motor output during a 60 minute lower limb cycling protocol. Masters thesis, Memorial University of Newfoundland.

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Abstract

The muscles working together to produce motion around a joint is called muscle coordination, and there are specific recruitment patterns for every movement. Exposure to a lowered oxygen environment can cause an acceleration of locomotor muscle fatigue (Romer et al., 2007), and when the muscle becomes fatigued, a change in the pattern of activation may be induced (Gandevia, 2001). The objective of this study was to investigate changes in muscle activation patterns (a cause of central fatigue) during cycling between hypoxic (15% O2) and normoxic (20.93% O2) conditions, and whether they take place before, during, or after the development of peripheral fatigue. Ten endurance trained males participated in three laboratory sessions. The first session was an incremental ramp cycling test to determine VO2max and peak power output (PPO). In the second and third sessions, the participants randomly underwent an hour long cycling test in hypoxia or normoxia consisting of eight 3-minute work intervals (70% of PPO) and eight 4.5-minute active rest intervals (35% of PPO). Electromyography (EMG) was collected continuously throughout the test from the vastus lateralis (VL), biceps femoris (BF), tibialis anterior (TA) and lateral gastrocnemius (LG) muscles. Maximal Voluntary Isometric Contractions (MVICs) were performed after every work interval. Heart rate (HR) was significantly lower between conditions in the active rest intervals, while rate of perceived exertion (RPE) and arterial oxygen saturation (SpO2) were significantly higher throughout the full test in hypoxia. MVIC force values decreased throughout the test in both conditions. Muscle activation changes included a main effect for time in RMS amplitude measures of the VL, BF and LG. There was a main effect for condition for VL:BF coactivation and VL delta time (length of activity over one second). Due to technical difficulties with the experimental setup, peripheral indicators of fatigue could not be identified; however, indicators of central fatigue were present. No conclusive remarks can be made on whether the limiting factor in the cessation of exercise was related to central or peripheral fatigue.

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