Glace, B. W., Kremenic, I. J., Ben-Avi, S., Nicholas, S., McHugh, M. P. (2010). Gender differences in relative contributions of central and peripheral mechanisms to fatigue in cyclists. Presentation 2301 at the 2010 Annual Meeting of the American College of Sports Medicine, Baltimore, Maryland; June 2-5.

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This study examined peripheral vs. central contributions to fatigue in men (N = 11; ~ 41 years) and women (N = 10; ~38 years) during prolonged cycling using a peripheral nerve magnetic stimulation-based technique. Ss cycled for two hours at ventilatory threshold [approximately 66% of VO2peak] interspersed with five one-minute sprints, followed by a 3-km time-trial. Oxygen consumption was measured every 20 minutes to verify energy expenditure at the ventilatory threshold. Quadriceps isometric strength testing was performed in a semi-reclined position pre- and post-cycling for: 1) maximum voluntary contraction; 2) maximum voluntary contraction with superimposed three-second magnetic stimulation to measure central activation ratio (a measure of central fatigue); 3) peripheral magnetic stimulation alone of the femoral nerve in a four-second pulse train (a measure of peripheral fatigue). Ss recovered for one minute between contractions. Changes in metabolic and strength measurements over time and between genders were analyzed.

Respiratory exchange ratios were similar throughout in both genders, declining over time from 0.94 to 0.85. Men were stronger than women, but changes in maximum voluntary contraction with time were similar between genders, declining 22% in men and 16% in women. Baseline central activation ratio was similar between genders and decreased significantly in both genders by 15% after exercise. However the change in peripheral magnetic stimulation elicited force was different between genders. Men, but not women, lost stimulated strength. Peripheral magnetic stimulation-induced force was >83% maximum voluntary contraction in both genders.

Implication. Quadriceps fatigue after more than two hours of cycling was of both central and peripheral origin in men but was solely due to central mechanisms in women.

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