Gender Differences in Relative Contributions of Central and Peripheral Mechanisms to Fatigue in Cyclists: 2301

Women are known to be more fatigue-resistant than men. However, the relative contributions of central vs. peripheral mechanisms to fatigue in men vs. women have not been examined. PURPOSE: To examine peripheral vs. central contributions to fatigue in men and women during prolonged cycling using a peripheral nerve magnetic stimulation-based technique. METHODS: 11 men [41±3 yrs] and 10 women [38±3 yrs] cycled for 2 hours at ventilatory threshold [approximately 66% of VO2peak] with 5, 1-minute sprints interspersed, followed by a 3-Km time trial. Oxygen consumption was measured every 20 minutes to verify energy expenditure at the ventilatory threshold. Quadriceps strength testing was performed isometrically in a semi-reclined position pre- and post-cycling: 1) MVC; 2) MVC with superimposed 3-second magnetic stimulation to measure central activation ratio [CAR], a measure of central fatigue; 3) peripheral magnetic stimulation [PMS] alone of the femoral nerve in a 4-second pulse train, a measure of peripheral fatigue. Subjects recovered for 1 minute between contractions. Changes in metabolic and strength measurements over time and between genders were analyzed with repeated measures ANOVA. RESULTS: Respiratory exchange ratios were similar throughout in both genders, declining over time from 0.94 to 0.85. Men were stronger than women [p=0.001], but changes in MVC with time were similar between genders, declining 22% in men and 16% in women [p=0.33]. Baseline CAR was similar between genders and decreased 15% after exercise in both men and women [effect of time, p<0.001]. However the change in PMS-elicited force was different between genders: men, but not women, lost stimulated strength [475 to 392 N vs. 331 to 337 N, interaction p=0.006]. Peripheral magnetic stimulation-induced force was >83% MVC in both genders. CONCLUSION: Results clearly demonstrate that quadriceps fatigue after > 2 hours of cycling was of both central and peripheral origin in men but was solely due to central mechanisms in women.