Central Fatigue in Male and Female Cyclists Evaluated by Peripheral Magnetic Stimulation

Abstract

It is well-known that men and women fatigue differently. However, the relative contributions of central vs. peripheral mechanisms to fatigue in men vs. women has 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 6 women [39±4 yrs] cycled for 2 hours at approximately 66% of VO2peak[56±2 ml/Kg/min men, 53±4 women, P =0.419] 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. Ratings of perceived exertion [RPE] were measured at the same time, as well as during each sprint using a Borg scale. Quadriceps isometric strength testing was performed 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]; 3) femoral nerve stimulation in a 4-second pulse train. Subjects recovered for 1 minute between contractions. Changes in metabolic and strength measurements over time and between gender were analyzed with repeated measures ANOVA. RESULTS: Heart rate [p=0.005] and RPE [p=0.013] increased over time during the 2 hours, with no differences between men and women. MVCs declined by 22% in men and 20% in women [effect of time, p90% MVC in men and >88% MVC in women. CONCLUSION: Results clearly demonstrate fatigue with a significant central component after prolonged cycling in both men and women.