Human muscle response to sprint exercise in a gender perspective

Sammanfattning: Anaerobic performance, muscle characteristics and acute and chronic response to sprint exercise were studied in physically active healthy women (n=35; age 24) and men (n=38; age 25). The aims of the present study were to: 1) Establish if women possess lower oxidative and glycolytic capacity, higher proportion of type I fibres and smaller type II fibre areas in relation to type I fibre areas in thigh musculature than men. 2) Investigate if the same muscle variables predict anaerobic performance in women and men. 3) Identify muscle variables explaining gender differences in anaerobic performance. 4) Investigate if the effect of anaerobic training on muscle characteristics and maximal power output differ between women and men. 5) Study if there is a gender difference in metabolic activation of type I and type II muscle fibres and in sympathoadrenergic activation, during 30-s cycle sprints. Methods: Sprint exercise or sprint training were performed using a 30-s Wingate-test. Muscle biopsies from vastus lateralis were obtained before and immediately after sprint exercise or before and after 4 weeks of sprint training. Biopsies were analysed for fibre types, fibre areas, enzyme activities, glycogen and total creatine content. Content of glycogen, lactate, creatine phosphate, creatine, ATP, inosine monophosphate (IMP), inosine, hypoxanthine and xanthine were also analysed in pools of type I and type II fibres. Venous blood was sampled and analysed for lactate, ammonia, catecholamines and breakdown products of ATP before, during and after sprint exercise. Results: Cross-sectional fibre areas of type I, IIA and IIB fibres were smaller and type II/I area ratio, relative area of fibre type 11, and activities of lactate dehydrogenase (LD) and M-subunit of LD were lower in women than in men, but not citrate synthase activity. Low proportion of type II fibres, phosphofructokinase activity and low relative M-subunit activity, seemed to reduce anaerobic performance in both genders. Lower M-subunit activity may contribute to the lower capacity of women than of men to perform anaerobic exercise. Sprint training decreased gender differences in mean power output, type 11 fibre cross-sectional area, but did not reduce gender difference in LD activity. Exercise-induced glycogen degradation was smaller in women than in men in type I fibres, but not in type Il fibres. This was also supported by lower lactate content in women's type I fibres after exercise. Reduction in ATP content and accumulation of IMP during bouts of sprint exercise was similar in men and women in both type I and 11 fibres. After recovery between bouts of sprint exercise, women showed lower muscle IMP and inosine than did men, especially in type II fibres. At systemic level, women as compared to men showed lower accumulation of ammonia, inosine, xanthine, hypoxanthine, uric acid and catecholamines in plasma, and of lactate in blood, following repeated sprint exercise. Conclusion: Knowledge about fibre-type-specific and gender related differences in the metabolic response to sprint exercise may, besides being of basic scientific value, have implications for response to sprint training and therefore also for the planning of gender-specific training programs, including the recovery period between bouts of sprint exercise.