The relationships between Muscle Fibre Composition, muscle carnosine and multiple sprint (Wingate) performance

Abstract

Muscle Fibre Composition (MFC) and resting carnosine levels are both important characteristics of skeletal muscle which contribute towards performance and fatigue during high-intensity exercise. It’s well documented that type II fibres are fast contracting, fast fatiguing, and are characterised by a high metabolic capacity for anaerobic metabolism. Despite the ability to produce higher forces, individuals with a relatively high proportion of type II muscle fibres are likely to experience more acidosis within the muscle. At the cellular level, type II fibers also have higher resting levels of carnosine. Carnosine, a buffer of hydrogen ions, is therefore important in delaying the rate of fatigue during high-intensity exercise. Higher levels of muscle carnosine found in some athletic individuals has largely been attributed to genetic factors such as type II fibres, however few studies have examined this relationship. Therefore, the main purpose of this thesis was to examine potential relationships between MFC, resting carnosine levels, and multiple sprint (Wingate) performance.Twenty-six healthy males (25 ± 4 years) were recruited for this study. Each participant had a muscle biopsy taken from the Vastus Lateralis (VL) to determine Muscle Fibre Composition (MFC) and resting muscle carnosine levels. After sufficient recovery from the biopsy procedure, participants completed 3 x 30second sprints (Wingate bouts) on a cycle ergometer; each separated by 4 minutes of rest. Mean Power (MP), anaerobic capacity (AC), peak power (PP), total work (TW) and a fatigue index (FI) was calculated for each Wingate. The statistical analysis included descriptive statistics, Pearson correlation and linear regressions.Resting muscle carnosine levels were not related to percentage of type II fibres (r= 0.056; p= 0.77), percentage area of type II fibres (p= 0.83; r= 0.048) or relative fibre area (p= 0.77; r= 0.065). In addition, resting carnosine levels were not related to any performance or fatigue measures in the repeated Wingate protocol. Significant relationships were found between both percentage area of type II fibres (p =0.043; r = 0.04) and percentage of type II fibres (p =0.0432; r = 0.4075) with fatigue index during the third Wingate bout. There were no significant relationships between MFC and fatigue in the first Wingate, however percentage of type II fibres was significantly related to the fatigue profile during the last 15 seconds of the 2nd (r=-0.42; p= 0.036) and 3rd (r= -0.44; p= 0.028) Wingate sprints.In summary, resting carnosine levels were not related to MFC nor any performance measure from the repeated Wingate protocol. This study did show however that individuals with a higher percentage of type II fibres may show greater levels of fatigue and decreased performance in the latter stages of maximal anaerobic exercise.