Limiting factors to high intensity exercise : the role of intramuscular pH and skeletal muscle buffering

Within the context of a metabolic model of fatigue, formulated from a review of theliterature, a decrease in intramuscular pH was identified as a potential limiting factorto the performance of high intensity exercise (HIE). This suggested a role forskeletal muscle buffering (B) in retarding the intramuscular acidosis typicallyincurred during HIE. Previous studies on human muscle, were largely unable toconfirm this role, partly due to the lack of a clearly defined and consistently utilisedmethod of measurement of B. The validity of the procedures currently employed inthe determination of B was therefore investigated, revealing that many of theindividual differences in B, previously attributed physiological significance, mayhave originated from inappropriate methodology.In a cross-sectional examination of the vastus lateralis muscle of young, activeindividuals, low correlations (p<0.05) between the muscle carnosine concentration([CAR]) and in the 'in vitro B ' (Bvit) (r=0.30), and between either [CAR] or Bvitand the % type II fibre area were observed. An elevated Bvit was shown to be ofimportance in minimising the decrement in pH during HIE, but did not per sepermit the accumulation of a higher muscle lactate concentration, or allow for anenhanced HIE performance; these factors were more dependent on the % type IIfibre area. The muscle pH, following dynamic HIE was highly variable betweenindividuals, and showed a significant (p<0.05) negative correlation with the % typeII fibre area.16 weeks of isokinetic training of the quadriceps resulted in significantimprovements (p