Fiber composition, fiber size and enzyme activities in vastus lateralis of elite athletes involved in high intensity exercise

In order to determine the influence of an extensive history of participation in high intensity activity on muscle fiber type, fiber size, and metabolic profile, elite ice hockey players were selected for investigation from three different leagues. Biopsy samples from the vastus lateralis muscle were obtained from different groups of players prior to and following the season and compared with control subjects. No significant differences were found in the percentage (49.6 vs. 43.8%) or the size of the ST fibers between the elite athletes and the control group, nor was there any significant alteration following the season of play in these variables. For the FT fiber subgroups, a reduction in the FTb (12.2 vs. 3.9%) and an increase in FTa (38.0 to 45.2%) fiber populations occurred over the season. Similarly, increases in fiber area were observed for both FT subgroups pre to post season. Of the enzymes studied only 3-hydroxyacyl CoA dehydrogenase was elevated in the post season measures, while total phosphorylase and phosphofructokinase were significantly lower. The metabolic pattern exhibited does not appear to be substantially different from what would be expected from an untrained group of similar fiber distribution.

Metabolic aspects of intermittent work with specific regard to ice hockey

The focus of this presentation was to examine the metabolic alterations that occur in muscle during ice hockey performance. An attempt was made to describe the significance of several factors that determine the nature and extent of energy producing processes during work and to relate these specifically to the ice hockey situation. The review concludes with an analysis of potential fatigue mechanisms that might occur with recommendations for their control.

Muscle glycogen depletion patterns in fast twitch fibre subgroups of man during submaximal and supramaximal exercise

Muscle glycogen depletion in ST, FTa and FTb fibres were studied in human subjects undergoing two distinctly different modes of bicycle exercise. Two hours of submaximal exercise (60% of VO2 max) produced a 77% decline in muscle glycogen concentration accompanied by only minor elevations in muscle and blood lactate levels whereas 10 one minute supramaximal work bouts resulted in a 52% decrease in total glycogen concentration and substantially elevated muscle and blood lactate contents. Moreover the patterns of glycogen depletion in the two conditions were also distinctly different. Based on the PAS staining intensity, glycogen was depleted the most in ST fibres and least in FTb fibres, during submaximal work. During supramaximal work FTb fibres were the lightest in PAS staining, with little loss of glycogen from ST fibres. In both situations the loss of glycogen in the FTa fibres was intermediate compared to the other two fibre types. These data support a selective recruitment of muscle fibres during work of different intensities, and further, suggest a physiological basis for the subgrouping of FT fibres in man.

Glycogen depletion in exercising rats infused with glucose, lactate, or pyruvate

The influence of an intravenous infusion of glucose, lactate, or pyruvate on the work capacity and rates of glycogen depletion in the liver and hindlimb skeletal muscles of rats has been studied. Running time to exhaustion at a speed of 21 m/min on a treadmill at a +10 degrees incline was prolonged by glucose infusion but shortened by lactate or pyruvate infusions. Blood glucose concentrations were only lowered in the terminal stages of the exercise, whereas at this point lactate was elevated. Declines in liver and muscle glycogen concentrations were retarded by glucose infusion but accelerated by either lactate or pyruvate infusions. In all cases a marked depletion of both muscle and liver glycogen existed at the point of exhaustion. It is concluded from the lack of any major elevation of glucose, lactate, or pyruvate in the blood of the rats during running that these materials were taken up and oxidized, presumably by the working muscles. These observations suggest that skeletal muscle can take up large amounts of glucose and when it is supplied from an external source this can exert a glycogen sparing effect on the liver and working skeletal muscles.