M. E. Houston

Muscle performance, morphology and metabolic capacity during strength training and detraining: a one leg model.

SummaryTo investigate biochemical, histochemical and contractile properties associated with strength training and detraining, six adult males were studied during and after 10 weeks of dynamic strength training for the quadriceps muscle group of one leg, as well as during and after a subsequent 12 weeks of detraining. Peak torque outputs at the velocities tested (0–270‡·s−1) were increased (p<0.05) by 39–60% and 12–37% after training for the trained and untrained legs, respectively. No significant changes in peak torques were observed in six control subjects tested at the same times. Significant decreases in strength performance of the trained leg (16–21%) and untrained leg (10–15%) were observed only after 12 weeks of detraining. Training resulted in an increase (p≪0.05) in the area of FTa (21%) and FTb (18%) fibres, while detraining was associated with a 12% decrease in FTb fibre cross-sectional area. However, fibre area changes were only noted in the trained leg. Neither training nor detaining had any significant effect on the specific activity of magnesium-activated myofibrillar ATPase or on the activities of enzymes of phosphagen, glycolytic or oxidative metabolism in serial muscle biopsy samples from both legs. In the absence of any changes in muscle enzyme activities and with only modest changes in FT fibre areas in the trained leg, the significant alterations in peak torque outputs with both legs suggest that neural adaptations play a prominent role in strength performance with training and detraining.

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

SummaryIn 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.

Myosin light chain phosphorylation and isometric twitch potentiation in intact human muscle

The effects of a single voluntary contraction of the quadriceps muscle group on phosphate incorporation into the phosphorylatable light chains (P-light chains) of fast and slow myosin isolated from the vastus lateralis muscle and potentiation of the electrically stimulated twitch tension was studied in intact human muscle. Twitch potentiation was maximal 20 s after the voluntary contraction. Thereafter, twitch potentiation declined, but was still significantly higher than pre-contraction values 2 min after the voluntary contraction. Phosphate incorporation into the P-light chain of fast myosin followed a similar time course to twitch potentiation, but no phosphate was incorporated into slow myosin P-light chains. These observations suggest that myosin light chain kinase activity is mainly associated with fast-twitch muscle fibers and, in agreement with previous studies, suggests that twitch potentiation associated with P-light chain phosphorylation is confined to the fast-twitch fibers of human muscle.

The Effect of Rapid Weight Loss on Physiological Functions in Wrestlers

In brief: To assess the effects of rapid weight reduction, four university wrestlers decreased their body weight by 8% over a four-day period by food and liquid intake reductions. Significant decreases in muscle glycogen concentration and dynamic strength, but not aerobic or anaerobic capacity, accompanied weight loss. A three-hour rehydration period did not improve glycogen levels or strength performance. These results suggest that rapid weight reduction may impair wrestling performance.

Vitamin E Status and Response to Exercise Training

SummaryVitamin E is an important intramembrane antioxidant and membrane stabiliser. Over the past 40 years, vitamin E supplementation has been advocated for athletes in the hope of improving performance, minimising exercise-induced muscle damage and maximising recovery. However, there is currently a lack of conclusive evidence that exercise performance or recovery would benefit in any significant way from dietary vitamin E supplementation. Exceeding current recommended intakes of vitamin E even by several orders of magnitude will result in relatively modest increases in tissue or serum vitamin E concentrations. Most evidence suggests that there is no discernible effect of vitamin E supplementation on performance, training effect or rate of postexercise recovery in either recreational or elite athletes. There is very little evidence, particularly involving humans, that exercise or training will significantly alter tissue or serum vitamin E levels. While there is some evidence that certain indices of tissue peroxidation may be reduced following dietary vitamin E supplementation, the physiological and performance consequences in humans of these relatively minor effects are unknown. Although there appears to be little reason for vitamin E supplementation among athletes, it does not appear that the practice of supplementation is harmful.

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

SummaryMuscle 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 V02 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.

The response of endurance-adapted adults to intense anaerobic training

SummaryThe effects of a 6 week program of intense, intermittent hill running was investigated in 5 endurance-trained men (34–37 years). Venous lactate responses averaged 10.7 mM×1−1 during training. Biopsies were obtained from the vastus lateralis before and after training for determinations of histochemical classification, phosphagen concentrations (ATP and CP) and activities of total LDH and selected LDH isozymes. Indices of aerobic and anaerobic capacity were also measured. Significant improvements (P<0.01) were noted in training distance and loads employed in leg presses, also part of the training: the treadmill test for anaerobic capacity improved by 16.7% and the terminal blood lactate level increased 14% (P<0.05). No changes occurred in

Energy metabolism in human slow and fast twitch fibres during prolonged cycle exercise.

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