Differential effects of exercise intensity on serum uric acid concentration.

To investigate the effects of exercise intensity and short-term training on alterations in plasma uric acid, two series of experiments were performed using untrained male subjects. In series 1, 6 subjects (age 19 to 23 yr) cycled at 120% VO2max for 1 min followed by 4 min recovery until fatigue or until 24 repetitions had been completed. In series 2, 7 subjects (age 19 to 25 yr) cycled continuously at 65% VO2max for 2 h. In both experiments, short-term training was performed by repeating the exercise protocol for three consecutive days. In series 1, a progressive increase of 40% (P less than 0.05) was observed on day 1 in plasma uric acid concentration over the duration of the exercise. On day 2, pre-exercise values remained elevated over day 1 (mean +/- SD, 476 +/- 77 vs 352 +/- 30 mumol.l-1) and showed a further 23% increase (P less than 0.05) with exercise. Although resting uric acid concentrations on day 3 were elevated (P less than 0.05) over day 1, the exercise levels between day 1 and day 3 were not different (P greater than 0.05). In contrast, in series 2, prolonged sub-maximal exercise failed to stimulate increases in uric acid concentration either between days or within days. It is concluded that exercise intensity rather than total work output is a critical factor mediating increases in blood uric acid concentration. These results are consistent with the interpretation that uric acid formation may arise from purine nucleotide degradation and fast-twitch fiber utilization during conditions of high energy utilization.

Fiber type specific glycogen utilization in rat diaphragm during treadmill exercise.

To examine the significance of endogenous stores of glycogen in specific fiber types (I, IIa, IIb) of the costal region of the diaphragm, adult male Wistar rats performed continuous running (25 m/min, 8 degrees grade) exercise for either 30 min or until fatigue. At 30 min of exercise, glycogen loss, as measured microphotometrically using the periodic acid-Schiff technique averaged between 73 and 80% (P less than 0.05) in the different fiber types. When exercise was performed to exhaustion, representing an additional 94 min, no further reduction in glycogen was observed in any fiber type. Biochemical determinations of glycogen from the diaphragm confirmed the extensive reduction in glycogen concentration with exercise. Large reductions (P less than 0.05) in glycogen were also noted in the soleus, plantaris, and vastus lateralis red. Although significant depletion (P less than 0.05) occurred in the vastus lateralis white, it was not as pronounced as in these other muscles. Repletion to preexercise glycogen concentration was complete by 4 h of recovery in all muscles except the vastus lateralis white. It is concluded that endogenous glycogen is a significant substrate in all muscles sampled regardless of fiber composition. In the case of the costal region of the diaphragm, the increased work of breathing resulting from heavy exercise leads to the recruitment of all fiber types, and each fiber type depends on glycogen as a substrate at least early in the exercise.

Male and female differences in enzyme activities of energy metabolism in vastus lateralis muscle.

To investigate sex differences in the organization of enzyme activities of energy supplying metabolism in skeletal muscle, samples of the vastus lateralis were extracted from active but untrained males (n = 16) and females (n = 17), ranging in age from 18 to 22 years. Muscle tissue from 2 different biopsy samples from each subject were analyzed for enzymes representative of the citric acid cycle (succinic dehydrogenase, SDH), beta-oxidation of fatty acids (3-hydroxyacyl CoA dehydrogenase, HAD), glycogenolysis (phosphorylase, PHOSPH), glycolysis (pyruvate kinase, PK; phosphofructokinase, PFK and lactate dehydrogenase, LDH) and glucose phosphorylation (hexokinase, HK). The results indicated that the maximal activities of PFK, PK, LDH and PHOSPH, HK and SDH averaged between 15 and 32% higher in the males than in the females. No significant differences between the sexes were found for HAD. When enzyme activity ratios were calculated, sex differences were only evident for the HAD/SDH ratio (mean +/- SD; females = 0.56 +/- 0.20; males = 0.41 +/- 0.11 and for the PFK/HAD ratio (females = 7.40 +/- 1.6; males = 9.58 +/- 1.9). The findings suggest that (1) the females have a significantly lower overall capacity for aerobic oxidation and for anaerobic glycolysis than the males; (2) the females have a greater capacity for beta-oxidation relative to the capacity of the citric acid cycle; and (3) the glycolytic potential relative to the potential for beta-oxidation is lower in the females.

Fiber type distribution and maximal activities of enzymes involved in energy metabolism following short-term supramaximal exercise.

Alterations in enzyme activities involved in muscle energy metabolism and the muscle fiber type distribution were investigated in six subjects, ranging in age from 19-23 years, following short-term, high intensity exercise. Changes in the vastus lateralis muscle were studied prior to exercise and approximately 24 h after each of 2 consecutive days of supramaximal cycling exercise (120% VO2 max) performed intermittently as 1-min work to 4-min rest until fatigue or until 24 repetitions had been completed. The results indicated that there were no changes (P greater than 0.05) in maximal in vitro activities for representative enzymes of beta-oxidation (3-hydroxyacyl CoA dehydrogenase, HAD), the citric acid cycle (succinic dehydrogenase, SDH), glucose phosphorylation (hexokinase, HK), glycogenolysis (total phosphorylase, PHOSPH), or glycolysis (phosphofructokinase, PFK; pyruvate kinase, PK; lactate dehydrogenase, LDH) in spite of the large increase in carbohydrate utilization and glycolytic flux rate. In addition, although no change in fiber type distribution was found in the pre-exercise biopsy between days, an acute reduction (P less than 0.05) in type I fiber distribution occurred with exercise. It is concluded that supramaximal exercise performed on a short-term basis does not alter the enzymatic profile or the fiber type distribution when measured 24 h following the activity.

Specificity of physiologic adaptations resulting from ice-hockey training.

The specificity of the metabolic and cardiorespiratory responses to varied seasonal training programs and to varied testing modalities and protocols were investigated in two groups of college hockey players. Training consisted of either ice hockey (IH) or a combination of ice hockey and prolonged low-intensity cycling (IH-C). Measurement of training-induced adaptations were determined during maximal and submaximal ice skating, and during maximal and submaximal cycling. Ice hockey training caused no change in VO2max, maximal heart rate (HRmax), and maximal ventilation (VEmax) during maximal ice skating. During submaximal ice skating following IH training, however, reductions (P less than 0.05) in blood lactate (La), VE/VO2, and respiratory exchange ratio (R) were observed. When maximal and submaximal cycling was employed as the test modality, no training-induced alteration was found. The IH-C training program (ice hockey-cycling) resulted in adaptations similar to those observed during submaximal ice skating following the IH training. In addition, a reduction (P less than 0.05) in heart rate was observed during submaximal cycling exercise. From these findings it appeared that the adaptive response to training may be specific to the type of work used in training, the type of ergometry used to evaluate training, and to specific physiological processes. In addition, these results suggested a dissociation between local and central adaptations.

Cross-adaptive responses to different forms of leg training: skeletal muscle biochemistry and histochemistry.

The influence of a program of high intensity training and of a combined program of high intensity training and prolonged submaximal training on adaptations to the vastus lateralis muscle was investigated in two groups of elite athletes. The high intensity training (H) consisted of ice hockey practices and games over a 14-week period while the combined program (HI-LO) included the addition of supplementary sessions of cycling, three times per week, progressively increasing from 30 to 45 min per session and at an intensity of 70% VO2max. Determinations of enzyme activities representative of energy supplying pathways revealed no change in 3-hydroxyacl CoA dehydrogenase (HADH), total phosphorylase (PHOSP), phosphofructokinase (PFK), lactate dehydrogenase (LDH), and a 7% increase (p less than 0.05) in succinate dehydrogenase (SDH). The addition of the supplementary program caused no further adaptation in the metabolic profile. Similarly, neither the HI nor the HI-LO program induced any alteration in the percentage fibre type (slow twitch (ST) vs. fast twitch (FT) or the subtypes (FTa, FTb, FTc). Reductions in the size (p less than 0.05) of ST fibres were noted for both the HI and the HI-LO training programs. In contrast, increases in capillarization (p less than 0.05) were found for both the ST (23%) and FTa (32%) fibres for the HI-LO program whereas a reduction in capillarization (21%) occurred in the FTa fibres as a result of HI training only. It is concluded that metabolic differentiation does not appear to occur in a manner consistent with the conditions of energy expenditure at least for high intensity work.