Eight competitive cyclists performed two cycling trials, one following a high carbohydrate diet (H-CHO) and the other following a low carbohydrate diet (L-CHO). Trials consisted of repeated 60s maximal effort sprints to fatigue at a workload designed to elicit 125-135% VO_2peak at 90rpm. Three min of recovery separated sprints. Muscle biopsies taken at rest (biopsy 1), 85% max interval rpm (biopsy 2), and 70% max interval rpm (biopsy 3) revealed a main effect of diet on muscle glycogen levels: 609 ± 38 HCHO vs. 390 ± 42 mmol/kgdw L-CHO at biopsy 1, 383 ± 29 vs. 252 ± 28 mmol/kgdw at biopsy 2, and 346 ± 29 vs. 196 ± 18 mmol/kgdw at biopsy 3 (p<0.01). Similar decreases in muscle glycogen (45%), creatine phosphate (CP) (35%), and sarcoplasmic reticulum (SR) Ca²⁺-uptake (56%) were shown in both trials from biopsy 1 to 3. SR Ca²⁺-release decreased by 53% in H-CHO subjects and 36% in L-CHO subjects. Total exercise time tended to be longer in H-CHO than L-CHO subjects (57.5 ± 10 vs. 42.0 ± .89min) (p=0.09). H-CHO subjects exercised significantly longer than L-CHO subjects from biopsy 2 to 3 (33.6 ± 10 vs. 18 ± 3.6min) (p< 0.05). Results suggest that fatigue from 40- 60min of intermittent 60s high intensity cycling intervals is associated with reductions in muscle glycogen, CP, and SR function, and that the latter part of performance is impaired by low muscle glycogen. These data do not support a relationship between muscle glycogen status and SR function in intermittent high intensity exercise. / Master of Science

Creatine is nitrogen-containing organic acid which naturally occurs in the human body. The aim of this work was to determine the optimal dose of creatine in combination with vitamin C and magnesium for male respondents aged 18-26 years. They were divided into two groups differing in the creatine dosage. Group 1 took smaller dose of creatine (3 g per day) and group 2 higher dose of creatine (10 g per day). Both groups took both magnesium and vitamin C at constant doses throughout the study. The effects of significantly different dose of creatine in the individual groups were compared with each other in terms of the performance of individuals in the powerlifting, the anthropological changes and the overal metabolism of the intakes. In all disciplines of powerlifting, group 1 recorded higher average weight gains, which were not found to be statistically significant at a significance level of alpha 0,05. Anthropological changes were measured using the InBody 160 and a diagnostic measuring tape. In both cases, group 1 recorded better results than group 2, but these results were not statistically significant at a significance level of alpha 0,05. The total metabolism of the accepted dietary supplements was investigated through analytical methods. The urine of each respondent was regularly collected and subsequently analyzed during the research. Determination of creatinine, a creatine waste product, was performed by UV-VIS spectrophotometry using the Jaffe reaction. Vitamin C was analyzed by RP-HPLC. Magnesium was determined by the ICP-OES method. After creatine suplemantion of 3 per day, group 1 showed a slight increase in creatinine in the urine, but still in the physiological range. At the significance level alpha 0,05 there was no statistically significant difference. Group 2 showed an increase above the physiological limit which was already a statistically significant difference. Overall, creatine supplementation of 3 g per day has been found as a sufficient intake of creatine needed to build up muscle mass, increase energy metabolism and overall physical performance. The metabolization itself works very well and within the physiological values.