Biomedical subjects

G C Gaitanos

Publications and source records attributed to G C Gaitanos.

4 recordsLinked to original sources

PubMed1999

High-intensity exercise and muscle glycogen availability in humans.

This study investigated the effects of muscle glycogen availability on performance and selected physiological and metabolic responses during high-intensity intermittent exercise. Seven male subjects completed a regimen of exercise and dietary intake (48 h) to either lower and keep low (LOW-CHO) or lower and then increase (HIGH-CHO) muscle glycogen stores, on two separate occasions at least a week apart. On each occasion the subjects completed a short-term (<10 min) and prolonged (>30 min) intermittent exercise (IEX) protocol, 24 h apart, which consisted of 6-s bouts of high-intensity exercise performed at 30-s intervals on a cycle ergometer. Glycogen concentration (mean +/- SEM) in m. vastus lateralis before both IEx(short) and IEx(long) was significantly lower following LOW-CHO [180 (14), 181 (17) mmol kg (dw)(-1)] compared with HIGH-CHO [397 (35), 540 (25) mmol kg (dw)(-1)]. In both IEx(short) and IEx(long), significantly less work was performed following LOW-CHO compared with HIGH-CHO. In IEx(long), the number of exercise bouts that could be completed at a pre-determined target exercise intensity increased by 265% from 111 (14) following LOW-CHO to 294 (29) following HIGH-CHO (P < 0.05). At the point of fatigue in IEx(long), glycogen concentration was significantly lower with the LOW-CHO compared with HIGH-CHO [58 (25) vs. 181 (46) mmol kg (dw)(-1), respectively]. The plasma concentrations of adrenaline and nor-adrenaline (in IEx(short) and IEx(long)), and FFAand glycerol (in IEx(long)), increased several-fold above resting values with both experimental conditions. Oxygen uptake during the exercise periods in IEx(long), approached 70% of Vo2max. These results suggest that muscle glycogen availability can affect performance during both short-term and more prolonged high-intensity intermittent exercise and that with repeated exercise periods as short as 6 s, there can be a relatively high aerobic contribution.

Adult↗

PubMed1994

Reduced oxygen availability during high intensity intermittent exercise impairs performance.

This study examined the influence of reduced oxygen availability on the ability to perform repeated bouts of high intensity exercise on a cycle ergometer. Seven male physical education students performed 10 exercise bouts (of 6 s each), interspersed with 30-s recovery periods, under hypoxic and normoxic conditions. The hypoxic condition was carried out in a low pressure chamber at 526 mmHg. Subjects were instructed to try to maintain a target pedalling speed of 140 rev min-1 during each exercise period. The mean power output of the first exercise bout was approximately 950 W. In both experimental conditions, all subjects were able to maintain the target speed for the first 3 s of each of the 10 exercise bouts. During the last 3-s interval of each exercise period the target speed was not maintained in both conditions over the 10 sprints. However, the reduction was greater in the hypoxic condition (P < 0.05). Post-exercise blood lactate accumulation was higher with hypoxia [10.3 (0.7) vs. 8.5 (0.8) mmol l-1, P < 0.05]. Oxygen uptake, measured during the exercise and recovery periods of sprints 6-9, was lower in the hypoxic condition [3.03 (0.2) vs. 3.19 (0.2) 1 min-1, P < 0.05]. These results indicate that a reduction in oxygen availability during high intensity intermittent exercise results in a higher accumulation of blood lactate and a lower oxygen uptake. The ability to maintain a high power output is impaired.

Adenosine Triphosphate↗

PubMed1993

Human muscle metabolism during intermittent maximal exercise.

Eight male subjects volunteered to take part in this study. The exercise protocol consisted of ten 6-s maximal sprints with 30 s of recovery between each sprint on a cycle ergometer. Needle biopsy samples were taken from the vastus lateralis muscle before and after the first sprint and 10 s before and immediately after the tenth sprint. The energy required to sustain the high mean power output (MPO) that was generated over the first 6-s sprint (870.0 +/- 159.2 W) was provided by an equal contribution from phosphocreatine (PCr) degradation and anaerobic glycolysis. Indeed, within the first 6-s bout of maximal exercise PCr concentration had fallen by 57% and muscle lactate concentration had increased to 28.6 mmol/kg dry wt, confirming significant glycolytic activity. However, in the tenth sprint there was no change in muscle lactate concentration even though MPO was reduced only to 73% of that generated in the first sprint. This reduced glycogenolysis occurred despite the high plasma epinephrine concentration of 5.1 +/- 1.5 nmol/l after sprint 9. In face of a considerable reduction in the contribution of anaerobic glycogenolysis to ATP production, it was suggested that, during the last sprint, power output was supported by energy that was mainly derived from PCr degradation and an increased aerobic metabolism.

Adenosine Triphosphate↗

PubMed1991

Repeated bouts of sprint running after induced alkalosis.

Seven healthy male subjects performed 10 maximal 6-s sprints, separated by 30-s recovery periods, on a non-motorized treadmill. On two occasions, separated by 3 days, the subjects ingested a solution of either sodium bicarbonate (NaHCO3; alkaline) or sodium chloride (NaCl; placebo), 2.5 h prior to exercise. The doses were 0.3 g kg-1 body mass for the alkaline treatment and 1.5 g total for the placebo, dissolved in 500 ml of water. The order of testing was randomly assigned. Pre-exercise blood pH was 7.43 +/- 0.02 and 7.38 +/- 0.01 for the alkaline and placebo trials respectively (P less than 0.01). Performance indices (i.e. mean and peak power outputs and mean and peak running speeds) were significantly reduced as a result of the cumulative effects of successive sprints, but not significantly affected by the treatments. However, the total work done (i.e. mean power output) in the alkaline condition was 2% higher than that achieved in the placebo condition. Post-exercise blood lactate concentrations were higher for the alkaline treatment than for the placebo condition (15.3 +/- 3.7 vs 13.6 +/- 3.0 mM respectively; P less than 0.01), but blood pH was similar in both conditions (alkaline: 7.15 +/- 0.13; placebo: 7.09 +/- 0.11). In both conditions, a relationship was found between post-exercise blood lactate and mean power output (alkaline: r = 0.82, P less than 0.01; placebo: r = 0.79, P less than 0.01). No significant differences were found in VE, VO2 and VCO2 between the two experimental conditions. This study demonstrates that alkali ingestion results in significant shifts in the acid-base balance of the blood, but has no effect on the power output during repeated bouts of brief maximal exercise.

Adult↗