PubMed Health⌕ Search

Biomedical subjects

D P MacLaren

Publications and source records attributed to D P MacLaren.

10 recordsLinked to original sources
PubMed2002

The effect of even, positive and negative pacing on metabolic, kinematic and temporal variables during breaststroke swimming.

The aim of this investigation was to determine the effect of even, negative and positive pacing on metabolic, kinematic and temporal variables during breaststroke swimming. Nine male swimmers [mean (SD): age 21 (3) years, height 178 (5) cm, body mass 77.2 (6.7) kg, 200 m-time 158.6 (13.6) s] completed a 200-m breaststroke time trial and then 72 h later three paced (even, positive, negative) 175-m breaststroke swims in random order, 48 h apart. The swimmers paced accurately in all trials. The evenly paced trial produced lower post-exercise peak blood lactate and rating of perceived exertion values compared to the positively paced trial ( P<0.05). Peak oxygen uptake was not significantly different between trials ( P>0.05). Heart rate immediately following exercise was lower in the negatively paced trial ( P<0.05) than the other paced trials. Stroke rates were lower during the first half of the evenly and negatively paced trials compared to the positively paced trial ( P<0.01), but no differences were observed between the second half of the trials. Across all trials the stroke count increased as the trials progressed ( P<0.01). Turning times were observed to be shorter during the first half of the positively paced trial compared to the other paced trials ( P<0.01). Even paced swimming appears to be less physically stressful than positively paced swimming during high intensity exercise, as indicated by a lower post-exercise blood lactate concentration, perceived exertion and variability within turning times.

Adult↗
PubMed2000

An analysis of selected kinematic variables in national and elite male and female 100-m and 200-m breaststroke swimmers.

The kinematic analysis of competition breaststroke swimming has tended to focus on the mean values of swimming speed, stroke rate and stroke length; values in individual lengths, as well as the start, turns and finish, have largely been ignored. This study includes all such variables and aims to improve the coach's holistic understanding of breaststroke racing by determining the relationships and differences between and within these selected kinematic variables. We also compare 100-m events with 200-m events to determine if there are characteristic differences between them. Competitive breaststroke swimming performances in 100-m events (males: n = 159, finishing time = 65.05 +/- 2.62 s; females: n = 158, finishing time = 74.04 +/- 3.66 s) and 200-m events (males: n = 159, finishing time = 141.47 +/- 6.15 s; females: n = 158, finishing time = 158.66 +/- 7.87 s) were collected and analysed from 12 world, international and national championships. The better 100-m and 200-m breaststroke swimmers were found to demonstrate greater competency in the kinematic variables measured, except stroke kinematics, which were unique to each individual. These findings suggest that coaches should place emphasis on all of the kinematic components in training and that they should attempt to identify the stroke rate to stroke length ratio most appropriate for the individual. Finally, characteristic differences do exist between the 100-m and 200-m events, which has implications for how swimmers might train for each event.

Biomechanical Phenomena↗
PubMed2000

Human erythrocyte and plasma amino acid concentrations during exercise.

PURPOSE: This investigation examined the effects of exercise and maltodextrin (Md) or placebo (Pl) ingestion on plasma and erythrocyte concentrations of amino acids. METHODS: The erythrocyte and plasma concentrations of 17 amino acids, as well as plasma glucose and insulin, were analyzed in eight healthy trained male subjects before, during, and 25 min after 90-min cycle ergometer exercise at 65% peak oxygen uptake. The two treatments involved ingestion of orange-flavored water (Pl) or orange-flavored 10% maltodextrin solution (Md). RESULTS: Two-way ANOVA revealed 1) that plasma concentrations of alanine and tyrosine changed significantly during the treatments, 2) that the plasma concentrations were significantly different between treatments for glycine and threonine, 3) that all erythrocyte concentrations increased significantly throughout the treatments except for arginine and tyrosine, and 4) that there were no significant differences in erythrocyte concentrations between the treatments. Three-way ANOVA highlighted the significant differences in the time responses between plasma and erythrocyte concentrations; the changes in erythrocyte levels from rest being significantly different from plasma for all amino acids except aspartic acid, glycine, and ornithine. Plasma glucose concentrations became elevated and remained above rest values in Md but fell below rest values in Pl: the differences in concentration between treatments were significant. Correspondingly, plasma insulin was significantly higher in Md during exercise. CONCLUSION: These results highlight that far from being slow in the uptake of amino acids, the erythrocyte in fact sequesters amino acids at an appreciable rate during exercise without a corresponding elevation in the plasma amino acids. For a greater understanding of amino acid changes during exercise, the analysis of both plasma and erythrocytes is recommended.

Administration, Oral↗
PubMed1999

Hormonal and metabolic responses to maintained hyperglycemia during prolonged exercise.

We studied the effects of maintained hyperglycemia (12 mmol/l) on endurance exercise to determine the hormonal and metabolic responses, the maximal rate of glucose infusion (i.e., utilization), and the effects on muscle glycogen stores. Eight men undertook two trials during which they exercised on a cycle ergometer at an intensity of approximately 70% peak O(2) uptake for 120 min. In the first trial (trial A), subjects had their blood glucose concentration clamped at 12 mmol/l 30 min before exercise and throughout exercise. The same rate and volume of infusion of saline as had occurred for trial A were used in a placebo trial (trial B). Maintained hyperglycemia resulted in significantly lowered plasma concentrations of nonesterified fatty acid, glycerol, 3-hydroxybutyrate, epinephrine, norepinephrine, and growth hormone (P < 0.001) during exercise, whereas concentrations of plasma insulin were significantly elevated (P < 0.001). Calculations of the rates of total carbohydrate oxidation showed that trial A resulted in significantly higher values when compared with trial B (P < 0.01) and that the maximal rates of glucose infusion varied between 1.33 and 2.78 g/min at 100-120 min. Muscle glycogen concentrations were significantly depleted (P < 0.01) after both trials (trial A, 170.3 micromol/g dry wt decrease; trial B, 206 micromol/g dry wt decrease), although this apparent difference may be accounted for by storage of 22.6 g glucose during the 30-min prime infusion. The results from this study confirm that maintained hyperglycemia attenuates the hormonal response and promotes carbohydrate oxidation and utilization and that muscle glycogen may not be spared.

3-Hydroxybutyric Acid↗
PubMed1998

Metabolic and performance responses during endurance exercise after high-fat and high-carbohydrate meals.

We studied the effects of preexercise meal composition on metabolic and performance-related variables during endurance exercise. Eight well-trained cyclists (maximal oxygen uptake 65.0 to 83.5 ml . kg-1 . min-1) were studied on three occasions after an overnight fast. They were given isoenergetic meals containing carbohydrate (CHO), protein (P), and fat (F) in the following amounts (g/70 kg body wt): high-carbohydrate meal, 215 CHO, 26 P, 3 F; high-fat meal, 50 CHO, 14 P, 80 F. On the third occasion subjects were studied after an overnight fast. Four hours after consumption of the meal, subjects started exercise for 90 min at 70% of their maximal oxygen uptake, followed by a 10-km time trial. The high-carbohydrate meal compared with the high-fat meal resulted in significant decreases (P < 0.05) in blood glucose, plasma nonesterified fatty acids, plasma glycerol, plasma chylomicron-triacylglycerol, and plasma 3-hydroxybutyrate concentrations during exercise. This was accompanied by an increase in plasma insulin (P < 0.01 vs. no meal), plasma epinephrine, and plasma growth hormone concentrations (each P < 0.05 vs. either of the other conditions) during exercise. Despite these large differences in substrate and hormone concentrations in plasma, substrate oxidation during the 90-min exercise period was similar in the three trials, and there were no differences in performance on the time trial. These results suggest that, although the availability of fatty acids and other substrates in plasma can be markedly altered by dietary means, the pattern of substrate oxidation during endurance exercise is remarkably resistant to alteration.

Adult↗
PubMed1995

Human gastrin and vasoactive intestinal polypeptide responses to endurance running in relation to training status and fluid ingested.

1. Plasma concentrations of gastrin, glucose, vasoactive intestinal polypeptide and non-esterified fatty acid were analysed in six male endurance runners and six male hockey players before, during and 15 min after 90 min treadmill running at 65% maximum oxygen uptake under two conditions: no fluid ingestion (trial A) and ingestion of 8% maltodextrin solution (trial B). 2. Exercise resulted in significantly elevated plasma gastrin concentrations compared with resting values in both groups after trial A (endurance runners, 69.4 ng/l; hockey players 71.4 ng/l) and trial B (endurance runners, 105.5 ng/l; hockey players, 83.2 ng/l). The gastrin response was not significantly different between the trials. 3. Plasma vasoactive intestinal polypeptide levels increased significantly beyond resting levels for both groups during trial A (endurance runners, 76.1 +/- 53.7 ng/l; hockey players 155.6 +/- 41.9 ng/l) and trial B (endurance runners 47.5 +/- 21.3 ng/l; hockey players 132.9 +/- 43.9 ng/l). The vasoactive intestinal polypeptide response to trial B was significantly attenuated compared with trial A. 4. There were no significant differences between endurance runners and hockey players for plasma gastrin, although hockey players produced significantly elevated concentrations of plasma vasoactive intestinal polypeptide after both trials compared with endurance runners. 5. Plasma glucose levels throughout trial B were significantly greater than after trial A irrespective of the group. Plasma glucose concentrations were not significantly different between endurance runners and hockey players. 6. Plasma non-esterified fatty acid concentrations rose significantly for both groups throughout exercise. Trial B resulted in an attenuated non-esterified fatty acid response compared with trial A.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Hormonal and metabolite responses to glucose and maltodextrin ingestion with or without the addition of guar gum.

The purpose of this study was to examine the effects of ingesting water (P), a glucose solution (GL), a maltodextrin solution (Md), a glucose solution with 8% guar gum (GL+G), and a maltodextrin solution with 8% guar gum (Md+G), on the hormonal and metabolite responses during cycling, and on subsequent time to exhaustion. Five male subjects undertook five 90 min rides on a bicycle ergometer at an exercise intensity corresponding to 65% VO2max after having ingested 1 g.kg-1 body weight of the test product in 400 ml of water immediately before the exercise. Blood samples were taken during the trials for analyses of adrenaline, noradrenaline, insulin, glucagon, glucose, lactate and non-esterified fatty acids (NEFA). Respiratory measures were also undertaken during the trials for the determination of oxygen consumption (VO2) and respiratory exchange ratio (RER), from which the carbohydrate oxidation rates were calculated. Rates of perceived exertion (RPE) were also assessed. Ten minutes after the 90 min ride, subjects exercised to volitional exhaustion at an exercise intensity of 75% VO2max. ANOVA revealed that there were significant differences between the treatments for adrenaline (p < 0.01), insulin (p < 0.05), glucose (p < 0.01), lactate (p < 0.01), NEFA (p < 0.01), RER (p < 0.001) and carbohydrate oxidation rate (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

The effect of sodium bicarbonate and sodium citrate ingestion on anaerobic power during intermittent exercise.

The effect of sodium bicarbonate and sodium citrate ingestion on cycling performance in three 30 s Wingate Anaerobic Tests separated by 6 min recovery periods has been studied using 6 male subjects. Subjects ingested either sodium bicarbonate (B), sodium bicarbonate plus sodium citrate (BC), sodium citrate (C) or sodium chloride (P) 2.5 h prior to exercise in a dose of 0.3 g kg-1 body weight. Pre-exercise blood pH was 7.44 +/- 0.06, 7.42 +/- 0.05, 7.41 +/- 0.05 and 7.38 +/- 0.04 in the C, BC, B and P conditions respectively. Mean and peak power output were significantly reduced by successive Wingate tests but not significantly affected by the treatments. Performance in the second and third tests was highest following C, BC and B ingestion. The total work done in the 3 tests was 103%, 102% and 101% of that achieved in the P condition after C, BC and B ingestion respectively. The increased alkali reserve recorded subsequent to bicarbonate and citrate treatment reduced mean post-exercise acidosis, although pH was significantly higher only in the C condition (p less than 0.05) compared to P after each exercise bout. No significant differences in plasma lactate concentration were recorded at any time. Citrate ingestion appears to be most effective in elevating blood pH and [HCO3-], and in enhancing performance in short-term intermittent exercise. This study demonstrates that alkali ingestion results in significant shifts in the acid-base balance of the blood and has a small, but non-significant, effect on anaerobic power and capacity as measured in a series of 3 Wingate Anaerobic Tests.

Acid-Base Equilibrium↗