Browsing by Author "Hawley, John"

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    The effects of water ingestion on high intensity cycling performance in a moderate ambient temperature
    (1994) Robinson, Tracy Anne; Hawley, John; Dennis, Steve
    Eight endurance~trained cyclists rode as far as possible in 1 h on a stationary cyclesimulator in a moderate environment (20°C, 60% relative humidity, 3 m/s wind speed) while randomly receiving either no fluid (NF) or attempting to replace their ~1.7 l sweat loss measured in a previous 1 h familiarisation performance ride at ~85% of peak oxygen uptake (VO₂ peak) with artificially sweetened, coloured water (F). During F the cyclists drank 1.49 ± 0.14 1 (values are mean± SEM), of which 0.27 ± 0.08 1 remained in the stomach at the end of exercise and 0.20 ± 0.05 1 was urinated after the trial. Thus, only 1.02 ± 0.12 l of the ingested fluid was available to replace sweat losses during the 1 h performance ride. That fluid decreased the average heart rate from 166 ± 3 to 157 ± 5 beats/min (P < 0.0001) and reduced the final serum [Na+] and osmolalities from 143 ± 0.6 to 139 ± 0.6 mEq/1 (P < 0.005) and from 294 ± 1.7 to 290 ± 1.9 mOsm/1 (P = 0.05), respectively. Fluid ingestion did not attenuate rises in plasma anti diuretic hormone and angiotensin concentrations, or decrease the ~-15% falls in estimated plasma volume in the F and NF trials. Nor did fluid ingestion significantly effect the ~1.7 l/h sweat rates, the rises in rectal temperature (~36.6° to 38.3°C) or the ratings of perceived exertion in the two trials. Ingestion of ~1.5 l of fluid produced an uncomfortable stomach fullness and reduced the distance covered in 1 h from 43.1 ± 0. 7 to 42.3 ± 0.6 km (P<0.05). Thus, trying to replace > 1.0 l/h sweat losses during high-intensity, short duration exercise in a moderate environment does not induce beneficial physiological effects, and may impair exercise performance.
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    Fuel kinetics during intense running and cycling when fed carbohydrate
    (1996) Derman, Kevin Dale; Hawley, John
    On two occasions six competitive, male triathletes performed in random order, two experimental trials consisting of either a timed ride to exhaustion on a cycle-ergometer or a run to exhaustion on a motor-driven treadmill at 80% of their respective peak cycling and peak running oxygen uptakes (VO₂peak)- At the start of exercise, subjects drank 250 ml of a 15 g.100 ml⁻¹ w.v⁻¹ glucose solution with U-¹⁴C glucose added as tracer and, thereafter, 150 ml of the same solution every 15 min. Despite identical metabolic rates (VO₂ 3.51 ±0.06 vs. 3.51 ±0.10 l.min⁻¹; values are mean± SEM for the cycling and running trials, respectively), exercise times to exhaustion were significantly longer during cycling than running (96 ±14 vs. 63 ±11 min; P<0.05). The superior cycling than running endurance was not associated with any differences in either the rate of blood glucose oxidation (3.8 ±0.1 vs. 3.9 ±0.4 mmol.min⁻¹ ), nor the rate of ingested glucose oxidation (2.0 ± 0.1 vs. 1.7 ±0.2 mmol.min⁻¹) at the last common time point (40 min) before exhaustion, despite higher blood glucose concentrations at exhaustion during running than cycling (7.0 ±0.9 vs. 5.8 ±0.5 mmol.l⁻¹; P<0.05). However, the final rate of total CHO oxidation was significantly greater during cycling than running (24.0 ±0.8 vs. 21.7 ±1.4 mmol C6 .min⁻¹;P<0.01). At exhaustion, the estimated contribution to energy production from muscle glycogen had declined to similar extents in both cycling and running (68 ±3 vs. 65 ± 5%). These differences between the rates of total CHO oxidation and blood glucose oxidation suggested that the direct and/or indirect (via lactate) oxidation of muscle glycogen was greater in cycling than running.
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    Physiological and metabolic responses to constant and variable load cycling performance
    (1999) Palmer, Gary Stanley; Hawley, John
    The experiments described in this thesis comprise a series of related, yet independent investigations examining the physiological and metabolic responses of well-trained amateur cyclists under conditions designed to mimic actual competitive situations, during individual and mass start races. In Section A the physiological responses to constant load and steady state exercise are determined. In Section B, the metabolic factors associated with constant and variable load cycling performance are examined.
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    The reliability of laboratory performance testing
    (1997) Schabort, Elske Jeanne; Hawley, John; Hopkins, Will
    The reproducibility of a measurement in a laboratory test impacts on the power of that test to detect the small, but significant changes in an athlete's performance when determining the influence of a new training or nutritional intervention. Until recently, however, sport scientists have not been concerned with establishing the reliability of many of their testing protocols. Therefore, the purpose of this thesis was to examine the reliability of several laboratory tests of performance and to determine those factors which may impact on the reproducibility of those tests. Possible factors that could contribute to the reliability of a performance test include the type of exercise protocol employed (continuous, intermittent), the equipment on which the subject performs the test, the intensity and duration of the testing protocol, the subject's state of fitness and whether he is familiar with the testing conditions.
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    The seasonal and lifetime incidence of low back pain in South African male first league squash players
    (1996) Burden, Stephen Barry; Hawley, John; Derman, Wayne
    Previous studies have been conducted to determine the incidence of low back pain (LBP) in both the general population as well as in participants of different sporting activities. The purpose of this study was to determine the seasonal and lifetime incidence of LBP in male first league squash players.