-
[show abstract]
[hide abstract]
ABSTRACT: The purpose of this study was to examine the effect of a decreased body core temperature before a simulated portion of a triathlon (swim,15 min; bike, 45 min) and examine whether precooling could attenuate thermal strain and increase subjective exercise tolerance in a warm environment (26.6 degrees C/60% relative humidity (rh)).
Six endurance trained triathletes (28+/-2 yr, 8.2+/-1.7% body fat) completed two randomly assigned trials 1 wk apart. The precooling trial (PC) involved lowering body core temperature (-0.5 degrees C rectal temperature, Tre) in water before swimming. The control trial (CON) was identical except no precooling was performed. Water temperature and environmental conditions were maintained at 25.6 degrees C and 26.6 degrees C/60% rh, respectively, throughout all testing.
Mean time to precool was 31+/-8 min and average time to reach baseline Tre during cycling was 9+/-7 min. Oxygen uptake (VO2), HR, skin temperature (Tsk), Tre, RPE, and thermal sensation (TS) were recorded following the swim segment and throughout cycling. No significant differences in mean body (Tb) or Tsk were noted between PC and CON, but a significant difference (P < 0.05) in Tre between treatments was noted through the early phases of cycling. No significant differences were reported in HR, VO2, RPE, TS, or sweat rate (SR) between treatments. Body heat storage (S) was negative following swimming in both PC (-92+/-6 W x m2) and CON (-66+/-9 W x m2). A greater S occurred in PC (109+/-6 W x m2) vs CON (79+/-4 W x m2) during cycling (P < 0.05).
Precooling attenuated the rise in Tre, but this effect was transient. Therefore, precooling is not recommended before a triathlon under similar environmental conditions.
Medicine & Science in Sports & Exercise 02/1999; 31(2):251-7. · 4.43 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This investigation was undertaken to determine whether consuming several small feedings of preexercise carbohydrate (CHO), rather than a single bolus, would affect blood glucose and insulin responses during rest and exercise. Eight trained cyclists ingested 22.5, 45, or 75 total g maltodextrin and dextrose dissolved in 473 ml of water or an equal volume of placebo (PL). Drinks were divided into four portions and consumed at 15-min intervals in the hour before a 120-min ride at 66% VO2max. Serum glucose values were elevated by the CHO feedings at rest and fell significantly below baseline and PL at 15 min of exercise. However, glucose concentrations were similar in each of the CHO trials. Insulin concentrations also increased rapidly during rest, then fell sharply at the onset of exercise. The findings demonstrate that CHO consumed within an hour before exercise, even when taken in several small feedings, can produce transient hypoglycemia near the onset of exercise. Additionally, the magnitude of the response appears to be unrelated to either the amount of CHO ingested or the insulin response.
International journal of sport nutrition 07/1997; 7(2):128-37.
-
[show abstract]
[hide abstract]
ABSTRACT: This study examined the effects of wearing a helmet on selected body temperatures and perceived heat sensation of the head and body while cycling in a hot-dry (D) (35 degrees C, 20% relative humidity (RH) and hot-humid (H) (35 degrees C, 70% RH) environment. Ten male and four female cyclists (mean +/- SD: males = age 27 +/- 7 yr, peak O2 uptake (VO2) 4.10 +/- 0.54 L.min-1; females = age 26 +/- 3 yr, peak O2 uptake (VO2) 3.08 +/- 0.49 L.min-1) performed four randomized 90-min cycling trials at 60% of peak VO2 both with (HE) and without (NH) a commercially available cycling helmet in both D and H environments. VO2, core (Te), skin (Tsk), and head skin temperatures, heart rate (HR), rating of perceived exertion (RPE), and perceived thermal sensation of head (TSH) and body (TSB) were measured throughout exercise. For all measured variables, no significant difference was evident between HE and NH. However, Tc, Tsk, and mean head skin temperatures were higher (P < 0.001) in H than D. Likewise, RPE, TSH, TSB (P < 0.001), and sweat rates (H = 1.33 +/- 0.32, D = 1.14 +/- 0.23 L.h-1) (P < 0.01) were higher in H versus D. Results indicate that use of a commercially available cycling helmet while riding in a hot-dry or hot-humid environment does not cause the subjects to become more hyperthermic or increase perceived heat sensation of the head or body.
Medicine & Science in Sports & Exercise 07/1997; 29(6):755-61. · 4.43 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Ten competitive male cyclists completed a Wingate Bike Test (WIN), a 30-min self-paced cycling performance bout (END), and a constant load, supramaximal cycling spring (SPN) to fatigue following 5 d of oral supplementation (5,000 mg.day-1) with inosine and placebo. Blood samples were obtained prior to and following both supplementation periods, and following each cycling test. Uric acid concentration was higher (P < 0.05) following supplementation with inosine versus placebo, but 2,3-DPG concentration was not changed. The data from WIN demonstrate that there were no significant differences in peak power (8.5 +/- 0.3 vs 8.4 +/- 0.3 W.kg body mass-1), end power (7.0 +/- 0.3 vs 6.9 +/- 0.2 W.kg body mass-1), fatigue index (18 +/- 2 vs 18 +/- 2%), total work completed (0.45 +/- 0.02 vs 0.45 +/- 0.02 kJ.kg body mass-1.30-s-1), and post-test lactate (12.2 +/- 0.5 vs 12.9 +/- 0.6 mmol.l-1) between the inosine and placebo trials, respectively. No difference was present in the total amount of work completed (6.1 +/- 0.3 vs 6.0 +/- 0.3 kJ.kg body mass-1) or post-test lactate (8.4 +/- 1.0 vs 9.9 +/- 1.3 mmol.l-1) during END between the inosine and placebo trials, respectively. Time to fatigue was longer (P < 0.05) during SPN for the placebo (109.7 +/- 5.6 s) versus the inosine (99.7 +/- 6.9 s) trial, but post-test lactate (14.8 +/- 0.7 vs 14.6 +/- 0.8 mmol.l-1) was not different between the treatments, respectively. These findings demonstrate that prolonged inosine supplementation does not appear to improve aerobic performance and short-term power production during cycling and may actually have an ergolytic effect under some test conditions.
Medicine & Science in Sports & Exercise 10/1996; 28(9):1193-8. · 4.43 Impact Factor
