Biomedical subjects

D R Bolster

Publications and source records attributed to D R Bolster.

4 recordsLinked to original sources

PubMed2001

Exercise affects protein utilization in healthy children.

Although health initiatives promote increased physical activity in children, the physiologic outcomes have not been well characterized. This investigation examined the effects of programmed aerobic exercise on protein metabolism in children (n = 7; mean +/- SEM: 9.14 +/- 0.46 y old; weight, 32.1 +/- 1.6 kg; height, 138 +/- 2.5 cm; and body mass index, 16.21 +/- 0.36 kg/m(2) ) using (15)N-glycine methodology. Boys (n = 5) and girls (n = 2) walked (5 d/wk, 3.2-6.4 km/d) for 6 wk. Criterion measures taken at baseline (Pre) and after the exercise program (Post) included anthropometric data, dietary assessment, nitrogen balance, nitrogen flux (Q), protein synthesis (PS), protein breakdown (PB) and net protein balance [(Net) = PS - PB]. After the walking program, there were no significant changes in body weight, fat-free mass or percentage of body fat, whereas height increased (P < 0.01). Energy and protein intakes were constant throughout the study. Nitrogen balance was significantly more positive Post than Pre (P < 0.05). There was a significant decrease in Q (P < 0.0001) with corresponding decreases in PS (P < 0.001) and PB (P < 0.01). These data provide the first evidence that programmed aerobic exercise alters whole-body protein utilization in healthy, nonobese children. Longitudinal studies are required to further examine changes in protein metabolism associated with increased physical activity in this population. In addition, findings suggest a need to evaluate nutrient requirements for healthy, physically active boys and girls.

Anthropometry↗

PubMed2000

Cardiovascular responses during prolonged exercise at ventilatory threshold in boys and men.

PURPOSE: The purpose of this study was to examine the cardiovascular responses during prolonged exercise in boys and men at an intensity set relative to ventilatory threshold (VT). METHODS: Eight boys (10-13 yr) and 10 men (18-25 yr) completed an orientation trial, a maximal exercise test, and a 40-min submaximal exercise bout at an intensity equal to the VO2 at VT (approximately 64.5% VO2max). RESULTS: Heart rate (HR) was higher and stroke volume (SV) was lower in the boys compared with the men (P < or = 0.05). From 10 to 40 min, HR significantly increased 9.5% and 13.6% and SV significantly decreased 8.8% and 11.6% in the boys and men, respectively. Despite the tendency for the changes in HR and SV to be greater in the men, the group-by-time interaction was not significant. Cardiac output was greater in the men (P < or = 0.05) but remained constant over time (P > 0.05). In men, mean arterial blood pressure was higher (P < or = 0.05) and decreased 4.2% over time. In boys, mean arterial blood pressure remained constant, which resulted in a significant group-by-time interaction. Total peripheral resistance (TPR) was significantly higher in the boys and remained constant over time (P > 0.05). From 0 to 40 min, the decrease in plasma volume was significantly greater in the men (-10.2%) than the boys (-5.7%) but was unrelated to the changes in SV in either group (P > 0.05). CONCLUSION: In conclusion, the cardiovascular responses during prolonged exercise are similar in boys and men, although there is a tendency for the magnitude of cardiovascular drift to be greater in the men.

Adolescent↗

PubMed1999

Effects of precooling on thermoregulation during subsequent exercise.

PURPOSE: 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)). METHODS: 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. RESULTS: 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). CONCLUSIONS: Precooling attenuated the rise in Tre, but this effect was transient. Therefore, precooling is not recommended before a triathlon under similar environmental conditions.

Adult↗

PubMed1997

Thermoregulatory responses to cycling with and without a helmet.

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.

Adult↗