Mild to moderate hypohydration reduces boys' high-intensity cycling performance in the heat.

PURPOSE: To evaluate the effect of 1 and 2 % hypohydration on high-intensity cycling performance of 10- to 12-year-old boys in the heat. METHODS: In a counterbalanced order, nine boys attended three sessions in which they cycled intermittently (6 × 10-min bouts at 40-45 % [Formula: see text]) in a climate chamber. During each session, environmental conditions and water intake were individually adjusted to achieve a target hypohydration level of 0, 1 or 2 %, based on change in body weight (BW). Following 45 min of rest in thermoneutral conditions when the target hypohydration was maintained, each boy re-entered the climate chamber (35 °C and 50-55 % RH) to perform the cycling performance test at 90 % [Formula: see text] until exhaustion. Heart rate (HR) and rectal temperature (T re) were recorded continuously throughout each session. Total mechanical work (TMW) was taken as a measure of cycling performance. RESULTS: Actual hypohydration level at the start of the cycling performance test in each session was: 0.1 ± 0.0 %, 1.1 ± 0.1 % and 2.0 ± 0.1 %. With 2 % hypohydration, TMW (35.5 ± 6.8 kJ) was significantly (p < 0.05) lower than with 0 % hypohydration (49.3 ± 9.8 kJ). When expressed as a percentage of TMW with 0 % hypohydration, TMW was reduced by 15.5 and 23.3 % with 1 and 2 % hypohydration, respectively (p < 0.05 for both). At the start of the cycling performance test, HR was 13 and 15 bpm higher, and T re was 0.3 °C higher (p < 0.05 for all) with 1 and 2 % hypohydration, respectively, compared with 0 % hypohydration. CONCLUSION: Mild (~1 %) to moderate (~2 %) hypohydration reduces high-intensity cycling performance of healthy young boys in the heat.

Body weight changes in child and adolescent athletes during a triathlon competition.

We examined young athletes during a triathlon performed in a hot climate. Complete or partial data were available for 95 athletes competing in the National Triathlon Championship in Costa Rica. Mean ± SD for age and body weight (BW) were 13.1 ± 2.5 years and 46.3 ± 11.5 kg, respectively. Race requirements included: 500 m swimming, 15 km cycling, 3.5 km running for juniors (9-13 years); 800 m swimming, 30 km cycling, 8 km running for seniors (14-17 years). WBGT on race day was >31 °C. BW recorded pre- and post-race was available for 92 athletes and performance data were available for 83 of these. Information regarding symptoms experienced during the race was available for 95 athletes. Change in BW (%ΔBW) was calculated and ranged from +0.6 to -2.4 % for junior boys (-1.2 ± 0.9 %), +0.7 to -2.5 % for junior girls (-1.3 ± 0.9 %), 0 to -2.8 % for senior girls (-1.3 ± 0.9 %), and +0.6 to -4.5 % for senior boys (-1.7 ± 1.1 %). Eighteen participants reported no medical symptoms. Of 77 participants who reported symptoms, 42.9 % reported exhaustion/fatigue, 36.4 % reported side stitch/cramp, and 23.4 % reported dizziness. Participants reporting no medical symptoms achieved almost identical (P = 0.99) %ΔBW as those reporting at least one symptom. %ΔBW was more negative (P = 0.005) in participants who reported dizziness (-1.9 %ΔBW) compared with those who did not (-1.4 %ΔBW). %ΔBW was associated with performance in junior girls (r = 0.47, P = 0.02) and senior boys (r = 0.51, P = 0.01), with a trend in junior boys (r = 0.41, P = 0.053) but not in senior girls (r = 0.004, P = 0.99). Young athletes participating in a triathlon in a hot climate can tolerate mild to moderate levels of dehydration, without detrimental effects to self-assessed health.

Influence of pubertal stage on local sweating patterns of girls exercising in the heat.

The influence of puberty on sweating patterns of girls exercising in the heat is not known. Nine- to 17-year-old girls, representing 4 stages of breast development: T1 (n = 21); T2 (n = 22); T3 (n = 25); and T4 (n = 22), cycled for 20 min at 60% in 35 °C. The population density of heat activated sweat glands was higher in T1 vs T3 and T4 and in T2 vs T4. Sweat drop area was lower in T1 vs T3 and in T1 vs T4, T2 vs T4 and T3 vs T4. The proportion of skin covered by sweat was lower in T1 vs T4. Sweating patterns of girls exercising in the heat are influenced by pubertal stage.

Energy substrate utilization during prolonged exercise with and without carbohydrate intake in preadolescent and adolescent girls.

Little information is available on energy metabolism during exercise in girls, particularly the contribution of exogenous carbohydrate (CHO(exo)). The purpose of this study was to determine substrate utilization during exercise with and without CHO(exo) intake in healthy girls. Twelve-yr-old preadolescent (YG; n = 12) and 14-yr-old adolescent (OG; n = 10) girls consumed flavored water (WT) or (13)C-enriched 6% CHO (CT) while cycling for 60 min at approximately 70% maximal aerobic power (Vo(2max)). Substrate utilization was calculated for the final 15 min of exercise. CHO(exo) decreased fat oxidation by approximately 50% in YG but not in OG (P < 0.001) and decreased endogenous CHO oxidation by approximately 15% in OG but not in YG (P = 0.006). Endogenous CHO oxidation was lower in YG than in OG regardless of trial (P < or = 0.01), whereas fat oxidation was higher in YG only during WT (P < 0.001). CHO(exo) oxidation rate was similar between YG and OG (7.1 +/- 0.5 and 6.8 +/- 0.4 mg.kg(-1).min(-1), respectively, P = 0.67), contributing approximately 19% to total energy expenditure. Serum estradiol levels in all girls correlated with fat (r = -0.50 to -0.59, P = 0.03 to 0.005) and endogenous CHO oxidation (r = 0.50 to 0.63, P = 0.03 to 0.005) but not with CHO(exo) oxidation (r = -0.09, P = 0.71). We conclude that CHO(exo) influences endogenous substrate utilization in an age-dependent manner in healthy girls but that total CHO(exo) oxidation during exercise is not different between YG and OG. Our results also point to potential sex-related differences in energy substrate utilization even during childhood.

Sex-based effects on the distribution of NK cell subsets in response to exercise and carbohydrate intake in adolescents.

Carbohydrate (CHO) supplementation and female sex independently influence the natural killer (NK) cell response to acute exercise. Consequently, this study sought to elucidate sex-based differences in the distribution of NK cell subsets (i.e., CD56dim and CD56bright) in response to exercise and CHO intake. Twenty-two healthy 14-yr-old girls (n = 11) and boys (n = 11) cycled for 60 min at 70% maximal oxygen consumption while drinking 6% CHO (CT) or flavored water (WT). Blood was collected at rest, during exercise (30 and 60 min), and during recovery (30 and 60 min) to identify CD3- CD56dim and CD3- CD56bright NK cells. The activation marker CD69 was also determined on CD3- CD56+ cells. CD56dim responses, expressed as proportions or cell counts, were greater (P < or = 0.01) in girls by 67 and 105%, respectively. CD56bright cell counts (P = 0.006), but not CD56bright proportions (P = 0.89), were greater in girls by 82%. Both CD56dim and CD56bright subset responses, expressed as proportions or cell counts, were lower (P < or = 0.01) in CT vs. WT by 33-36%. The CD56bright-to-CD56dim ratio decreased at 30 min of exercise but increased during recovery (P < 0.001), with no effect of sex or CHO. Regardless of trial, CD3- CD56+ cells expressed approximately 18% higher levels of CD69 during recovery in girls but not boys (P = 0.03), despite similar proportions and counts of CD69+ cells. These results demonstrate sex-based differences in the distribution of NK cell subsets and activation status in response to exercise, but not CHO intake, and further support the need to control for sex in exercise immunology studies.

Immunological changes in response to exercise: influence of age, puberty, and gender.

PURPOSE: This study tested the hypothesis that exercise-induced perturbation and recovery of the immune system would vary with age, puberty, and gender in healthy children and adolescents. METHODS: Twelve-year-old girls (YG; N = 14) and boys (YB; N = 20), and 14-yr-old girls (OG; N = 11) and boys (OB; N = 13) cycled for 60 min at 70% VO2max. Blood was collected before, at 30 and 60 min of exercise, and at 30 and 60 min of recovery to measure total leukocytes, leukocyte and lymphocyte subsets, and cytokines. Age and pubertal (Tanner stage) effects within genders and gender effects within age and pubertal groups were determined. RESULTS: Exercise-induced increases in lymphocytes, CD3-CD16+CD56+ counts, and IL-6 were approximately 83, 90, and 390% greater in OG versus YG (P < 0.05). Recovery leukocytosis and neutrophilia were approximately 56 and 35% greater in OB versus YB (P < 0.05). Pubertal stage did not have a statistically significant influence on responses in girls, but the lowest pubertal stage consistently showed smaller changes in lymphocytes and CD3-CD16+CD56+ counts. Recovery neutrophilia was approximately 120% greater in postpubertal boys versus prepubertal or pubertal boys (P < 0.05). Responses of lymphocytes and CD3-CD16+CD56+ counts, respectively, were approximately 120 and 82% greater in OG versus OB (P < 0.05), with no differences between YG and YB. Exercise-induced increases in total leukocytes, lymphocytes, and CD3-CD16+CD56+ counts were at least 35% greater in girls versus boys of similar pubertal status (P < 0.05). Regardless of age, puberty, or gender, IL-8 levels were significantly higher during recovery versus rest (P < 0.05). CONCLUSION: These results highlight the need to control for age, puberty, and gender when interpreting immunologic responses to exercise in a pediatric population.

Puberty effects on NK cell responses to exercise and carbohydrate intake in boys.

UNLABELLED: Previous research has demonstrated that younger versus older animals and humans experience smaller perturbations in natural killer (NK) cells in response to physiological stress. PURPOSE: To determine whether the smaller perturbations in NK cells induced by strenuous exercise and carbohydrate (CHO) intake, previously reported in children, are influenced by puberty. METHODS: Twenty 12-yr-old boys, distinguished as prepubertal (Tanner (T) 1, N = 7), early pubertal (T2, N = 7), or pubertal (T3-5, N = 6), cycled for 60 min at 70% VO(2max) while drinking 6% CHO (CT) or flavored water (WT). Blood was collected at rest and during (30 and 60 min) and following (30 and 60 min) exercise to identify NK cells as CD3(-)CD56(dim) or CD3(-)CD56(dim). CD69 expression on CD3(-)CD56(+) cells was also determined. RESULTS: A puberty x CHO x exercise interaction was found for the proportion, but not number, of CD56(dim) cells (P = 0.06). CD56(dim) cell counts were lower in CT versus WT (P < 0.001). Responses of CD56(bright) proportions (P = 0.007) and counts (P = 0.03) depended on pubertal status, but not CHO. The CD56(bright):CD56(dim) ratio remained stable during exercise, but during recovery was higher in T1 and T3-5 versus T2 (P = 0.08) and in CT versus WT (P = 0.04). During recovery, CD3(-)CD56(+) cells expressed higher levels of CD69 (P = 0.01), with no change in the proportion of CD69(+) cells. CONCLUSION: These results confirm the influence of puberty on the distribution of NK cell subsets in response to exercise and CHO intake. Increased CD69 expression suggests that NK cells increase activation status during recovery from physiological stress.

Effect of ipratropium bromide on EIB in children depends on vagal activity.

PURPOSE: Ipratropium bromide (IB) has been used to prevent exercise-induced bronchoconstriction (EIB), but its effect varies among individuals. We hypothesized that such variability may reflect individual differences in vagal activity (VA), and therefore determined whether a correlation exists between VA and the effect of IB on EIB in 13.0 (+/-0.8)-yr-old children with asthma and documented EIB. METHODS: Subjects served as their own control and were tested on three occasions in an ambient temperature of 5 degrees C. Visit I included no treatment. In visits II and III (counterbalanced sequence) subjects inhaled either 500 microg IB or 0.9% NaCl as a placebo, 45 min before exercise provocation. Investigators and the subjects were blinded to the inhaled substance. VA was assessed by a 4-s exercise test (3). The ratio of resting ECG R-R-interval at full inspiration to the lowest R-R interval during 4-s cycling was taken as an index of VA. Eight-minute cycling at constant work rate (HR=173+/-4 bpm) at 5 degrees C was used to provoke EIB. A two-factor (treatment x time) repeated-measures ANOVA was used. RESULTS: The exercise-induced drop in FEV1 was similar in the three sessions. However, because the IB caused a 15.7+/-4.1 increase in FEV1 preexercise, the postexercise values after a placebo or no treatment were consistently lower than after IB. The beneficial response to IB, compared with no treatment and with placebo, was positively correlated to VA (for FEV1: r=0.91, P=0.002; and r=0.90, P=0.002, respectively). CONCLUSION: We suggest that the therapeutic effect of IB on exercise-induced asthma may be related to vagal activity.

Physical activity level is associated with the O2 cost of walking in cerebral palsy.

PURPOSE: To determine, in children and adolescents with cerebral palsy (CP), the relationship between physical activity level (PAL) and i) oxygen cost of walking, and ii) peak VO2. METHODS: In 11 subjects (10.6-16.3 yr) with mild CP, PAL, the ratio of total energy expenditure to resting energy expenditure, was determined from 3 d of heart rate (HR) monitoring (field), with individual HR-VO2 calibrations done in the lab. The oxygen cost of walking was measured during three 3-min walks on a treadmill at 60, 75, and 90% of each subject's fastest treadmill walking speed (FWS). Subjects also performed a maximal treadmill exercise test. Alpha was set at 0.05. RESULTS: One subject was an outlier and eliminated from all simple linear regression analyses. For the remaining 10 subjects, PAL (1.37+/-0.18) was related (r=-0.70 to -0.84) to net VO2 at 60 and 75% FWS (13.1+/-4.1 and 16.2+/-4.2 mL.kg.min), net VO2.m, averaged across the three speeds (0.32+/-0.23 mL.kg.m), and percent peak VO2 at all three speeds (54.5+/-21.5, 63.5+/-20.9, and 75.5+/-15.1%). PAL was not significantly related to net VO2 at 90% FWS (20.8+/-5.3 mL.kg.min) or to peak VO2 (34.0+/-9.2 mL.kg.min). CONCLUSION: For this population, those with low PAL may also have a high oxygen cost of walking. These individuals' PAL was not related to their peak VO2. Further research is required to determine whether interventions that decrease the oxygen cost of walking also affect PAL and whether changes in PAL affect the oxygen cost of walking.

Relationship between summer vacation weight gain and lack of success in a pediatric weight control program.

The purpose was to measure the effect of holidays or season on changes in body weight to determine if this was the reason for the low success rate of weight control program participants. Changes in percent ideal body weight were gathered on 73 overweight youth (average age: 10.5+/-2.8 years; percent ideal body weight: 150+/-28%) over 2-month intervals in a 1-year time span. There was a statistically significant gain in percentage of body weight during July-August compared to January-February at p<0.004, March-April at p<0.04, May-June at p<0.001 and September-October at p<0.04. Sixty-six percent of subjects gained weight during the summer months. When the subjects who lost weight in the summer period were removed from the analysis, the average weight gain was 2.8% of ideal body weight. For a weight control program for children and adolescents to be effective, strategies need to be developed to deal with the summer vacation period as this can affect the overall success in the program.

Oxidation rate of exogenous carbohydrate during exercise is higher in boys than in men.

To determine whether the relative utilization of exogenous carbohydrate (CHO(exo)) differs between children and adults, substrate utilization during 60 min of cycling at 70% peak O(2) uptake was studied in 12 pre- and early pubertal boys (9.8 +/- 0.1 yr) and 10 men (22.1 +/- 0.5 yr) on two occasions. Subjects consumed either a placebo or a (13)C-enriched 6% CHO(exo) beverage (total volume per trial: 24 ml/kg). Substrate utilization was calculated for the final 30 min of exercise. During both trials, total fat oxidation was higher (5.4 +/- 0.5 vs. 3.0 +/- 0.4 mg x kg(-1) x min(-1), P < 0.001) and total CHO oxidation lower (27.4 +/- 1.5 vs. 34.8 +/- 1.2 mg x kg(-1) x min(-1), P < 0.001) in boys than in men, respectively. During the CHO(exo) trial, CHO(exo) oxidation was higher (P < 0.001) in boys (8.8 +/- 0.5 mg x kg(-1) x min(-1)) than in men (6.2 +/- 0.5 mg x kg(-1) x min(-1)) and provided a greater (P < 0.001) relative proportion of total energy in boys (21.8 +/- 1.4%) than in men (14.6 +/- 0.9%). These results suggest that, although endogenous CHO utilization during exercise is lower, the relative oxidation of ingested CHO is considerably higher in boys than in men. The greater reliance on CHO(exo) in boys may be important in preserving endogenous fuels and may be related to pubertal status.

Temperature regulation during rest and exercise in the cold in premenarcheal and menarcheal girls.

Temperature regulation during exercise in the cold was examined in 13 adolescent female individuals, aged 13-18 yr. Six girls with established menstrual cycles comprised the eumenorrheic menarcheal (EM) group, and seven nonmenstruating girls comprised the premenarcheal (PM) group. During the first visit, maximal oxygen consumption (Vo(2 max)), height, weight, and percent body fat were measured. The second visit included a determination of metabolic rate in thermoneutrality (21 degrees C), consisting of a 10-min rest period and 20 min of cycling (30% of Vo(2 max)), and a cold test (5 degrees C, 40% humidity, <0.3 m/s air velocity) involving a 20-min rest period and 40 min of cycling (30% of Vo(2 max)). Subjects in the EM group were tested twice in the chamber: once during the follicular and once during the luteal phase. Heat production per kilogram in thermoneutrality and in the cold was significantly (P < 0.05) higher in the PM compared with the EM girls. However, the PM girls had a significantly (P < 0.05) lower core temperature in the cold than the EM group. PM girls also had a significantly higher body surface area-to-mass ratio compared with the EM girls. Although percent body fat between groups was not significantly different, within the PM group percent body fat explained 79% (P < 0.01) of the variance in the decrease of core temperature. There were no menstrual phase-related differences in temperature regulation in either the thermoneutral or cold environment. In conclusion, menstrual phase does not influence temperature regulation in female individuals during adolescence. EM girls had lower metabolic heat production but maintained their core temperature more effectively in the cold than did the PM girls. This thermoregulatory difference between PM and EM girls is mainly a function of geometric differences with maturation-related peripheral vasoconstrictive differences maybe limiting the effectiveness of the mechanism of increased heat storage in younger female individuals.

Energy cost of walking in boys who differ in adiposity but are matched for body mass.

PURPOSE: To compare the energy cost of treadmill walking, in pairs of obese and lean adolescents who were matched for total body mass. METHODS: Metabolic energy expenditure was determined at 67, 83, and 100 m.min-1, in nine obese and nine nonobese 11- to 18-yr-old boys. Total adiposity and fat distribution in the trunk and limbs were assessed using DXA. RESULTS: There were no intergroup differences in the net (exercise minus rest) energy cost at the two lower speeds, but the obese boys expended more energy at 100 m.min-1 (12%, P < 0.05). Heart rate was consistently higher in the obese boys: 18% at 67 m.min-1, 22% at 83 m.min-1, and 28% at 100 m.min-1. Pooling all subjects together, body mass, rather than adiposity, was the main predictor of energy cost: 89.1%, 76.3%, and 62.1% (P < 0.05 for all) of the total variance at 67, 83, and 100 m.min-1, respectively. The variance explained by total body fat was only 2.1%, 8.4%, and 16%, respectively. There was no relationship between [OV0312]O(2net) and the proportion of fat in body segments. CONCLUSION: It is total body mass, more than adiposity (total and regional) per se, that affects the energy cost of locomotion in obese boys.

RPE during prolonged cycling with and without carbohydrate ingestion in boys and men.

PURPOSE: To examine the effect of prolonged cycling on ratings of perceived exertion (RPE) in boys and men and whether carbohydrate (CHO) ingestion would lower RPE during exercise. METHODS: Ten boys (9-10 yr) and 10 men (20-25 yr) cycled for 60 min at approximately 70% VO2peak on two occasions. In a double-blind, counterbalanced design, a total volume of 24 mL.kg(-1) body mass of either a 6% CHO-electrolyte (CT) or flavored water (WT) beverage was consumed intermittently before and during exercise in each trial. Oxygen consumption (VO2), ventilation (VE), respiratory rate (RR), RPE (Borg's 6-20 scale), and heart rate (HR) were recorded periodically throughout exercise. Plasma glucose (GLU) was determined before and after exercise. RESULTS: Postexercise GLU was not different between age groups but higher (P<0.001) during CT (5.6 +/- 0.2 mmol.L(-1)) compared with WT (4.7 +/- 0.1 mmol.L(-1)). CHO ingestion had no effect (P>0.05) on VO2, VE, RR, or RPE in either group. RR during exercise was higher (P<0.01) in boys (39.0 +/- 2.2 breaths.min(-1)) than in men (30.9 +/- 1.3 breaths.min(-1)). HR was slightly higher (P=0.047) during CT (160 +/- 3 beats.min(-1)) compared with WT (156 +/- 4 beats.min(-1)) and increased less over time (P<0.01) in boys compared with men. RPE at 5 min of exercise was similar (P>0.05) between boys (11.8 +/- 0.7) and men (12.0 +/- 0.7) but increased faster (P<0.01) over time in boys. The average exercise RPE was higher (P<0.01) in boys (15.8 +/- 0.5) than in men (14.0 +/- 0.4). CONCLUSIONS: The higher and faster increase in RPE during exercise in boys, compared with men, may reflect a sensitivity to RR that outweighed any effect of CHO ingestion on RPE.

Repeated treadmill walks affect physiologic responses in children with cerebral palsy.

PURPOSE: To determine whether physiologic responses during treadmill walking in children with cerebral palsy (CP) are affected by repeated walking bouts on different days, and whether effects are different at different speeds. METHODS: Three girls and five boys (9.2-15.7 yr, 23.3-64.4 kg) with mild CP received 12-15 min of treadmill walking practice and had their fastest walking speed (FWS) determined during an introductory visit. During each of three subsequent visits (day 1, day 2, day 3), subjects walked for 3 min at 60, 75, and 90% FWS. Resting physiologic measures were taken on day 1. RESULTS: From day 1 to day 3, net ventilation ([OV0312]E), and net heart rate (HR) at 90% FWS decreased by 3.6 L.min-1 and 8 beats.min-1, respectively. There were no differences between day 1 and day 2 or day 1 and day 3 for any other physiologic variable at any speed. Day 3 was less than day 2 for net HR (60% FWS) and, independent of speed, net [OV0312]O2 (per kilogram of body mass and per stride) and net energy expenditure (kJ.min-1). Between-day reliability (R) of physiologic responses was > or = 0.95, except respiratory rate (R = 0.75). Intrasubject, between-day variability for the [OV0312]O2 measures was 7.6-12.9%. CONCLUSION: Because there were no day 1 to day 3 reductions in metabolic variables, day 1 to day 3 reductions at 90% FWS in net HR may reflect decreased emotional stress over time and reductions in net [OV0312]E, an uncoupling of [OV0312]O2 and [OV0312]E. Despite between-day differences, reliable net physiologic and stable net metabolic variables may be collected in subjects with mild CP after one treadmill walking practice session.

Responses of children with cerebral palsy to arm-crank exercise in the heat.

PURPOSE: In response to passive heating, adults with hemispheric brain infarction demonstrate lower skin temperatures (Tsk) and higher sweating rates (SR) on the affected side. It is unknown whether children with similar conditions demonstrate a similar response and whether this response is advantageous to defending body temperature during exercise in the heat. The purpose of this study was to determine whether children with spastic cerebral palsy (CP) demonstrate less thermal strain than healthy peers during short (10 min each) bouts of arm cranking, a mode of exercise where metabolic rate can be matched between the two groups. METHODS: Eleven young people (8.3-18.3 yr) with spastic CP and 11 individually matched (body size, age, and maturity) healthy controls (CON) performed 3 x 10-min arm-cranking bouts (40 rpm) in 35 degrees C, 50% RH. Body mass, metabolic and heart rate (HR) responses, and body temperatures were periodically measured. Individuals within each CP-CON pair worked at the same intensity (0.55 +/- 0.18 W.kg-1 body mass). Data were analyzed using a repeated measures ANOVA (alpha = 0.05). RESULTS: Subjects with CP showed no difference from CON in metabolic and HR responses, or SR (as inferred from body mass changes corrected for fluid intake and output). There were also no differences between the groups in the rectal temperature change from room temperature (21-23 degrees C). The increase in Tsk from room temperature, however, was slightly (0.6 degrees C) but significantly lower (P < 0.0001; 95% CI = 0.5-0.7 degrees C) in the subjects with CP compared with CON. CONCLUSION: Subjects with CP demonstrate thermal strain responses similar to CON during upper-body exercise at relatively low intensities for short duration in a warm climate.

Responses of children with cerebral palsy to treadmill walking exercise in the heat.

PURPOSE: When metabolic rate during arm-cranking in the heat is equated between children and adolescents with cerebral palsy (CP) and matched controls (CON), there are no relevant intergroup differences in heat strain. The metabolic rate, however, is known to be higher in CP during treadmill walking. The purpose of this study was to determine if during treadmill walking in the heat, the higher oxygen uptake (VO2), and thus greater metabolic heat production in those with CP would result in greater heat strain compared with able-bodied, matched CON. METHODS: Ten boys and girls (10.3-16.3 yr) with spastic CP and 10 individually matched (age, body size, biological maturity, gender, race) healthy CON performed 3 x 10-min treadmill walking bouts in 35 degrees C, 50% RH. Body mass, metabolic variables, heart rate (HR), body temperatures, and rating of perceived exertion (RPE) were periodically measured. Individuals within each CP-CON pair walked at the same speed and slope (0.9 +/- 0.4 m x s(-1), 3.3 +/- 0.6%). RESULTS: Steady-state VO2 during walking, body temperatures, and HR were all higher in the CP group compared with CON. VO2 was on average 40% higher, rectal temperature was 0.4 degrees C (99% CI = 0.1-0.6 degrees C) higher and HR (during the final minute of each exercise bout) was 37 beats x min(-1) (99% CI = 19-56 beats x min(-1)) higher. There were no differences between the groups in sweating rate (as inferred from body mass changes corrected for fluid intake and output) or in RPE. CONCLUSION: The subjects with CP demonstrated greater thermal strain than CON during treadmill walking where they require more metabolic energy and thus produce more metabolic heat than CON.

Facial cooling enhances exercise-induced bronchoconstriction in asthmatic children.

PURPOSE: Exercising in cold air enhances bronchial responsiveness (BR) as compared with exercising in warm air. This may be due to intrathoracic cooling or to increased vagal activity caused by facial cooling. The purpose of this study was to compare the effects on BR of cold air inhalation and of facial exposure to cold air, as well as the combined effect of both. METHODS: Fourteen children with asthma (eight girls) performed four exercise challenge tests in a climatic chamber, under one of the following conditions: 1) inhaling warm air while the face was exposed to warm air (WW, 21 degrees C, 25% relative humidity (RH)); 2) inhaling warm air while the face was exposed to cold air (WC, 0 degrees C, 80% RH); 3) inhaling cold air while the face was exposed to cold air (CC); and 4) inhaling cold air while the face was exposed to warm air (CW). The study was analyzed, using a one- and two-way ANOVA. RESULTS: Postexercise forced expiratory volume in the first second (FEV1) and maximal mid-expiratory flow (MMEF) values as percent predicted (% pred) showed significant reductions over time (P < 0.001), significant differences among the four experimental conditions (P < 0.001) and a significant condition x time interaction (FEV1:P < 0.001, MMEF:P < 0.01). FEV1 was significantly lower for CC and WC, as compared with WW and CW at 5 and 10 min postexercise. The lowest postexercise values for FEV1 occurred in the CC and WC sessions (76% predicted in both). A similar pattern was obtained for MMEF. CONCLUSION: Facial cooling combined with either cold or warm air inhalation causes the greatest EIB, as compared with the isolated challenge with cold air inhalation. We suggest that vagal mechanisms play a major role in exercise and cold-induced bronchoconstriction.

Effect of drink pattern and solar radiation on thermoregulation and fluid balance during exercise in chronically heat acclimatized children.

The purposes of this study were to examine the thermoregulatory and body fluid balance responses in chronically heat acclimatized children, i.e., indigenous to a tropical climate, during exercise in four outdoor conditions and the effects of dehydration on their thermoregulatory response. Nine children (age = 13.3 ± 1.9 yr, VO2 max = 45.5 ± 9.2 ml · kg-1 · min-1 ) cycled at 60% VO2 max each under four conditions: sun exposure voluntary drinking (SuVD), sun exposure forced drinking (SuFD), shaded voluntary drinking (ShVD), and shaded forced drinking (ShFD). Exercise sessions consisted of four 20-min exercise bouts alternating with 25-min rest periods. Globe temperature and the WBGT index were higher during SuVD and SuFD compared to ShVD and ShFD (P < 0.05). The change in rectal temperature, metabolic heat production, and heat storage did not differ among the conditions. Total water intake (% IBW) was higher during SuFD (4.1 ± 0.01) and ShFD (3.7 ± 0.1) compared to SuVD (2.1 ± 0.1) and ShVD (1.0 ± 0.1) and during SuVD compared to ShVD (P < 0.05). Sweating rate (L · hr-1 ) was higher during SuFD (0.7 ± 0.1) and ShFD (0.6 ± 0.1) compared to SuVD (0.5 ± 0.1) and ShVD (0.4 ± 0.1) (P < 0.05). Total fluid loss did not differ among conditions (SuVD = 1.7 ± 0.4; SuFD = 1.5 ± 0.4; ShVD = 2.1 ± 0.2; ShFD = 1.3 ± 0.3). Results indicate that when exercising in a tropical climate, chronically heat acclimatized children demonstrate mild voluntary dehydration and adequate heat dissipation. © 1995 Wiley-Liss, Inc.