Cardiorespiratory and Muscular Fitness in Children and Adolescents with Obesity

PURPOSE OF REVIEW

Examine the current state of literature related to the impact of obesity in children and adolescents on health-related physical fitness and the resultant cardiometabolic disease risk.

RECENT FINDINGS

Cardiorespiratory fitness of children and adolescents has declined over the past few decades which corresponds with an increase in obesity rates. Children with obesity are more likely to have low cardiorespiratory fitness which is associated with higher cardiometabolic disease risk and poorer mental health. The impact of obesity on muscular fitness in children and adolescents is more difficult to ascertain, but in general measures of physical function are lower in children with obesity which has also been associated with higher cardiometabolic disease risk. Components of health-related physical fitness are trending negatively in children and adolescents and appear to be related to the increase in prevalence of obesity. The resultant cardiometabolic disease risk has also risen which suggests a greater disease burden in the future. These disparaging findings highlight the need for aggressive interventions to improve physical fitness in children and adolescents.

Effect of maturation on parasympathetic modulation during exercise and recovery

OBJECTIVES

This study examined the effect of maturation on parasympathetic nervous system (PNS) response from rest to light- to moderate-intensity exercise and recovery from maximal exercise in pre- (n = 10; maturity offset = -3.0 ± 1.2 years; age = 10.1 ± 1.9 years), mid- (n = 9; maturity offset = -0.1 ± 0.6 years; age = 13.7 ± 1.0 years), and postpubertal (n = 10; maturity offset = 1.9 ± 0.6 years; age = 15.6 ± 1.2 years) boys and men (n = 10; age = 24.1 ± 2.0 years).

DESIGN

Participants completed seated rest, light-intensity exercise (50% HR_max), and moderate-intensity exercise (65% HR_max). Following moderate-intensity exercise, intensity was ramped to elicit maximal HR and followed by 25 min of seated recovery. Log transformed values for root mean square of successive differences (lnRMSSD), high-frequency power (lnHF) and normalized HF power (lnHFnu) assessed PNS modulation during 3 min of rest, light-intensity exercise, moderate-intensity exercise, and 3-min epochs throughout recovery.

RESULTS

During light-intensity exercise, lnRMSSD and lnHF were greater in prepubertal (lnRMSSD = 3.4 ± 0.3 ms; lnHF = 5.4 ± 0.7 ms²) compared to men (lnRMSSD = 2.8 ± 0.5 ms; lnHF = 4.0 ± 0.9 ms²). During moderate-intensity exercise, lnHF differed between prepubertal and men (2.8 ± 1.0 vs. 1.4 ± 1.0 ms²). During recovery, HRV variables were greater in prepubertal compared to postpubertal and men.

CONCLUSIONS

Prepubertal boys have reduced PNS withdrawal during light-intensity exercise and greater PNS reactivation following exercise.

Carbohydrate consumption and variable-intensity exercise responses in boys and men

PURPOSE

The effect of carbohydrate (CHO) supplementation on physiological and perceptual responses to steady-state exercise has been studied in children. However, little is known about these responses to variable-intensity exercise (VIE) and how these responses might differ from adults. This study examined the physiological and perceptual effects of CHO on VIE in boys and men.

METHODS

Eight boys (11.1 ± 0.9 years) and 11 men (23.8 ± 2.1 years) consumed CHO or a placebo (PL) beverage before and throughout VIE (three 12-min cycling bouts with intensity varying every 20-30 s between 25, 50, 75, and 125% peak work rate). Pulmonary gas exchange was assessed during the second 12-min bout. RPE was assessed twice per bout.

RESULTS

In CHO, blood glucose increased and then decreased more from pre-exercise to 12 min and was higher in this trial at the end of exercise in men versus boys. In boys, blood glucose in CHO was higher at 24 and 36 min of exercise than in PL. RER during the CHO trial was higher in both groups; the other physiological responses were unaffected by CHO. All RPE measures (whole body, legs and chest) increased over time, but were not different between groups or trials.

CONCLUSION

Blood glucose patterns during VIE were differentially affected by CHO in boys and men, but most physiological and perceptual responses to VIE were unaffected by CHO in either group. Knowledge of the underlying mechanisms of glucose regulation and effects on physical performance during this type of exercise in children is warranted.

Heart rate response and parasympathetic modulation during recovery from exercise in boys and men

The purpose of this study was to examine the influence of postexercise parasympathetic modulation, measured by heart rate variability (HRV), on heart rate recovery (HRR) in boys (n = 13, 10.1 ± 0.8 years) and men (n = 13, 23.9 ± 1.5 years) following maximal and submaximal exercise. Subjects completed 10 min of supine rest, followed by graded exercise on a cycle ergometer to maximal effort. On a separate day, subjects exercised at an intensity equivalent to ventilatory threshold. Immediately following both exercise bouts, 1-min HRR was assessed in the supine position. HRV was analyzed under controlled breathing during the final 5 min of rest and recovery in the time and frequency domains and transformed to natural log (ln) values. Boys had a greater 1-min HRR than men following maximal (58 ± 8 vs. 47 ± 11 beats·min−1) and submaximal (59 ± 8 vs. 47 ± 15 beats·min−1) exercise (p < 0.05). Following maximal exercise, boys had greater ln root mean square successive differences in R-R intervals (2.52 ± 0.95 ms), ln standard deviation of NN intervals (3.34 ± 0.57 ms), ln high-frequency power (4.32 ± 2.00 ms2), and ln low-frequency power (4.98 ± 1.17 ms2) than men (1.33 ± 0.37 ms, 2.52 ± 0.24 ms, 1.32 ± 1.06 ms2 and 2.80 ± 0.74 ms2, respectively) (p < 0.05). There were no differences in any HRV variables between groups following submaximal exercise (p > 0.05). In conclusion, it appears that greater parasympathetic modulation accounts for greater HRR following maximal exercise in boys versus men. Although submaximal HRR was greater in boys, parasympathetic responses were similar between groups.

Application of Stable Isotope Tracers in the Study of Exercise Metabolism in Children: A Primer

Exercise metabolism in children has traditionally been assessed using the respiratory exchange ratio (RER) to determine the contributions of fat and carbohydrate to the exercise energy demands. Although easily measured, RER measurements have limitations. Other methods to assess metabolism such as the obtainment of a muscle biopsy and the use of nuclear magnetic resonance spectroscopy carry ethical and feasibility concerns, respectively, which limit their use in studies involving children. Stable isotopes, used routinely in studies involving adults, can also be applied in studies involving children in an ethical and feasible manner. Two common stable isotopes used in metabolic studies involving children include carbon-13 (C) and nitrogen-15 (N). C-glucose can be used to study carbohydrate metabolism and N-glycine can be used to assess protein metabolism. This article reviews the use of C-glucose and N-glycine to study exercise metabolism in children, considers some of the associated ethical aspects, explains the general methodology involved in administering these isotopes and the resources required, and describes studies involving children utilizing these methods. Finally, suggestions for future research are provided to encourage further use of these techniques.

Evaluating the prediction of maximal heart rate in children and adolescents

In this study, we compared measured maximal heart rate (HRmax) to two different HRmax prediction equations [22 - age and 208 - 0.7(age)] in 52 children ages 7-17 years. We determined the relationship of chronological age, maturational age, and resting HR to measured HRmax and assessed seated resting HR and HRmax during a graded exercise test. Maturational age was calculated as the maturity offset in years from the estimated age at peak height velocity. Measured HRmax was 201 +/- 10 bpm, whereas predicted HRmax ranged from 199 to 208 bpm. Measured HRmax and the predicted value from the 208 - 0.7(age) prediction were similar but lower (p < .05) than the 220 - age prediction. Absolute differences between measured and predicted HRmax were 8 +/- 5 and 10 +/- 8 bpm for the 208 - 0.7 (age) and 220 - age equations, respectively, and were greater than zero (p < .05). Regression equations using resting HR and maturity offset or chronological age significantly predicted HRmax, although the R2 < .30 and the standard error of estimation (8.2-8.5) limits the accuracy. The 208 - 0.7(age) equation can closely predict mean HRmax in children, but individual variation is still apparent.

Exercise responses in boys with attention deficit/hyperactivity disorder: effects of stimulant medication

OBJECTIVE

The effect of stimulant medication on exercise responses was studied in 14 boys (10.9 +/- 1.1 years) with attention deficit/hyperactivity disorder (ADHD).

METHOD

Exercise, with and without medication, was performed at 25 W, 50 W, and 75 W, followed by a peak exercise test.

RESULT

Submaximal heart rate (HR) was significantly higher by ~8 to 13 b.min(-1) across the three intensities during the medication trial, but oxygen uptake (VO(2)), respiratory exchange ratio (RER), and perceived exertion were similar (p > .05). At peak exercise, VO(2), HR, and work rate were attenuated (p < or = .05) in the absence of medication but not RER or perceived exertion. The decreased peak exercise responses were apparent in 6 of 13 participants.

CONCLUSION

Stimulant medication raises submaximal HR but does not affect other cardiorespiratory measures or perceived exertion. Without medication physiological responses at peak exercise are attenuated in some but not all boys with ADHD.

Preexercise Carbohydrate Consumption and Repeated Anaerobic Performance in Pre- and Early-Pubertal Boys

This study examined the effect of pre exercise carbohydrate (CHO) feeding on performance on a Wingate anaerobic test (WAnT) in 11 boys (10.2 ± 1.3 y old). Four WAnTs with 2 min recovery were performed 30 min after consuming a CHO (1 g CHO/kg) or placebo drink. Peak power (PP) and mean power (MP) were similar between trials. PP ranged from 241.1 ± 82.2 to 223.1 ± 57.9 W with carbohydrate and from 238.2 ± 76.1 to 223.4 ± 52.3 W with placebo. MP ranged from 176.3 ± 58.4 to 151.1 ± 37.5 W with carbohydrate versus 178.0 ± 45.8 to 159.1 ± 32.7 W with placebo. Pre exercise glucose was significantly higher in CHO versus placebo (7.0 ± 1.0 vs. 5.5 ± 0.5 mmol/L), but post exercise values were not different. Blood lactate was similar between trials but increased over time. This study found that the ingestion of a CHO solution before exercise did not influence power output during repeated performances of the WAnT.

Perceived exertion : influence of age and cognitive development

Because little is known about the effects of aging on perceived exertion, the aim of this article is to review the key findings from the published literature concerning rating of perceived exertion (RPE) in relation to the developmental level of a subject. The use of RPE in the exercise setting has included both an estimation paradigm, which is the quantification of the effort sense at a given level of exercise, and a production paradigm, which involves producing a given physiological effort based on an RPE value. The results of the review show that the cognitive developmental level of children aged 0-3 years does not allow them to rate their perceived exertion during a handgrip task. From 4 to 7 years of age, there is a critical period where children are able to progressively rate at first their peripheral sensory cues during handgrip tests, and then their cardiorespiratory cues during outdoor running in an accurate manner. Between 8 and 12 years of age, children are able to estimate and produce 2-4 cycling intensities guided by their effort sense and distinguish sensory cues from different parts of their body. However, most of the studies report that the exercise mode and the rating scale used could influence their perceptual responsiveness. During adolescence, it seems that the RPE-heart rate (HR) relationship is less pronounced than in adults. Similar to observations made in younger children, RPE values are influenced by the exercise mode, test protocol and rating scale. Limited research has examined the ability of adolescents to produce a given exercise intensity based on perceived exertion. Little else is known about RPE in this age group. In healthy middle-aged and elderly individuals, age-related differences in perceptual responsiveness may not be present as long as variations in cardiorespiratory fitness are taken into account. For this reason, RPE could be associated with HR as a useful tool for monitoring and prescribing exercise. In physically deconditioned elderly persons, a rehabilitation training programme may increase the subject's ability to detect muscular sensations and the ability to utilise these sensory cues in the perception of effort. RPE appears to be a cognitive function that involves a long and progressive developmental process from 4 years of age to adulthood. In healthy middle-aged and elderly individuals, RPE is not impaired by aging and can be associated with HR as a useful tool to control exercise intensity. While much is known about RPE responses in 8- to 12-year-old children, more research is needed to fully understand the influence of cognitive development on perceived exertion in children, adolescents and elderly individuals.

Aerobic Exercise Adaptations in Trained Adolescent Runners Following a Season of Cross-country Training

Adaptations in aerobic exercise responses as well as the relationship between aerobic exercise responses and running performance were examined in a group of previously trained adolescent runners (n = 9; 15.9 +/- 1.0 years) over the course of a competitive cross-country season. Running economy (RE), submaximal blood lactate concentration [BLa] and VO2max were assessed before and immediately after the season. Five-km race time improved (P < 0.05) from 18.68 +/- 1.10 min at the beginning of the season to 18.16 +/- 1.11 min at the end of the season. Significant increases were observed in peak VO2 (61.6 +/- 3.5 to 65.3 +/- 2.9 mL x kg(-1) x min(-1)) and graded exercise test time (11.32 +/- 1.56 to 12.22 +/- 0.79 min). There was a tendency for RE (P = 0.051) to worsen slightly and for [BLa] (P = 0. 057) to decline as a result of training. At the beginning of the season submaximal [BLa] at 14 km x hr(-1) (r = 0.86) and graded exercise test time (r = -0.87) were significantly related to 5-km time. At the end of the season, RE (r = 0.78) and [BLa] (r = 0.77) at 14 km x hr(-1) and graded exercise test time (r = -0.69) were significantly related to race time. In this well-trained group of runners, further training during the cross-country season increased peak VO2 and improved race time. Submaximal [BLa] and graded exercise test time appear to be the most robust predictors of performance, while RE became a significant predictor of race time at the end of the season.

The influence of biological maturation on fat and carbohydrate metabolism during exercise in males

This study examined substrate use during exercise in early-pubertal (EP), mid-pubertal (MP), late-pubertal (LP), and young-adult (YA) males. Fuel use was calculated using the RER and VO2 response during cycling exercise at 30 to 70% of VO2speak. Significant group by intensity interactions were found for lactate, RER, percent CHO, and fat use, in addition to fat and CHO oxidation rates, which suggest a maturation effect on substrate use during exercise. While significance was not achieved at all intensities, post hoc analyses revealed greater fat use, lower CHO use, and lower lactate concentrations in EP and MP compared to LP or YA. No differences were noted between EP and MP or LP and YA at any intensity, suggesting the development of an adult-like metabolic profile occurs between mid- to late-puberty and is complete by the end of puberty.

Running performance in middle-school runners

AIM

This study examined the relationship of 3-km run time to indices of aerobic and anaerobic ability in 9 male runners (13.4+/-0.6 years, mean+/-SD).

METHODS

Anthropometric measurements were made, and an exercise test to determine running economy at 187 m x min(-1) and (.-)VO(2max) were assessed on a treadmill. On a separate day, 2 55-m sprints followed by a 3-km run were performed on a 200-m indoor track. Capillary blood samples were obtained from a finger tip immediately after the run to determine blood lactate level. Fractional utilization (%(.-)VO(2max) used during the 3-km run) was calculated. Correlations were used to examine the relationship between run time and the physiological measurements.

RESULTS

Mean values for (.-)VO(2), HR and RER at maximal exercise were 61.7+/-4.4 ml x kg(-1)xmin(-1), 198.9+/-6.7 b x min(-1), and 1.16+/-0.04, respectively. The average time to run 3 km was 13.27+/-0.97 min (90.1+/-7.2% of (.-)VO(2max)). Post-run blood lactate level was 8.3+/-3.2 mmol x L(-1) and was significantly related (r=-0.73, p=0.02) to 3-km time. Fractional utilization tended to be related (r=-0.56, p=0.12) to time.

CONCLUSIONS

In this age group the ability to run at a high percentage of (.-)VO(2max) and tolerate a high blood lactate appear to be important determinants of running performance in young male runners.

Heart Rate Recovery from Submaximal Exercise in Boys and Girls

PURPOSE

To examine the changes in heart rate (HR) after two different submaximal exercise bouts in boys and girls.

METHODS

Eleven boys (10.5 +/- 1.0 yr) and 10 girls (10.8 +/- 0.7 yr) participated in this study. Each child completed an initial graded exercise test to determine peak VO2. On subsequent and separate days, a 5-min submaximal exercise bout on a cycle ergometer was performed. One bout was conducted at 70 W, and the other bout corresponded to an intensity of 85-90% of peak VO2. VO2 and HR were measured during and after (1 min and 3 min). HR recovery responses from each submaximal exercise bout were analyzed using a group by time ANOVA, and Pearson-product correlations were determined between resting HR, peak VO2, and postexercise HR responses.

RESULTS

HR in the boys was lower at the end of exercise and the first minute of recovery versus girls but not at the 3rd min of recovery. There were no differences in HR recovery after the relative exercise bout. Resting HR was significantly correlated with postexercise HR from both bouts (r = 0.52-0.69), whereas peak VO2 did not correlate to postexercise HR. ANCOVA using resting HR as the covariate eliminated the gender different noted with the recovery from the 70-W bout.

CONCLUSIONS

In summary, postexercise HR responses differed between boys and girls when submaximal exercise was performed at an absolute work rate. When exercise was performed at a relative intensity, HR recovery responses were similar between the two groups. Resting HR appears to account for variations in postexercise HR better than peak VO2.

The influence of exercise test protocol on perceived exertion at submaximal exercise intensities in children

This study examined ratings of perceived exertion (RPE) using Borg's 6-20 scale at 50 W, 80 W, and ventilatory threshold (VT) in 10-year-old children (n = 15) during two different graded exercise tests. Power output was increased by 10 W.min(-1) in one protocol and by 30 W.3 min(-1) in the other. The cardiorespiratory responses at VT and peak exercise were similar between protocols. At 50 W and 80 W the cardiorespiratory responses were generally lower (P < 0.05) in the 10W trial. However, RPE was 11.5 +/- 2.9 and 12.1 +/- 3.2 at 50 W and 15.1 +/- 2.7 and 15.3 +/- 2.8 at 80 W in the 10-W and 30-W trials, respectively (P > 0.05). The RPE at VT was 13.9 +/- 2.4 in the 10-W trial and 12.4 +/- 2.4 in the 30-W trial (P < 0.05). In that variations in submaximal RPE did not coincide with variations in central mediators of exertion, locals cues of exertion may have provided the dominate sensory signal.

Attainment of maximal exercise criteria in boys and men

BACKGROUND

This study tested the hypothesis that the occurrence of a VO(2) plateau at maximal exercise would be greater in men versus boys. Secondary indicators of maximal effort also were examined.

METHODS

Sixteen boys (10.7+/-0.6 yrs) and 21 men (22.5+/-2.0 yrs) performed a graded exercise test on a treadmill at a constant speed of 8.04 km x hr(-1) with 2.5% increments in elevation. The men also performed a second test at 11.26 km x hr(-1) with similar increases in slope.

RESULTS

At 8.04 km x hr(-1) , VO(2) max was 52.3+/-6.0 and 52.5+/-5.1 ml x kg(-1) x min(-1) in boys and men, respectively (p>0.05). In the men, VO(2) max (53.3+/-5.4 ml x kg(-1) x min(-1) ) was higher (p<0.05) in the faster protocol. The percentage of men achieving the criterion was nearly double the percentage of boys (23.8 vs 12.5%), although the difference was not significant. Age-specific criteria heart rate (HR) and respiratory exchange ratio (RER) were achieved in a similar manner; however, more men (100%) than boys (86.7%) achieved an age-specific blood lactate (BLa) criterion (p<0.05). Plateau achievement increased to 33.0% in the 11.26 km x hr(-1) protocol, but was not significantly different from 8.04 km x hr(-1). HR, RER and BLa criteria achievement were comparable.

CONCLUSIONS

Maturation may influence the achievement of a plateau and BLa criteria, but not age-specific criteria for RER or HR.

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.

Differentiated ratings of perceived exertion at ventilatory threshold in children and adults

The purpose of this study was to examine overall, leg and chest ratings of perceived exertion (RPE) at ventilatory threshold (Thvent) in 16 children (mean age 10.9 years) and 17 adults (mean age 24.3 years). Thvent and maximum oxygen consumption (VO2max) were measured during a graded exercise test on a cycle ergometer. Overall, leg and chest RPE were obtained at the end of each exercise stage. VO2max was 49.9 (8.5) and 47.1 (6.1) ml x kg(-1) x min(-1) [mean (SD)] in the adults and children, respectively (P > 0.05). Relative to VO2max, Thvent was 61.7 (5.3)% in the adults and 64.7 (5.2)% in the children (P > 0.05). Overall, leg, and chest RPE values at Thvent for the adults were 11.5 (2.6), 11.9 (2.5), and 10.5 (2.5), while for the children these values were 13.6 (2.2), 14.1 (2.2), and 12.6 (2.3), respectively. All RPE values were higher for the children (P < 0.05). These results suggest that children are able to discriminate levels of exertion in different parts of their body during graded exercise. Furthermore, children rate an intensity corresponding to Thvent to require a greater overall, leg and chest effort than adults exercising at a similar intensity. This indicates that children experience more pronounced cardiorespiratory and muscular sensations during this type of exercise.

Respiratory sinus arrhythmia during exercise in aerobically trained and untrained men

Respiratory sinus arrhythmia (RSA) was examined in aerobically trained (AT) and untrained (NT) college-aged males during 12 periods consisting of a 3-min sitting baseline, six common 3-min absolute exercise stages, and five 3-min recovery stages that followed voluntary exhaustion to determine the relationship of work and training status to parasympathetic influence upon the heart. RSA systematically decreased during absolute exercise, was observed at heart rates (HR) above 100 beats x min(-1), and progressively increased during recovery. Additionally, independent of work stages, comparative regression analyses were conducted for both the exercise and recovery phases, separately, in which HR was regressed on RSA, as well as RSA on % VO2max, to contrast the obtained relationships for the AT and NT. No differences were revealed as a function of endurance training status as the slopes and intercepts obtained for the two groups from each of these analyses were similar. The within-subject correlations between RSA and % VO2max, calculated for each of the individuals across all 12 periods, were consistently negative. Between-subjects correlations of RSA with RR and tidal volume were predominantly nonsignificant, indicating that RSA, as measured here, is independent of individual differences in ventilatory activity and, as such, can be compared between groups during exercise. The findings demonstrate that RSA is detectable during both exercise and recovery, even at HR beyond 100 beats x min(-1), and reveals a similar relationship to HR and metabolic state in both aerobically trained and untrained populations.

Blood lactate and perceived exertion relative to ventilatory threshold: boys versus men

The purpose of this study was to examine blood lactate (BLa) levels and ratings of perceived exertion (RPE) in nine boys (10.5 +/- 0.7 yr) and nine men (25.3 +/- 2.0 yr) during exercise relative to ventilatory threshold (VT). VT and VO2max were determined during a graded exercise test on a cycle ergometer. On three additional days each subject exercised for 10 min at either 80, 100, or 120% of the VO2 at VT. Capillary BLa levels and RPE were assessed at minutes 5 and 10 of each trial. VO2max averaged 47.7 +/- 5.4 and 50.2 +/- 6.2 mL x g(-1) x min(-1) in the boys and men, respectively (P > 0.05). VT expressed as %VO2max was 67.2 +/- 3.5% in the boys and 67.3 +/- 4.9% in the men (P > 0.05). BLa levels ranged from 2.0 +/- 0.7 to 4.7 +/- 0.9 mmol x L(-1) in the boys and from 2.6 +/- 0.5 to 8.2 +/- 2.1 mmol x L(-1) in the men across the three intensities. Corresponding RPE values ranged from 11.2 +/- 1.8 to 16.2 +/- 2.2 in the boys and from 10.2 +/- 1.2 to 15.8 +/- 1.7 in the men. A group x time x intensity interaction (P < 0.05) indicated that BLa in the men increased more so across time and intensity. There were no significant group difference or interactions involving RPE during exercise. Setting exercise intensity relative to VT did not abolish child-adult differences with respect to submaximal BLa levels. Despite maintaining lower BLa levels, RPE values were similar between boys and men.

Physiological correlates of 3-kilometer running performance in male children

The purpose of this study was to examine the influence of body fatness, aerobic and anaerobic ability on 3-km running performance in 19 physically active boys (mean +/- SD, age = 10.4 +/- 0.9 yrs). The sum of six skinfolds, VO2 at 8.04 and 9.65 km.hr-1, and VO2max were measured in the laboratory. Run time for 3 km was assessed twice on separate days on a 200-meter indoor track. Prior to each run, every child performed two 55-meter sprints and two vertical jumps. Mean +/- SD values for the sum of skinfolds, %VO2max at each running speed, VO2max and 3-km run time were: 33.9 +/- 14.9 mm; 70.6 +/- 6.6% and 81.0 +/- 7.9%; 54.6 +/- 5.0 ml.kg-1.min-1; 16.41 +/- 2.58 min, respectively. Significant (p < 0.05) correlations were observed between the following variables and run time: sum of skinfolds (r = 0.72); vertical jump (r = 0.67); sprint time (r = 0.59); VO2max (r = 0.61); and, %VO2max at each treadmill speed (r = 0.79 and r = 0.75, respectively). Stepwise multiple regression analysis indicated that the combination of the %VO2max at 8.04 km.hr-1 and vertical jump accounted for 83% (adjusted R2) of the variance in running time (SEE = 1.06 min, p < 0.05). This study suggests that 3-km run time in physically active boys is influenced by aerobic and anaerobic indices as well as body fatness, supporting the notion that children, compared to adults, are not metabolic specialists.

Ratings of perceived exertion at maximal exercise in children performing different graded exercise test

The purpose of this study was to examine the rating of perceived exertion (RPE) at maximal exercise in children performing three different graded exercise tests on a treadmill. Eighteen children with a mean +/- SD age of 10.3 +/- 1.4 years volunteered for this study. Each subject performed three different graded exercise test protocols on a treadmill. The protocols consisted of walking only, running only, and combination walk/run. Mean VO2max (ml.kg-1.min-1) during the walking trial (47.3 +/- 5.0) was significantly (p < 0.05) less than during the running (52.1 +/- 4.9) and combination trials (51.9 +/- 5.1). Mean HRmax (bpm) was significantly (p < 0.05) lower during the walking test (195.2 +/- 7.9) compared to the running (202.2 +/- 7.4) and combination tests (202.3 +/- 6.6). Mean RPE at maximal exercise was 18.1 +/- 2.1 in the walking trial, 16.8 +/- 3.0 in the running trial, and 16.8 +/- 2.6 in the combination trial, and was significantly (p < 0.05) greater in the walking trial compared to the other two testing protocols. These data indicate that although VO2max during a walking test is lower, effort sensation is higher compared to protocols that use running as the mode of exercise. The factors involved with RPE selection in this age-group remain to be established.

The effect of exercise on serum and salivary cortisol in male children

The purpose of this study was to examine serum and salivary cortisol responses to cycling exercise in male children, 10.6 +/- 0.2 yr (mean +/- SE). Each child performed a graded exercise test on a cycle ergometer to determine VO2max. On a separate day, a 30-min bout of exercise at 70% of VO2max was performed. Blood, obtained from a venous catheter, and saliva samples were collected at rest, at 15 and 30 min of exercise, and 15 min post-exercise. The mean serum cortisol level at 15 min (7.94 +/- 1.43 micrograms.dl-1) and 30 min (8.72 +/- 1.77 micrograms.dl-1) of exercise and at 15 min post-exercise (8.21 +/- 1.59 micrograms.dl-1) were significantly greater than rest (5.54 +/- 0.86 micrograms.dl-1). The increase in salivary cortisol levels over time approached (P = 0.08), but did not reach significance. However, effect size analyses indicated that the increase in salivary cortisol at 30 min of exercise (0.64) and 15 min post-exercise (0.62) was similar to the change in serum cortisol at these same two time points (0.72 and 0.66, respectively). Serum and salivary cortisol were correlated (P < 0.05) at 15 min of exercise (r = 0.77), 30 min of exercise (r = 0.90), and 15 min post-exercise (r = 0.84), but not at rest (r = 0.46). In conclusion, 30 min of submaximal exercise at 70% of VO2max significantly increased serum cortisol level; and salivary and serum cortisol are correlated during and after exercise.

Cardiovascular adaptations in 8- to 12-year-old boys following a 14-week running program

This study examined the effects of a 14-week running program on VO2max, as well as cardiac output (Q) and arterial-venous O2 difference (a-vO2 dif) at submaximal intensities corresponding to 50 and 75% of VO2max. Thirteen boys (mean age 10.6 +/- 1.2 yrs) served as experimental subjects while 13 other boys of similar age (mean age 10.2 +/- 1.2 yrs) served as controls. Mean VO2max in the runners increased 13%, from 44.2 +/- 7.0 to 49.9 +/- 6.3 ml.kg-1.min-1. Posttraining VO2 during submaximal and maximal exercise was significantly (p < 0.05) greater in the runners than in the controls. Q and SV exhibited an increase of 10% at each intensity, but posttraining differences between groups were not significant (p > 0.05). A-vO2 dif increased by 8% at 50% of VO2max and by 6% at 75% of VO2max, and was significantly greater in the runners following training. These results indicate that increases in submaximal relative VO2 in children are mediated by increases in a-vO2 dif and Q.

Evaluation of a shallow water running test for the estimation of peak aerobic power

The purpose of this investigation was to assess the validity of a 500-yard shallow water run test to determine peak aerobic power (VO2peak) and to compare it with the commonly used 1.5-mile run test. Subjects included 15 men and 28 women who completed two trials each of a 500-yard shallow water run test and a 1.5-mile run and then completed a graded exercise test on a treadmill to determine VO2peak. Correlation coefficients with measured VO2peak were -0.89 and -0.80 for the 1.5-mile and 500-yard water runs, respectively. Multiple regression analyses revealed that prediction of VO2peak from 1.5-mile run time was significantly improved by including the 1.5-mile run peak HR (R2 = 0.82, SEE = 3.52 ml.kg-1.min-1). Similarly, for the 500-yard water run test, percent body fat and height were significant additional predictors of VO2peak (R2 = 0.86, SEE = 3.19 ml.kg-1.min-1). We conclude that the 500-yard shallow water run test, especially when used with the descriptive measures of percent body fat and height, can provide a reasonable estimate of an individuals' cardiorespiratory fitness classification. However, caution is advised when administering these tests in older populations or in those with multiple coronary risk factors.

Reliability of the rating of perceived exertion at ventilatory threshold in children

The purpose of this study was to examine the reliability of the rating of perceived exertion (RPE), using the Borg 6-20 scale, at ventilatory threshold (VT) in children. Thirty children (19 male, 11 female) with a mean +/- SD age of 10.4 +/- 1.1 yrs performed two graded exercise tests for the assessment of VT and VO2max. RPE was recorded throughout each exercise test. There were no significant (p > 0.05) differences between the mean VO2max (50.9 +/- 6.0 vs 51.0 +/- 5.7 ml.kg-1.min-1; r = 0.95) or the mean VO2 at VT (36.2 +/- 4.4 vs 36.7 +/- 4.5 ml.kg-1.min-1; r = 0.87) between trials. The mean RPE at VT during trial 1 (12.4 +/- 2.7) was significantly higher than during trial 2 (11.4 +/- 3.3; p < 0.05). The test-retest reliability correlation for the RPE at VT was r = 0.78. The lower RPE in the second trial may have been due to a greater comfort and familiarity with the testing procedures. The reliability analysis indicates that the RPE at VT within a given child is fairly consistent from trial to trial. However, large inter-individual variability in the RPE at VT (range = 6 to 19) was noted and was not related to variations in the onset of VT. This raises some concern over the use of a given RPE value or range of RPE values in the regulation of exercise intensity for this age group. The test-retest reliability of VT and VO2max in this age group is similar to previous reports.

The effect of psychological strategies upon cardiorespiratory and muscular activity during treadmill running

Twelve aerobically trained males (age 22 +/- 1.3 yr, range 18-31) were studied to determine the effects of VE and EMG feedback upon cardiorespiratory and muscular activity during one segment of a continuous 36-min bout of treadmill running just below ventilatory threshold (VT). Ventilatory, metabolic, cardiovascular, RPE, and EMG variables recorded during a 12-min feedback segment were compared with those observed during 12-min attentional distraction and control conditions. The three treatments were counterbalanced. Mean VO2 (2987 ml.min-1) remained constant across the three periods as did VCO2 (3102 ml.min-1), HR (168 bpm), RQ (0.95), and O2 pulse (18.5 ml.beat-1). However, VE was significantly reduced during feedback (Fb) as compared with both the distraction (D) and control (C) conditions (mean +/- SE: 83.2 +/- 3.6 vs 86.6 +/- 4.2 and 87.8 +/- 4.2 l.min-1, respectively). This effect was marked by a reduction in respiratory rate (RR) (41.1 +/- 2.1 vs 44.5 +/- 1.9 and 46.8 +/- 1.9 breaths.min-1 for Fb, D, and C, respectively) and an increase in tidal volume (TV) (2115 +/- 144 vs 1904 +/- 110 and 2020 +/- 102 ml.breath-1 for Fb, D, and C, respectively). These changes resulted in significant reductions in VE/VO2 (26.5 +/- 0.7 vs 28.9 +/- 1.0 and 28.3 +/- 0.9 ratio magnitudes), VE/VO2 (28.1 +/- 0.8 vs 30.2 +/- 1.0 and 29.7 +/- 1.0 ratio magnitudes), and PETO2 (105.5 +/- 1.0 vs 108.4 +/- 1.1 and 107.6 +/- 1.2 mm Hg) during Fb as compared with D and C, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of exercise on coronary heart disease risk factors in children

Coronary heart disease (CHD) is now recognised as a paediatric problem despite the fact that clinical symptoms of this disease do not become apparent until much later in life. Epidemiological studies of risk factors in children have now been conducted. These studies suggest that the risk factors for cardiovascular disease in adults, which include a family history of heart disease, elevated blood lipids (serum cholesterol and triglycerides), obesity, hypertension, smoking, diabetes mellitus and inadequate physical activity, can be identified in children. Several investigators have reported the existence of one or more risk factors in more than 50% of the children they have examined. It is now clear that we can detect most children who are potentially at risk for CHD. The notion of 'tracking' some of the most common CHD risk factors in children has been used in several studies. Results from this type of research indicate that children who are at the extreme end of the distribution and have high levels of blood pressure, adverse lipid levels and are obese will continue to exhibit these coronary risk factors as they grow. The research completed at present does not answer the question of whether children who exhibit a coronary-prone risk factor profile will exhibit this same profile at an age when one is most likely to develop the clinical manifestations of CHD. It does make sense, however, to identify those children who may be at risk for developing premature CHD and to initiate safe interventions such as behaviour modification, changes in diet and increases in physical activity. These have all been shown to alter risk factors which are associated with increased relative risk of CHD in adults. It should be noted that in adults regular aerobic exercise often may alter all risk factors for CHD, including hypertension and diabetes. Whether regular aerobic exercise will induce similar changes in children is not fully understood.

Ventilatory threshold and VO2max changes in children following endurance training

There are conflicting data with regard to the effect of endurance training in children. On the basis of this information, the effects of 8 wk of run training on ventilatory threshold (VT) and VO2max of eight male children were investigated. Children ranged in age from 10 to 14 yr, with a mean age of 12.4 yr. All subjects were previously untrained. Training consisted of running 4 d.wk-1 for a period of 8 wk. Continuous running was performed 2 d.wk-1 for 10-30 min at 70-80% of VO2max. Interval running was performed the remaining 2 d.wk-1. Repeated intervals of 100-800 m at 90-100% of VO2max were used in this phase of the training. The total distance run for this type of training was 1.5-2.5 km. Incremental treadmill testing prior to and after the training period indicated a 19.4% increase in VT from 30.5 to 36.4 ml.kg-1.min-1 (P less than 0.05). When VT was expressed as a percentage of VO2max, there was a significant (P less than 0.05) increase from 66.6% to 73.8%. VO2max increased 7.5% from 45.9 to 49.4 ml.kg-2.min-2 (P less than 0.05). None of these changes was noted in eight age- and size-matched children who served as control subjects. The results of this study indicate that 8 wk of endurance running training which is of sufficient frequency, intensity, and duration can significantly improve VT and aerobic capacity in male children.