Anthony D. Mahon

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.

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 [220 — 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.

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

Abstract 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 (V˙O2max) 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. V˙O2max was 49.9 (8.5) and 47.1 (6.1) ml · kg−1· min−1 [mean (SD)] in the adults and children, respectively (P > 0.05). Relative to V˙O2max, 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.

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.

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.

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.

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)

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.

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 (VO2), respiratory exchange ratio (RER), and perceived exertion were similar (p > .05). At peak exercise, VO2, HR, and work rate were attenuated (p ≤ .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. (J. of Att. Dis. 2008; 12(2) 170-176)

The relationship between ventilatory and lactate thresholds in boys and men.

The relationship between ventilatory (VT) and lactate threshold (LT) in 8 boys (11.1 ± 0.7 yrs) and 9 men (24.0 ± 3.3 yrs) with similar peak VO2 levels was assessed. Percent peak VO2 at VT and LT were higher (P < 0.05) in the boys (67.9 ± 2.6% and 63.9 ± 5.0%, respectively) compared with men (59.0 ± 3.2% and 54.8 ± 2.7%, respectively). VO2 (mL·kg−1·min−1) at VT was higher (P < 0.05) and at LT tended to be higher in boys. Correlations between VT and LT were r = 0.95 for VO2 (mL·kg−1·min−1) and r = 0.82 for % peak VO2 (P < 0.05) in boys and r = 0.87 (P < 0.05) and r = 0.60 (P > 0.05), respectively, in men. The mechanisms mediating VT and LT in children are not established fully and warrant further study.