Anthony D. Mahon
Anthony D. Mahon and Paul Vaccaro
Whether the point of deflection from linearity of heart rate (HRD) coincides with ventilatory threshold (VT) has not been extensively examined in children. The purpose of this study was to assess the relationship between the VO2 measured at VT and the VO2 measured at HRD. Twenty-two boys with a mean age of 10.7 years (±1.0) performed a graded exercise test to determine VT, HRD, and VO2max. There was no significant difference between mean VO2 (ml/kg/min) at VT and at HRD (33.5±3.5 vs. 34.1±4.4; p>0.05). Linear regression analysis revealed a correlation of r = 0.76 (p<0.01) between the VO2 measured at VT and the VO2 measured at HRD. These results indicate that HRD may be an accurate predictor of VT in most but not all children, and caution should be used when interpreting the significance of HRD.
Gregory B. Dwyer and Anthony D. Mahon
Little is known about the responses to graded exercise in athletes with cerebral palsy (CP). This study compared the ventilatory threshold (VT) and peak VO2 among athletes with CP during treadmill and cycle ergometry exercise. Six (4 men, 2 women) track athletes with CP volunteered to participate in the study. Graded exercise tests on a treadmill and cycle ergometer were performed on separate days to assess VT and peak VO2. Paired t tests were used to compare the two exercise modes. The VT, expressed as a percentage of peak VO2, was significantly higher on the cycle ergometer than on the treadmill. The absolute VO2 at the VT was similar during both testing modes, and peak VO2 was significantly higher on the treadmill than on the cycle ergometer. Similar to responses seen in able-bodied individuals, the VO2 at VT was similar during both modes of exercise, while the peak VO2 was 10% lower on the cycle than on the treadmill. Cycle ergometer peak VO2 in these athletes was higher than previous reports of individuals with CP for the cycle ergometer.
Anthony D. Mahon and Melinda L. Marsh
This study examined the occurrence of a V̇O2 plateau at maximal exercise, and whether ventilatory threshold (VT) differend between children who do and children who do not achieve a V̇O2 plateau at maximal exercise. After performing a graded exercise test on a treadmill to assess VT and V̇O2max, the children were divided into a plateau group (n = 14) and a nonplateau group (n = 12). There were no differences with respect to the V̇O2 at VT (36.7 ± 3.4 vs. 37.9 ± 5.4 ml · kg−1 · min−1) and V̇O2max (51.6 ± 5.4 vs. 54.6 ± 3.6 ml · kg−1 · min−1) in the plateau and nonpiateau groups, respectively. The mean HR, RER, and RPE at maximal exercise were also similar between groups. These results indicate that VT and V̇O2max are similar in children regardless of the occurrence of a V̇O2 plateau at maximal exercise. Furthermore, a plateau in V̇O2 during a maximal exercise test is not mandatory for assessment of V̇O2max in this age group.
Anthony D. Mahon and Christopher C. Cheatham
Ventilatory threshold (VT) is an important index of aerobic exercise function. The non-invasive nature of assessing VT and the fact that VT can be determined without obtaining a maximal exertion makes it broadly appealing to study in both healthy and diseased populations. Much of the understanding of the physiological and biochemical events underlying the occurrence and significance of VT is based on research involving adults. Several conclusions can be made from the studies which have examined VT in children. First, VT can be determined in a reliable manner. Second, heart rate deflection has been used as an alternative method to estimate VT and, based on limited information, appears to have reasonable accuracy. Third, although there is some evidence suggesting that VT (relative to maximal oxygen uptake [V̇O2max]) declines with maturation, the evidence is not overwhelming and it is based primarily on cross-sectional comparisons. Fourth, endurance training will increase VT in children to a greater extent than the increase in V̇O2max. Lastly, the physiological significance of VT and the metabolic consequences when exercise intensities exceeds VT are not well understood in children and are fruitful areas of research.
Anthony D. Mahon and Brian W. Timmons
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 (13C) and nitrogen-15 (15N). 13C-glucose can be used to study carbohydrate metabolism and 15N-glycine can be used to assess protein metabolism. This article reviews the use of 13C-glucose and 15N-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.
Andrea D. Marjerrison, Jonah D. Lee and Anthony D. Mahon
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.
Brooke R. Stephens, Andrew S. Cole and Anthony D. Mahon
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 VO2peak. 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.
Justin P. Guilkey, Brandon Dykstra, Jennifer Erichsen and Anthony D. Mahon
This study examined heart rate recovery (HRR) and heart rate variability (HRV) following maximal exercise in lean (<85th percentile age- and sex-BMI percentile; n = 11 (♂=5; ♀=6); 10.1 ± 0.7 years) and overweight (≥85th age- and sex-BMI percentile; n = 11 (♂=5; ♀=6); 10.5 ± 1.2 years) children.
Participants completed a 10-min rest, followed by a graded exercise test to maximal effort. HRV, in the time and frequency domains, was assessed during rest and recovery. Also during recovery, one-minute HRR and the time constant of a monoexponential line of best fit (HRRt) were determined.
There were no significant differences in one-minute HRR and HRRt between the lean (56 ± 7 beats∙min-1 and 160.4 ± 80.1 s, respectively) and overweight (51 ± 16 beats∙min-1 and 141.1 ± 58.1 s, respectively) groups. There also were no significant interactions between groups from rest to recovery for any HRV variables. Root mean square of successive differences (RMSSD) and high frequency power (HF) during recovery was 2.05 ± 0.49 ms and 3.30 ± 1.02 ms2 in the lean children, respectively. In the overweight children, RMSSD and HF were 1.88 ± 0.65 ms and 2.94 ± 1.27 ms2, respectively.
HRR and HRV findings suggest there are no differences in autonomic function during recovery from maximal exercise in lean and obese 8- to 12-year old children.
Anthony D. Mahon, Kira Q. Stolen and Julie A. Gay
This study examined overall, leg, and chest ratings of perceived exertion (RPE) in 16 children (10.7 ± 0.8 yr) and 16 adults (24.2 ± 1.8 yr) during 16 min of exercise performed at an intensity equal to ventilatory threshold (~64% of V̇O2max for the children and 61% of V̇O2max for the adults). Physiological and perceptual responses were measured at 8 and 16 min. RPE in the children ranged from 11.6 ± 2.3 (chest) to 12.6 ± 2.6 (leg) at 8 min, and from 13.3 ± 2.8 (chest) to 15.1 ± 2.9 (leg) at 16 min. In adults, RPE ranged from 10.9 ± 1.9 (chest) to 12.0 ± 1.8 (leg) at 8 min, and from 11.8 ± 2.1 (chest) to 13.3 ± 1.6 (leg) at 16 min. Between groups, RPE tended to be higher and increased more over time in the children compared to the adults (P < .08). RPE at 8 min was less than RPE at 16 min, and overall and leg RPE were greater than chest RPE. Children were able to discriminate sensory information arising from different physiological variables; however, the specific physiological cues underlying the perception of effort remains uncertain in this age group.