Heart rate variability assessment of overreaching in active and sedentary females.

Resting heart rate variability (HRV) profile was compared between sedentary and active females before, during, and after a 2-week overreaching protocol. Twenty currently active and 20 sedentary females were subdivided within their groups to either an experimental or control group. The active and sedentary experimental groups completed an overreaching protocol; endurance exercise, 40 minutes per session at an intensity of 70-90 % heart rate reserve, 7 d.wk(-1). The active experimental group showed an increase in low frequency power and a decrease in high frequency power over the intervention weeks (LF : HF ratio; Baseline = 2.0 [1.1], End week 1 = 2.4 [1.9], End week 2 = 3.2 [1.9], Recovery = 1.9 [1.0] mean [SD]) although this was not statistically significant (p > or = 0.05) for within group effects. The sedentary experimental group however, showed a significant (p < or = 0.05) increase in low frequency power and a decrease in high frequency power during the overreaching phase suggesting a move towards a predominance of resting sympathetic cardiac modulation (LF:HF ratio; Baseline = 1.6[1.1], End week 1 = 3.4 [1.6], End week 2 = 4.4 [3.0], Recovery = 1.8 [0.9]). These findings arose in the absence of any significant change in resting heart rate. Time domain analysis however failed to provide similar findings in either experimental group. Neither control group showed any significant changes. These data suggest a more marked change in sympathovagal balance in sedentary people when exposed to an overreaching protocol than in active individuals.

Reliability of heart rate variability measures at rest and during light exercise in children.

OBJECTIVES: To investigate the reliability of heart rate variability (HRV) measures at rest and during light exercise in children. METHODS: Short term (five minute) HRV was assessed in 12 children (11-12 years of age). HRV measures were collected at rest with the children supine, breathing at 12 breaths/min, and during exercise on a cycle ergometer while exercising at 25% of peak oxygen uptake. Both resting and exercise data were collected twice from each child. RESULTS: Intraclass correlation coefficients were low to moderate for most measures with wide confidence intervals for each variable in both resting and exercise conditions. Random variation (typical error) within repeated measurements ranged from 31% to 187%. CONCLUSIONS: These preliminary findings suggest that HRV measures are unreliable at rest and during light exercise in children aged 11-12 years. Tighter control of extraneous influences is recommended.

Exercise performance and magnetic resonance imaging-determined thigh muscle volume in children.

This study examined the relationships between thigh muscle volume (TMV) and aerobic and anaerobic performance in children. A total of 32 children, 16 boys and 16 girls, aged 9.9 (0.3) years completed a treadmill running test to exhaustion for the determination of peak oxygen uptake (peak VO2) and a Wingate Anaerobic Test (WAnT) for the determination of peak power (PP) and mean power (MP). The volume of the right thigh muscle was determined using magnetic resonance imaging. TMV was not significantly different in boys and girls [2.39 (0.29) l vs 2.18 (0.38) l, P > 0.05]. Peak VO2 and MP were significantly higher in boys than girls (P < 0.01) whether expressed in absolute, mass-related or allometrically scaled terms. Absolute PP was not significantly different in boys and girls but mass-related and allometrically scaled values were higher in boys (P < 0.01). TMV was correlated with absolute peak VO2, PP and MP in both sexes (r = 0.52-0.89, P < 0.01). In boys, mass-related PP was correlated with TMV (r = 0.53, P < 0.01), and in girls mass-related peak VO2 was correlated with TMV (r = -0.61, P < 0.01). However, in neither sex were allometrically scaled peak VO2, PP or MP correlated with TMV (P > 0.05). There were no significant differences between boys and girls in terms of peak VO2, PP or MP when expressed in a ratio to TMV or allometrically scaled TMV. In conclusion, this study has demonstrated that, when body size is appropriately accounted for using allometric scaling, TMV is unrelated to indices of aerobic and anaerobic power in 10-year-old children. Furthermore, there appear to be no qualitative differences in the muscle function of boys and girls in respect of aerobic and anaerobic function.