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High-intensity interval training (HIT) has been proposed as a time-efficient alternative to traditional cardiorespiratory exercise training, but is very fatiguing. In this study, we investigated the effects of a reduced-exertion HIT (REHIT) exercise intervention on insulin sensitivity and aerobic capacity. Twenty-nine healthy but sedentary young men and women were randomly assigned to the REHIT intervention (men, n = 7; women, n = 8) or a control group (men, n = 6; women, n = 8). Subjects assigned to the control groups maintained their normal sedentary lifestyle, whilst subjects in the training groups completed three exercise sessions per week for 6 weeks. The 10-min exercise sessions consisted of low-intensity cycling (60 W) and one (first session) or two (all other sessions) brief 'all-out' sprints (10 s in week 1, 15 s in weeks 2-3 and 20 s in the final 3 weeks). Aerobic capacity ([Formula: see text]) and the glucose and insulin response to a 75-g glucose load (OGTT) were determined before and 3 days after the exercise program. Despite relatively low ratings of perceived exertion (RPE 13 ± 1), insulin sensitivity significantly increased by 28% in the male training group following the REHIT intervention (P < 0.05). [Formula: see text] increased in the male training (+15%) and female training (+12%) groups (P < 0.01). In conclusion we show that a novel, feasible exercise intervention can improve metabolic health and aerobic capacity. REHIT may offer a genuinely time-efficient alternative to HIT and conventional cardiorespiratory exercise training for improving risk factors of T2D.

This study examined longitudinal changes in the pulmonary oxygen uptake (pVO(2)) kinetic response to heavy-intensity exercise in 14-16 yr old boys. Fourteen healthy boys (age 14.1 +/- 0.2 yr) completed exercise testing on two occasions with a 2-yr interval. Each participant completed a minimum of three 'step' exercise transitions, from unloaded pedalling to a constant work rate corresponding to 40% of the difference between the pVO(2) at the gas exchange threshold and peak pVO(2) (40% Delta). Over the 2-yr period a significant increase in the phase II time constant (25 +/- 5 vs. 30 +/- 5 s; p = .002, omega(2) = 0.34), the relative amplitude of the pVO(2) slow component (9 +/- 5 vs. 13 +/- 4%; p = .036, omega(2) = 0.14) and the pVO(2) gain at end-exercise (11.6 +/- 0.6 vs. 12.4 +/- 0.7 mL x min(-1) x W(-1); p < .001, omega(2) = 0.42) were observed. These data indicate that the control of oxidative phosphorylation in response to heavy-intensity cycling exercise is age-dependent in teenage boys.

The objective of this study was to determine the energy expended and intensity of physical activity achieved by adolescent girls while playing on a dance simulation game. Twenty adolescent girls were recruited from a local secondary school. Resting oxygen uptake (VO(2)) and heart rate were analysed while sitting quietly and subsequently during approximately 30 min of game play, with 10 min at each of three increasing levels of difficulty. Energy expenditure was predicted from VO(2) at rest and during game play at three levels of play, from which the metabolic equivalents (METS) of game playing were derived. Mean +/- standard deviation energy expenditure for levels 1, 2, and 3 was 3.63 +/- 0.58, 3.65 +/- 0.54, and 4.14 +/- 0.71 kcal . min(-1) respectively, while mean activity for each level of play was at least of moderate intensity (>3 METS). Dance simulation active computer games provide an opportunity for most adolescent girls to exercise at moderate intensity. Therefore, regular playing might contribute to daily physical activity recommendations for good health in this at-risk population.

The purpose of this study was to apply a series of mathematical models in order to investigate the nature of the kinetic response to heavy intensity exercise with children and identify a suitable model with which to estimate parameters of the response. Sixty two children (35 male, 27 female aged 10-15 years) completed four transitions from baseline pedalling to 40% of the difference between their previously determined anaerobic threshold and peak VO2 on an electronically braked cycle ergometer. Initially three models were fitted to the averaged response profiles following the end of phase 1. and their residuals compared; 1, a single exponential with a delay term; 2, an exponential and linear term with independent delays; and 3, a double exponential with independent delays. Up to 95% of the response profiles were better fitted by either model 2 or 3 (p < 0.05), and model 3 was a statistically better fit (p < 0.05) than model 2 in 77% of cases. Residual inspection confirmed the superior fit by model 3. A fourth model which consisted of a single exponential with a delay term was fitted within the phase 2 fitting window. Estimated parameters (A1 and tau1), using model 4 were not significantly different from model 3, and model 4 was identified as the model of choice due to the wide confidence intervals in tau2 and A2 using model 3. It was concluded that the nature of the response to heavy intensity exercise in children is similar to that previously reported with adults and that the response should be modelled accordingly.

It has been demonstrated that there are no sex differences in the oxygen uptake (V(.)O(2)) kinetic response to moderate intensity exercise. However, sex differences in the response to maximal exercise are readily apparent even in the prepubertal years. The purpose of this study was therefore to investigate if sex differences exist in the V(.)O(2) kinetic response to heavy-intensity exercise. Forty-eight prepubertal children (25 male, 23 female) completed four transitions from baseline to 40% of the difference between their previously determined T(V-slope) (ventilatory threshold determined by the V-slope method) and peak V(.)O(2) on an electronically braked cycle ergometer. Each subject's breath-by-breath responses were interpolated to 1 s intervals, time aligned and averaged. The data following phase 1 were fit with: (1) a double exponential model and (2) a single exponential model within a fitting window that was previously identified to exclude the slow component. There were no significant differences in the parameters of the primary component between each model. Subsequent analysis was carried out using model 2. The primary time constant (tau(1)) was significantly (P<0.05) faster in boys [17.6 (5.8) s] than girls [21.9 (8.2) s], and the slow component contribution to the total change in amplitude after 9 min was significantly greater in girls [11.8 (5.5)%] than boys [8.9 (3.7)%]. Sex differences in the kinetic response to heavy-intensity exercise were identified and suggest that during the prepubertal years, sex differences exist in the ability to deliver and/or utilise oxygen in children.

The purpose of this study was to investigate longitudinal changes with age in the kinetic response to cycling at heavy-intensity exercise in boys and girls. Twenty-two prepubertal children (13 male, 9 female) carried out a series of exercise tests on two test occasions with a 2-yr interval. On each test occasion, the subject completed multiple transitions from baseline to 40% of the difference between their previously determined V-slope and peak O(2) uptake (Vo(2)) for 9 min on an electronically braked cycle ergometer. Each subject's breath-by-breath responses were interpolated to 1-s intervals, time aligned, and averaged. The data after phase 1 were fit with 1) a double exponential model and 2) a single exponential model within a fitting window that was previously identified to exclude the slow component. There were no significant differences in the parameters of the primary component between each model. Subsequent analysis was carried out using model 2. The Vo(2) slow component was computed as the difference between the amplitude of the primary component and the end-exercise Vo(2) and was expressed as the percent contribution to the total change in Vo(2). Over the 2-yr period, the primary time constant (boys 16.8 +/- 5.3 and 21.7 +/- 5.3 s, girls 21.1 +/- 8.1 and 26.4 +/- 8.4 s, first and second occasion, respectively) and the relative amplitude of the slow component (boys 9.4 +/- 4.6 and 13.8 +/- 5.3%, girls 10.3 +/- 2.4 and 15.5 +/- 2.8%, first and second occasion, respectively) significantly increased with no sex differences. The data demonstrate that children do display a slow-component response to exercise and are consistent with an age-dependent change in the muscles' potential for O(2) utilization.

The literature suggests that the oxygen uptake (VO2) response to the onset of moderate-intensity exercise may be both mature from childhood and independent of sex. Yet the cardiorespiratory response to exercise and the metabolic profile of the muscle appear to change with growth and development and to differ between the sexes. The aim of this study was to investigate further changes in the VO2 kinetic response with age and sex. Participants completed a series of no less than four step change transitions, from unloaded pedalling to a constant work rate corresponding to 80% of their previously determined ventilatory threshold. Each participant's breath-by-breath responses were interpolated to 1 s intervals, time aligned and then averaged. A single exponential model that included a time delay was used to analyse the averaged response following phase 1 (15 s). Participants with parameter confidence intervals more than +/- 5 s were removed from the sample; the results for the remaining 13 men and 12 women (age 19-26 years), 12 boys and 11 girls (age 11-12 years) were used for statistical analysis. Children had a significantly shorter time constant than adults, both for males (19.0+/-2.0 and 27.9+/-8.6 s respectively; P<0.01) and females (21.0+/-5.5 and 26.0+/-4.5 s respectively; P<0.05). There were no significant differences in the time constant between the sexes for either adults or children (P>0.05). A significant relationship between the time constant and peak VO2 was found only in adult males (P<0.05). A shorter time constant in children may reflect an enhanced potential for oxidative metabolism.