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 3 exercise sessions per week for 6 weeks. The 10-min exercise sessions consisted of low intensity cycling (60 Watts) and one (1 st 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 (V O2peak) 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). V O2peak 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.

Adolescent girls have been targeted as a priority group for promoting physical activity levels however it is unclear how this can be achieved. There is some evidence to suggest that social support could impact the physical activity levels of adolescent girls, although the relationship is complex and not well understood. We aimed to systematically review and meta-analyse the relationship between social support and physical activity in adolescent girls, exploring how different types and providers of social support might influence the relationship. Articles were identified through a systematic search of the literature using 14 electronic databases, personal resources, grey literature, and reference lists of included studies and previous reviews. Search terms representing social support, physical activity and adolescent girls were identified and used in various combinations to form a search strategy which was adapted for different databases. Cross-sectional or longitudinal articles published in English that reported an association between social support and physical activity in adolescent girls between the ages of 10 to 19 years were included. Studies that focused only on clinical or overweight populations were excluded. Data extraction was carried out by one reviewer using an electronic extraction form. A random 25 % of included articles were selected for data extraction by a second reviewer to check fidelity. Risk of bias was assessed using a custom tool informed by the Critical Appraisal Skills Programme Cohort Study Checklist in conjunction with data extraction. Cross-sectional results were meta-analysed and longitudinal results were presented narratively. Small but significant associations between all available providers of total social support (except teachers) and physical activity were found (r = .14-.24). Small but significant associations were also identified for emotional, instrumental and modelling support for some providers of support (r = .10-.21). Longitudinal research supported the cross-sectional analyses. Many of the meta-analysis results suggested high heterogeneity and there was some evidence of publication bias, therefore, the meta-analysis results should be interpreted with caution. In conclusion, the meta-analysis results suggest that social support is not a strong predictor of physical activity in adolescent girls though parents and friends may have a role in enhancing PA.Trial registrationPROSPERO 2014:CRD42014006738Electronic supplementary materialThe online version of this article (doi:10.1186/s12966-016-0405-7) contains supplementary material, which is available to authorized users.

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.

Purpose: Adolescent girls are not sufficiently active to achieve health benefits. Social support from friends and family has been positively associated with physical activity in adolescent girls; however it is unclear how social support influences physical activity behaviour. This study aimed to develop a grounded theory of how social support influences physical activity in adolescent girls. Methods: A qualitative, constructivist grounded theory approach was adopted. Individual interviews explored adolescent girls’ perspectives of how significant others’ influenced their physical activity through providing social support, and through modelling physical activity. Results: Participants perceived social support to influence physical activity behaviour through performance improvements, self-efficacy, enjoyment, motivation and by enabling physical activity. Improvements in performance and self-efficacy were also linked to motivation to be active. Girls perceived modelling to influence behaviour through providing opportunities for them to be physically active, and by inspiring them to be active. Conclusion: The grounded theory outlines adolescent girls’ perceptions of how significant others influence their physical activity and provides a framework for future research examining the role of social support on physical activity.