Limited data exist regarding the impact of an acute bout of exercise with varying intensities on irisin levels in the youth of different obesity statuses. The objectives were to (1) compare an acute bout of moderate continuous intensity (MCI) exercise and an acute bout of high‐intensity interval training (HIIT) on irisin response in youth with different obesity statuses and, (2) investigate whether changes in irisin levels are correlated with exploratory outcomes. A randomized crossover design study was conducted on 25 youth aged 12–18 years old. Participants were classified as either healthy weight (BMI percentile <85; n = 14) or overweight/obese (BMI percentile ≥85; n = 11). Participants performed an MCI exercise session at 50% of heart rate reserve for 35 min and a HIIT exercise session for 35 min, with intervals every 5 min increasing from 50% heart rate reserve to 85–90% for 2 min. Irisin was measured using an enzyme‐linked immunoabsorbent assay from plasma sampling obtained throughout the exercise (at times 0, 7, 14, 21, 28, and 35 min). A time effect was observed throughout the HIIT session [F(1,5) = 6.478, p < 0.001]. Bonferonni post‐hoc analysis revealed significant differences in irisin levels post‐exercise (35 min) compared to times 7, 14, 21, and 28 min. Irisin increased during HIIT (81.0% ± 71.3; p = 0.012) in youth with a healthy weight. No differences were observed for youth living as overweight or with obesity. Overall, HIIT elicits a higher peak irisin response compared to MCI exercise training in youth.

Metabolic flexibility is the ability to adapt substrate oxidation according to metabolic demand. Exercise increases fat oxidation responses in individuals living with obesity; however, limited research exists on the relationship between substrate oxidation and insulin sensitivity after sprint interval training (SIT). The primary objective was to investigate changes in substrate oxidation at rest and during submaximal exercise, and in insulin sensitivity after 4 weeks of SIT in individuals living with or without obesity. The secondary objective was to investigate correlations between changes in substrate oxidation and insulin sensitivity following SIT. Adults living with obesity (n = 16, body mass index (BMI) = 34.1 kg/m2 ± 3.8) and without obesity (n = 18, BMI = 22.9 kg/m2 ± 1.6) took part in a 4‐week SIT intervention. Participants completed three sessions of SIT per week, consisting of repeated sets of a 30‐s Wingate separated by 4 m of active recovery. Substrate oxidation at rest and during submaximal exercise was measured using VCO2/VO2. Insulin sensitivity was calculated using the Matsuda index. No difference in substrate oxidation at rest was observed for either group (p > 0.05), while a significant increase in fat oxidation was observed in individuals living with obesity [F(1,31) = 14.55, p = 0.001] during the submaximal exercise test. A significant decrease in insulin sensitivity was observed among individuals without obesity [F(1,31) = 5.010, p = 0.033]. No correlations were observed between changes in substrate oxidation and insulin sensitivity (p > 0.05). Following SIT, individuals living with obesity increased submaximal fat oxidation compared to individuals without obesity. No correlations were observed between substrate oxidation and insulin sensitivity. Thus, SIT impacts fat oxidation during exercise in individuals living with obesity while having no such influence on insulin sensitivity.

To investigate cross-sectional association between sedentary activities and moderate-to-vigorous physical activities' (MVPA) patterns, and the likelihood of having diabetes, MetS, or both conditions. This cross-sectional analysis from the National Health and Nutrition Examination Survey 2003-2004 and 2005-2006 cycles included 2456 adults. The primary exposure variables were sedentary and MVPA patterns (1-, 5-, 10-, 30-, and 60-minute bouts) measured by accelerometer. The primary outcome measure was the subgroup categorization: healthy group, MetS group, diabetes group, and Mets & diabetes group. No differences were observed regarding proportion of sedentary patterns among groups, but differences were observed for the proportion of time spent doing MVPA in 5-, 10-, and 30-minute bouts among groups (all P < .05). When comparing individuals having both MetS & diabetes to the MetS group and the diabetes group, all bout lengths of sedentary behavior were significantly different (P < .05). The patterns of sedentary behavior were not associated with higher odds of being classified with Mets & diabetes when adjusted for total MVPA time (all P > .05). Interestingly, the odds of being in the healthy group were associated with MVPA patterns following adjustment for total sedentary time. The findings suggest it is more important to focus on exercise performed at moderate-tovigorous intensity, of any bout length, compared to sitting less to lower the odds of MetS and diabetes.

Objective To determine the association between having simultaneously high body mass index (BMI) and high relative lean body mass (LBM) and cardio‐metabolic risk factors, metabolic syndrome (MetS), and diabetes in adults. Materials and Methods A cross‐sectional analysis was performed on 4982 adults aged 19‐85 years that participated in the National Health and Nutrition Examination Survey (cycles 1999‐2000‐2005‐2006). The primary exposure variable was categorization into four groups: (a) Low‐BMI/Low‐LBM, (b) Low‐BMI/High‐LBM, (c) High‐BMI/Low‐LBM, and (d) High‐BMI/High‐LBM. LBM was assessed using dual‐energy X‐ray absorptiometry. The primary outcome measures were cardio‐metabolic risk factors, MetS based on the ATP III definition; participants were required to have at least three of the following five criteria: high waist circumference, low HDL cholesterol, elevated triglyceride levels, high resting blood pressure, and self‐reported diabetes. Results Compared to the High‐BMI/High‐LBM, most cardio‐metabolic risk factors were significantly different among groups (P < .05) while no such differences were observed for the High‐BMI/Low‐LBM (P > .05). Exception of waist circumference (OR [95%]: 21.8 [8.84‐53.82]), there was no increased odds of having cardio‐metabolic risk factors in the High‐BMI/Low‐LBM compared with the High‐BMI/High‐LBM (P > .05). The odds of having MetS and diabetes for the High‐BMI/Low‐LBM compared with the High‐BMI/High‐LBM were OR (95% CI): 1.68 (0.84‐3.36) and 0.59 (0.26‐1.34), respectively. Conclusions Our results suggest that having a high‐BMI as well as high relative LBM levels is not associated with cardio‐metabolic risk factors, MetS, and diabetes. Therefore, maintaining a BMI below 30 kg/m2 appears to be clinically relevant, regardless of LBM levels.

No abstract

No abstract

Endurance exercise training and weight loss (WL) have been associated with changes in fat oxidation. However, there is limited evidence investigating the impact of sprint interval training (SIT)‐induced WL on fat oxidation in adults. To investigate the impact of SIT with or without WL on fat oxidation, 34 adults aged 19–60 years (males, n = 15) took part in 4‐week SIT. SIT consisted of 30‐s Wingates starting with two intervals and working up to four interspersed with 4 min of active recovery. Fat oxidation was estimated via indirect calorimetry using a metabolic cart during submaximal cycling. Following the intervention, participants were classified into a WL group (weight change >0 kg) or a non‐WL group (weight change ≤0 kg). No difference in resting fat oxidation (p = 0.642) and respiratory exchange ratio (RER) (p = 0.646) were observed between the groups. There was a significant interaction for the WL group with increased submaximal fat oxidation usage (p = 0.005) and decreased submaximal RER over the duration of the study (p = 0.017). When adjusted for baseline weight and sex, submaximal fat oxidation usage remained significant (p < 0.05), while RER did not (p = 0.081). The WL group had higher work volume, relative peak power, and mean power than the non‐WL group (p < 0.05). Short‐term SIT elicited significant improvements in submaximal RER and fat oxidation (FOx) in adults that lost weight, which may be explained by an increase in work volume throughout SIT training.

No abstract