The impact of sprint interval training with or without weight loss on substrate oxidation in adults: A secondary analysis of the i-FLEX study.

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.

Irisin response to acute moderate intensity exercise and high intensity interval training in youth of different obesity statuses: A randomized crossover trial.

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.

Exploring the Association of a Total Physical Activity Energy Expenditure and Diabetes Mellitus in Adults: A Cross-Sectional Analysis of the Canadian Health Measures Survey.

Background: Physical activity (PA) guidelines for adults recommend participation in aerobic activities of moderate-to-vigorous intensity and a minimum of two sessions of resistance training (RT) weekly. These guidelines account for a small amount of the total PA energy expenditure and include no recommendation for low intensity activities (sleeping, sedentary behavior, and light intensity PA). Consequently, there is a need to investigate the benefits of total PA energy expenditure and diabetes mellitus (DM); to investigate the association between total PA energy expenditure and DM in adults aged 45 years or above. Methods: Data from the Canadian Health Measures Survey (CHMS; n = 5591) were used for the cross-sectional analysis. DM was measured using hemoglobin glycated (A1c) and questionnaires in adults aged 45 and above. PA and sedentary behavior were estimated using accelerometry. Sleep and RT were self-reported. Total PA energy expenditure was computed using the sum of metabolic equivalent of task-min/week. Results: The mean age of the sample was 58.0 ± 0.2 years old. No associations were observed between total PA energy expenditure and self-reported T2DM in all models (P > 0.05). For objectively measured DM, this association was significant when adjusted for age, sex, ethnicity, and smoking [OR: 0.45; 95% CI (0.25-0.80)]; however, the association was no longer significant once adjusted for waist circumference and further adjusted for meeting the International PA Guidelines [OR: 0.64; 95% CI (0.33-1.27)] (P > 0.05). Conclusion: Total PA energy expenditure performed weekly is not associated with DM when considering other known risk factors, including waist circumference and meeting the PA guidelines.

Effects of sprint interval training on substrate oxidation in adults living with and without obesity: The i-FLEX study.

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.

Difference in total workload during sprint interval training for adults living with or without obesity.

PURPOSE: The primary objective of the study was to compare the implications of body composition on work volume, power outputs (peak, mean, and minimum), and relative drop load throughout 4 weeks of sprint interval training (SIT) in individuals living with and without obesity. METHODS: Thirty-four participants living with (n = 16) and without (n = 18) obesity took part in 12 sessions of SIT over 4 weeks. SIT consisted of repeated 30-s Wingate with a drop load of 7.5% of the participant's body mass separated by 4 min of active recovery. Fat-free mass was estimated using a BOD POD. Work volume, drop load, and power output (peak, mean, and minimum) relative to body mass and fat-free mass were calculated using a Monark 874E Weight cycle ergometer. RESULTS: Individuals living with obesity had a significantly larger drop load relative to fat-free mass (p < 0.001) and absolute drop load (p < 0.001) as well as a lower cycling cadence (p < 0.001) compared to individuals without obesity. No significant difference was observed in work volume (p = 0.167) as well as mean (p = 0.903), peak (p = 0.294), and minimum (p = 0.103) power relative to fat-free mass between groups. CONCLUSION: The findings suggest that individuals living with obesity work at a higher relative drop load when utilizing a percentage of body mass; however, a reduced cycling cadence results in similar total work volume throughout SIT.

Does lean body mass equal health despite body mass index?

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.