Only minor additional metabolic health benefits of high as opposed to moderate dose physical exercise in young, moderately overweight men

Effect of exercise training on insulin-stimulated glucose disposal: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND AND OBJECTIVE

The effect of exercise training on whole-body insulin sensitivity has not been systematically summarized. We aimed to summarize the data from randomized controlled trials evaluating the effect of exercise training on insulin action, in adults.

SUBJECTS

MEDLINE, EMBASE, and CENTRAL databases were searched until January 2021. Randomized controlled trials lasting ≥4 weeks, including adults, and evaluating the effect of exercise on insulin-stimulated glucose disposal measured using the hyperinsulinemic euglycemic clamp, were included.

METHODS

Three reviewers extracted summary data from published trials. The primary outcome was insulin-stimulated glucose disposal. Standardized weighted mean differences (SMD) in glucose disposal between intervention and control were compared. The PEDro scale was used to assess risk of bias.

RESULTS

We included 25 trials (36 interventions, N = 851). Exercise increased insulin-stimulated glucose disposal relative to control, SMD = 0.52 (95% confidence interval [CI]: 0.39, 0.65; p < 0.001; I2 = 47%) without significantly suppressing hepatic glucose production. In trials without isotopic tracers, exercise increased glucose disposal (SMD = 0.63; 95% CI: 0.48, 0.77; p < 0.001, I2 = 55%). In trials with isotopic tracers, exercise increased glucose disposal only when tracers were added to the exogenous glucose used for clamping (SMD = 0.34; 95% CI: 0.03, 0.66, p = 0.034. I2 = 0%). In a meta-regression model including aerobic exercise, weight change, and tracer technique, only percent weight change explained between trial heterogeneity (β = 0.069; 95% CI: 0.005, 0.013). The PEDro rating indicated relatively low risk of bias (5.8 ± 0.22).

CONCLUSIONS

Exercise training for at least four weeks significantly increases insulin-stimulated glucose disposal. Weight loss maximizes the effect and may be needed to improve hepatic insulin sensitivity. Differences in tracer methodology contribute to divergent outcomes and should be considered when assessing conclusions from research examining the effect of exercise on insulin action.

REGISTRATION

PROSPERO (CRD42019124381).

Insights into the development of insulin resistance: Unraveling the interaction of physical inactivity, lipid metabolism and mitochondrial biology

While impairments in peripheral tissue insulin signalling have a well-characterized role in the development of insulin resistance and type 2 diabetes (T2D), the specific mechanisms that contribute to these impairments remain debatable. Nonetheless, a prominent hypothesis implicates the presence of a high-lipid environment, resulting in both reactive lipid accumulation and increased mitochondrial reactive oxygen species (ROS) production in the induction of peripheral tissue insulin resistance. While the etiology of insulin resistance in a high lipid environment is rapid and well documented, physical inactivity promotes insulin resistance in the absence of redox stress/lipid-mediated mechanisms, suggesting alternative mechanisms-of-action. One possible mechanism is a reduction in protein synthesis and the resultant decrease in key metabolic proteins, including canonical insulin signaling and mitochondrial proteins. While reductions in mitochondrial content associated with physical inactivity are not required for the induction of insulin resistance, this could predispose individuals to the detrimental effects of a high-lipid environment. Conversely, exercise-training induced mitochondrial biogenesis has been implicated in the protective effects of exercise. Given mitochondrial biology may represent a point of convergence linking impaired insulin sensitivity in both scenarios of chronic overfeeding and physical inactivity, this review aims to describe the interaction between mitochondrial biology, physical (in)activity and lipid metabolism within the context of insulin signalling.

Maintenance of cardiorespiratory fitness, body composition, and a physically active lifestyle after structured exercise interventions in individuals with overweight and obesity: A mixed-method follow-up study

Objectives

The aim of this mixed-method study was to explore maintenance of physical activity and health effects one year after completion of exercise interventions in transport and leisure-time domains of everyday life. We hypothesised that routinisation of active commuting would lead to better maintenance of physical activity and health effects compared with leisure-time exercise.

Study design

Mixed-methods follow-up study.

Methods

Individuals with overweight/obesity, who completed a 6-month exercise intervention (active commuting by bike (BIKE), moderate (MOD) or vigorous intensity leisure-time exercise (VIG)), were after one year invited to participate in a follow-up visit which included measurements of cardiorespiratory fitness during an incremental bicycle test and body composition using dual-energy X-ray absorptiometry. Variability in maintenance practices was assessed in a sub-sample of participants who experienced the greatest improvements ('VO₂peak improvers') and reductions ('VO₂peak reducers'), respectively, in cardiorespiratory fitness. Semi-structured interviews were conducted (15-30 min) and analysed using systematic text condensation to identify barriers and facilitators associated with maintenance of physical activity.

Results

Out of the 74 participants completing an exercise intervention, 46 (62%) completed follow-up (BIKE: n = 14; MOD: n = 14; VIG: n = 18). Improvements in VO₂peak and reductions in fat mass were maintained in BIKE and VIG. Body weight decreased in BIKE and fat free mass increased in VIG. Changes in VO₂peak and anthropometry at follow-up did not differ between BIKE and MOD + VIG. Fat mass decreased and recreational physical activity increased in 'VO₂peak improvers'. Findings from the interviews suggested that self-monitoring, collective exercising, and new personal exercise challenges facilitate maintenance of a physically active lifestyle.

Conclusion

Completion of a structured exercise intervention consisting of 6 months of active commuting or vigorous intensity leisure-time exercise was associated with long-term maintenance of improvements in VO₂peak and body composition, whereas moderate intensity leisure-time exercise was not. In contrast to our hypothesis, active commuting was not associated with better maintenance of physical activity and health effects after the intervention compared with leisure-time exercise.

Effect of different types of regular exercise on physical fitness in adults with overweight or obesity: Systematic review and meta-analyses

This systematic review examined the effect of exercise training interventions on physical fitness in adults with overweight or obesity and compared the effectiveness of different types of exercise training. Four electronic databases were searched. Articles were included if they described randomized controlled trials of exercise training interventions and their effect on maximal oxygen consumption or muscle strength in adults with overweight or obesity. Changes in outcome parameters were analyzed using random effects meta-analyses for different training types (aerobic, resistance, combined aerobic plus resistance, and high-intensity interval training). Eighty-eight articles satisfied the inclusion criteria of which 66 (3964 participants) could be included in the meta-analyses. All training types increased VO_2max (mean difference 3.82 ml/min/kg (95% CI 3.17, 4.48), P < 0.00001; I² = 48%). In direct comparisons, resistance training was less effective in improving VO_2max than aerobic training, HIIT was slightly more effective than aerobic training, and no difference between aerobic and combined aerobic plus resistance training was found. For muscle strength benefits, incorporation of resistance exercise in the training program is indicated. Exercise training increases VO_2max and muscle strength in adults with overweight or obesity. Differences between training types should be weighed with other needs and preferences when health professionals advise on exercise training to improve physical fitness.

Effect of exercise training on skeletal muscle protein expression in relation to insulin sensitivity: Per-protocol analysis of a randomized controlled trial (GO-ACTIWE)

Exercise training improves peripheral insulin sensitivity and leads to molecular adaptations in the skeletal muscle. We investigated changes in the expression of key muscle proteins in the glucose metabolic pathway following active commuting by bike or leisure-time exercise at two different intensities. In addition, potential associations between insulin sensitivity and muscle protein expression were examined. This per-protocol analysis included 72 out of 130 physically inactive, healthy women and men (20-45 years) with overweight/obesity (BMI: 25-35 kg/m2 ) who completed 6 months of no intervention (CON, n = 12), active commuting by bike (BIKE, n = 14), or leisure-time exercise of moderate (MOD, n = 28) or vigorous (VIG, n = 18) intensity. Exercise was prescribed 5 days/week with a weekly exercise energy expenditure of 1,600 kcal for women and 2,100 kcal for men. Insulin sensitivity was determined by a hyperinsulinemic euglycemic clamp and skeletal muscle biopsies were obtained from m. vastus lateralis and analyzed for protein expression at baseline and after 3 and 6 months of intervention. We found an increased expression of pyruvate dehydrogenase (PDH) in the exercise groups compared with the control group following 6 months of training. No differential effects were observed on the protein expression following moderate versus vigorous intensity exercise. In addition, we found a positive association between insulin sensitivity and the expression of glucose transporter type 4 as well as PDH. The positive association and the increase in expression of PDH after exercise training points toward a role for PDH in the training-induced enhancement of insulin sensitivity.

PPARG Pro12Ala Ala carriers exhibit greater improvements in peripheral insulin sensitivity in response to 12 weeks of aerobic exercise training

The Ala allele of PPARG Pro12Ala ( rs1801282 ) is associated with greater improvements to the glucose metabolism in exercise studies, but whether this extends to peripheral insulin sensitivity is unknown. Our objective was to investigate the effect of PPARG Pro12Ala on exercise-induced changes in peripheral insulin sensitivity. A total of 124 (91 Pro homozygotes and 33 Ala carriers) previously physically inactive healthy young men and women with overweight or class 1 obesity who completed a 12 wk aerobic exercise intervention were included in the analysis. All participants underwent a hyperinsulinemic euglycemic clamp before and after the 12 wk intervention. The prescribed exercise frequency was 5–7 days/wk, and the exercise energy expenditure was 2,100 4,200 kcal/wk for men and 1,600 kcal/wk for women. Insulin sensitivity improved significantly in both genotype groups. However, Ala carriers had a 1.13-fold (95% confidence interval 1.01; 1.26, P = 0.032) greater improvement in insulin sensitivity from baseline compared with Pro homozygotes. Our data support that PPARG Pro12Ala modifies the effect of aerobic exercise on peripheral insulin sensitivity.

How does 6 months of active bike commuting or leisure-time exercise affect insulin sensitivity, cardiorespiratory fitness and intra-abdominal fat? A randomised controlled trial in individuals with overweight and obesity

Objectives

To evaluate effects of active bike commuting or leisure-time exercise of two intensities on peripheral insulin sensitivity (primary outcome), cardiorespiratory fitness and intra-abdominal adipose tissue mass (secondary outcomes).

Methods

188 physically inactive, healthy women and men (20-45 years) with overweight or class 1 obesity were recruited. In the 6-month trial, 130 participants were randomised to either: no intervention (CON), active commuting (BIKE) or leisure-time exercise of moderate (MOD, 50% VO2peak) or vigorous (VIG, 70% VO2peak) intensity. 100 completed follow-up testing. Exercise prescription was 5 days/week with a weekly exercise energy expenditure of 1600 kcal for women and 2100 kcal for men. Testing was performed at baseline, 3 months and 6 months.

Results

Peripheral insulin sensitivity (ml/min/pmol insulin/L) increased (improved) by 24% (95% CI 6% to 46%, p=0.01) in VIG compared with CON at 3 months. Peripheral insulin sensitivity increased (improved) by 20% in BIKE (95% CI 1% to 43%, p=0.04) and 26% in VIG (95% CI 7% to 47%, p<0.01) compared with CON at 6 months. Cardiorespiratory fitness increased in all exercise groups compared with CON at 6 months; but the increase was higher in those that undertook vigorous exercise than those who did moderate exercise. Intra-abdominal adipose tissue mass diminished across all exercise groups in comparison to CON at 6 months.

Conclusions

Active bike commuting improved cardiometabolic health; as did leisure-time exercise. Leisure-time exercise of vigorous intensity conferred more rapid effects on peripheral insulin sensitivity as well as additional effects on cardiorespiratory fitness than did moderate intensity exercise.

Trial registration

NCT01962259

Exercise Dose Effects on Body Fat 12 Months after an Exercise Intervention: Follow-up from a Randomized Controlled Trial

BACKGROUND

Exercise interventions can result in weight loss, which is associated with reductions in disease risk. It is unknown how the volume of exercise prescribed in a one-time exercise intervention impacts long-term body fatness. We compared 24-month body fat changes among postmenopausal women previously prescribed 300 versus 150 minutes/week of exercise in a year-long exercise intervention trial.

METHODS

The Breast Cancer and Exercise Trial in Alberta (BETA) was a two-centred randomized controlled trial in Alberta, Canada. The trial consisted of a 12-month intervention and 12-month observation period. For the intervention, participants were randomized to either a moderate-volume exercise group (150 min/week) or a high-volume exercise group (300 min/week). Participants in this study were 334 inactive postmenopausal women who had been followed-up to 24 months. The primary outcome for this study was 24-month change in total body fat using dual energy X-ray absorptiometry scans. Other measures included weight, waist and hip circumferences, subcutaneous and intra-abdominal fat from computed tomography scans, and lean mass. Researchers were blinded to randomization group when measuring body fat.

RESULTS

Both groups self-reported ∼180 minutes/week moderate-vigorous activity at 24 months. No statistically significant difference was found in total body fat at 24 months between the two groups. Statistically significant effects (comparing high versus moderate groups) were found for BMI (least-square mean change (95% CI): -0.66 (-0.97, -0.36) versus -0.25 (-0.55, 0.05) kg/m², P=0.04), waist-to-hip ratio (-0.033 (-0.040, -0.026) versus -0.023 (-0.030, -0.016), P=0.05), and subcutaneous abdominal fat area (-32.18 (-39.30, -25.06) versus -22.20 (-29.34, -15.05) cm², P=0.04).

CONCLUSION

Prescribing 300 versus 150 minutes/week of exercise to inactive postmenopausal women resulted in some long-term greater decreases in measures of body composition but no overall differences in total body fat loss. This trail is registered with NCT01435005.

Accumulated or continuous exercise for glycaemic regulation and control: a systematic review with meta-analysis

OBJECTIVE

To compare the effectiveness of accumulating exercise in multiple bouts of at least 10 min throughout a day with exercise completed in a single bout (continuous or interval), or no exercise, on glycaemic control and regulation in inactive people without diagnosed glycaemic dysfunction.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Seven electronic databases were searched: CINAHL (EBSCO), Cochrane Library, EMBASE (Ovid), MEDLINE 1948-(Ovid), SCOPUS (Elsevier), SPORTDiscus (EBSCO) and Web of Science (ISI) with no restrictions on date and included all titles indexed up to February 2018.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Articles reporting insufficiently active adults (19 to 64 years) without metabolic dysfunction, measuring glycaemic control or regulation following at least 6 weeks of aerobic exercise.

RESULTS

Only one study compared accumulated exercise to single-bout exercise with no significant effect on fasting glucose (95% CI: -0.04 to 0.24 mmol·L-1) or fasting insulin (95% CI: -1.79 to 9.85 pmol·L-1) reported 48 hours after the final bout. No studies compared accumulated exercise with no-exercise. Compared with no-exercise, single-bout exercise reduces insulin resistance (mean difference (MD): -0.53 pmol·L-1; 95% CI: -0.93 to -0.13). Insulin resistance was clearly reduced with moderate-intensity (-0.68 (-1.28 to -0.09)) but not with high-intensity (-0.38 (-1.20 to 0.44)) exercise. Single-bout exercise was not statistically more beneficial than no-exercise for glycated haemoglobin (HbA1c) (MD: -0.11 %; 95% CI: -0.24 to 0.02) in metabolically healthy individuals.

SUMMARY/CONCLUSION

The glycaemic response to accumulated exercise or single-bout exercise might not be different, however exercise intensity might influence the mechanisms generating the response.

PROSPERO REGISTRATION NUMBER

CRD42015025042.

Dose-Response Effects of Aerobic Exercise on Quality of Life in Postmenopausal Women: Results from the Breast Cancer and Exercise Trial in Alberta (BETA)

BACKGROUND

Exercise generally improves quality of life (QoL) and psychosocial functioning in adult populations but few randomized trials have examined dose-response effects.

PURPOSE

The purpose of the present study was to report the QoL and psychosocial outcomes from the Breast Cancer and Exercise Trial in Alberta (BETA).

METHODS

Healthy but inactive postmenopausal women at risk for breast cancer were randomized to a year-long aerobic exercise intervention consisting of either 150 min/week (moderate volume group, n = 200) or 300 min/week (high volume group, n = 200). QoL was assessed at baseline and 1 year using the short form-36 health survey. Sleep quality, depression, anxiety, stress, self-esteem, and happiness were also assessed. Participant preference for group assignment (i.e., exercise volume) was assessed at baseline and tested as a moderator.

RESULTS

There were no statistically significant dose-response effects of aerobic exercise on any QoL, sleep quality, or psychosocial outcome. Participant preference for group assignment did not moderate any QoL, sleep quality, or psychosocial responses. Marital status was a significant moderator (p for interaction = 0.01) and obesity showed a trend towards being a moderator (p for interaction = 0.08) of the dose-response effects of aerobic exercise on global sleep quality such that unmarried and obese women improved sleep quality with the higher volume of aerobic exercise.

CONCLUSIONS

A higher volume of aerobic exercise, approximately double the minimum public health guideline, did not provide additional QoL or psychosocial benefits compared to the minimum public health guideline in inactive postmenopausal women, even for women who preferred the higher volume of exercise at baseline.

TRIAL REGISTRATION

Trial Registration clinicaltrials.gov identifier: NCT1435005.

Effect of Exercise Training on Cardiac Biomarkers in At-Risk Populations: A Systematic Review

BACKGROUND

Studies have demonstrated beneficial effects of exercise on cardiovascular disease biomarkers for healthy individuals; however, a comprehensive review regarding the effect of exercise on cardiovascular disease biomarkers in at-risk populations is lacking.

METHODS

A literature search was performed to identify studies meeting the following criteria: randomized controlled study, participants with pathology/activity limitations, biomarker outcome (total cholesterol, high-density lipoprotein, low-density lipoprotein, C-reactive protein, insulin, triglycerides, or glucose), and exercise intervention. Means and standard deviations from each biomarker were used to calculate standardized Cohen's d effect sizes with 95% confidence intervals.

RESULTS

In total, 37 articles were included. The majority (44/57; 77%) of data points demonstrated moderate to strong effects for the reduction in total cholesterol, triglycerides, and low-density lipoprotein, and elevation in high-density lipoprotein following exercise. The majority of data points demonstrated strong effects for reductions in blood glucose (24/30; 80%) and insulin (23/24; 96%) levels following exercise intervention.

CONCLUSION

Evidence is heterogeneous regarding the influence of exercise on cardiovascular disease biomarkers in at-risk patients, which does not allow a definitive conclusion. Favorable effects include reductions in triglycerides, total cholesterol, low-density lipoprotein, glucose, and insulin, and elevation in high-density lipoprotein following exercise intervention. The strongest evidence indicates that exercise is favorable for the reduction in glucose and cholesterol levels among obese patients, and reduction of insulin regardless of population.

The effect of exercise interventions on inflammatory biomarkers in healthy, physically inactive subjects: a systematic review

BACKGROUND

Increases in physical activity ameliorate low-grade systemic inflammation in disease populations such as type 2 diabetes mellitus and coronary artery disease. The effects of aerobic and resistance training (RT) on inflammatory biomarker profiles in non-disease, physically inactive individuals are unknown.

METHODS

A systematic review of randomized controlled trials measuring the effect of aerobic and resistance exercise on pro-inflammatory biomarkers in healthy, inactive adult populations was conducted. The available peer-reviewed literature was searched from January 1990 to June 2016 using the electronic databases PubMed and Scopus. A narrative synthesis of review findings was constructed with discussion of the impact of aerobic, resistance and combined training on C-reactive protein (CRP), interleukin-6 (IL-6), interleukin-8, interleukin-1β and tumour necrosis factor-α.

RESULTS

The initial search revealed 1596 potentially relevant studies. Application of the study eligibility criteria led to the full-text review of 54 articles with 11 studies deemed suitable for inclusion. Review of related articles and the reference lists of the 54 full-text articles led to the inclusion of 2 additional studies. The review revealed inconsistent findings relating to the effect of aerobic training and RT on CRP and IL-6. Studies of older-aged adults (>65 years old) demonstrated the greatest and most consistent reduction in inflammatory biomarkers post-training intervention.

CONCLUSIONS

A paucity of evidence exists relating to the effect of exercise training on inflammatory markers in non-disease, physically inactive adults. The available evidence suggests potential for the greatest benefit to be seen in older populations and with higher intensity aerobic exercise.

A systematic review and narrative synthesis of interventions for uncomplicated obesity: weight loss, well-being and impact on eating disorders

OBJECTIVE

Most weight loss research focuses on weight as the primary outcome, often to the exclusion of other physiological or psychological measures. This study aims to provide a holistic evaluation of the effects from weight loss interventions for individuals with obesity by examining the physiological, psychological and eating disorders outcomes from these interventions.

METHODS

Databases Medline, PsycInfo and Cochrane Library (2011-2016) were searched for randomised controlled trials and systematic reviews of obesity treatments (dietary, exercise, behavioural, psychological, pharmacological or surgical). Data extracted included study features, risk of bias, study outcomes, and an assessment of treatment impacts on physical, psychological or eating disorder outcomes.

RESULTS

From 3628 novel records, 134 studies met all inclusion criteria and were evaluated in this review. Lifestyle interventions had the strongest evidence base as a first-line approach, with escalation to pharmacotherapy and bariatric surgery in more severe or complicated cases. Quality of life was the most common psychological outcome measure, and improved in all cases where it was assessed, across all intervention types. Behavioural, psychological and lifestyle interventions for weight loss led to improvements in cognitive restraint, control over eating and binge eating, while bariatric surgery led to improvements in eating behaviour and body image that were not sustained over the long-term.

DISCUSSION

Numerous treatment strategies have been trialled to assist people to lose weight and many of these are effective over the short-term. Quality of life, and to a lesser degree depression, anxiety and psychosocial function, often improve alongside weight loss. Weight loss is also associated with improvements in eating disorder psychopathology and related measures, although overall, eating disorder outcomes are rarely assessed. Further research and between-sector collaboration is required to address the significant overlap in risk factors, diagnoses and treatment outcomes between obesity and eating disorders.

Update on the effects of physical activity on insulin sensitivity in humans

PURPOSE AND METHODS

This review presents established knowledge on the effects of physical activity (PA) on whole-body insulin sensitivity (SI) and summarises the findings of recent (2013-2016) studies.

DISCUSSION AND CONCLUSIONS

Recent studies provide further evidence to support the notion that regular PA reduces the risk of insulin resistance, metabolic syndrome and type 2 diabetes, and SI improves when individuals comply with exercise and/or PA guidelines. Many studies indicate a dose response, with higher energy expenditures and higher exercise intensities, including high intensity interval training (HIIT), producing greater benefits on whole-body SI, although these findings are not unanimous. Aerobic exercise interventions can improve SI without an associated increase in cardiorespiratory fitness as measured by maximal or peak oxygen consumption. Both aerobic and resistance exercise can induce improvements in glycaemic regulation, with some suggestions that exercise regimens including both may be more efficacious than either exercise mode alone. Some studies report exercise-induced benefits to SI that are independent of habitual diet and weight loss, while others indicate an association with fat reduction, hence the debate over the relative importance of PA and weight loss continues. During exercise, muscle contraction stimulated improvements in SI are associated with increases in AMPK activity, which deactivates TCB1D1, promoting GLUT4 translocation to the cell membrane and thereby increasing glucose uptake. Postexercise, increases in Akt deactivate TCB1D4 and thereby increase GLUT4 translocation to the cell membrane. The reduction in intramuscular saturated fatty acids and concomitant reductions in ceramides, but not diacylglycerols, provide a potential link between intramuscular lipid content and SI. Increased skeletal muscle capillarisation provides another independent adaptation through which SI is improved, as does enhanced β cell activity. Recent studies are combining exercise interventions with dietary and feeding manipulations to investigate the potential for augmenting the exercise-induced improvements in SI and glycaemic control.

Assessment of six commercial plasma small RNA isolation kits using qRT-PCR and electrophoretic separation: higher recovery of microRNA following ultracentrifugation

Growing interest in blood-borne microRNAs (miRNAs) as biomarkers has led to the introduction of a number of commercial kits for isolating small RNAs from plasma/serum. We sought to compare the efficacy of six such kits in isolating miRNAs from either whole plasma or a plasma-derived ultracentrifugation (UC) fraction from 2 healthy volunteers with some of the results being validated in 10 additional subjects. To assess the overall yield and concentration of isolated small RNAs, we measured the levels of one spiked-in and four endogenous miRNAs by quantitative reverse transcription and polymerase chain reaction (qRT-PCR). We also tested the performance of the Agilent Bioanalyzer small RNA assay with these RNA samples. Additionally, we tested the effects of hemolysis on measured miRNA levels in whole plasma and in the UC fraction. Both the efficiency of RNA isolation and the relative levels of specific miRNAs in different samples varied considerably between the tested extraction methods. Of all kits tested, the QIAGEN miRNeasy kits (Mini and Serum/Plasma kits) and the Macherey-Nagel NucleoSpin kit produced the highest RNA yields. The QIAGEN Exo kit produced lesser yields than what could be extracted from the UC fraction using the QIAGEN miRNeasy kits and the Macherey-Nagel NucleoSpin kit. Bioanalyzer results showed an average correlation of R² = 0.8 with endogenous miRNA qRT-PCR results, for sample concentrations >40 pg/µl. The levels of the endogenous miRNAs measured in the two volunteer samples were compared with those in a larger group of subjects (n = 10) and found to be typical. Our comparison favors the use of the QIAGEN Serum/Plasma kit and the Macherey-Nagel NucleoSpin kit for plasma miRNA applications. Furthermore, extraction of miRNAs from the UC fraction results in higher yield than extraction from whole plasma.

Physiological adaptations to interval training and the role of exercise intensity

Interval exercise typically involves repeated bouts of relatively intense exercise interspersed by short periods of recovery. A common classification scheme subdivides this method into high-intensity interval training (HIIT; 'near maximal' efforts) and sprint interval training (SIT; 'supramaximal' efforts). Both forms of interval training induce the classic physiological adaptations characteristic of moderate-intensity continuous training (MICT) such as increased aerobic capacity (V̇O2 max ) and mitochondrial content. This brief review considers the role of exercise intensity in mediating physiological adaptations to training, with a focus on the capacity for aerobic energy metabolism. With respect to skeletal muscle adaptations, cellular stress and the resultant metabolic signals for mitochondrial biogenesis depend largely on exercise intensity, with limited work suggesting that increases in mitochondrial content are superior after HIIT compared to MICT, at least when matched-work comparisons are made within the same individual. It is well established that SIT increases mitochondrial content to a similar extent to MICT despite a reduced exercise volume. At the whole-body level, V̇O2 max is generally increased more by HIIT than MICT for a given training volume, whereas SIT and MICT similarly improve V̇O2 max despite differences in training volume. There is less evidence available regarding the role of exercise intensity in mediating changes in skeletal muscle capillary density, maximum stroke volume and cardiac output, and blood volume. Furthermore, the interactions between intensity and duration and frequency have not been thoroughly explored. While interval training is clearly a potent stimulus for physiological remodelling in humans, the integrative response to this type of exercise warrants further attention, especially in comparison to traditional endurance training.

Compliance with physical exercise: using a multidisciplinary approach within a dose-dependent exercise study of moderately overweight men

AIMS

Sixty-one healthy, sedentary, moderately overweight young men participated in a randomised controlled trial to examine the effects of two different doses of endurance exercise on health behaviour and exercise compliance.

METHODS

Participants were randomised to a sedentary control group, a moderate (MOD; 300 kcal/day) or a high-dose (HIGH; 600 kcal/day) endurance exercise group for 12 weeks. A sub-set of the subjects were interviewed using pre-determined, qualitative questions to elucidate physical activity and health behaviour. In combination with the Theory of Planned Behaviour (TPB), a post hoc thematic analysis was conducted to connect qualitative and quantitative data in a joint analysis.

RESULTS

Of the subjects interviewed, exercise compliance expressed as 95% CI was [96.8; 103%] in the MOD group and [82.9; 99.6%] in the HIGH group. The different doses of daily exercise equally improved various metabolic health parameters. The MOD group was untroubled by the exercise load and had a positive attitude towards exercise. The HIGH group expressed increased fatigue, less positivity and perceived exercise as time-consuming. The MOD group described themselves as more energetic, and thereby may have increased physical activity levels in areas of their everyday lives that were not related to the intervention.

CONCLUSIONS

A multidisciplinary approach provided explanations for similar effects of two different doses of exercise. This could not have been determined via either qualitative or quantitative methodology alone. The preconditions of the TBP were fulfilled, and it represents a methodological model to explain the high degree of compliance and motivation to exercise.