Aims Little is known about the effects of exercise training on brown adipose tissue (BAT) metabolism in humans. We tested the hypothesis that high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) improve BAT insulin sensitivity. Materials and methods Healthy middle-aged men (n = 18, age 47 years [95% confidence interval {CI} 49, 43}, body mass index 25.3 kg/m2 [95% CI 24.1, 26.3], peak oxygen uptake (VO2peak) 34.8 mL/kg/min [95% CI 32.1, 37.4]) were recruited and randomized into six HIIT or MICT sessions within 2 weeks. Insulin-stimulated glucose uptake was measured using 2-[18F]fluoro-2-deoxy-D-glucose positron-emission tomography in BAT, skeletal muscle and abdominal and femoral subcutaneous and visceral white adipose tissue (WAT) depots before and after the training interventions. Results Training improved VO2peak (P=0.0005), insulin-stimulated glucose uptake into quadriceps femoris muscle (P=0.0009) and femoral subcutaneous white adipose tissue (P=0.02), but not into BAT, with no difference between the training modes. Using pre-intervention BAT glucose uptake, we next stratified subjects into high BAT (>2.9μmol/100g/min; n=6) or low BAT (<2.9 μmol/100g/min; n=12) groups. Interestingly, training decreased insulin-stimulated BAT glucose uptake in the high BAT group (4.0 [2.8, 5.5] vs. 2.5 [1.7, 3.6]) (training*BAT, P=0.02), whereas there was no effect of training in the low BAT group (1.5 [1.2, 1.9] vs. 1.6 [1.2, 2.0] μmol·100g·min−1). High BAT subjects had lower levels of inflammatory markers compared to low BAT subjects. Conclusions Subjects with functionally active BAT have an improved metabolic profile compared to subjects with low BAT activity. Short-term exercise training decreases insulin-stimulated BAT glucose uptake in subjects with active BAT, suggesting that training does not work as a potent stimulus for BAT activation.

Background Short-term exercise training programs that consist of moderate intensity endurance training or high intensity interval training have become popular choices for healthy lifestyle modifications, with as little as two weeks of training being shown to improve cardiorespiratory fitness and whole-body glucose metabolism. An emerging concept in exercise biology is that exercise stimulates the release of cytokines and other factors into the blood that contribute to the beneficial effects of exercise on metabolism, but whether these factors behave similarly in response to moderate and high intensity short term training is not known. Here, we determined the effects of two short-term exercise training programs on the concentrations of select secreted cytokines and Klotho, a protein involved in anti-aging. Methods Healthy, sedentary men (n = 22) were randomized to moderate intensity training (MIT) or sprint intensity training (SIT) treatment groups. SIT consisted of 6 sessions over 2 weeks of 6 × 30 s all out cycle ergometer sprints with 4 min of recovery between sprints. MIT consisted of 6 sessions over 2 weeks of cycle ergometer exercise at 60% VO2peak, gradually increasing in duration from 40 to 60 min. Blood was taken before the intervention and 48 h after the last training session, and glucose uptake was measured using [18F]FDG‐PET/CT scanning. Cytokines were measured by multiplex and Klotho concentrations by ELISA. Results Both training protocols similarly increased VO2peak and decreased fat percentage and visceral fat (P < 0.05). MIT and SIT training programs both reduced the concentrations of IL-6, Hepatocyte Growth Factor (HGF) and Leptin. Interestingly, MIT, but not SIT increased monocyte chemoattractant protein-1 (MCP-1) concentrations, an exercise-induced cytokine, as well as Klotho concentrations. Conclusion Short-term exercise training at markedly different intensities similarly improves cardiovascular fitness but results in intensity-specific changes in cytokine responses to exercise.

IntroductionWe investigated the effects of a supervised progressive sprint interval training (SIT) and moderate-intensity continuous training (MICT) on adipocyte morphology and adipose tissue metabolism and function; we also tested whether the responses were similar regardless of baseline glucose tolerance and sex.Research design and methods26 insulin-resistant (IR) and 28 healthy participants were randomized into 2-week-long SIT (4–6×30 s at maximum effort) and MICT (40–60 min at 60% of maximal aerobic capacity (VO2peak)). Insulin-stimulated glucose uptake and fasting-free fatty acid uptake in visceral adipose tissue (VAT), abdominal and femoral subcutaneous adipose tissues (SATs) were quantified with positron emission tomography. Abdominal SAT biopsies were collected to determine adipocyte morphology, gene expression markers of lipolysis, glucose and lipid metabolism and inflammation.ResultsTraining increased glucose uptake in VAT (p<0.001) and femoral SAT (p<0.001) and decreased fatty acid uptake in VAT (p=0.01) irrespective of baseline glucose tolerance and sex. In IR participants, training increased adipose tissue vasculature and decreased CD36 and ANGPTL4 gene expression in abdominal SAT. SIT was superior in increasing VO2peak and VAT glucose uptake in the IR group, whereas MICT reduced VAT fatty acid uptake more than SIT.ConclusionsShort-term training improves adipose tissue metabolism both in healthy and IR participants independently of the sex. Adipose tissue angiogenesis and gene expression was only significantly affected in IR participants.