Bone Marrow Metabolism Is Impaired in Insulin Resistance and Improves After Exercise Training.

CONTEXT: Exercise training improves bone mineral density, but little is known about the effects of training on bone marrow (BM) metabolism. BM insulin sensitivity has been suggested to play an important role in bone health and whole-body insulin sensitivity. OBJECTIVE: To study the effects of exercise training on BM metabolism. DESIGN: Randomized controlled trial. SETTING: Clinical research center. PARTICIPANTS: Sedentary healthy (n = 28, 40-55 years, all males) and insulin resistant (IR) subjects (n = 26, 43-55 years, males/females 16/10). INTERVENTION: Two weeks of sprint interval training or moderate-intensity continuous training. MAIN OUTCOME MEASURES: We measured femoral, lumbar, and thoracic BM insulin-stimulated glucose uptake (GU) and fasting free fatty acid uptake (FFAU) using positron-emission tomography and bone turnover markers from plasma. RESULTS: At baseline, GU was highest in lumbar, followed by thoracic, and lowest in femoral BM (all Ps < 0.0001). FFAU was higher in lumbar and thoracic than femoral BM (both Ps < 0.0001). BM FFAU and femoral BM GU were higher in healthy compared to IR men and in females compared to males (all Ps < 0.05). Training increased femoral BM GU similarly in all groups and decreased lumbar BM FFAU in males (all Ps < 0.05). Osteocalcin and PINP were lower in IR than healthy men and correlated positively with femoral BM GU and glycemic status (all Ps < 0.05). CONCLUSIONS: BM metabolism differs regarding anatomical location. Short-term training improves BM GU and FFAU in healthy and IR subjects. Bone turnover rate is decreased in insulin resistance and associates positively with BM metabolism and glycemic control. CLINICAL TRIAL REGISTRATION NUMBER: NCT01344928.

Exercise training improves adipose tissue metabolism and vasculature regardless of baseline glucose tolerance and sex.

INTRODUCTION: We 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 METHODS: 26 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. RESULTS: Training 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. CONCLUSIONS: Short-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.

Exercise Training Modulates Gut Microbiota Profile and Improves Endotoxemia.

INTRODUCTION: Intestinal metabolism and microbiota profiles are impaired in obesity and insulin resistance. Moreover, dysbiotic gut microbiota has been suggested to promote systemic low-grade inflammation and insulin resistance through the release of endotoxins particularly lipopolysaccharides. We have previously shown that exercise training improves intestinal metabolism in healthy men. To understand whether changes in intestinal metabolism interact with gut microbiota and its release of inflammatory markers, we studied the effects of sprint interval (SIT) and moderate-intensity continuous training (MICT) on intestinal metabolism and microbiota in subjects with insulin resistance. METHODS: Twenty-six, sedentary subjects (prediabetic, n = 9; type 2 diabetes, n = 17; age, 49 [SD, 4] yr; body mass index, 30.5 [SD, 3]) were randomized into SIT or MICT. Intestinal insulin-stimulated glucose uptake (GU) and fatty acid uptake (FAU) from circulation were measured using positron emission tomography. Gut microbiota composition was analyzed by 16S rRNA gene sequencing and serum inflammatory markers with multiplex assays and enzyme-linked immunoassay kit. RESULTS: V˙O2peak improved only after SIT (P = 0.01). Both training modes reduced systematic and intestinal inflammatory markers (tumor necrosis factor-α, lipopolysaccharide binding protein) (time P < 0.05). Training modified microbiota profile by increasing Bacteroidetes phylum (time P = 0.03) and decreasing Firmicutes/Bacteroidetes ratio (time P = 0.04). Moreover, there was a decrease in Clostridium genus (time P = 0.04) and Blautia (time P = 0.051). Only MICT decreased jejunal FAU (P = 0.02). Training had no significant effect on intestinal GU. Colonic GU associated positively with Bacteroidetes and inversely with Firmicutes phylum, ratio Firmicutes/Bacteroidetes and Blautia genus. CONCLUSIONS: Intestinal substrate uptake associates with gut microbiota composition and whole-body insulin sensitivity. Exercise training improves gut microbiota profiles and reduces endotoxemia.

Effects of short-term sprint interval and moderate-intensity continuous training on liver fat content, lipoprotein profile, and substrate uptake: a randomized trial.

Type 2 diabetes (T2D) and increased liver fat content (LFC) alter lipoprotein profile and composition and impair liver substrate uptake. Exercise training mitigates T2D and reduces LFC, but the benefits of different training intensities in terms of lipoprotein classes and liver substrate uptake are unclear. The aim of this study was to evaluate the effects of moderate-intensity continuous training (MICT) or sprint interval training (SIT) on LFC, liver substrate uptake, and lipoprotein profile in subjects with normoglycemia or prediabetes/T2D. We randomized 54 subjects (normoglycemic group, n = 28; group with prediabetes/T2D, n = 26; age = 40-55 yr) to perform either MICT or SIT for 2 wk and measured LFC with magnetic resonance spectroscopy, lipoprotein composition with NMR, and liver glucose uptake (GU) and fatty acid uptake (FAU) using PET. At baseline, the group with prediabetes/T2D had higher LFC, impaired lipoprotein profile, and lower whole body insulin sensitivity and aerobic capacity compared with the normoglycemic group. Both training modes improved aerobic capacity (P < 0.001) and lipoprotein profile (reduced LDL and increased large HDL subclasses; all P < 0.05) with no training regimen (SIT vs. MICT) or group effect (normoglycemia vs. prediabetes/T2D). LFC tended to be reduced in the group with prediabetes/T2D compared with the normoglycemic group posttraining (P = 0.051). When subjects were divided according to LFC (high LFC, >5.6%; low LFC, <5.6%), training reduced LFC in subjects with high LFC (P = 0.009), and only MICT increased insulin-stimulated liver GU (P = 0.03). Short-term SIT and MICT are effective in reducing LFC in subjects with fatty liver and in improving lipoprotein profile regardless of baseline glucose tolerance. Short-term MICT is more efficient in improving liver insulin sensitivity compared with SIT. NEW & NOTEWORTHY In the short term, both sprint interval training and moderate-intensity continuous training (MICT) reduce liver fat content and improve lipoprotein profile; however, MICT seems to be preferable in improving liver insulin sensitivity.

Intramyocellular lipid accumulation after sprint interval and moderate-intensity continuous training in healthy and diabetic subjects.

The effects of sprint interval training (SIT) on intramyocellular (IMCL) and extramyocellular (EMCL) lipid accumulation are unclear. We tested the effects of SIT and moderate-intensity continuous training (MICT) on IMCL and EMCL accumulation in a randomized controlled setting in two different study populations; healthy untrained men (n 28) and subjects with type 2 diabetes (T2D) or prediabetes (n 26). Proton magnetic resonance spectroscopy (1 H MRS) was used to determine IMCL and EMCL in the Tibialis anterior muscle (TA) before and after a 2-week exercise period. The exercise period comprised six sessions of SIT or MICT cycling on a cycle ergometer. IMCL increased after SIT compared to MICT (P = 0.042) in both healthy and T2D/prediabetic subjects. On EMCL the training intervention had no significant effect. In conclusion, IMCL serves as an important energy depot during exercise and can be extended by high intensity exercise. The effects of high intensity interval exercise on IMCL seem to be similar regardless of insulin sensitivity or the presence of T2D.

Exercise training decreases pancreatic fat content and improves beta cell function regardless of baseline glucose tolerance: a randomised controlled trial.

AIMS/HYPOTHESIS: Pancreatic fat accumulation may contribute to the development of beta cell dysfunction. Exercise training improves whole-body insulin sensitivity, but its effects on pancreatic fat content and beta cell dysfunction are unclear. The aim of this parallel-group randomised controlled trial was to evaluate the effects of exercise training on pancreatic fat and beta cell function in healthy and prediabetic or type 2 diabetic participants and to test whether the responses were similar regardless of baseline glucose tolerance. METHODS: Using newspaper announcements, a total of 97 sedentary 40-55-year-old individuals were assessed for eligibility. Prediabetes (impaired fasting glucose and/or impaired glucose tolerance) and type 2 diabetes were defined by ADA criteria. Of the screened candidates, 28 healthy men and 26 prediabetic or type 2 diabetic men and women met the inclusion criteria and were randomised into 2-week-long sprint interval or moderate-intensity continuous training programmes in a 1:1 allocation ratio using random permuted blocks. The primary outcome was pancreatic fat, which was measured by magnetic resonance spectroscopy. As secondary outcomes, beta cell function was studied using variables derived from OGTT, and whole-body insulin sensitivity and pancreatic fatty acid and glucose uptake were measured using positron emission tomography. The measurements were carried out at the Turku PET Centre, Finland. The analyses were based on an intention-to-treat principle. Given the nature of the intervention, blinding was not applicable. RESULTS: At baseline, the group of prediabetic or type 2 diabetic men had a higher pancreatic fat content and impaired beta cell function compared with the healthy men, while glucose and fatty acid uptake into the pancreas was similar. Exercise training decreased pancreatic fat similarly in healthy (from 4.4% [3.0%, 6.1%] to 3.6% [2.4%, 5.2%] [mean, 95% CI]) and prediabetic or type 2 diabetic men (from 8.7% [6.0%, 11.9%] to 6.7% [4.4%, 9.6%]; p = 0.036 for time effect) without any changes in pancreatic substrate uptake (p ≥ 0.31 for time effect in both insulin-stimulated glucose and fasting state fatty acid uptake). In prediabetic or type 2 diabetic men and women, both exercise modes similarly improved variables describing beta cell function. CONCLUSIONS/INTERPRETATION: Two weeks of exercise training improves beta cell function in prediabetic or type 2 diabetic individuals and decreases pancreatic fat regardless of baseline glucose tolerance. This study shows that short-term training efficiently reduces ectopic fat within the pancreas, and exercise training may therefore reduce the risk of type 2 diabetes. TRIAL REGISTRATION: ClinicalTrials.gov NCT01344928 FUNDING: This study was funded by the Emil Aaltonen Foundation, the European Foundation for the Study of Diabetes, the Finnish Diabetes Foundation, the Orion Research Foundation, the Academy of Finland (grants 251399, 256470, 281440, and 283319), the Ministry of Education of the State of Finland, the Paavo Nurmi Foundation, the Novo Nordisk Foundation, the Finnish Cultural Foundation, the Hospital District of Southwest Finland, the Turku University Foundation, and the Finnish Medical Foundation.

Short-term interval training alters brain glucose metabolism in subjects with insulin resistance.

Brain insulin-stimulated glucose uptake (GU) is increased in obese and insulin resistant subjects but normalizes after weight loss along with improved whole-body insulin sensitivity. Our aim was to study whether short-term exercise training (moderate intensity continuous training (MICT) or sprint interval training (SIT)) alters substrates for brain energy metabolism in insulin resistance. Sedentary subjects ( n = 21, BMI 23.7-34.3 kg/m2, age 43-55 y) with insulin resistance were randomized into MICT ( n = 11, intensity≥60% of VO2peak) or SIT ( n = 10, all-out) groups for a two-week training intervention. Brain GU during insulin stimulation and fasting brain free fatty acid uptake (FAU) was measured using PET. At baseline, brain GU was positively associated with the fasting insulin level and negatively with the whole-body insulin sensitivity. The whole-body insulin sensitivity improved with both training modes (20%, p = 0.007), while only SIT led to an increase in aerobic capacity (5%, p = 0.03). SIT also reduced insulin-stimulated brain GU both in global cortical grey matter uptake (12%, p = 0.03) and in specific regions ( p < 0.05, all areas except the occipital cortex), whereas no changes were observed after MICT. Brain FAU remained unchanged after the training in both groups. These findings show that short-term SIT effectively decreases insulin-stimulated brain GU in sedentary subjects with insulin resistance.

Sprint interval training decreases left-ventricular glucose uptake compared to moderate-intensity continuous training in subjects with type 2 diabetes or prediabetes.

Type 2 diabetes mellitus (T2DM) is associated with reduced myocardial glucose uptake (GU) and increased free fatty acid uptake (FFAU). Sprint interval training (SIT) improves physical exercise capacity and metabolic biomarkers, but effects of SIT on cardiac function and energy substrate metabolism in diabetic subjects are unknown. We tested the hypothesis that SIT is more effective than moderate-intensity continuous training (MICT) on adaptations in left and right ventricle (LV and RV) glucose and fatty acid metabolism in diabetic subjects. Twenty-six untrained men and women with T2DM or prediabetes were randomized into two-week-long SIT (n = 13) and MICT (n = 13) interventions. Insulin-stimulated myocardial GU and fasted state FFAU were measured by positron emission tomography and changes in LV and RV structure and function by cardiac magnetic resonance. In contrast to our hypothesis, SIT significantly decreased GU compared to MICT in LV. FFAU of both ventricles remained unchanged by training. RV end-diastolic volume (EDV) and RV mass increased only after MICT, whereas LV EDV, LV mass, and RV and LV end-systolic volumes increased similarly after both training modes. As SIT decreases myocardial insulin-stimulated GU compared to MICT which may already be reduced in T2DM, SIT may be metabolically less beneficial than MICT for a diabetic heart.

Exercise Training Reduces Intrathoracic Fat Regardless of Defective Glucose Tolerance.

PURPOSE: Epicardial (EAT) and pericardial (PAT) fat masses and myocardial triglyceride content (MTC) are enlarged in obesity and insulin resistance. We studied whether the high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) similarly decrease ectopic fat in and around the heart and whether the decrease is similar in healthy subjects and subjects with defective glucose tolerance (DGT). METHODS: A total of 28 healthy men (body mass index = 20.7-30.0 kg·m, age = 40-55 yr) and 16 men with DGT (body mass index = 23.8-33.5 kg·m, age = 43-53 yr) were randomized into HIIT and MICT interventions for 2 wk. EAT and PAT were determined by computed tomography and MTC by H-MRS. RESULTS: At baseline, DGT subjects had impaired aerobic capacity and insulin sensitivity and higher levels of whole body fat, visceral fat, PAT, and EAT (P < 0.05, all) compared with healthy subjects. In the whole group, HIIT increased aerobic capacity (HIIT = 6%, MICT = 0.3%; time × training P = 0.007) and tended to improve insulin sensitivity (HIIT = 24%, MICT = 8%) as well as reduce MTC (HIIT = -42%, MICT = +23%) (time × training P = 0.06, both) more efficiently compared with MICT, and without differences in the training response between the healthy and the DGT subjects. However, both training modes decreased EAT (-5%) and PAT (-6%) fat (time P < 0.05) and not differently between the healthy and the DGT subjects. CONCLUSION: Whole body fat, visceral fat, PAT, and EAT masses are enlarged in DGT. Both HIIT and MICT effectively reduce EAT and PAT in healthy and DGT subjects, whereas HIIT seems to be superior as regards improving aerobic capacity, whole-body insulin sensitivity, and MTC.

Two weeks of moderate-intensity continuous training, but not high-intensity interval training, increases insulin-stimulated intestinal glucose uptake.

Similar to muscles, the intestine is also insulin resistant in obese subjects and subjects with impaired glucose tolerance. Exercise training improves muscle insulin sensitivity, but its effects on intestinal metabolism are not known. We studied the effects of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on intestinal glucose and free fatty acid uptake from circulation in humans. Twenty-eight healthy, middle-aged, sedentary men were randomized for 2 wk of HIIT or MICT. Intestinal insulin-stimulated glucose uptake and fasting free fatty acid uptake from circulation were measured using positron emission tomography and [18F]FDG and [18F]FTHA. In addition, effects of HIIT and MICT on intestinal GLUT2 and CD36 protein expression were studied in rats. Training improved aerobic capacity (P = 0.001) and whole body insulin sensitivity (P = 0.04), but not differently between HIIT and MICT. Insulin-stimulated glucose uptake increased only after the MICT in the colon (HIIT = 0%; MICT = 37%) (P = 0.02 for time × training) and tended to increase in the jejunum (HIIT = -4%; MICT = 13%) (P = 0.08 for time × training). Fasting free fatty acid uptake decreased in the duodenum in both groups (HIIT = -6%; MICT = -48%) (P = 0.001 time) and tended to decrease in the colon in the MICT group (HIIT = 0%; MICT = -38%) (P = 0.08 for time × training). In rats, both training groups had higher GLUT2 and CD36 expression compared with control animals. This study shows that already 2 wk of MICT enhances insulin-stimulated glucose uptake, while both training modes reduce fasting free fatty acid uptake in the intestine in healthy, middle-aged men, providing an additional mechanism by which exercise training can improve whole body metabolism.NEW & NOTEWORTHY This is the first study where the effects of exercise training on the intestinal substrate uptake have been investigated using the most advanced techniques available. We also show the importance of exercise intensity in inducing these changes.

Left ventricular vascular and metabolic adaptations to high-intensity interval and moderate intensity continuous training: a randomized trial in healthy middle-aged men.

KEY POINTS: High-intensity interval training (HIIT) has become popular, time-sparing alternative to moderate intensity continuous training (MICT), although the cardiac vascular and metabolic effects of HIIT are incompletely known. We compared the effects of 2-week interventions with HIIT and MICT on myocardial perfusion and free fatty acid and glucose uptake. Insulin-stimulated myocardial glucose uptake was decreased by training without any significantly different response between the groups, whereas free fatty acid uptake remained unchanged. Adenosine-stimulated myocardial perfusion responded differently to the training modes (change in mean HIIT: -19%; MICT: +9%; P = 0.03 for interaction) and was correlated with myocardial glucose uptake for the entire dataset and especially after HIIT training. HIIT and MICT induce similar metabolic and functional changes in the heart, although myocardial vascular hyperaemic reactivity is impaired after HIIT, and this should be considered when prescribing very intense HIIT for previously untrained subjects. ABSTRACT: High-intensity interval training (HIIT) is a time-efficient way of obtaining the health benefits of exercise, although the cardiac effects of this training mode are incompletely known. We compared the effects of short-term HIIT and moderate intensity continuous training (MICT) interventions on myocardial perfusion and metabolism and cardiac function in healthy, sedentary, middle-aged men. Twenty-eight healthy, middle-aged men were randomized to either HIIT or MICT groups (n = 14 in both) and underwent six cycle ergometer training sessions within 2 weeks (HIIT session: 4-6 × 30 s all-out cycling/4 min recovery, MICT session 40-60 min at 60% V̇O2 peak ). Cardiac magnetic resonance imaging (CMRI) was performed to measure cardiac structure and function and positron emission tomography was used to measure myocardial perfusion at baseline and during adenosine stimulation, insulin-stimulated glucose uptake (MGU) and fasting free fatty acid uptake (MFFAU). End-diastolic and end-systolic volumes increased and ejection fraction slightly decreased with both training modes, although no other changes in CMRI were observed. MFFAU and basal myocardial perfusion remained unchanged. MGU was decreased by training (HIIT from 46.5 to 35.9; MICT from 47.4 to 44.4 mmol 100 g-1  min-1 , P = 0.007 for time, P = 0.11 for group × time). Adenosine-stimulated myocardial perfusion responded differently to the training modes (change in mean HIIT: -19%; MICT: +9%; P = 0.03 for group × time interaction). HIIT and MICT induce similar metabolic and functional changes in the heart, although myocardial vascular hyperaemic reactivity is impaired after HIIT. This should be taken into account when prescribing very intense HIIT for previously untrained subjects.

Right ventricular metabolic adaptations to high-intensity interval and moderate-intensity continuous training in healthy middle-aged men.

Despite the recent studies on structural and functional adaptations of the right ventricle (RV) to exercise training, adaptations of its metabolism remain unknown. We investigated the effects of short-term, high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on RV glucose and fat metabolism. Twenty-eight untrained, healthy 40-55 yr-old-men were randomized into HIIT (n = 14) and MICT (n = 14) groups. Subjects performed six supervised cycle ergometer training sessions within 2 wk (HIIT session: 4-6 × 30 s all-out cycling/4-min recovery; MICT session: 40-60 min at 60% peak O2 uptake). Primary outcomes were insulin-stimulated RV glucose uptake (RVGU) and fasted state RV free fatty acid uptake (RVFFAU) measured by positron emission tomography. Secondary outcomes were changes in RV structure and function, determined by cardiac magnetic resonance. RVGU decreased after training (-22% HIIT, -12% MICT, P = 0.002 for training effect), but RVFFAU was not affected by the training (P = 0.74). RV end-diastolic and end-systolic volumes, respectively, increased +5 and +7% for HIIT and +4 and +8% for MICT (P = 0.002 and 0.005 for training effects, respectively), but ejection fraction mildly decreased (-2% HIIT, -4% MICT, P = 0.034 for training effect). RV mass and stroke volume remained unaltered. None of the observed changes differed between the training groups (P > 0.12 for group × training interaction). Only 2 wk of physical training in previously sedentary subjects induce changes in RV glucose metabolism, volumes, and ejection fraction, which precede exercise-induced hypertrophy of RV.

Affective Responses to Repeated Sessions of High-Intensity Interval Training.

PURPOSE: Vigorous exercise feels unpleasant, and negative emotions may discourage adherence to regular exercise. We quantified the subjective affective responses to short-term high-intensity interval training (HIT) in comparison with moderate-intensity continuous training (MIT). METHODS: Twenty-six healthy middle-age (mean age, 47 ± 5 yr; mean VO2peak, 34.2 ± 4.1 mL·kg⁻¹·min⁻¹) sedentary men were randomized into HIT (n = 13, 4-6 × 30 s of all-out cycling efforts at approximately 180% of peak workload with 4-min recovery) or MIT (n = 13, 40- to 60-min continuous cycling at 60% of peak workload) groups, performing six sessions within two weeks. Perceived exertion, stress, and affective state were recorded before, during, and after each session. RESULTS: Perceived exertion and arousal were higher, and affective state, more negative during the HIT than that during MIT sessions (P < 0.001). HIT versus MIT exercise acutely increased the experience of stress, tension, and irritation and decreased positive affect (P < 0.05). In addition, satisfaction was lower and pain and negative affect were higher in the HIT than those in the MIT group (P < 0.05). However, perceived exertion and displeasure experienced during exercise alleviated similarly in response to HIT and MIT over the 6 d of training. Peak oxygen consumption increased (P < 0.001) after intervention (HIT, 34.7 ± 3.9 vs 36.7 ± 4.5; MIT, 33.9 ± 4.6 vs 35.0 ± 4.6) and was not different between HIT and MIT (P = 0.28 for group × training). CONCLUSIONS: Short-term HIT and MIT are equally effective in improving aerobic fitness, but HIT increases experience of negative emotions and exertion in sedentary middle-age men. This may limit the adherence to this time-effective training mode, even though displeasure lessens over time and suggests similar mental adaptations to both MIT and HIT.

Muscle-specific glucose and free fatty acid uptake after sprint interval and moderate-intensity training in healthy middle-aged men.

We tested the hypothesis that sprint interval training (SIT) causes larger improvements in glucose and free fatty acid uptake (FFAU) in lower and upper body muscles than moderate-intensity training (MIT). Twenty-eight healthy, untrained, middle-aged men were randomized into SIT (n = 14, 4-6 × 30 s of all-out cycling/4 min recovery) and MIT groups [n = 14, 40-60 min cycling at 60% of peak O2 uptake (V̇o2 peak)] and completed six training sessions within 2 wk. Pre- and postmeasurements included V̇o2 peak, whole body (M-value), muscle-specific insulin-stimulated glucose uptake (GU), and fasting FFAU measured with positron emission tomography in thigh [quadriceps femoris (QF) and hamstrings] and upper body (deltoids, biceps, and triceps brachii) muscles. V̇o2 peak and M-value improved significantly by 6 and 12% in SIT, and 3 and 8% in MIT, respectively,. GU increased significantly only in the QF, and there was no statistically significant difference between the training modes. GU increased in all four heads of QF in response to SIT, but only in the vasti muscles in response to MIT, whereas in rectus femoris the response was completely lacking. Training response in FFAU in QF was smaller and nonsignificant, but it also differed between the training modes in the rectus femoris. In conclusion, SIT and MIT increased insulin-stimulated GU only in the main working muscle QF and not in the upper body muscles. In addition, the biarticular rectus femoris did not respond to moderate-intensity training, reflecting most probably poor activation of it during moderate-intensity cycling.

Different Predictors of Right and Left Ventricular Metabolism in Healthy Middle-Aged Men.

Dysfunction of the right ventricle (RV) plays a crucial role in the outcome of various cardiovascular diseases. Previous studies on RV metabolism are sparse although evidence implies it may differ from left ventricular (LV) metabolism. Therefore, the aims of this study were (1) to determine predictors of RV glucose uptake (GU) and free fatty acid uptake (FFAU) and (2) to compare them to predictors of LV metabolism in healthy middle-aged men. Altogether 28 healthy, sedentary, middle-aged (40-55 years) men were studied. Insulin-stimulated GU and fasting FFAU were measured by positron emission tomography and RV and LV structural and functional parameters by cardiac magnetic resonance. Several parameters related to whole-body health were also measured. Predictors of RV and LV metabolism were determined by pairwise correlation analysis, lasso regression models, and variable clustering using heatmap. RVGU was most strongly predicted by age and moderately by RV ejection fraction (EF). The strongest determinants of RVFFAU were exercise capacity (peak oxygen uptake), resting heart rate, LVEF, and whole-body insulin-stimulated glucose uptake rate. When considering LV metabolism, age and RVEF were associated also with LVGU. In addition, LVGU was strongly, and negatively, influenced by whole-body insulin-stimulated glucose uptake rate. LVFFAU was predicted only by LVEF. This study shows that while RV and LV metabolism have shared characteristics, they also have unique properties. Age of the subject should be taken into account when measuring myocardial glucose utilization. Ejection fraction is related to myocardial metabolism, and even so that RVEF may be more closely related to GU of both ventricles and LVEF to FFAU of both ventricles, a finding supporting the ventricular interdependence. However, only RV fatty acid utilization associates with exercise capacity so that better physical fitness in a relatively sedentary population is related with decreased RV fat metabolism. To conclude, this study highlights the need for further study designed specifically on less-known RV, as the results on LV metabolism and physiology may not be directly applicable to the RV.