High-intensity interval training combining rowing and cycling improves but does not restore beta-cell function in type 2 diabetes

Aim

We investigated whether a high-intensity interval training (HIIT) protocol could restore beta-cell function in type 2 diabetes compared with sedentary obese and lean individuals.

Materials and methods

In patients with type 2 diabetes, and age-matched, glucose-tolerant obese and lean controls, we examined the effect of 8 weeks of supervised HIIT combining rowing and cycling on the acute (first-phase) and second-phase insulin responses, beta-cell function adjusted for insulin sensitivity (disposition index), and serum free fatty acid (FFA) levels using the Botnia clamp (1-h IVGTT followed by 3-h hyperinsulinemic-euglycemic clamp).

Results

At baseline, patients with type 2 diabetes had reduced insulin sensitivity (~40%), acute insulin secretion (~13-fold), and disposition index (>35-fold), whereas insulin-suppressed serum FFA was higher (⁓2.5-fold) compared with controls (all P < 0.05). The HIIT protocol increased insulin sensitivity in all groups (all P < 0.01). In patients with type 2 diabetes, this was accompanied by a large (>200%) but variable improvement in the disposition index (P < 0.05). Whereas insulin sensitivity improved to the degree seen in controls at baseline, the disposition index remained markedly lower in patients with type 2 diabetes after HIIT (all P < 0.001). In controls, HIIT increased the disposition index by ~20-30% (all P < 0.05). In all groups, the second-phase insulin responses and insulin-suppressed FFA levels were reduced in response to HIIT (all P < 0.05). No group differences were seen in these HIIT-induced responses.

Conclusion

HIIT combining rowing and cycling induced a large but variable increase in beta-cell function adjusted for insulin sensitivity in type 2 diabetes, but the disposition index remained severely impaired compared to controls, suggesting that this defect is less reversible in response to exercise training than insulin resistance.

Trial registration

ClinicalTrials.gov (NCT03500016).

Acute exercise increases the contact between lipid droplets and mitochondria independently of obesity and type 2 diabetes

Intramuscular lipid droplets (LDs) and mitochondria are essential organelles in cellular communication and metabolism, supporting local energy demands during muscle contractions. While insulin resistance impacts cellular functions and systems within the skeletal muscle, it remains unclear whether the interaction of LDs and mitochondria is affected by exercise and the role of obesity and type 2 diabetes. By employing transmission electron microscopy (TEM), we aimed to investigate the effects of 1-hour ergometry cycling on LD morphology, subcellular distribution, and mitochondrial contact in skeletal muscle fibres of patients with type 2 diabetes and glucose-tolerant lean and obese controls, matched for equal exercise intensities. Exercise did not change LD volumetric density, numerical density, profile size, or subcellular distribution. However, evaluated as the magnitude of inter-organelle contact, exercise increased the contact between LDs and mitochondria with no differences between the three groups. This effect was most profound in the subsarcolemmal space of type 1 muscle fibres, and here the absolute contact length increased on average from ∼275 to ∼420 nm. Furthermore, the absolute contact length before exercise (ranging from ∼140 to ∼430 nm) was positively associated with the fat oxidation rate during exercise. In conclusion, we showed that acute exercise did not mediate changes in the LD volume fractions, numbers, or size but increased the contact between LDs and mitochondria, irrespective of obesity or type 2 diabetes. These data suggest that the increased LD-mitochondrial contact with exercise is not disturbed in obesity or type 2 diabetes. KEY POINTS: Type 2 diabetes is associated with altered interactivity between lipid droplets (LDs) and mitochondria in the skeletal muscle. Physical contact between the surface of LDs and the surrounding mitochondrial network is considered favorable for fat oxidation. We show that one hour of acute exercise increases the length of contact between LDs and mitochondria, irrespective of obesity or type 2 diabetes. This contact length between LDs and mitochondria is not associated with a net decrease in the LD volumetric density after the acute exercise. However, it correlates with the fat oxidation rate during exercise. Our data establish that exercise mediates contact between LDs and the mitochondrial network and that this effect is not impaired in individuals with type 2 diabetes or obesity. Abstract figure legend One hour of acute exercise increases the absolute and relative measured contact between lipid droplets and mitochondria, irrespective of obesity or type 2 diabetes. Increases in lipid droplet-mitochondrial contact were not associated with changes in lipid droplet content (volume fractions) nor volumetric composition (number or size). The figure was designed using BioRender and resources from Flaticon.com. This article is protected by copyright. All rights reserved.

Altered intramuscular network of lipid droplets and mitochondria in type 2 diabetes

Excessive storage of lipid droplets (LDs) in skeletal muscles is a hallmark of type 2 diabetes. However, LD morphology displays a high degree of subcellular heterogeneity and varies between single muscle fibers, which impedes the current understanding of lipid-induced insulin resistance. Using quantitative transmission electron microscopy (TEM), we conducted a comprehensive single-fiber morphological analysis to investigate the intramuscular network of LDs and mitochondria, and the effects of 8 wk of high-intensity interval training (HIIT) targeting major muscle groups, in patients with type 2 diabetes and nondiabetic obese and lean controls. We found that excessive storage of intramuscular lipids in patients with type 2 diabetes was exclusively explained by extremely large LDs situated in distinct muscle fibers with a location-specific deficiency in subsarcolemmal mitochondria. After HIIT, this intramuscular deficiency was improved by a remodeling of LD size and subcellular distribution and mitochondrial content. Analysis of LD morphology further revealed that individual organelles were better described as ellipsoids than spheres. Moreover, physical contact between LD and mitochondrial membranes indicated a dysfunctional interplay between organelles in the diabetic state. Taken together, type 2 diabetes should be recognized as a metabolic disease with high cellular heterogeneity in intramuscular lipid storage, underlining the relevance of single-cell technologies in clinical research. Furthermore, HIIT changed intramuscular LD storage toward nondiabetic characteristics.

High-intensity interval training combining rowing and cycling efficiently improves insulin sensitivity, body composition and VO2max in men with obesity and type 2 diabetes

AIMS

Non-weight-bearing high-intensity interval training (HIIT) involving several muscle groups may efficiently improve metabolic health without compromising adherence in obesity and type 2 diabetes. In a non-randomized intervention study, we examined the effect of a novel HIIT-protocol, recruiting both lower and upper body muscles, on insulin sensitivity, measures of metabolic health and adherence in obesity and type 2 diabetes.

METHODS

In 15 obese men with type 2 diabetes and age-matched obese (n=15) and lean (n=18) glucose-tolerant men, the effects of 8-weeks supervised HIIT combining rowing and cycling on ergometers (3 sessions/week) were examined by DXA-scan, incremental exercise test and hyperinsulinemic-euglycemic clamp combined with indirect calorimetry.

RESULTS

At baseline, insulin-stimulated glucose disposal rate (GDR) was ~40% reduced in the diabetic vs the non-diabetic groups (all p<0.01). In response to HIIT, insulin-stimulated GDR increased ~30-40% in all groups (all p<0.01) entirely explained by increased glucose storage. These changes were accompanied by ~8-15% increases in VO₂max, (all p<0.01), decreased total fat mass and increased lean body mass in all groups (all p<0.05). There were no correlations between these training adaptations and no group-differences in these responses. HbA1c showed a clinically relevant decrease in men with type 2 diabetes (4±2 mmol/mol; p<0.05). Importantly, adherence was high (>95%) in all groups and no injuries were reported.

CONCLUSIONS

A novel HIIT-protocol recruiting lower and upper body muscles efficiently improves insulin sensitivity, VO₂max and body composition with intact responses in obesity and type 2 diabetes. The high adherence and lack of injuries show that non-weight-bearing HIIT involving several muscle groups is a promising mode of exercise training in obesity and type 2 diabetes.

Effect of Exercise Training on Fat Loss-Energetic Perspectives and the Role of Improved Adipose Tissue Function and Body Fat Distribution

In obesity, excessive abdominal fat, especially the accumulation of visceral adipose tissue (VAT), increases the risk of metabolic disorders, such as type 2 diabetes mellitus (T2DM), cardiovascular disease, and non-alcoholic fatty liver disease. Excessive abdominal fat is associated with adipose tissue dysfunction, leading to systemic low-grade inflammation, fat overflow, ectopic lipid deposition, and reduced insulin sensitivity. Physical activity is recommended for primary prevention and treatment of obesity, T2DM, and related disorders. Achieving a stable reduction in body weight with exercise training alone has not shown promising effects on a population level. Because fat has a high energy content, a large amount of exercise training is required to achieve weight loss. However, even when there is no weight loss, exercise training is an effective method of improving body composition (increased muscle mass and reduced fat) as well as increasing insulin sensitivity and cardiorespiratory fitness. Compared with traditional low-to-moderate-intensity continuous endurance training, high-intensity interval training (HIIT) and sprint interval training (SIT) are more time-efficient as exercise regimens and produce comparable results in reducing total fat mass, as well as improving cardiorespiratory fitness and insulin sensitivity. During high-intensity exercise, carbohydrates are the main source of energy, whereas, with low-intensity exercise, fat becomes the predominant energy source. These observations imply that HIIT and SIT can reduce fat mass during bouts of exercise despite being associated with lower levels of fat oxidation. In this review, we explore the effects of different types of exercise training on energy expenditure and substrate oxidation during physical activity, and discuss the potential effects of exercise training on adipose tissue function and body fat distribution.

[Infrared tympanic thermometry. Experience and training does not improve the quality of measurement results]

Nurses, with and without training in the use of infrared tympanic thermometry, performed measurement sequences on patients. One rectal and two repeated measurements with each of two types of equipment for infrared tympanic thermometry (Genius, Core Check) were used in each sequence. Rectal measurements showed temperatures significantly higher than infrared tympanic thermometry, but there were variations (Genius 0.3 +/- 0.58 (SD) degree C, Core Check 0.5 +/- 0.42 (SD) degree C). The sensitivity of infrared tympanic thermometry for fever, as defined by rectal measurements, was 36% for Genius and 21% for Core Check. The quality of the measurements was not improved by training. Our results indicate that infrared tympanic thermometry should be used with caution when screening for fever in hospitals.

Can training improve the results with infrared tympanic thermometers?

BACKGROUND

Infrared tympanic thermometry (ITT) is a method for body temperature measurement. Correct measuring technique is said to be important to achieve good results with this method. The objective of this study was to investigate the accuracy and effect of training in the use of infrared tympanic thermometry (ITT) on the measurement results.

METHOD

Nurses trained in the use of ITT, and nurses not trained performed measurement sequences on 65 patients: one rectal and two ITT measurements in each sequence.

RESULTS

Mean rectal temperatures were significantly (P < 0.01) higher than with ITT (0.44 +/- 0.42 (SD) degree C for trained, 0.56 +/- 0.4 (SD) degree C for untrained). Coefficient of repeatability for ITT measurements was +/- 0.54 degree C for trained nurses, and +/- 0.48 degree C for untrained. With ITT temperatures adjusted upwards of 0.5 degree C, the sensitivity of ITT for detecting fever as defined by rectal measurements would be 70% for trained, and 54% for untrained nurses. Repeatability and sensitivity for trained and untrained nurses were not significantly (P > 0.05) different.

CONCLUSION

Training had little effect on the accuracy of the measurements. According to our results, ITT is often unreliable and should be used with caution.

Phase transitions in the membrane of a marine bacterium, Pseudomonas BAL-31

An unsaturated fatty acid auxotroph, strain UFA, isolated from the marine pseudomonad Pseudomonas BAL-31, host cell of the lipid-containing bacteriophage PM2, was grown in media supplemented with different unsaturated fatty acids. Under these conditions the fatty acid composition of the cell could be altered drastically. The phase transition in the native membrane and in the extracted lipids was analyzed by electron spin resonance using a nitroxide spin probe. Membranes prepared from strain UFA grown in cis16:1 or trans16:1 showed one transition at 9.4 degrees C and 12.4 degrees C respectively. Extracted lipids in both cases had almost the same transition temperature as that of the intact membrane. Membranes prepared from Pseudomonas BAL-31 had one transition at approximately 12 degrees C, on the other hand there was no clear cut phase transition using extracted lipids. Replication of bacteriophage PM2 took place below the transition temperature of the membrane lipids in the case where strain UFA was grown in tran16:1. Other cases were not studied.