Lipid droplet remodelling and reduced muscle ceramides following sprint interval and moderate-intensity continuous exercise training in obese males.

BACKGROUND: In obesity, improved muscle insulin sensitivity following exercise training has been linked to the lowering of diacylglycerol (DAG) and ceramide concentrations. Little is known, however, about how improved insulin action with exercise training in obese individuals relates to lipid droplet (LD) adaptations in skeletal muscle. In this study we investigated the hypothesis that short-term sprint interval training (SIT) and moderate intensity continuous training (MICT) in obese individuals would increase perilipin (PLIN) expression, increase the proportion of LDs in contact with mitochondria and reduce muscle concentrations of DAGs and ceramides. METHODS: Sixteen sedentary obese males performed 4 weeks of either SIT (4-7 × 30 s sprints at 200% Wmax, 3 days.week(-1)) or MICT (40-60 min cycling at ~65% VO2peak, 5 days.week(-1)), and muscle biopsies were obtained pre- and post-training. RESULTS: Training increased PLIN2 (SIT 90%, MICT 68%) and PLIN5 (SIT 47%, MICT 34%) expression in type I fibres only, and increased PLIN3 expression in both type I (SIT 63%, MICT 67%) and type II fibres (SIT 70%, MICT 160%) (all P<0.05). Training did not change LD content but increased the proportion of LD in contact with mitochondria (SIT 12%, MICT 21%, P<0.01). Ceramides were reduced following training (SIT -10%, MICT -7%, P<0.05), but DAG was unchanged. No training × group interactions were observed for any variables. CONCLUSIONS: These results confirm the hypothesis that SIT and MICT results in remodelling of LDs and lowers ceramide concentrations in skeletal muscle of sedentary obese males.International Journal of Obesity accepted article preview online, 24 July 2017. doi:10.1038/ijo.2017.170

Sprint interval and moderate-intensity continuous training have equal benefits on aerobic capacity, insulin sensitivity, muscle capillarisation and endothelial eNOS/NAD(P)Hoxidase protein ratio in obese men

Sprint interval training (SIT) has been proposed as a time efficient alternative to moderate-intensity continuous training (MICT), leading to similar improvements in skeletal muscle capillary density and microvascular function in young healthy humans. In this study we made the first comparisons of the muscle microvascular response to SIT and MICT in an obese population. Sixteen young obese men (age 25±1 yr, BMI 34.8±0.9 kg.m-2) were randomly assigned to 4 weeks of MICT (40-60 min cycling at ~65% VO2peak, 5 times per wk.) or constant load SIT (4-7 constant workload intervals of 200% Wattmax 3 times per wk.). Muscle biopsies were taken before and after training from the m. vastus lateralis to measure muscle microvascular endothelial eNOS content, eNOS serine1177 phosphorylation, NOX2 content and capillarization using quantitative immunofluorescence microscopy. Maximal aerobic capacity (VO2peak), whole body insulin sensitivity and arterial stiffness were also assessed. SIT and MICT increased skeletal muscle microvascular eNOS content and eNOS ser1177 phosphorylation in terminal arterioles and capillaries (P<0.05), but the later effect was eliminated when normalised to eNOS content (P = 0.217). SIT and MICT also reduced microvascular endothelial NOX2 content (P<0.05) and both increased capillary density and capillary-fibre-perimeter exchange index (P<0.05). In parallel, SIT and MICT increased VO2peak (P<0.05), whole body insulin sensitivity (P<0.05) and reduced central artery stiffness (P<0.05). As no significant differences were observed between SIT and MICT it is concluded that SIT is a time efficient alternative to MICT to improve aerobic capacity, insulin sensitivity and muscle capillarisation and endothelial eNOS/NAD(P)Hoxidase protein ratio in young obese men

Ultrasound Does Not Detect Acute Changes in Glycogen in Vastus Lateralis of Man.

PURPOSE: To examine the validity of ultrasound (via cloud based software that measures pixilation intensity according to a scale of 0-100) to non-invasively assess muscle glycogen in human skeletal muscle. METHODS: In Study 1, 14 professional male rugby league players competed in an 80-minute competitive rugby league game. In Study 2 (in a randomized repeated measures design), 16 recreationally active males completed an exhaustive cycling protocol to deplete muscle glycogen followed by 36 hours of HIGH or LOW carbohydrate intake (8 v 3 g.kg body mass). In both studies, muscle biopsies and ultrasound scans were obtained from the vastus lateralis (at 50% of the muscle length) before and after match play in Study 1 and at 36 h after glycogen depletion in Study 2. RESULTS: Despite match play reducing (P0.05) were present between changes in muscle glycogen concentration and changes in ultrasound scores. CONCLUSION: Data demonstrate that ultrasound (as based on measures of pixilation intensity) is not valid to measure muscle glycogen status within the physiological range (i.e. 200-500 mmol.kg dw) that is applicable to exercise-induced muscle glycogen utilization and post-exercise muscle glycogen re-synthesis

Home-based high-intensity interval training reduces barriers to exercise in people with type 1 diabetes

People with type 1 diabetes (T1D) are recommended to engage in regular exercise for a variety of health and fitness reasons. However, many lead a sedentary lifestyle and fail to meet the physical activity guidelines, in part because of the challenge of managing blood glucose concentration and fear of hypoglycaemia. A number of strategies designed to help people with T1D to manage their blood glucose during and after exercise have been investigated. Although many of these strategies show promise in facilitating blood glucose management during and after exercise, they do not target the many other common barriers to exercise that people with T1D face, such as difficulty with cost and travel time to gyms, limited access to exercise bikes and treadmills, and a possible dislike of exercising in front of others in public places. In this symposium review, we provide an overview of ongoing research into a virtually monitored home‐based high‐intensity interval training (Home‐HIT) programme that is designed to reduce these other common barriers to exercise. The conclusion of this review is that Home‐HIT seems to offer a strategy to reduce fear of hypoglycaemia, while simultaneously removing other known barriers preventing people with T1D from taking up exercise, such as being time efficient, requiring no travel time or costs associated with gym memberships, and giving them the opportunity to exercise in their chosen environment, reducing the embarrassment experienced by some when exercising in public

Exercise-induced vasodilation is not impaired following radial artery catheterization in coronary artery disease patients.

Diagnosis and treatment for coronary artery disease (CAD) often involves angiography and/or percutaneous coronary intervention. However, the radial artery catheterization required during both procedures may result in acute artery dysfunction/damage. Whilst exercise-based rehabilitation is recommended for CAD patients following catheterization, it is not known if there is a period when exercise may be detrimental due to catheter-induced damage. Animal studies have demonstrated exercise-induced paradoxical vasoconstriction post-catheterization. This study aimed to examine arterial responses to acute exercise following catheterization. Thirty-three CAD patients (65.8±7.3yr, 31.5±6.3kg.m-2, 82%♂) undergoing transradial catheterization were assessed pre- and 1 week post-catheterization. Radial artery (RA) diameter and shear rate were assessed during handgrip exercise (HE), in both the catheterized (CATH) and control (CON) arms. Endothelial function was also assessed via simultaneous bilateral radial flow mediated dilation (FMD) at both time-points. We found that the increase in RA diameter and shear stress in response to HE (P<0.0001) was maintained post-catheterization in both the CATH and CON arms, whereas FMD following catheterization was impaired in the CATH [6.5±3.3% to 4.7±3.5% (P=0.005)] but not in the CON [6.2±2.6% to 6.4±3.5% (P=0.797)] limb. Whilst endothelial dysfunction, assessed by FMD, was apparent 1 week post-catheterization, the ability of the RA to dilate in response to exercise was not impaired. The impact of catheterization and consequent endothelial denudation on vascular dys/function in humans may therefore be stimulus specific and a highly level of redundancy appears to exist that preserves exercise-mediated vasodilator responses

Impact of catheterization on shear-mediated arterial dilation in healthy young men

Purpose; Animal studies have shown that endothelial denudation abolishes vasodilation in response to increased shear stress. Interestingly, shear-mediated dilation has been reported to be reduced, but not abolished, in coronary artery disease (CAD) patients following catheterization. However, it is not known whether this resulted from a priori endothelial dysfunction in this diseased population. In this study, we evaluated shear-mediated dilation following catheterization in healthy young men. Methods: Twenty-six (age: 24.4 ± 3.8 years, BMI: 24.3 ± 2.8 kg m−2, VO2peak: 50.5 ± 8.8 ml/kg/min) healthy males underwent unilateral transradial catheterization. Shear-mediated dilation of both radial arteries was measured using flow-mediated dilation (FMD) pre-, and 7 days post-catheterization. Results: FMD was reduced in the catheterized arm [9.3 ± 4.1% to 4.3 ± 4.1% (P < 0.001)] post-catheterization, whereas no change was observed in the control arm [8.4 ± 3.8% to 7.3 ± 3.8% (P = 0.168)]. FMD was completely abolished in the catheterized arm in five participants. Baseline diameter (P = 0.001) and peak diameter during FMD (P = 0.035) were increased in the catheterized arm 7 days post-catheterization (baseline: 2.3 ± 0.3 to 2.6 ± 0.2 mm, P < 0.001, peak: 2.5 ± 0.3 to 2.7 ± 0.3 mm, P = 0.001), with no change in the control arm (baseline: 2.3 ± 0.3 to 2.3 ± 0.3 mm, P = 0.288, peak: 2.5 ± 0.3 to 2.5 ± 0.3 mm, P = 0.608). Conclusion: This is the first study in young healthy individuals with intact a priori endothelial function to provide evidence of impaired shear-mediated dilation following catheterization. When combined with earlier studies in CAD patients, our data suggest the catheterization impairs artery function in humans

Skeletal muscle, haematological and splenic volume characteristics of elite breath-hold divers

Purpose The aim of the study was to provide an evaluation of the oxygen transport, exchange and storage capacity of elite breath-hold divers (EBHD) compared with non-divers (ND). Methods Twenty-one healthy males’ (11 EBHD; 10 ND) resting splenic volumes were assessed by ultrasound and venous blood drawn for full blood count analysis. Percutaneous skeletal muscle biopsies were obtained from the m. vastus lateralis to measure capillarisation, and fibre type-specific localisation and distribution of myoglobin and mitochondrial content using quantitative immunofluorescence microscopy. Results Splenic volume was not different between groups. Reticulocytes, red blood cells and haemoglobin concentrations were higher (+ 24%, p < 0.05; + 9%, p < 0.05; + 3%, p < 0.05; respectively) and mean cell volume was lower (− 6.5%, p < 0.05) in the EBHD compared with ND. Haematocrit was not different between groups. Capillary density was greater (+ 19%; p < 0.05) in the EBHD. The diffusion distance (R95) was lower in type I versus type II fibres for both groups (EBHD, p < 0.01; ND, p < 0.001), with a lower R95 for type I fibres in the EBHD versus ND (− 13%, p < 0.05). Myoglobin content was higher in type I than type II fibres in EBHD (+ 27%; p < 0.01) and higher in the type I fibres of EBHD than ND (+ 27%; p < 0.05). No fibre type differences in myoglobin content were observed in ND. Mitochondrial content was higher in type I than type II fibres in EBHD (+ 35%; p < 0.05), with no fibre type differences in ND or between groups. Conclusions In conclusion, EBDH demonstrate enhanced oxygen storage in both blood and skeletal muscle and a more efficient oxygen exchange capacity between blood and skeletal muscle versus ND

Home-Based HIIT and Traditional MICT Prescriptions Improve Cardiorespiratory Fitness to a Similar Extent Within an Exercise Referral Scheme for At-Risk Individuals

Exercise referral schemes (ERS) are used to promote physical activity within primary care. Traditionally, ERS are conducted in a gym or leisure-center setting, with exercise prescriptions based on moderate-intensity continuous training (MICT). Home-based high-intensity interval training (Home-HIIT) has the potential to reduce perceived barriers to exercise, including lack of time and access to facilities, compared to traditional MICT prescription used with ERS and improve health related outcomes. We hypothesized that Home-HIIT would mediate greater improvement in cardiorespiratory fitness (CRF) by virtue of greater adherence and compliance to the exercise prescription, compared to MICT. Methods: Patients enrolled on an ERS (Liverpool, United Kingdom) were recruited for a pragmatic trial. Participants self-selected either 12 weeks of MICT (45–135 min/week at 50–70% HRmax or Home-HIIT (4–9 min × 1 min intervals at ≥80% of HRmax, interspersed with 1 min rest). The primary outcome was the change in CRF (VO2peak) at post-intervention (12 weeks) and follow-up (3-month post intervention), using intention-to-treat analysis. Results:154 participants (age 48 ± 10y; BMI 30.5 ± 6.1 kg/m20.05). Adherence to the prescribed programs was similar (MICT 48 ± 35%, Home-HIIT 39 ± 36%, P [ClinicalTrials.gov], identifier [NCT04553614]

Evidence-based vs. social media based high-intensity interval training protocols: Physiological and perceptual responses.

OBJECTIVE: High intensity interval training (HIIT) is a time-efficient exercise modality to improve cardiorespiratory fitness, and has recently been popularised by social media influencers. However, little is known regarding acute physiological and perceptual responses to these online protocols compared to HIIT protocols used within research. The aim was to investigate acute physiological, perceptual and motivational responses to two HIIT protocols popular on social media, and compare these to two evidence-based protocols. METHODS: Twenty-seven recreationally active (>1 exercise session /week) participants (Age: 22±3y, BMI: 24.3±2.4) completed a randomised cross-over study, whereby each participant completed four HIIT protocols, two already established in research (Ergo-60:60 (cycling 10x60s at 100%Wmaxwith 60s rest), BW-60:60 (body-weight exercises 10x60swith 60s rest)) and two promoted on social media (SM-20:10 (body-weight exercises 20x20swith 10s rest) and SM-40:20 (body-weight exercises 15x40s with 20s rest)). Blood lactate, heart rate (HR), feeling scale (FS), felt arousal scale (FSA), enjoyment and perceived competence were measured in response to each protocol. RESULTS: Significant differences were observed between BW-60:60 and SM-20:10 for the proportion of intervals meeting the ACSM high-intensity exercise criterion (>80% of HRmax) (BW-60:60 93±10%, SM-20:10 74±20%, P = 0.039) and change in lactate (BW-60:60 +7.8±3.7mmol/L, SM-20:10 +5.5±2.6mmol/L, P = 0.001). The percentage of time spent above the criterion HR was also significantly lower in SM-20:10 compared to all other protocols (Ergo-60:60 13.9±4.9min, BW-60:60 13.5±3.5min, SM-40:20 12.1±2.4min, SM-20:10 7.7±3.1, P0.05). Enjoyment was higher upon completion of BW-60:60 compared to Ergo-60:60 and SM-40:20 (P<0.05). CONCLUSIONS: This study shows that HIIT protocols available on social media offer an interesting real-world alternative for promoting exercise participation. Future studies should continue to investigate these highly popular and practical HIIT protocols

Fasted High-Intensity Interval and Moderate-Intensity Exercise do not Lead to Detrimental 24-Hour Blood Glucose Profiles.

Aims: To compare the effect of a bout of high-intensity interval training (HIT) with a bout of moderate-intensity continuous training (MICT) on glucose concentrations over the subsequent 24h period. METHODS: Fourteen people with type 1 diabetes (duration of type 1 diabetes 8.2±1.4 years), all on basal-bolus regimen, completed a randomised, counterbalanced, crossover study. Continuous glucose monitoring was used to assess glycaemic control following a single bout of HIT (6 x 1min intervals) and 30 mins of moderate-intensity continuous training (MICT) on separate days, compared to a non-exercise control day (CON). Exercise was undertaken following an overnight fast with omission of short-acting insulin. Capillary blood glucose samples were recorded pre and post-exercise to assess the acute changes in glycaemia during HIT and MICT. RESULTS: There was no difference in the incidence of or percentage time spent in hypoglycaemia, hyperglycaemia or target glucose range over the 24h and nocturnal period (24:00-06:00h) between CON, HIT and MICT (P>0.05). Blood glucose concentrations were not significantly (P=0.49) different from pre to post-exercise with HIT (+0.39±0.42 mmol/L) or MICT (-0.39±0.66 mmol/L), with no difference between exercise modes (P=1.00). CONCLUSIONS: HIT or 30 mins of MICT can be carried out after an overnight fast with no increased risk of hypoglycaemia or hyperglycaemia, and provided the pre-exercise glucose concentration is 7-14 mmol/L, no additional carbohydrate ingestion is necessary to undertake these exercises. As HIT is a time-efficient form of exercise, the efficacy and safety of long-term HIT should now be explored