High intensity interval training as a novel treatment for impaired awareness of hypoglycaemia in people with type 1 diabetes (HIT4HYPOS): a randomised parallel-group study.

AIMS/HYPOTHESIS: Impaired awareness of hypoglycaemia (IAH) in type 1 diabetes may develop through a process referred to as habituation. Consistent with this, a single bout of high intensity interval exercise as a novel stress stimulus improves counterregulatory responses (CRR) to next-day hypoglycaemia, referred to as dishabituation. This longitudinal pilot study investigated whether 4 weeks of high intensity interval training (HIIT) has sustained effects on counterregulatory and symptom responses to hypoglycaemia in adults with type 1 diabetes and IAH. METHODS: HIT4HYPOS was a single-centre, randomised, parallel-group study. Participants were identified using the Scottish Diabetes Research Network (SDRN) and from diabetes outpatient clinics in NHS Tayside, UK. The study took place at the Clinical Research Centre, Ninewells Hospital and Medical School, Dundee, UK. Participants were aged 18-55 years with type 1 diabetes of at least 5 years' duration and HbA1c levels <75 mmol/mol (<9%). They had IAH confirmed by a Gold score ≥4, modified Clarke score ≥4 or Dose Adjustment For Normal Eating [DAFNE] hypoglycaemia awareness rating of 2 or 3, and/or evidence of recurrent hypoglycaemia on flash glucose monitoring. Participants were randomly allocated using a web-based system to either 4 weeks of real-time continuous glucose monitoring (RT-CGM) or RT-CGM+HIIT. Participants and investigators were not masked to group assignment. The HIIT programme was performed for 20 min on a stationary exercise bike three times a week. Hyperinsulinaemic-hypoglycaemic (2.5 mmol/l) clamp studies with assessment of symptoms, hormones and cognitive function were performed at baseline and after 4 weeks of the study intervention. The predefined primary outcome was the difference in hypoglycaemia-induced adrenaline (epinephrine) responses from baseline following RT-CGM or RT-CGM+HIIT. RESULTS: Eighteen participants (nine men and nine women) with type 1 diabetes (median [IQR] duration 27 [18.75-32] years) and IAH were included, with nine participants randomised to each group. Data from all study participants were included in the analysis. During the 4 week intervention there were no significant mean (SEM) differences between RT-CGM and RT-CGM+HIIT in exposure to level 1 (28 [7] vs 22 [4] episodes, p=0.45) or level 2 (9 [3] vs 4 [1] episodes, p=0.29) hypoglycaemia. The CGM-derived mean glucose level, SD of glucose and glucose management indicator (GMI) did not differ between groups. During the hyperinsulinaemic-hypoglycaemic clamp studies, mean (SEM) change from baseline was greater for the noradrenergic responses (RT-CGM vs RT-CGM+HIIT: -988 [447] vs 514 [732] pmol/l, p=0.02) but not the adrenergic responses (-298 [687] vs 1130 [747] pmol/l, p=0.11) in those participants who had undergone RT-CGM+HIIT. There was a benefit of RT-CGM+HIIT for mean (SEM) change from baseline in the glucagon CRR to hypoglycaemia (RT-CGM vs RT-CGM+HIIT: 1 [4] vs 16 [6] ng/l, p=0.01). Consistent with the hormone response, the mean (SEM) symptomatic response to hypoglycaemia (adjusted for baseline) was greater following RT-CGM+HIIT (RT-CGM vs RT-CGM+HIIT: -4 [2] vs 0 [2], p<0.05). CONCLUSIONS/INTERPRETATION: In this pilot clinical trial in people with type 1 diabetes and IAH, we found continuing benefits of HIIT for overall hormonal and symptomatic CRR to subsequent hypoglycaemia. Our findings also suggest that HIIT may improve the glucagon response to insulin-induced hypoglycaemia. TRIAL REGISTRATION: ISRCTN15373978. FUNDING: Sir George Alberti Fellowship from Diabetes UK (CMF) and the Juvenile Diabetes Research Foundation.

Temporal tracking of cysteine 34 oxidation of plasma albumin as a biomarker of muscle damage following a bout of eccentric exercise.

PURPOSE: Exercise-induced muscle damage (EIMD) results in the generation of reactive oxygen species (ROS), but little is known about the temporal profile of change in ROS post-EIMD and how ROS levels relate to the onset of and recovery from EIMD. Our primary aim was to examine the effect of EIMD on the pattern of change in the blood level of thiol-oxidised albumin, a marker of oxidative stress. METHODS: Seven male participants were subjected on separate days to eccentric muscle contraction to cause EIMD or a no-exercise condition. After each session, the participants collected daily dried blood spots to measure thiol-oxidised albumin and returned to the laboratory every 2 days for the assessment of indirect markers of EIMD, namely maximal voluntary contraction (MVC), delayed onset muscle soreness (DOMS), creatine kinase (CK), and myoglobin. RESULTS: Eccentric exercise resulted in a significant decrease in MVC and increase in DOMS, CK, myoglobin, and thiol-oxidised albumin with the latter reaching above baseline level within 24-48 h post-exercise. All the markers of EIMD returned to baseline level within 6 days post-exercise, but not the level of thiol-oxidised albumin which remained elevated for 10 days after exercise. There was a moderate correlation between changes in thiol-oxidised albumin and DOMS, but no significant relationship between any other markers of muscle damage. CONCLUSION: The levels of thiol-oxidised albumin increase in response to EIMD and remain elevated for several days post-exercise. The temporal pattern of change in the level of thiol-oxidised albumin suggests that this may be a useful biomarker of muscle repair post-EIMD.

The Effect of Exercise Intensity on Carbohydrate Sparing Postexercise: Implications for Postexercise Hypoglycemia.

The purpose of this study was to determine the effect of exercise intensity on the proportion and rate of carbohydrate oxidation and glucoregulatory hormone responses during recovery from exercise. Six physically active participants completed 1 hr of low-intensity (LI; 50% lactate threshold) or moderate-intensity (MI; 100% lactate threshold) exercise on separate days following a randomized counterbalanced design. During exercise and for 6 hr of recovery, samples of expired air were collected to determine oxygen consumption, respiratory exchange ratio, energy expenditure, and substrate oxidation rates. Blood samples were also collected to measure glucoregulatory hormones (catecholamines, GH) and metabolites (glucose, free fatty acids, lactate, pH, and bicarbonate). During exercise, respiratory exchange ratio, energy expenditure, and the proportion and rate of carbohydrate (CHO) oxidation were higher during MI compared with LI. However, during recovery from MI, respiratory exchange ratio and the proportion and rate of CHO oxidation were lower than preexercise levels and corresponding LI. During exercise and early recovery, catecholamines and growth hormone were higher in MI than LI, and there was a trend for higher levels of free fatty acids in the early recovery from MI compared with LI. In summary, CHO oxidation during exercise increases with exercise intensity but there is a preference for CHO sparing (and fat oxidation) during recovery from MI exercise compared with LI exercise. This exercise intensity-dependent shift in substrate oxidation during recovery is explained, in part, by the pattern of change of key glucoregulatory hormones including catecholamines and growth hormone and plasma fatty acid concentrations.

Reproducibility of plasma glucose responses to moderate-intensity exercise in individuals with type 1 diabetes.

AIM: To examine the within-person variability in plasma glucose responses to moderate-intensity morning exercise in young individuals with type 1 diabetes after overnight fasting and under basal insulin conditions. METHODS: In this pilot study, eight participants completed 40 min of moderate-intensity exercise at 60% V̇O2 peak on three separate days. The within-person standard deviation (SDw) in plasma glucose response was analysed both during and 1 h after exercise using the two visits per participant most closely matched by pre-exercise plasma glucose level. RESULTS: When the two closest matched visits per individual were included for analysis, mean (±SD) change in plasma glucose level was -1.8 ± 1.1 mmoL/L during exercise and -0.6 ± 1.0 mmoL/L during recovery, with the SDw of these changes being 0.5 mmol (95% CI 0.2, 0.8) during exercise and 0.8 mmoL/L (95% CI 0.4, 1.3) during recovery. The median intra-individual difference in plasma glucose level change was 0.3 mmoL/L [IQR 0.1, 0.7] during exercise and 0.8 mmoL/L [IQR 0.4, 1.0] during recovery. CONCLUSION: Within-person plasma glucose responses to moderate-intensity exercise may be reproducible under fasting and basal insulin conditions and similar pre-exercise plasma glucose levels. This finding may assist the design of future studies investigating both the reproducibility of glycaemic responses to exercise and blood glucose management for individuals with type 1 diabetes.

Acute hyperglycaemia does not have a consistent adverse effect on exercise performance in recreationally active young people with type 1 diabetes: a randomised crossover in-clinic study.

AIMS/HYPOTHESIS: In individuals with type 1 diabetes, chronic hyperglycaemia impairs aerobic fitness. However, the effect of acute marked hyperglycaemia on aerobic fitness is unclear, and the impact of insulin level has not been examined. In this study, we explored if acute hyperglycaemia with higher or low insulin levels affects [Formula: see text] and other exercise performance indicators in individuals with type 1 diabetes. METHODS: Eligible participants were aged 14 to 30 years, with complication-free, type 1 diabetes and HbA1c ≤ 75 mmol/mol (≤9%). Participants exercised in a clinical laboratory under three clamp (constant insulin, variable glucose infusion) conditions: euglycaemia (5 mmol/l) with 20 mU [m2 BSA]-1 min-1 insulin (where BSA is body surface area) (Eu20); hyperglycaemia (17 mmol/l) with 20 mU [m2 BSA]-1 min-1 insulin (Hyper20); and hyperglycaemia (17 mmol/l) with 5 mU [m2 BSA]-1 min-1 insulin (Hyper5) on separate days. Participants and the single testing assessor were blinded to condition, with participants allocated to randomised testing condition sequences as they were consecutively recruited. Standardised testing (in order) conducted on each of the three study days included: triplicate 6 second sprint cycling, grip strength, single leg static balance, vertical jump and modified Star Excursion Balance Test, ten simple and choice reaction times and one cycle ergometer [Formula: see text] test. The difference between conditions in the aforementioned testing measures was analysed, with the primary outcome being the difference in [Formula: see text]. RESULTS: Twelve recreationally active individuals with type 1 diabetes (8 male, mean ± SD 17.9 ± 3.9 years, HbA1c 61 ± 11 mmol/mol [7.7 ± 1.0%], 7 ± 3 h exercise/week) were analysed. Compared with Eu20, [Formula: see text] was lower in Hyper20 (difference 0.17 l/min [95% CI 0.31, 0.04; p = 0.02] 6.6% of mean Eu20 level), but Hyper5 was not different (p = 0.39). Compared with Eu20, sprint cycling peak power was not different in Hyper20 (p = 0.20), but was higher in Hyper5 (64 W [95% CI 13, 115; p = 0.02] 13.1%). Hyper20 reaction times were not different (simple: p = 0.12) but Hyper5 reaction times were slower (simple: 11 milliseconds [95% CI 1, 22; p = 0.04] 4.7%) than Eu20. No differences between Eu20 and either hyperglycaemic condition were observed for the other testing measures (p > 0.05). CONCLUSIONS/INTERPRETATION: Acute marked hyperglycaemia in the higher but not low insulin state impaired [Formula: see text] but to a small extent. Acute hyperglycaemia had an insulin-dependent effect on sprint cycling absolute power output and reaction time but with differing directionality (positive for sprint cycling and negative for reaction time) and no effect on the other indicators of exercise performance examined. We find that acute hyperglycaemia is not consistently adverse and does not impair overall exercise performance to an extent clinically relevant for recreationally active individuals with type 1 diabetes. FUNDING: This research was funded by Diabetes Research Western Australia and Australasian Paediatric Endocrine Group grants.

The competitive athlete with type 1 diabetes.

Regular exercise is important for health, fitness and longevity in people living with type 1 diabetes, and many individuals seek to train and compete while living with the condition. Muscle, liver and glycogen metabolism can be normal in athletes with diabetes with good overall glucose management, and exercise performance can be facilitated by modifications to insulin dose and nutrition. However, maintaining normal glucose levels during training, travel and competition can be a major challenge for athletes living with type 1 diabetes. Some athletes have low-to-moderate levels of carbohydrate intake during training and rest days but tend to benefit, from both a glucose and performance perspective, from high rates of carbohydrate feeding during long-distance events. This review highlights the unique metabolic responses to various types of exercise in athletes living with type 1 diabetes. Graphical abstract.

Enhancing energy expenditure and enjoyment of exercise during pregnancy through the addition of brief higher intensity intervals to traditional continuous moderate intensity cycling.

BACKGROUND: Current guidelines recommend that pregnant women without contraindications should engage in 30 min or more of moderate intensity exercise on most days of the week, however, many women fail to achieve this goal. This study examined the effect of adding brief higher intensity intervals to traditional continuous moderate intensity exercise on energy expenditure and the enjoyment of exercise in late pregnancy. This is important to determine given that any additional energy expenditure resulting from higher intensity intervals may be meaningless if enjoyment is compromised, since long-term adherence will likely be low. METHODS: In this study, 12 healthy pregnant women at 30 ± 1 weeks gestation, aged 35 ± 6 years with a BMI of 27.1 ± 4.3 kg/m(2) performed either 30 min of continuous cycling exercise (CONT) at a steady power output equivalent to 65 % age-predicted heart rate maximum or an equivalent period of interval cycling (INTV) consisting of continuous cycling at the same power output as CONT, but with the addition of six 15-s self-paced higher intensity efforts throughout, performed at regular intervals, on separate occasions in a counterbalanced order. RESULTS: Mean cycling power output, heart rate, oxygen consumption and energy expenditure were higher during INTV compared with CONT (P < 0.05). However, there was no difference in mean rate of perceived exertion between conditions. Enjoyment of exercise was higher with INTV (P = 0.01). CONCLUSIONS: The addition of six 15-s higher intensity intervals to continuous moderate intensity exercise effectively increased energy expenditure by 28 %, at the same time as enhancing the enjoyment of exercise in late pregnancy. While these findings may be specific to recreationally active women, this study provides a rationale for future studies to examine the physiological and psychological responses to regular interval training during pregnancy to optimise exercise prescription. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry ACTRN12616000680460 . 25 May 2016 (Registered retrospectively).

Mouth rinsing with a bitter solution without ingestion does not improve sprint cycling performance.

PURPOSE: Recently, we have shown that combining mouth rinsing with the ingestion of a 2 mM quinine solution immediately before a 30-s cycling sprint significantly improves performance. However, the strong bitterness of such a solution produces an unpleasant taste and evokes nausea at higher concentrations. Given the possibility that mouth rinsing with quinine without ingesting it may not produce nausea, a mouth rinse only protocol may be a more practical approach to administer quinine for improving exercise performance. The purpose of the present study was to determine whether mouth rinsing with quinine without ingesting it improves 30-s sprint cycling performance. METHODS: Twelve competitive male cyclists performed a 30-s maximal cycling sprint immediately after rinsing their mouth for 10 s with either a 10 mM bitter quinine solution (QUI), plain water (WAT), a 7.1 % w/v sweet glucose solution (GLU), or no solution at all (control; CON). Sprint performance was assessed, and heart rate, ratings of perceived exertion and blood variables were measured pre- and post-exercise. RESULTS: Mean power output during the 30-s sprint (QUI 888 ± 38; CON 873 ± 39; WAT 885 ± 37; GLU 873 ± 42 W; p = 0.431) as well as peak power (QUI 1230 ± 61; CON 1,208 ± 65; WAT 1,220 ± 70; GLU 1,202 ± 59 W; p = 0.690) were similar between the four conditions. There were no significant differences in any other performance measures, heart rate, subjective ratings or blood variables between conditions. CONCLUSIONS: Mouth rinsing with a bitter tasting quinine solution without ingestion does not improve 30-s sprint cycling performance.

Mouth rinsing and ingestion of a bitter-tasting solution increases corticomotor excitability in male competitive cyclists.

PURPOSE: Recently, we have shown that the combination of mouth rinsing and ingesting a bitter-tasting quinine solution immediately prior to the performance of a maximal 30-s cycling sprint significantly improves mean and peak power output. This ergogenic effect was proposed to be related to the activation of the corticomotor pathway by afferent taste signals originating from bitter taste receptors in the oral cavity. The aim of the present study was to use single-pulse transcranial magnetic stimulation to investigate whether mouth rinsing and ingestion of a bitter quinine solution increases corticomotor excitability. METHODS: A series of 10 motor-evoked potentials (MEPs) were recorded from the relaxed first dorsal interosseus muscle in 16 male competitive cyclists immediately before and after they rinsed their mouth for 10 s and then ingested either a 2 mM bitter quinine solution or plain water. RESULTS: Mean MEP amplitude was significantly increased in response to quinine administration by 16% (p < 0.05), with no evidence of a time-dependent effect over the 10 pulses. Mean MEP amplitude also increased by 10% in response to water administration (p < 0.05), though this increase was significantly smaller than the response to quinine (p < 0.05). CONCLUSIONS: We conclude that the activation of bitter taste receptors in the oral cavity and upper gastrointestinal tract has the capacity to increase corticomotor excitability in male competitive cyclists.

Antecedent hypoglycaemia does not diminish the glycaemia-increasing effect and glucoregulatory responses of a 10 s sprint in people with type 1 diabetes.

AIMS/HYPOTHESIS: A 10 s sprint has been reported to provide a means to prevent acute post-exercise hypoglycaemia in young adults with type 1 diabetes because of its glycaemia-raising effect, but it is unclear whether this effect is impaired by antecedent hypoglycaemia. The purpose of this study was to investigate whether antecedent hypoglycaemia impairs the glycaemia-raising effect of a 10 s sprint in individuals with type 1 diabetes. METHODS: Eight individuals underwent a hyperinsulinaemic-hypoglycaemic or hyperinsulinaemic-euglycaemic clamp on two separate mornings. Thereafter, the participants underwent a basal insulin-euglycaemic clamp before performing a 10 s sprint on a cycle ergometer. The levels of blood glucose and glucoregulatory hormones and rates of glucose appearance (Ra) and disappearance (Rd) were compared between conditions. RESULTS: During the morning clamps, blood glucose levels were significantly different between conditions of hypoglycaemia (2.8 ± 0.1 mmol/l) and euglycaemia (5.4 ± 0.2 mmol/l; p < 0.001). Mean glycaemia prior to sprinting was similar (5.6 ± 0.4 and 5.5 ± 0.3 mmol/l for hypoglycaemic and euglycaemic conditions, respectively; p = 0.83). In response to the afternoon sprint, the pattern of increase in blood glucose levels did not differ between conditions, reaching similar maximal levels 45 min after exercise (6.5 ± 0.4 and 6.6 ± 0.3 mmol/l, respectively; p = 0.43). The early post-exercise patterns in glucose Ra and Rd and increases in plasma adrenaline (epinephrine), growth hormone and cortisol levels did not differ between conditions. CONCLUSIONS/INTERPRETATION: Hypoglycaemia in the morning does not diminish the glycaemia-raising effect of an afternoon 10 s sprint in young adults with type 1 diabetes, suggesting that sprinting is a useful strategy for opposing hypoglycaemia, regardless of prior hypoglycaemia.

Combined glucose ingestion and mouth rinsing improves sprint cycling performance.

This study investigated whether combined ingestion and mouth rinsing with a carbohydrate solution could improve maximal sprint cycling performance. Twelve competitive male cyclists ingested 100 ml of one of the following solutions 20 min before exercise in a randomized double-blinded counterbalanced order (a) 10% glucose solution, (b) 0.05% aspartame solution, (c) 9.0% maltodextrin solution, or (d) water as a control. Fifteen min after ingestion, repeated mouth rinsing was carried out with 11 × 15 ml bolus doses of the same solution at 30-s intervals. Each participant then performed a 45-s maximal sprint effort on a cycle ergometer. Peak power output was significantly higher in response to the glucose trial (1188 ± 166 W) compared with the water (1036 ± 177 W), aspartame (1088 ± 128 W) and maltodextrin (1024 ± 202 W) trials by 14.7 ± 10.6, 9.2 ± 4.6 and 16.0 ± 6.0% respectively (p < .05). Mean power output during the sprint was significantly higher in the glucose trial compared with maltodextrin (p < .05) and also tended to be higher than the water trial (p = .075). Glucose and maltodextrin resulted in a similar increase in blood glucose, and the responses of blood lactate and pH to sprinting did not differ significantly between treatments (p > .05). These findings suggest that combining the ingestion of glucose with glucose mouth rinsing improves maximal sprint performance. This ergogenic effect is unlikely to be related to changes in blood glucose, sweetness, or energy sensing mechanisms in the gastrointestinal tract.

Opposition of carbohydrate in a mouth-rinse solution to the detrimental effect of mouth rinsing during cycling time trials.

Studies have reported that rinsing the mouth with a carbohydrate (CHO) solution improves cycling time-trial performance compared with rinsing with a placebo solution. However, no studies have compared the effect of mouth rinsing with a no-mouth-rinse control condition. The aim of this study was to compare the effects of a CHO mouth rinse with those of a placebo rinse and a no-rinse condition. Ten male cyclists completed three 1,000-kJ cycling time trials in a randomized, counterbalanced order. At every 12.5% of the time trial completed, participants were required to rinse their mouths for 5 s with either a 6.4% maltodextrin solution (CHO), water (WA), or no solution (CON). Heart rate and ratings of perceived exertion (RPE) were recorded every 25% of the time trial completed. Time to completion was faster in both CHO (65.7 ± 11.07 min) and CON (67.6 ± 12.68 min) than in WA (69.4 ± 13.81 min; p = .013 and p = .042, respectively). The difference between CHO and CON approached significance (p = .086). There were no differences in heart rate or RPE between any conditions. In summary, repeated mouth rinsing with water results in decreased performance relative to not rinsing at all. Adding CHO to the rinse solution appears to oppose this fall in performance, possibly providing additional benefits to performance compared with not rinsing the mouth at all. This brings into question the magnitude of the effect of CHO mouth rinsing reported in previous studies that did not include a no-rinse condition.

Effect of Neck-Deep Immersion in Cool or Thermoneutral Water on Blood Glucose Levels in Individuals With Type 1 Diabetes.

Context: It is unclear whether immersion in cool water, typical of many beaches, increases the concentration of blood glucose in individuals with type 1 diabetes mellitus (T1DM). Objective: To test the hypothesis in individuals with T1DM that immersion neck-deep in cool water (COOL) causes an increase in blood glucose concentration, but not exposure to thermoneutral water (THERMO) or thermoneutral air. Methods: Eight overnight-fasted participants with T1DM were exposed for 60 minutes on separate days to 3 experimental conditions: cool water (COOL, 23 °C); thermoneutral water (THERMO, 33.5 °C); or thermoneutral air (24 °C). They then recovered for 60 minutes on land at 24 °C. At time intervals, we measured: blood glucose and plasma insulin concentration, rate of carbohydrate and fat oxidation, skin and core temperature, subcutaneous blood flow, and shivering via electromyography. Results: There was no change in blood glucose concentration during the 3 experimental conditions (P > .05). During recovery after COOL, blood glucose increased (P < .05) but did not change in the other 2 conditions. The rate of carbohydrate oxidation during and early after COOL was higher than in the other 2 conditions (P < .05), and COOL led to a decrease in subcutaneous blood flow and the concentration of plasma insulin (P < .05). Conclusion: Cool or thermoneutral neck-deep immersion in water does not cause a change in the concentration of blood glucose in people with T1DM, but on-land recovery from COOL causes an increase in blood glucose that may be due, at least in part, to the accompanying decrease in plasma insulin.

Protein Ingestion in Reducing the Risk of Late-Onset Post-Exercise Hypoglycemia: A Pilot Study in Adolescents and Youth with Type 1 Diabetes.

Dietary protein causes dose-dependent hyperglycemia in individuals with type 1 diabetes (T1D). This study investigated the effect of consuming 50 g of protein on overnight blood glucose levels (BGLs) following late-afternoon moderate-intensity exercise. Six participants (3M:3F) with T1D, HbA1c 7.5 ± 0.8% (58.0 ± 8.7 mmol/mol) and aged 20.2 ± 3.1 years exercised for 45 min at 1600 h and consumed a protein drink or water alone at 2000 h, on two separate days. A basal insulin euglycemic clamp was employed to measure the mean glucose infusion rates (m-GIR) required to maintain euglycemia on both nights. The m-GIR on the protein and water nights during the hypoglycemia risk period and overnight were 0.27 ± 043 vs. 1.60 ± 0.66 mg/kg/min (p = 0.028, r = 0.63) and 0.51 ± 0.16 vs. 1.34 ± 0.71 mg/kg/min (p = 0.028, r = 0.63), respectively. Despite ceasing intravenous glucose infusion on the protein night, the BGLs peaked at 9.6 ± 1.6 mmol/L, with a hypoglycemia risk period mean of 7.8 ± 1.5 mmol/L compared to 5.9 ± 0.4 mmol/L (p = 0.028) on the water night. The mean plasma glucagon levels were 51.5 ± 14.1 and 27.2 ± 10.1 ng/L (p = 0.028) on the protein and water night, respectively. This suggests that an intake of protein is effective at reducing the post-exercise hypoglycemia risk, potentially via a glucagon-mediated stimulation of glucose production. However, 50 g of protein may be excessive for maintaining euglycemia.

Does exercise duration affect Fatmax in overweight boys?

To compare the assessment of Fat(max) using a single graded exercise test with 3 min stages against 30 min prolonged exercise bouts in overweight boys. Ten overweight boys (8-12 years) attended the laboratory on seven separate occasions. On the first visit, body anthropometrics and peak aerobic capacity ([Formula: see text]O(2peak)) were assessed. Following this, each participant attended the laboratory after an overnight fast for six morning cycling sessions. During the first session, participants completed a continuous, submaximal graded exercise protocol with seven 3 min stages (GRAD) at 35, 40, 45, 50, 55, 60 and 65% [Formula: see text]O(2peak). The final five visits consisted of a 30 min bout of prolonged exercise (PROL) performed in a counterbalanced order at 40, 45, 50, 55 and 60% [Formula: see text]O(2peak). There was no effect of exercise duration on Fat(max) or the absolute rate of fat oxidation during PROL (p > 0.05). At the group level, GRAD and PROL provided similar estimates of Fat(max) (GRAD: 53 ± 10% [Formula: see text]O(2peak); PROL: 53 ± 10% [Formula: see text]O(2peak); p = 0.995); however, individual variation between the two protocols is shown by a systematic bias and residual error of 0 ± 11% [Formula: see text]O(2peak). Fat oxidation rates remained stable across 30 min of steady-state exercise in overweight boys. Furthermore, Fat(max) was similar at 3, 10, 20 and 30 min of exercise, suggesting that for exercise lasting ≤ 30 min, exercise duration does not affect Fat(max). However, Fat(max) determined with GRAD may need to be interpreted with caution at the individual level given the variation in Fat(max) between protocols.

Effects of Simulated High Altitude on Blood Glucose Levels During Exercise in Individuals With Type 1 Diabetes.

CONTEXT: Current exercise guidelines for individuals with type 1 diabetes (T1D) do not consider the impact that high altitude may have on blood glucose levels (BGL) during exercise. OBJECTIVE: To investigate the effect of acute hypoxia (simulated high altitude) on BGL and carbohydrate oxidation rates during moderate intensity exercise in individuals with T1D. METHODS: Using a counterbalanced, repeated measures study design, 7 individuals with T1D completed 2 exercise sessions; normoxia and hypoxia (~4200 m simulated altitude). Participants cycled for 60 min on an ergometer at 45% of their sea-level V̇O2peak, and then recovered for 60 min. Before, during, and after exercise, blood samples were taken to measure glucose, lactate, and insulin levels. Respiratory gases were collected to measure carbohydrate oxidation rates. RESULTS: Early during exercise (<30 min), there was no fall in BGL in either condition. After 1 h of exercise and during recovery, BGL were significantly lower under the hypoxic condition compared to both pre-exercise levels (P = 0.008) and the normoxic condition (P = 0.027). Exercise in both conditions resulted in a significant rise in carbohydrate oxidation rates, which returned to baseline levels postexercise. Before, during, and after exercise, carbohydrate oxidation rates were higher under the hypoxic compared with the normoxic condition (P < 0.001). CONCLUSIONS: The greater decline in BGL during and after exercise performed under acute hypoxia suggests that exercise during acute exposure to high altitude may increase the risk of hypoglycemia in individuals with T1D. Future guidelines may have to consider the impact altitude has on exercise-mediated hypoglycemia.

Nausea after Repeated Sprints: Is Lactic Acidosis Really the Culprit?

INTRODUCTION: Nausea caused by exhaustive sprinting is associated with high lactate ([La-]) and hydrogen ion concentrations ([H+]) and fall in blood pCO2, thus raising the issue of whether there is a causal link between nausea and these variables. For this reason, this study aimed to determine whether interspersing repeated sprints (RS) with periods of active, compared with passive, recovery results in lower levels of both nausea and changes in [La-], [H+], and pCO2. METHODS: Twelve male participants completed two separate sessions comprising four 30-s sprints separated by 20 min of either active (AR; cycling at 40% V˙O2peak) or passive recovery (PR). At 6 and 18 min of each recovery period, nausea was assessed via a visual analog scale (VAS), and blood samples were collected to measure [La-], [H+], and pCO2. RESULTS: RS significantly increased VAS score in both AR (P < 0.001) and PR (P < 0.01). After the first sprint, VAS was higher than preexercise in only AR (P < 0.01). AR was associated with lower VAS, [La-], [H+], and higher pCO2 (all P = 0.001) compared with PR after sprints 2-4. Linear mixed modeling indicated that each of the variables significantly predicts VAS scores (P < 0.0001). Repeated-measures correlation (rrm2) indicated that [La-] had the closest association with VAS (rrm2 = 0.22, P < 0.0001). CONCLUSION: The lower levels of both nausea and changes in [La-], [H+], and pCO2 in response to AR suggest that nausea associated with RS may be causally related with these variables. However, the absence of a close relationship between these variables after the first sprint and the findings that [La-], [H+], and pCO2 only account for 13%-22% of the variation in VAS indicate that other mechanisms may also mediate nausea.

A 1-week diet break improves muscle endurance during an intermittent dieting regime in adult athletes: A pre-specified secondary analysis of the ICECAP trial.

Athletes undergoing energy restriction for weight/fat reduction sometimes apply 'diet breaks' involving increased energy intake, but there is little empirical evidence of effects on outcomes. Twenty-six resistance-trained athletes (11/26 or 42% female) who had completed 12 weeks of intermittent energy restriction participated in this study. Participants had a mean (SD) age of 29.3 (6.4) years, a weight of 72.7 (15.9) kg, and a body fat percentage of 21.3 (7.5) %. During the 1-week diet break, energy intake was increased (by means of increased carbohydrate intake) to predicted weight maintenance requirements. While the 1-week diet break had no significant effect on fat mass, it led to small but significant increases in mean body weight (0.6 kg, P<0.001), fat-free mass (0.7 kg, P<0.001) and in resting energy expenditure, from a mean (and 95% confidence interval) of 7000 (6420 to 7580) kJ/day to 7200 (6620 to 7780) kJ/day (P = 0.026). Overall, muscle endurance in the legs (but not arms) improved after the diet break, including significant increases in the work completed by the quadriceps and hamstrings in a maximum-effort 25-repetition set, with values increasing from 2530 (2170 to 2890) J to 2660 (2310 to 3010) J (P = 0.018) and from 1280 (1130 to 1430) J to 1380 (1220 to 1540) J (P = 0.018) following the diet break, respectively. However, muscle strength did not change. Participants reported significantly lower sensations of hunger (P = 0.017), prospective consumption (P = 0.020) and irritability (P = 0.041) after the diet break, and significantly higher sensations of fullness (P = 0.002), satisfaction (P = 0.002), and alertness (P = 0.003). In summary, a 1-week diet break improved muscle endurance in the legs and increased mental alertness, and reduced appetite and irritability. With this considered, it may be wise for athletes to coordinate diet breaks with training sessions that require muscle endurance of the legs and/or mental focus, as well as in the latter parts of a weight loss phase when increases in appetite might threaten dietary adherence. Trial registration: Australian New Zealand Clinical Trials Registry Reference Number: ACTRN12618000638235 anzctr.org.au.