Impact of physical exercise on sensor performance of the FreeStyle Libre intermittently viewed continuous glucose monitoring system in people with Type 1 diabetes: a randomized crossover trial

AIMS

To evaluate the sensor performance of the FreeStyle Libre intermittently viewed continuous glucose monitoring system using reference blood glucose levels during moderate-intensity exercise while on either full or reduced basal insulin dose in people with Type 1 diabetes.

METHODS

Ten participants with Type 1 diabetes [four women, mean ± sd age 31.4 ± 9.0 years, BMI 25.5±3.8 kg/m² , HbA_1c 55±7 mmol/mol (7.2±0.6%)] exercised on a cycle ergometer for 55 min at a moderate intensity for 5 consecutive days at the clinical research facility, while receiving either their usual or a 75% basal insulin dose. After a 4-week washout period, participants performed the second exercise period having switched to the alternative basal insulin dose. During exercise, reference capillary blood glucose values were analysed using the fully enzymatic-amperometric method and compared with the interstitial glucose values obtained. Intermittently viewed continuous glucose monitoring accuracy was analysed according to median (interquartile range) absolute relative difference, and Clarke error grid and Bland-Altman analysis for overall glucose levels during exercise, stratified by glycaemic range and basal insulin dosing scheme (P<0.05).

RESULTS

A total of 845 glucose values were available during exercise to evaluate intermittently viewed continuous glucose monitoring sensor performance. The median (interquartile range) absolute relative difference between the reference values and those obtained by the sensor across the glycaemic range overall was 22 (13.9-29.7)%, and was 36.3 (24.2-45.2)% during hypoglycaemia, 22.8 (14.6-30.6)% during euglycaemia and 15.4 (9-21)% during hyperglycaemia. Usual basal insulin dose was associated with a worse sensor performance during exercise compared with the reduced (75%) basal insulin dose [median (interquartile range) absolute relative difference: 23.7 (17.2-30.7)% vs 20.5 (12-28.1)%; P<0.001).

CONCLUSIONS

The intermittently viewed continuous glucose monitoring sensor showed diminished accuracy during exercise. Absolute glucose readings derived from the sensor should be used cautiously and need confirmation by additional finger-prick blood glucose measurements.

Cardiovascular risk assessments at occupational health services: employee experiences

BACKGROUND

Across England in the UK, population screening for cardiovascular disease (CVD) primarily takes place within general practice in the form of the National Health Service Health Check. Additional screening sites such as occupational health are advocated to improve the population impact.

AIMS

To investigate participant experiences with cardiovascular and type 2 diabetes risk assessment (RA) at occupational health and subsequent support-seeking at general practice.

METHODS

Face-to-face interviews were conducted for this qualitative study. Participants were recruited at three workplaces; a steel works and two hospital sites. Using interpretive phenomenological analyses, themes were drawn from salient narratives and categorically organized.

RESULTS

There were 29 participants. Themes (n = 16) were organized into two domains; factors that facilitated (n = 9) or thwarted (n = 7) participant engagement with the RA and general practice. All participants described the RA as worthwhile and strongly valued RA at occupational health. Those with obesity and high CVD risk highlighted their difficulties in making lifestyle changes. Participants reported confusion and anxiety when GP advice about medication appeared to contradict what participants had interpreted during RA at occupational health.

CONCLUSIONS

This study highlights factors that facilitate or thwart engagement in cardiovascular RA at occupational health services and general practice follow-up. Stakeholders can integrate these factors into standard operating procedures to enhance participant engagement and enable safeguards that minimize potential harm to participants.

Physical exercise and non-insulin glucose-lowering therapies in the management of Type 2 diabetes mellitus: a clinical review

In the UK the National Institute of Health and Care Excellence (NICE) advocates intensive lifestyle programmes that attain the levels of daily physical activity set out by the Chief Medical Officer as a first-line strategy for improving the health of people at risk of developing diabetes or reducing the risk of development of Type 2 diabetes. For people with Type 2 diabetes, lifestyle measures complement pharmacological treatments that include both oral and injectable therapies. In line with this, NICE guidelines also support intensification of efforts to improve patient lifestyle along with these glucose-lowering therapies. There is a paucity of evidence, however, in the available published literature examining the association between glucose-lowering therapies and exercise metabolism. In the present review we explore the current knowledge with regard to the potential interactions of oral and non-insulin injectable therapies with physical activity in people at risk of, or who have, Type 2 diabetes, and present evidence that may inform healthcare professionals of the need to monitor patients more closely in their adaptation to both pharmacological therapy and physical activity.

Cardiorespiratory fitness testing and cardiovascular disease risk in male steelworkers

BACKGROUND

The workplace has been advocated as a setting to perform cardiovascular disease (CVD) risk assessments. These risk assessments usually focus on traditional risk factors rather than cardiorespiratory fitness (CRF) despite established associations between CRF and CVD. The lack of guidance on interpreting health-related CRF values has been suggested as a barrier to utilizing CRF in practice.

AIMS

To assess the merits of CRF testing in the workplace and explore whether a CRF value identified male individuals above the recommended threshold for further clinical investigation.

METHODS

Cross-sectional analysis of male steelworkers from Carmarthenshire, South Wales, UK who completed a workplace-based CVD risk assessment with an added CRF protocol based on heart rate responses (Chester Step Test). Receiver operating characteristic (ROC) analysis was undertaken to explore the possibility of a CRF value to identify individuals at an increased 10-year risk of CVD (QRISK2 ≥ 10%).

RESULTS

There were 81 participants. ROC analysis revealed that a CRF level of 34.5ml/kg/min identified those individuals above the ≥10% QRISK2 threshold with the best sensitivity (0.800) and specificity (0.687) to discriminate against true- and false-positive rates. Further analysis revealed that individuals with either 'Average' or 'Below Average' CRF would be five times more likely to have a 10-year CVD risk above the ≥10% QRISK2 threshold than individuals with an 'Excellent' or 'Good' level of fitness [OR 5.10 (95% CI 1.60-16.3)].

CONCLUSIONS

This study suggests CRF assessments are a useful addition to a workplace CVD assessment and could identify male individuals at increased predicted risk of the condition.

Algorithm that delivers an individualized rapid-acting insulin dose after morning resistance exercise counters post-exercise hyperglycaemia in people with Type 1 diabetes

AIMS

To develop an algorithm that delivers an individualized dose of rapid-acting insulin after morning resistance exercise to counter post-exercise hyperglycaemia in individuals with Type 1 diabetes.

METHODS

Eight people with Type 1 diabetes, aged 34 ± 7 years with HbA1c concentrations 72 ± 12 mmol/mol (8.7 ± 1.1%), attended our laboratory on two separate mornings after fasting, having taken their usual basal insulin the previous evening. These people performed a resistance exercise session comprising six exercises for two sets of 10 repetitions at 60% of the maximum amount of force that was generated in one maximal contraction (60% 1RM). In a randomized and counterbalanced order, the participants were administered an individualized dose of rapid-acting insulin (2 ± 1 units, range 0-4 units) immediately after resistance exercise (insulin session) by means of an algorithm or were not administered this (no-insulin session). Venous blood glucose concentrations were measured for 125 min after resistance exercise. Data (mean ± sem values) were analysed using anova (P ≤ 0.05).

RESULTS

Participants had immediate post-resistance exercise hyperglycaemia (insulin session 13.0 ± 1.6 vs. no-insulin session 12.7 ± 1.5 mmol/l; P = 0.834). The decline in blood glucose concentration between peak and 125 min after exercise was greater in the insulin exercise session than in the no-insulin session (3.3 ± 1.0 vs. 1.3 ± 0.4 mmol/l: P = 0.015). There were no episodes of hypoglycaemia (blood glucose <3.9 mmol/l).

CONCLUSIONS

Administration of rapid-acting insulin according to an individualized algorithm reduced the hyperglycaemia associated with morning resistance exercise without causing hypoglycaemia in the 2 h post-exercise period in people with Type 1 diabetes.

Similar risk of exercise-related hypoglycaemia for insulin degludec to that for insulin glargine in patients with type 1 diabetes: a randomized cross-over trial

We compared changes in blood glucose (BG) and risk of hypoglycaemia during and after exercise in 40 patients with type 1 diabetes (T1D) treated with insulin degludec (IDeg) or insulin glargine (IGlar) in a randomized, open-label, two-period, crossover trial. After individual titration and a steady-state period, patients performed 30 min of moderate-intensity cycle ergometer exercise (65% peak rate of oxygen uptake). BG, counter-regulatory hormones and hypoglycaemic episodes were measured frequently during and for 24 h after exercise. BG changes during exercise were similar with IDeg and IGlar [estimated treatment difference (ETD) for maximum BG decrease: 0.14 mmol/l; 95% confidence interval (CI) -0.15, 0.42; p = 0.34], as was mean BG (ETD -0.16 mmol/l; 95% CI -0.36, 0.05; p = 0.13). No hypoglycaemic episodes occurred during exercise. Post-exercise mean BG, counter-regulatory hormone response and number of hypoglycaemic episodes in 24 h after starting exercise were similar with IDeg (18 events in 13 patients) and IGlar (23 events in 15 patients). This clinical trial showed that, in patients with T1D treated with a basal-bolus regimen, the risk of hypoglycaemia induced by moderate-intensity exercise was low with IDeg and similar to that with IGlar.

Relationships between match activities and peak power output and Creatine Kinase responses to professional reserve team soccer match-play

The specific movement demands of soccer that are linked to post-match recovery and readiness to train are unclear. Therefore, we examined the relationship between Global Positioning System (GPS) variables and the change (Δ; from baseline) in Creatine Kinase (CK) concentrations and peak power output (PPO; during the countermovement jump) at 24h and 48h post-match. Fifteen English Premier League reserve team players were examined over 1-4 matches. Measurements of CK and PPO were taken before (24h prior to match-play) and after (+24h and +48h) each game during which movement demands were quantified using 10Hz GPS data. High intensity distance covered (r=0.386, p=0.029; r=-0.349; p=0.050), high intensity distance covered⋅min(-1) (r=0.365, p=0.040; r=-0.364, p=0.040), high speed running distance (r=0.363, p=0.041; r=-0.360, p=0.043) and the number of sprints⋅min(-1) (r=0.410, p=0.020; r=-0.368, p=0.038) were significantly related to ΔCK and ΔPPO at +24h post-match, respectively. No relationships were observed between any match variables and ΔCK and ΔPPO after +48h of recovery. These findings highlight that high intensity match activities are related to ΔCK and ΔPPO in the 24h, but not 48h, following soccer match-play. Such information is likely of interest to those responsible for the design of soccer player's training schedules in the days following a match.

Similar magnitude of post-exercise hyperglycemia despite manipulating resistance exercise intensity in type 1 diabetes individuals

The aim of this study was to compare the glycemic and glucoregulatory hormone responses to low- and moderate-intensity morning resistance exercise (RE) sessions in type 1 diabetes (T1DM). Following maximal strength assessments (1RM), eight T1DM (HbA1C :72 ± 12 mmol/mol, age:34 ± 7 years, body mass index:25.7 ± 1.6 kg/m(2) ) participants attended the research facility on two separate occasions, having fasted and taken their usual basal insulin but omitting rapid-acting insulin. Participants performed six exercises for two sets of 20 repetitions at 30%1RM during one session [low-intensity RE session (LOW)] and two sets of 10 repetitions at 60%1RM during another session [moderate-intensity RE session (MOD)], followed by 65-min recovery. Sessions were matched for total mass lifted (kg). Venous blood samples were taken before and after exercise. Data (mean ± SEM) were analyzed using analysis of variance (P ≤ 0.05). There were no hypoglycemic occurrences throughout the study. Blood glucose rose similarly between sessions during exercise (P = 0.382), remaining comparable between sessions throughout recovery (P > 0.05). There was no effect of RE intensity on metabolic acidosis (P > 0.05) or peak growth hormone responses (P = 0.644), but a tendency for greater catecholamine responses under LOW (individualized peak concentrations: adrenaline MOD 0.55 ± 0.13 vs LOW 1.04 ± 0.37 nmol/L, P = 0.155; noradrenaline MOD 4.59 ± 0.86 vs LOW 7.11 ± 1.82 nmol/L, P = 0.082). The magnitude of post-exercise hyperglycemia does not differ between equal volume low and moderate intensity RE sessions performed in the morning.

'Prosiect Sir Gâr': workplace-based cardiovascular disease and diabetes risk assessments

BACKGROUND

Cardiovascular disease (CVD) and diabetes remain two of the greatest health challenges in the UK. Government guidelines recommend screening for both of these conditions to identify individuals at high risk. Assessing individuals in the work environment for these two conditions as part of routine annual medicals could have benefits for both the employee and employer.

AIMS

To introduce the Prosiect Sir Gâr workplace-based initiative for CVD and diabetes prevention and report some of the baseline measurements in regards to CVD and diabetes risk.

METHODS

Individuals from two workplaces (local health board and steelworks) attended a medical health check with an added CVD and diabetes risk assessment component. Demographic and anthropometric data, systolic and diastolic blood pressure, smoking status and family and medical histories were recorded. Blood samples were analysed for total and high-density lipoprotein cholesterol and HbA1c. Ten year risk of CVD and diabetes were predicted using the QRISK2 and QDiabetes algorithms. Individuals at high risk of either condition were referred to a lifestyle intervention programme.

RESULTS

Among over 800 individuals screened a high prevalence of central obesity (75%), systolic hypertension (20%) and diastolic hypertension (23%) were observed in both workforces. In addition, a substantial proportion of the workers were either 'overweight' (42%) or 'obese' (28%).

CONCLUSIONS

Introducing CVD and diabetes risk assessments to routine annual medicals in the workplace uncovered significant isolated risk factors for both CVD and diabetes that may otherwise have remained undiagnosed. This approach also gave employers a more detailed awareness of the current health of their employees.

Reductions in resistance exercise-induced hyperglycaemic episodes are associated with circulating interleukin-6 in type 1 diabetes

AIMS

To determine the influence of different volumes of resistance exercise on circulating interleukin-6 (IL-6) and to explore the relationships between IL-6 and glycaemia.

METHODS

Eight participants with complication-free type 1 diabetes, whose mean ± SEM age was 38 (6) years, mean ± SEM HbA(1c) concentration was 71 ±11 mmol/mol (8.7 ±1.0%) and mean ± SEM type 1 diabetes duration was 15 ±13 years, attended the research facility after an overnight fast on four separate occasions, having administered their basal insulin the night before (glargine 27.5±3.1U, n=8), but omitted morning rapid-acting insulin. Participants completed either a one-set (14-min), two-set (28-min), or three-set (42-min) resistance exercise trial (eight exercises × 10 repetitions) at 67±3% one-repetition maximum followed by a 60-min recovery, or a resting control trial. Venous blood samples were taken before and after exercise. Data were analysed using repeated-measures ANOVA (P≤0.05).

RESULTS

Whereas IL-6 levels remained similar to baseline levels after one set of resistance exercises (30 min, P=0.287; 60 min, P=0.318), IL-6 levels were > baseline levels at 60 min post-exercise after a two-set exercise trial (2.94 ± 0.94 pg/ml, P=0.002) and doubled at both 30 min (4.01 ± 1.00 pg/ml, P=0.048) and 60 min (4.28 ± 1.25 pg/ml, P=0.084) post-exercise after the three-set resistance exercise trial. Post-exercise blood glucose area under the curve (mmol/l/60 min) was greater after both the one-set (P=0.025) and two-set trials (P=0.008), than after the control trial, but similar between the three-set trial and the control trial (P=0.240). The rise in IL-6 from baseline to peak concentration significantly correlated inversely with blood glucose area under the curve (r=-0.65, P=0.041).

CONCLUSIONS

Circulating IL-6 is increased by resistance exercise in a volume-dependent manner, and resistance exercise-induced increases in IL-6 correlated with reductions in post-exercise hyperglycaemia in type 1 diabetes, suggesting a role for IL-6 in improving post-resistance exercise glycaemic disturbances in type 1 diabetes.

Simulated games activity vs continuous running exercise: a novel comparison of the glycemic and metabolic responses in T1DM patients

To compare the glycemic and metabolic responses to simulated intermittent games activity and continuous running exercise in type 1 diabetes. Nine patients (seven male, two female; 35 ± 4 years; HbA1c 8.1 ± 0.2%/65 ± 2 mmol/mol) treated on a basal-bolus regimen completed two main trials, a continuous treadmill run (CON) or an intermittent running protocol (INT). Patients arrived to the laboratory fasted at ∼ 08:00 h, replicating their usual pre-exercise meal and administering a 50% reduced dose of rapid-acting insulin before exercising. Blood glucose (BG), K(+) , Na(++) , pH, triglycerides, serum cortisol and NEFA were measured at baseline and for 60 min post-exercise. Interstitial glucose was measured for a further 23 h under free-living conditions. Following exercise, BG declined under both conditions but was less under INT (INT -1.1 ± 1.4 vs CON -5.3 ± 0.4 mmol/L, P = 0.037), meaning more patients experienced hypoglycemia (BG ≤ 3.5 mmol/L; CON n = 3 vs INT n = 2) but less hyperglycemia (BG ≥ 10.9 mmol/L; CON n = 0 vs INT n = 6) under CON. Blood lactate was significantly greater, and pH lower, with a temporal delay in K(+) under INT (P < 0.05). No conditional differences were observed in other measures during this time, or in interstitial glucose concentrations during the remaining 23 h after exercise. Simulated games activity carries a lower risk of early, but not late-onset hypoglycemia than continuous running exercise in type 1 diabetes.

Strength and power predictors of sprinting performance in professional rugby players

AIM

The ability to accelerate and attain high levels of speed is an essential component of success in team sports; however, the physical qualities that underpin these activities remain unclear. This study aimed to determine some of the key strength and power predictors of speed within professional rugby union players.

METHODS

Twenty professional male rugby union players participated in this study. Subjects were tested for speed (0-10 m sprint and a flying 10 m sprint), strength (3 repetition maximum squat), lower body power (countermovement jumps [CMJ] and drop jumps [DJ]), reactive strength and leg spring stiffness. The strength and power variables were expressed as absolute values and relative values for analysis.

RESULTS

Both relative strength (r=-0.55, P<0.05) and relative power (-0.82, P<0.01) were negatively correlated with 10 m time. Leg spring stiffness and DJ contact time were also related to the flying 10 m time (r=-0.46 and 0.47, respectively, P<0.05) while reactive strength index was negatively related to both the 10 m and flying 10 m times (r=-0.60 and r=-0.62, P<0.05).

CONCLUSION

This study provides an insight into those physical attributes that underpin sprinting performance in professional rugby union players and specifically highlights the importance of relative strength and power in the expression and development of different speed components (e.g. acceleration, maximum velocity).

Relationships between salivary free testosterone and the expression of force and power in elite athletes

AIM

This study examined the predictive relationships between the salivary free testosterone (T) concentrations of elite athletes and the expression of force and power.

METHODS

A group of elite male rugby players (N.=64) were assessed for peak force (PF), peak rate of force development (PRFD), force at 100 milliseconds (F100 ms) and 250 milliseconds (F250 ms) during an isometric mid-thigh pull (IMTP), and/or peak power (PP) and height during a countermovement jump (CMJ). Saliva samples were collected before testing and assayed for free T. Relationships between individual T concentrations and performance were assessed as a pooled group and 4 sub-groups of equal size.

RESULTS

As pooled data sets, none of the IMTP and CMJ performance variables were significantly correlated with free T in either the PF or PP groups (r=0.01-0.23). The PF and PP abilities of the 4 sub-groups were significantly different, so that PF1>PF2>PF3>PF4 (P<0.001) and PP1>PP2>PP3>PP4 (P<0.01). When the 4 sub-groups were analysed, the T concentrations of the PF4 group were significantly (P<0.05-0.01) correlated to PRFD (r=0.69) and F100 ms (r=0.55) during the IMTP, as was F100 ms in the PF1 group (r=0.66). In the PP1 group, free T also correlated to CMJ height (r=0.62).

CONCLUSION

The key conclusion is that the expression of force and power in an elite athletic group may be dependent, to some extent, on individual variation in salivary free T concentrations and existing strength or power levels. The current results also confirm that the grouping of elite athletes of mixed strength or power ability may bias predictive results in a manner not reflective of sub-groups within this population.

Scaling strength and power for body mass differences in rugby union players

AIM

This study on professional rugby union players was undertaken to: 1) confirm a relationship between body mass (BM) and peak force (PF) and peak power (PP); 2) evaluate the effect of ratio and allometric scaling on these relationships; and 3) compare the PF and PP abilities of different positional groups with each approach.

METHODS

Seventy-nine rugby players were assessed for PF during an isometric mid-thigh pull and/or countermovement jump PP. Athlete performance was normalized for BM using standard ratio and allometric scaling methods. The performance data from inside backs (IB), outside backs (OB), tight forwards (TF) and loose forwards (LF) were compared before and after scaling for BM.

RESULTS

Significant relationships were identified between BM and the absolute expression of PF (r=0.25) and PP (r=0.44). These relationships improved with the application of ratio scaling (r=-0.53 to -0.57), but were eliminated after allometric scaling with the derived exponents (r=0.00-0.02). No positional group differences in absolute and allometrically scaled PF and PP were seen, but ratio scaled performance favoured the lighter IB and OB over the heavier TF and/or LF (P<0.05).

CONCLUSION

The PF and PP abilities of professional rugby union players were related to individual BM and these relationships were differentially affected by ratio (enhanced) and allometric (removed) scaling. Ratio scaled performance favoured the lighter backs over the heavier forwards, which could be explained by their specific movement patterns within a game. Comparing positional data in such a manner may help practitioners to better quantify, assess and monitor the position-specific needs of athletes in team sport.

Effects of short-term therapy with glibenclamide and repaglinide on incretin hormones and oxidative damage associated with postprandial hyperglycaemia in people with type 2 diabetes mellitus

AIM

To examine the effects of glibenclamide and repaglinide on glucose stimulated insulin release, incretins, oxidative stress and cell adhesion molecules in patients with type 2 diabetes suboptimally treated with metformin.

METHODS

A randomized clinical trial was performed recruiting 27 subjects (HbA(1c) between 7.5 and 10.5%) free from cardiovascular and renal disease. Glucose, insulin, C-peptide, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), total antioxidant status, F(2)-isoprostane, interleukin-6 and cell adhesion molecules were measured during an oral glucose load at baseline and after eight weeks of treatment. The areas under the curve were analysed at 45, 60 and 120 min (AUC(45), AUC(60), AUC(120)).

RESULTS

Significant improvements in glucose were observed with repaglinide (HBA(1c): -1.5%, fasting glucose: -2.8 mmol/L, 2-h glucose: -3.7 mmol/L, AUC(120): -18.9%) and glibenclamide (-1.0%, -2.2 mmol/L, -2.5 mmol/L, -17.5%). Repaglinide was also associated with an increase in the AUC(60) and AUC(120) for insulin (+56%, +61%) and C-peptide (+41%, +36%). GLP-1, GIP, IL-6, ICAM-1 and E-selectin levels did not change in either group. No association was observed between GLP-1, GIP-1 and plasma markers of oxidative stress.

CONCLUSION

Repaglinide is associated with improved postprandial glycaemic control via insulin and C-peptide release. We observed no direct effects of glibenclamide or repaglinide on plasma levels of GLP-1 or GIP. We observed no associations of GLP-1 and GIP with plasma markers of oxidative stress.

Impact of pre-exercise rapid-acting insulin reductions on ketogenesis following running in Type 1 diabetes

AIM

This study examined the effects of reductions to pre-exercise rapid-acting insulin dose on changes in blood beta-hydroxybutyrate, glucose, acid-base balance and counter-regulatory hormone responses to prolonged running in individuals with Type 1 diabetes.

METHODS

Following ethical approval, seven participants with Type 1 diabetes (34±2 years, BMI 27±1 kg/m(2) ) completed this study. After preliminary testing, participants attended the laboratory four times, each time consuming a 1.12 MJ meal (60 g carbohydrate, 2 g fat, 2 g protein), with randomized amounts of their rapid-acting insulin: Full dose (mean 7.3±0.2 units), 75% dose (mean 5.4±0.1 units), 50% dose (mean 3.7±0.1 units) or 25% dose (mean 1.8±0.1 units). After 2-h rest, participants completed 45 min running at 70±1% peak rate of oxygen consumption (VO(2peak) ). Blood metabolites and hormones were recorded over the 2-h rest and 3-h recovery. Data were analysed using repeated-measures ANOVA.

RESULTS

  Serum insulin peaked at 60 min in all conditions and was lowest after 25% insulin dose compared with full dose (P=0.03). After the 25% insulin dose immediately pre-exercise glucose concentration was higher than after the full or 50% dose (P<0.05). Resting beta-hydroxybutyrate gradually decreased during 2-h rest (P<0.05) with a similar post-exercise peak of beta-hydroxybutyrate at 3 h (P>0.05). Post-exercise blood pH increased for 5 min to a similar extent with all insulin doses , but the rise with the 25% dose was less compared with the full dose (P=0.01). Blood lactate and plasma catecholamines increased after running similarly with all insulin reduction conditions (P<0.05). Blood glucose area under the curve (BG(auc) ) after the 25% insulin dose was greater than after the 75% dose (P=0.02).

CONCLUSION

Ketogenesis following running was not influenced by reductions in pre-exercise rapid-acting insulin dose. This important preparatory strategy aids preservation of blood glucose but poses no greater risk to exercise-induced ketone body formation.

Effects of hyperthermia on the metabolic responses to repeated high-intensity exercise

In this study, we investigated the metabolic and performance responses to hyperthermia during high-intensity exercise. Seven males completed two 30-s cycle sprints (SpI and SpII) at an environmental temperature of 20.6 (0.3) degrees C [mean (SD)] with 4 min recovery between sprints. A hot or control treatment preceded the sprint exercise. For the hot trial, subjects were immersed up to the neck in hot water [43 degrees C for 16.0 (3.2) min] prior to entering an environmental chamber [44.2 (0.8) degrees C for 30.7 (7.1) min]. For the control trial, subjects were seated in an empty bath (15 min) and thereafter in a normal environment [20.2 (0.6) degrees C for 29.0 (1.9) min]. Subjects' core temperature prior to exercise was 38.1 (0.3) degrees C in the hot trial and 37.1 (0.3) degrees C in the control trial. Mean power output (MPO) was significantly higher in the hot condition for SpI [683 (130) W hot vs 646 (119) W control ( P<0.025)]. Peak power output (PPO) tended to be higher in the hot trial compared with the control trial for SpI [1057 (260) W hot vs 990 (245) W control ( P=0.03, NS)]. These differences in power output were a consequence of a faster pedal cadence in the hot trial ( P<0.025). There were no differences in sprint performance in SpII in the hot trial compared to the control trial; however, MPO was significantly reduced from SpI to SpII in the hot condition but not in the control condition ( P<0.025). Plasma ammonia was higher in the hot trial at 2 min post-SpI [169 (65) micromol l(-1 )hot vs 70 (26) micromol l(-1) control ( P<0.01)], immediately and at 2 min post-SpII [231 (76) micromol l(-1) hot vs 147 (72) micromol l(-1) control ( P<0.01)]. Blood lactate was higher in the hot trial compared with the control trial at 5 min post-SpII ( P<0.025). The results of this study suggest that an elevation in core body temperature by 1 degrees C can improve performance during an initial bout of high-intensity cycle exercise but has no further beneficial effect on subsequent power production following a 4-min recovery period.