Exercise duration: Independent effects on acute physiologic responses and the need for an individualized prescription.

An individualization of exercise prescription is implemented mainly in terms of intensity but not for duration. To survey the need for an individualized exercise duration prescription, we investigated acute physiologic responses during constant-load exercise of maximal duration (tmax ) and determined so-called duration thresholds. Differences between absolute (min) and relative terms (% tmax ) of exercise duration were analyzed. Healthy young and trained male and female participants (n = 11) performed an incremental exercise test and one tmax constant-load exercise test at a target intensity of 10% of maximal power output below the second lactate turn point (LTP2 ). Blood lactate, heart rate, and spirometric data were measured during all tests. tmax was markedly different across subjects (69.6 ± 14.8 min; range: 40-90 min). However, distinct duration phases separated by duration thresholds (DTh) were found in most measured variables. These duration thresholds (except DTh1) were significantly related to tmax (DTh2: r2  = 0.90, p < 0.0001; DTh3: r2  = 0.98, p < 0.0001) and showed substantial interindividual differences if expressed in absolute terms (DTh2: 24.8 ± 6.0 min; DTh3: 47.4 ± 10.6 min) but not in relative terms (DTh2: 35.4 ± 2.7% tmax ; DTh3: 67.9 ± 2.4% tmax ). Our data showed that (1) maximal duration was individually different despite the same relative intensity, (2) duration thresholds that were related to tmax could be determined in most measured variables, and (3) duration thresholds were comparable between subjects if expressed in relative terms. We therefore conclude that duration needs to be concerned as an independent variable of exercise prescription.

Different Heart Rate Patterns During Cardio-Pulmonary Exercise (CPX) Testing in Individuals With Type 1 Diabetes.

To investigate the heart rate during cardio-pulmonary exercise (CPX) testing in individuals with type 1 diabetes (T1D) compared to healthy (CON) individuals. Fourteen people (seven individuals with T1D and seven CON individuals) performed a CPX test until volitional exhaustion to determine the first and second lactate turn points (LTP1 and LTP2), ventilatory thresholds (VT1 and VT2), and the heart rate turn point. For these thresholds cardio-respiratory variables and percentages of maximum heart rate, heart rate reserve, maximum oxygen uptake and oxygen uptake reserve, and maximum power output were compared between groups. Additionally, the degree and direction of the deflection of the heart rate to performance curve (kHR) were compared between groups. Individuals with T1D had similar heart rate at LTP1 (mean difference) -11, [(95% confidence interval) -27 to 4 b.min-1], at VT1 (-12, -8 to 33 b.min-1) and at LTP2 (-7, -13 to 26 b.min-1), at VT2 (-7, -13 to 28 b.min-1), and at the heart rate turn point (-5, -14 to 24 b.min-1) (p = 0.22). Heart rate expressed as percentage of maximum heart rate at LTP1, VT1, LTP2, VT2 and the heart rate turn point as well as expressed as percentages of heart rate reserve at LTP2, VT2 and the heart rate turn point was lower in individuals with T1D (p < 0.05). kHR was lower in T1D compared to CON individuals (0.11 ± 0.25 vs. 0.51 ± 0.32, p = 0.02). Our findings demonstrate that there are clear differences in the heart rate response during CPX testing in individuals with T1D compared to CON individuals. We suggest using submaximal markers to prescribe exercise intensity in people with T1D, as the heart rate at thresholds is influenced by kHR. Clinical Trial Identifier: NCT02075567 (https://clinicaltrials.gov/ct2/show/NCT02075567).

Atypical blood glucose response to continuous and interval exercise in a person with type 1 diabetes: a case report.

BACKGROUND: Therapy must be adapted for people with type 1 diabetes to avoid exercise-induced hypoglycemia caused by increased exercise-related glucose uptake into muscles. Therefore, to avoid hypoglycemia, the preexercise short-acting insulin dose must be reduced for safety reasons. We report a case of a man with long-lasting type 1 diabetes in whom no blood glucose decrease during different types of exercise with varying exercise intensities and modes was found, despite physiological hormone responses. CASE PRESENTATION: A Caucasian man diagnosed with type 1 diabetes for 24 years performed three different continuous high-intensity interval cycle ergometer exercises as part of a clinical trial (ClinicalTrials.gov identifier NCT02075567). Intensities for both modes of exercises were set at 5% below and 5% above the first lactate turn point and 5% below the second lactate turn point. Short-acting insulin doses were reduced by 25%, 50%, and 75%, respectively. Measurements taken included blood glucose, blood lactate, gas exchange, heart rate, adrenaline, noradrenaline, cortisol, glucagon, and insulin-like growth factor-1. Unexpectedly, no significant blood glucose decreases were observed during all exercise sessions (start versus end, 12.97 ± 2.12 versus 12.61 ± 2.66 mmol L-1, p = 0.259). All hormones showed the expected response, dependent on the different intensities and modes of exercises. CONCLUSIONS: People with type 1 diabetes typically experience a decrease in blood glucose levels, particularly during low- and moderate-intensity exercises. In our patient, we clearly found no decline in blood glucose, despite a normal hormone response and no history of any insulin insensitivity. This report indicates that there might be patients for whom the recommended preexercise therapy adaptation to avoid exercise-induced hypoglycemia needs to be questioned because this could increase the risk of severe hyperglycemia and ketosis.

Accuracy of Continuous Glucose Monitoring (CGM) during Continuous and High-Intensity Interval Exercise in Patients with Type 1 Diabetes Mellitus.

Continuous exercise (CON) and high-intensity interval exercise (HIIE) can be safely performed with type 1 diabetes mellitus (T1DM). Additionally, continuous glucose monitoring (CGM) systems may serve as a tool to reduce the risk of exercise-induced hypoglycemia. It is unclear if CGM is accurate during CON and HIIE at different mean workloads. Seven T1DM patients performed CON and HIIE at 5% below (L) and above (M) the first lactate turn point (LTP1), and 5% below the second lactate turn point (LTP2) (H) on a cycle ergometer. Glucose was measured via CGM and in capillary blood (BG). Differences were found in comparison of CGM vs. BG in three out of the six tests (p < 0.05). In CON, bias and levels of agreement for L, M, and H were found at: 0.85 (-3.44, 5.15) mmol·L(-1), -0.45 (-3.95, 3.05) mmol·L(-1), -0.31 (-8.83, 8.20) mmol·L(-1) and at 1.17 (-2.06, 4.40) mmol·L(-1), 0.11 (-5.79, 6.01) mmol·L(-1), 1.48 (-2.60, 5.57) mmol·L(-1) in HIIE for the same intensities. Clinically-acceptable results (except for CON H) were found. CGM estimated BG to be clinically acceptable, except for CON H. Additionally, using CGM may increase avoidance of exercise-induced hypoglycemia, but usual BG control should be performed during intense exercise.

Effects of High-Intensity Interval Exercise versus Moderate Continuous Exercise on Glucose Homeostasis and Hormone Response in Patients with Type 1 Diabetes Mellitus Using Novel Ultra-Long-Acting Insulin.

INTRODUCTION: We investigated blood glucose (BG) and hormone response to aerobic high-intensity interval exercise (HIIE) and moderate continuous exercise (CON) matched for mean load and duration in type 1 diabetes mellitus (T1DM). MATERIAL AND METHODS: Seven trained male subjects with T1DM performed a maximal incremental exercise test and HIIE and CON at 3 different mean intensities below (A) and above (B) the first lactate turn point and below the second lactate turn point (C) on a cycle ergometer. Subjects were adjusted to ultra-long-acting insulin Degludec (Tresiba/ Novo Nordisk, Denmark). Before exercise, standardized meals were administered, and short-acting insulin dose was reduced by 25% (A), 50% (B), and 75% (C) dependent on mean exercise intensity. During exercise, BG, adrenaline, noradrenaline, dopamine, cortisol, glucagon, and insulin-like growth factor-1, blood lactate, heart rate, and gas exchange variables were measured. For 24 h after exercise, interstitial glucose was measured by continuous glucose monitoring system. RESULTS: BG decrease during HIIE was significantly smaller for B (p = 0.024) and tended to be smaller for A and C compared to CON. No differences were found for post-exercise interstitial glucose, acute hormone response, and carbohydrate utilization between HIIE and CON for A, B, and C. In HIIE, blood lactate for A (p = 0.006) and B (p = 0.004) and respiratory exchange ratio for A (p = 0.003) and B (p = 0.003) were significantly higher compared to CON but not for C. CONCLUSION: Hypoglycemia did not occur during or after HIIE and CON when using ultra-long-acting insulin and applying our methodological approach for exercise prescription. HIIE led to a smaller BG decrease compared to CON, although both exercises modes were matched for mean load and duration, even despite markedly higher peak workloads applied in HIIE. Therefore, HIIE and CON could be safely performed in T1DM. TRIAL REGISTRATION: ClinicalTrials.gov NCT02075567 http://www.clinicaltrials.gov/ct2/show/NCT02075567.

How to regulate the acute physiological response to "aerobic" high-intensity interval exercise.

The acute physiological processes during "aerobic" high-intensity interval exercise (HIIE) and their regulation are inadequately studied. The main goal of this study was to investigate the acute metabolic and cardiorespiratory response to long and short HIIE compared to continuous exercise (CE) as well as its regulation and predictability. Six healthy well-trained sport students (5 males, 1 female; age: 25.7 ± 3.1 years; height: 1.80 ± 0.04 m; weight: 76.7 ± 6.4 kg; VO2max: 4.33 ± 0.7 l·min(-1)) performed a maximal incremental exercise test (IET) and subsequently three different exercise sessions matched for mean load (Pmean) and exercise duration (28 min): 1) long HIIE with submaximal peak workloads (Ppeak = power output at 95 % of maximum heart rate), peak workload durations (tpeak) of 4 min, and recovery durations (trec) of 3 min, 2) short HIIE with Ppeak according to the maximum power output (Pmax) from IET, tpeak of 20 s, and individually calculated trec (26.7 ± 13.4 s), and 3) CE with a target workload (Ptarget) equating to Pmean of HIIE. In short HIIE, mean lactate (Lamean) (5.22 ± 1.41 mmol·l(-1)), peak La (7.14 ± 2.48 mmol·l(-1)), and peak heart rate (HRpeak) (181.00 ± 6.66 b·min(-1)) were significantly lower compared to long HIIE (Lamean: 9.83 ± 2.78 mmol·l(-1); Lapeak: 12.37 ± 4.17 mmol·l(-1), HRpeak: 187.67 ± 5.72 b·min(-1)). No significant differences in any parameters were found between short HIIE and CE despite considerably higher peak workloads in short HIIE. The acute metabolic and peak cardiorespiratory demand during "aerobic" short HIIE was significantly lower compared to long HIIE and regulable via Pmean. Consequently, short HIIE allows a consciously aimed triggering of specific and desired or required acute physiological responses. Key pointsHigh-intensity interval exercise (HIIE) with short peak workload durations (tpeak) induce a lower acute metabolic and peak cardiorespiratory response compared to intervals with long tpeak despite higher peak workload intensities (Ppeak) and identical mean load (Pmean).Short HIIE response is the same as in continuous exercise (CE) matched for Pmean.It is possible to regulate and predict the acute physiological response by means of Pmean for short HIIE but not for long HIIE.The use of fixed percentages of maximal heart rate (HRmax) for exercise intensity prescription yields heterogeneous exercise stimuli across subjects. Therefore, objective individual markers such as the first and the second lactate turn point are recommend prescribing exercise intensity not only for continuous but also for intermittent exercise.