Abstract
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).
Highlights
Low amounts of structured exercise such as 3 × 30 min per week are associated with consistent improvements in health status in already healthy and physically active individuals [1]
Using percentages of maximum heart rate might be problematic as degree and direction of the deflection of the heart rate to performance curve during Cardio-Pulmonary Exercise (CPX) testing are altered in some healthy individuals [12] and might be further impaired by autonomic cardiac neuropathy in type 1 diabetes (T1D) individuals [13]
No significant differences were found for power output, heart rate, oxygen uptake and lactate concentration at First lactate turn point (LTP1), Second lactate turn point (LTP2), heart rate turn point, and maximum power output between T1D and compared to matched healthy individuals (CON) individuals, except for lactate concentration at LTP1 (Table 1)
Summary
Low amounts of structured exercise such as 3 × 30 min per week are associated with consistent improvements in health status in already healthy and physically active individuals [1]. In people with both type 1 (T1D) and type 2 diabetes high doses of physical activity were found to be associated with a 40% and 29% lower risk of all-cause mortality and cardiovascular disease in comparison with inactivity [2]. The American Diabetes Association (ADA) recommends prescribing exercise intensity as percentages of maximum heart rate [5] even though there is an ongoing debate on how to prescribe exercise intensity [6, 7]. Using percentages of maximum heart rate might be problematic as degree and direction of the deflection of the heart rate to performance curve (kHR) during CPX testing are altered in some healthy individuals [12] and might be further impaired by autonomic cardiac neuropathy in T1D individuals [13]
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