Metabolic and physiological responses to graded exercise testing in individuals with type 1 diabetes using insulin pump therapy

Abstract

Aims: To profile acute glycaemic dynamics during graded exercise testing (GXT) and explore the influence of glycaemic indicators on the physiological responses to GXT in adults with type 1 diabetes using insulin pump therapy.

Methods: This was a retrospective analysis of pooled data from four clinical trials with identical GXT protocols. Data were obtained from 45 adults with type 1 diabetes using insulin pumps [(30 females); haemoglobin A1c 59.5 ± 0.5 mmol/mol (7.6 ± 1.0%); age 49.7 ± 13.0 years; diabetes duration 31.2 ± 13.5 years; V̇O_2peak 29.5 ± 8.0 ml/min/kg]. Integrated cardiopulmonary variables were collected continuously via spiroergometry. Plasma glucose was obtained every 3 min during GXT as well as the point of volitional exhaustion. Data were assessed via general linear modelling techniques with age and gender adjustment. Significance was accepted at p ≤ .05.

Results: Despite increasing duration and intensity, plasma glucose concentrations remained similar to rest values (8.8 ± 2.3 mmol/L) throughout exercise (p = .419) with an overall change of +0.3 ± 1.1 mmol/L. Starting glycaemia bore no influence on subsequent GXT responses. Per 1% increment in haemoglobin A1c there was an associated decrease in V̇O_2peak of 3.8 ml/min/kg (p < .001) and power_peak of 0.33 W/kg (p < .001) concomitant with attenuations in indices of peripheral oxygen extraction [(O₂ pulse) -1.2 ml/beat, p = .023].

Conclusion: In adults with long-standing type 1 diabetes using insulin pump therapy, circulating glucose remains stable during a graded incremental cycle test to volitional exhaustion. Glycaemic indicators are inversely associated with aerobic rate, oxygen economy and mechanical output across the exercise intensity spectrum. An appreciation of these nexuses may help guide appropriate decision making for optimal exercise management strategies.

Trial registration: ClinicalTrials.gov NCT04472962 NCT05268705 NCT05134025 NCT05133765.

Keywords: cardiopulmonary exercise testing; exercise; graded exercise testing; insulin pump therapy; plasma glucose; type 1 diabetes.

FIGURE 1

Plasma glucose responses to graded exercise testing when data are expressed as (A) the absolute concentrations across the work domain, (B) the change from starting values at each stage across the work domain (C) the relationship between immediately pre‐ and post‐exercise concentrations, and (D) the individualized change from rest to end when participants have been ranked in descending order (highest to lowest) based on their starting plasma glucose levels. AT, anaerobic threshold; CD, cool down; WU, warm up