Assessment of Physical Capacity and Metabolic Parameters in Marathon Runners With Type 1 Diabetes: an Observational Study

This observational, cross-sectional case-control study aims to compare physical capacity and metabolic parameters between male marathon runners with type 1 diabetes mellitus (T1DM) and healthy male marathon runners without diabetes. The study focuses on evaluating differences in cardiopulmonary fitness, resting metabolic rate, and body composition between the two groups.

Participants attended a single study visit after overnight fasting. The visit included anthropometric measurements, assessment of medical history, and structured questionnaires on diabetes management (for T1DM participants) and physical activity habits. Body composition was assessed using dual-energy X-ray absorptiometry (DXA), providing detailed analysis of total and regional fat mass, lean tissue mass, and bone mineral density. Daily calibration of the DXA scanner ensured data accuracy and consistency.

Resting metabolic rate (RMR) was measured by indirect calorimetry using a ventilated hood system. Measurements were performed in a controlled environment with standardized temperature and low light to minimize variability. Data collection spanned 25 minutes, with the first 5 minutes discarded for acclimatization and the subsequent 20 minutes analyzed. Energy expenditure and substrate oxidation rates were calculated using established equations (Weir equation and Zuntz table).

Cardiorespiratory fitness was assessed through a maximal exercise test on a cycle ergometer with continuous respiratory gas analysis. The test protocol began with a resting phase and warm-up, followed by incremental workload increases until volitional exhaustion. Parameters such as VO₂max, ventilatory efficiency, gas exchange threshold, and peak workload were measured using a calibrated metabolic cart.

Data analysis involved descriptive statistics, Mann-Whitney U tests for numerical comparisons, and Chi-square tests for categorical variables. Dedicated manufacturer software was used for CPET data processing, and statistical analyses were conducted using R software (version 4.4.1).