Introduction
Cold exposure appears to be beneficial for glucose homeostasis. Observational research shows a positive association between ambient temperature and type 2 diabetes prevalence. Experimental research finds increased glucose uptake during a hyperinsulinemic-euglycemic clamp after cold acclimation (14°C air, 6h/d, 10d). However, when observable shivering was prevented, glucose uptake was not increased after cold acclimation. This suggests that shivering increases glucose uptake. Therefore, we aimed to determine the effects of 1h of cold-induced shivering on glucose metabolism in healthy and overweight adults.

Methods
Experiment 1: 15 healthy men completed two trials. Cold exposure (10°C) was applied during the first trial with a water-perfused suit to induce at least 1h of shivering in each subject. For comparison, a thermoneutral (32°C) condition was applied during the second trial. After the thermal exposures, participants rested under a duvet for 90 min, which was followed by a 3h oral glucose tolerance test (OGTT).

Experiment 2 (ongoing): 15 overweight adults completed a 10-day cold acclimation protocol. The cold exposures were performed with a water-perfused suit (10°C) with the aim of inducing 1h of shivering per session. In the morning after an overnight fast, three OGTTs were performed: before the cold acclimation, after the first cold exposure, and after cold acclimation. 

Results
Experiment 1: Energy expenditure during the 1h of shivering was greater than that during the time-matched thermoneutral condition (619 ± 23 vs 309 ± 7 kJ, P < 0.001). Cold exposure increased the areas under the glucose and insulin curves by 4.8% (P = 0.066) and 24% (P = 0.112), respectively.

Experiment 2: Currently 12 subjects have completed the experiment and preliminary results will be presented.

Conclusion
In contrast to our hypothesis for Experiment 1, glucose tolerance was not improved. Instead, results indicate an acute post-shivering response whereby glucose metabolism is altered possibly by insulin resistance and/or by an increased appearance of glucose.