Physical Activity Measured by PAMS device Correlates with First- and Second-Order Glucose Concentration Derivatives

Objective: The quantification of the effect of physical activity (PA) on glucose concentration and its variability is a challenging topic. In the present study, we evaluated possible correlations between PA, measured using the PAMS (Physical Activity Monitoring System: a system with accelerometers and inclinometers for recording body posture and movement) and first- and second-order derivatives of glucose concentration measured by the DexCom Seven Plus® continuous glucose monitoring system (CGM). Method: 13 type-1 diabetic and 17 control subjects were studied in the Clinical Research Unit at Mayo Clinic (Rochester, MN) for 88 hours. Each day, subjects underwent 4-6 consecutive sessions of low intensity PA, during which they alternated 26.5 min of walking on treadmill (1.2 mph) with 33.5 min of sitting. First- and second-order glucose derivatives were estimated using a Bayesian smoothing procedure. Their correlation with PAMS output was assessed at various delays in the range 0-60 min. Result: We found that in diabetic subjects glycemic concentration decreases during PA, and increases during rest sessions. The decreasing effect is maximum after 15 min of PA, while the increasing effect is maximum after 15 min of rest. Furthermore, we found that, when glucose is decreasing, PA makes it decrease more rapidly, while if glucose is increasing, PA makes it stop increasing and start decreasing, or increase less rapidly. Results on control subjects are similar, but the correlation is inferior (in absolute terms) and the effects of PA starts after only 5 min. Conclusion: We demonstrate that low intensity PA correlates with fluctuations of glucose concentrations and, in particular, has the effect of lowering glucose concentration or makes it increase less rapidly.