HEART RATE RECOVERY AFTER EXERCISE AND MAXIMAL OXYGEN UPTAKE IN SEDENTARY PATIENTS WITH TYPE 2 DIABETES

Abstract

Aims: Heart rate recovery after exercise (HRR) is an estimate of autonomic modulation of the heart, and has been shown to be inversely associated with insulin resistance, metabolic syndrome, and type 2 diabetes [1]. Type 2 diabetes is associated with poor exercise tolerance and maximal aerobic capacity (VO2max) [2]. Aim of our study was to assess the relationship between HRR and VO2max in sedentary patients with type 2 diabetes. Methods: Maximal treadmill exercise testing using standard or modified Bruce protocol was performed in 16 (8 males and 8 females) sedentary patients with type 2 diabetes (T2D), and in 16 (9 males and 7 females) age-matched sedentary non-diabetic controls (ND). HRR (bpm) was defined as the difference between maximum heart rate during the exercise test and heart rate 2 minutes after cessation of the exercise (Fig. 1). The recovery protocol consisted of walking on treadmill at 2.0 Km/h of speed and 0% of grade. Oxygen uptake was recorded and VO2max (ml/Kg/min) was defined as the highest 30 seconds average achieved during the test. For the statistical analysis of the data, Student’s t-test for independent samples and linear regression analysis were used. Results: The characteristics of subjects are shown in Table 1. The two groups were similar in age and body weight. BMI was higher in T2D (30.1 ± 3.6 vs. 26.9 ± 4.2, p = 0.029). VO2max was significantly lower in T2D compared to ND (20.6 ± 8.4 vs. 28.2 ± 8.1 ml/Kg/min, p = 0.002) and, according to “Normative Table by age and gender" from ACMS, the aerobic capacity was classified very poor in all T2D and in 11/16 of ND. HRR was significantly lower in T2D (28 ± 8.4 vs. 37 ± 8.9 bpm, p = 0.008). A significant correlation between HRR and VO2max has been found in both T2D (Fig. 2) and ND (r = 0.672, p = 0.004 and r = 0.620, p = 0.010 respectively). Conclusions: The results of our study showed that both HRR and VO2max were significantly reduced in T2D versus ND. The positive linear correlation between HRR and VO2max suggests that in T2D the heart rate recovery after exercise, index of autonomic modulation, might improve in response to a training aimed to increase aerobic capacity.