Simple exercise recovery index for sympathetic overactivity is linked to insulin resistance.

UNLABELLED

Exercise HR recovery (HRR) has proven an effective clinical means to assess parasympathetic dysfunction linked to all-cause mortality, but an analogous functional assessment for sympathetic dysfunction has not been developed.

PURPOSE

We investigated whether exercise recovery provides additional cardiorespiratory information, beyond the initial HRR period, to index sympathetic overactivity associated with insulin resistance.

METHODS

Young people (N = 20) with diverse percent body fat (9%-52%) were studied using fasting, oral glucose tolerance test (OGTT), and high-carbohydrate meal measurements. Participants also completed a graded fitness test (oxygen consumption peak test on cycle ergometer) after which HR and oxygen consumption (V x O2) measurements were continued for 3 min into recovery. The first, rapid phase of exercise recovery was used as the clinical measurement for parasympathetic control (HRR = HR2 min - HRmax). The second, initial plateau phase of exercise recovery was used to calculate a novel functional index for sympathetic overactivity (the plateau value for the ratio of HR normalized for V x O2 (HR/V x O2 plat)).

RESULTS

As expected, parasympathetic function (HRR) was within the normal range in these young people (-58 +/- 2 bpm). The index for sympathetic overactivity varied over a wide range from 9 to 34 bpm/(mL x kg x min(-1)), with obese adolescents having values in the highest 25th percentile. We found that this simple index was correlated to both the OGTT-derived whole-body insulin sensitivity index (r = -0.74, P < 0.001) and Homeostasis Assessment Model for Insulin Resistance (r = 0.76, P < 0.001), independent of percent body fat and parasympathetic function. Meal-induced thermogenesis was also associated with HR/V x O2 plat (r = -0.64, P < 0.01) but not with HRR.

CONCLUSION

In young individuals, recovery from intense exercise may provide a simple means to quantify both parasympathetic and sympathetic function. The exercise recovery index for sympathetic overactivity was linked to insulin resistance.