Grant D. Brinkworth, PhD; Manny Noakes, PhD; Jonathan D. Buckley, PhD; Peter M. Clifton, PhD
Abstract and Introduction
Background: Heart rate recovery (HRR) is an independent risk factor for cardiovascular disease (CVD) and mortality, but whether it is modifiable and can improve with weight loss is unclear. We sought to determine the effects of weight loss on HRR and its association with traditional CVD risk markers.
Methods: Heart rate recovery (defined as the decrease in heart rate from peak heart rate to that measured 1 minute after a standardized graded treadmill test) and a range of established cardiovascular risk factors were measured in 42 overweight and obese men (body mass index 33.8 ± 0.6 kg/m2, mean age 46.5 ± 1.3 years) who had no symptoms of CVD but had components of the metabolic syndrome before and after 12 weeks of weight loss.
Results: There was a 9% weight reduction (P < .001), with losses of 6.3 ± 0.6 kg of fat mass (P < .001) and 3.1 ± 0.6 kg of non-bone fat-free mass (P < .001). There were significant reductions in waist circumference, blood pressure, plasma triglycerides, total cholesterol, low-density lipoprotein cholesterol, triglyceride/high-density lipoprotein ratio, C-reactive protein, plasma insulin, glucose, and insulin resistance (P < .05). Although peak heart rate remained unchanged, HRR at 1 minute improved from 33.1 ± 1.4 to 36.9 ± 1.3 beats/min (P < .001) after weight loss. There was no change in cardiorespiratory fitness (P = .30); neither was there any change in physical activity levels (P = .67). The improvement in HRR was significantly correlated with decreases in body weight, body mass index, waist circumference, plasma glucose, serum triglycerides, and triglyceride/high-density lipoprotein ratio; however, it was only independently associated with changes in weight and plasma glucose concentrations.
Conclusion: In addition to improving a range of well-accepted cardiovascular and metabolic risk factors, weight loss also improves HRR after exercise, a less recognized risk factor.
Heart rate recovery (HRR) or the rate of decrease in heart rate after a graded exercise test has been identified as a powerful independent predictor of cardiovascular and all-cause mortality in healthy adults[1,2,3,4,5] and in those with either cardiovascular disease (CVD) or risk factors for CVD[6,7] and diabetes.
Heart rate recovery is mainly thought to be a function of vagal (ie, parasympathetic nervous system) reactivation, with a delayed decrease in HRR reflecting a reduction in vagal tone. Abnormal HRR after exercise is therefore considered to be a measure of autonomic dysfunction. Previous studies have demonstrated that insulin resistance and compensatory hyperinsulinemia are associated with autonomic imbalance with increased sympathetic activity and reduced parasympathetic activity.[10,11,12,13] Accordingly, HRR has been shown to be inversely associated with insulin resistance and other risk factors that tend to cluster with insulin resistance,[14,15] including body mass index (BMI), abdominal obesity, and low high-density lipoprotein cholesterol in older men and triglyceride/high-density lipoprotein ratio in healthy subjects. Panzer et al demonstrated a strong independent relationship between fasting plasma glucose and abnormal HRR in healthy adults and in patients with diabetes.
Weight loss that is known to reduce insulin resistance as well as enhance insulin sensitivity[19,20] and to improve an array of established CVD risk markers, including fasting glucose levels and blood lipids, also increases vagal tone.[22,23] However, not much is known about the effect of weight loss on HRR and whether it is a modifiable risk factor. This information is of importance, considering the increased cardiovascular risk in the obese population. We hypothesized that weight loss via energy restriction would be associated with a heightened HRR after maximal exercise in overweight and obese patients and that it would be related to changes in risk factors. To our knowledge, the association between any change in HRR and other established metabolic risk factors with weight loss has not been studied.