The Influence of Fitness and Fatness on Heart Rate Variability in Black and White Teens

Abstract

1786 Heart rate variability (HRV) is a non-invasive measurement of cardiac autonomic activity. The root mean square of successive differences (RMSSD), a measurement of HRV in the time domain, provides an index of parasympathetic neural activity (PNA). Higher PNA is linked with longevity. The degree to which lifestyle factors, such as cardiovascular fitness (CVF) and body fatness (%BF), in black and white adolescents influences PNA is not known. PURPOSE: This study investigated the relationships between fitness and fatness and cardiac autonomic activity in teens. METHODS: Subjects were 303 13–18 y olds (119 males; 156 blacks, 147 whites). Each subject completed a graded treadmill test for the determination of sub-maximal CVF and a whole-body dual-energy x-ray absorptiometric scan for %BF. Following 5–10 min of supine rest, 256 beats were captured using a Schiller Cardiovit CS 100 and HRV was recorded as RMSSD. RESULTS: Group comparisons revealed that whites had higher RMSSD than blacks (p<0.05). RMSSD was inversely associated with age (r = −0.16, p<0.01) and positively associated with CVF (r<0.05, p<0.01), but was not associated with %BF (r = −0.07, p>0.05). After adjusting for age, race and sex: (1) CVF explained 2.8% of the variance in RMSSD (p<0.01), and (2) there was an interaction between %BF and race (p<0.05), such that higher %BF was associated with lower RMSSD in blacks, while the reverse was true for whites. CONCLUSIONS: High CVF is associated with more favorable PNA whereas the deleterious affects of high fatness on PNA seemed more clearly defined in blacks than in whites. Supported by NIH (HL64157)