Cardiac autonomic regulation in response to functional power threshold testing in elite cyclists.

Abstract

Objective: To evaluate the impact of a functional power threshold test (FTP) on cardiac autonomic regulation indicators in high performance cyclists. 
 Methods: A total of 12 male elite cyclists (mean age 36.1 ± 11.2 years) were recruited. Body composition parameters were measured using bioimpedancemetry and heart rate variability (HRV) before and after the application of the FTP assessment. 
 Results: We observed that a greater sympathetic nervous system (SNS) index and Stress index on baseline were correlated with a smaller decrease in the parasympathetic nervous system (PNS) activity in response to the FTP test (rho = 0.69, p = 0.013). Concerning morphological parameters, the skeletal muscle index (SMI) was the only one that was inversely correlated with ∆PNS (rho = -0.69, p = 0.02) whereas the muscle-bone index (MBI) displayed a positive correlation with ∆SNS (rho = 0.82, p = 0.001). In fully adjusted models we found that waist-to-hip ratio (beta = 7.90, CI95%[4.16, 11.63], t(8) = 4.88, p = 0.001) and SMI significantly influenced ∆PNS (beta = -1.38, CI95%[-1.84, -0.92], t(8) = -6.94, p < 0.001), whereas MBI (beta = 10.26, CI95%[8.10, 12.42], t(8) = 10.96, p < 0.001) and the interaction between the latter and Power achieved during FTP influenced ∆SNS (beta = -0.05, CI95%[-0.09, -4.99e-03], t(8) = -2.56, p = 0.033). 
 Conclusion: Our findings indicate that the SMI had a negative effect on the ∆PNS, while the MBI was positively correlated with the ∆SNS in cyclists. These findings suggest that a higher SMI and MBI could have a detrimental impact on the cardiac autonomic response to maximal aerobic exercise in high-performance cyclists, such as FTP.