Cardiac Vagal Modulation with Combined Endurance and Strength Training: Use of pNN Time Domain Statistics

Abstract

Cardiac vagal modulation can be quantified from heart rate variability (HRV) using time and frequency domain measures, including pNN50 and high frequency (HF) power. The use of pNN thresholds lower than the traditional 50 ms may provide more information about cardiac vagal modulation, and be useful in detecting changes in parasympathetic activity induced by endurance training. Due to the specific effects of endurance and strength training, information is limited about the effects of combining these two training modes on cardiac autonomic function. PURPOSE: To examine the effects of combined endurance and strength training on cardiac vagal modulation in short (< 15 min) recordings of RR intervals. METHODS: 93 healthy men (mean age = 55 yr, SD = 7 yr) completed a 21 week progressive training period consisting one of the following: two endurance (E, n=23), two strength (S, n=25), two endurance and two strength (ES, n=29) training sessions per week, or no systematic training (control group, n=16). RR intervals were recorded during 10 min supine rest, and probability distributions for pNN10, 20, 30, 40, and 50 were calculated. HF domain power was computed using Fourier spectral methods. RESULTS: At baseline, for low pNN50 (< 5 %) or low HF power (< 250 ms2), pNN10 ranged widely from approximately 15 to 70 %. These results indicate that pNN10 describes different characteristics of short-term RR interval dynamics than traditional pNN50 or HF power among healthy middle-aged men. After training, significant changes (p < 0.05 between groups) were only observed in the ES group in pNN10 [from 59 (18) % to 63 (20) %, p = 0.023] and pNN20 [from 34 (20) % to 39 (23) %, p = 0.043]. Other training groups did not show significant changes after the 21 week training period. No significant changes were seen in HF power. CONCLUSION: pNN time domain statistics with thresholds lower than the conventional 50 ms may be sensitive in detecting training-induced changes in short term recordings of HRV. Based on the increases in pNN10 and pNN20, combining endurance and strength training may be especially beneficial for enhancing cardiac autonomic function in middle-aged men, even though endurance or strength training alone did not lead to significant changes in these measures in very short-term recordings. Supported by Ministry of Education, Finland.