Immediate recovery index after exercise is related to heart rate variability

BACKGROUND: In the practice of sports medicine the Immediate Recovery Index (IRI) is used as a measure of fitness and of vagal reactivation and it is based upon the number of heartbeats after a 3 minutes step test at the rate of 30 cycles/minute. The Heart Rate Variability (HRV) analysis is a non invasive method to assess autonomic cardiac regula- tion. The aim of this study is to examine the relationship between HRV during resting state and IRI. METHODS: Heart rate was monitored in 41 healthy male athletes, during the pre-exercise phase (5 min supine). The HRV analysis was performed using 5-min electrocardiographic recording and evaluated in time domain, in frequency domain and using Poincaré Plot analysis, before and after a 3 min step test. RESULTS: Interesting correlation emerged between IRI and Mean RR (ms), IRI and STD RR (ms), IRI and Mean HR (1/ min), IRI and RMSSD (ms), IRI and TP (ms^2), IRI and LF (ms^2), IRI and HF (ms^2), IRI and SD1 (ms), IRI and SD2 (ms). CONCLUSIONS: In this study was evident the relationship between HRV and IRI. In particular it seems that subjects with higher variability shows also higher recovery after exercise.