Are there relantionship between internal and external load of aerobic training with heart rate variability in women?

The purpose was to investigate the relationship between internal training load (ITL), external training load (ETL) and heart rate variability (HRV) in women. 16 women (48.2 ± 6.4 yrs) performed HRV recordings (i.e. lnRMSSD – cardiovagal modulation) and Incremental Shuttle Walk Test (ISWT) before and after 12 aerobic training sessions. HRV threshold (HRVT) were used to prescribe aerobic ETL. The session rating of perceived exertion (s-RPE) was analyzed and served as the measure of ITL. The score found for ITL in the 12 sessions was 2878 ± 380 arbitrary units and ETL were 36822 ± 5852 m. A significant difference was observed in the lnRMSSD (3.14 ± 0.30 vs. 3.43 ± 0.38 ms−1; P = 0.001). There were observed large correlation between lnRMSSD at baseline vs ISWT (r = 0.73, P = 0.001), HRVT (r = 0.67, P = 0.004) and ITL (r = 0.62, P = 0.011). Very large correlation between individual smallest worthwhile change lnRMSSD after training and ITL (r = 0.81, P = 0.0001) was observed. There is a strong association between the HRV and aerobic performance (HRVT and ISWTdistance) and strong relationship between HRV and the potential to accumulate ITL, but not aerobic ETL in women.