Who, what & why?

The measurement of the amount of training someone has done is called their Training Load (TL), and is important as a means of controlling training so that sessions can be created which ensure an athlete does the right amount at the right time.

However, there are a variety of measures in common use and they all have limitations – see our earlier review here.

All ithlete users will (hopefully) have noticed that a hard training session brings down their HRV score the next morning, and important review papers such as Cardiac Parasympathetic Reactivation Following Exercise: Implications for Training Prescription found HRV consistently lower after high intensity training (HIT).  Now a group of French researchers, led by Damien Saboul, have set out to create a more formal method to see whether HRV recording before and after a session could provide a better insight as to the TL that session had produced.

What did they do?

Eleven well-trained distance runners participated in a study where they had to perform four different training sessions with full recovery in between. They had their HRV (RMSSD) measured immediately before, 5 minutes and then 30 minutes after each session.  The runners had to sit quietly and were allowed 0.5L of water but no food between the post exercise measures.

The composition of the four sessions was as follows, the intensities refer to the individual’s maximum aerobic speed (MAS).

Session Warm up Middle Cool down
1. Aerobic 10 mins @ 70% 34 mins @ 70% 10 mins @ 50%
2. Long intervals 20 mins @ 70% 3x 10 mins @ 85% 10 mins @ 50%
3. Short intervals 20 mins @ 70% 8x 2 mins @ 95% 10 mins @ 50%
4. All out max 25 mins @ 70% 6 mins @ 100% 10 mins @ 50%

The Authors defined a TLHRV index as follows:

TLHRV = ln (T x (Pre5 – Post5)/(Post30 – Post5) )

In other words this new formula calculates the ratio of the change in HRV before to 5 minutes after the session to the change during the first 30 minutes recovery.  This is then multiplied by the duration of the session in minutes.

Bannister’s TRIMP (Training Impulse) and Foster’s session RPE were used to compare the HRV calculated training loads for each runner in each of the four sessions to commonly used measures in the field.

What did they find?

The table below from the paper contains all the key data – the HRV values, effect sizes of the changes in HRV, and data to enable calculation of the three different TL measures.


All three techniques rated the long intervals as having the largest TL, followed by the short intervals, but the Bannister method rated the aerobic session as more demanding than the all out effort whereas the Foster & HRV method both rated the all out as more demanding than the aerobic session.

As expected, the pre to post session HRV difference correlated to the session intensity whereas the post 5 to post 30 difference was not correlated either to intensity or volume for all participants.  The authors point out that it did provide normalization with respect to inter-individual differences (always an issue in HRV studies).

What does it mean?

This is an interesting study that suggest that HRV has the potential to deliver a sport independent comparable training load number, a goal long sought after by sports scientists and coaches.

Best of all this is a technique which can be quite easily deployed by ithlete users – simply perform three one minute measures, just before your workout, 5 minutes after and then 30 minutes after.  All three will be shown in the app dashboard and you can get to work in Excel to calculate the TL values (remember to transform the ithlete HRV numbers back to raw RMSSD = EXP(ithlete HRV/20)).

It does require further studies to validate and refine this technique and we would be pleased to hear from coaches and students who would like to do this in their sports settings.

You can find the original paper here.

by Simon Wegerif