Who, what & why?

The three week long cycling Grand Tours (Italy, France, Spain) are well known to be amongst the hardest multi day endurance events in the World. But for most of us that will never experience one, how fatigued do the riders actually become, and does this fatigue vary between team members with different roles, such as a domestique vs the team leader?

A group of distinguished researchers, including Dr Conrad Earnest and Dr Alejandro Lucia wanted to examine the relation between quantified levels of exertion (TRIMP, TSS), and resting heart rate variability (HRV) at key points throughout the race for multiple team members.

What did they do?

They calculated an individualized training load measure known as Lucia’s TRIMP for each stage using continuous heart rate measurements performed on each of 8 riders every day during the race.

Lucia’s TRIMP allocates 1 point per minute for time spent below first threshold (easy pace), 2 points per minute for time spent between first & second threshold (steady pace), and 3 points per minute for time spent above second threshold (hard, HIT pace).

This generated a number between 120 and 500 for each racing day that reflected both duration and intensity, so can be thought of (like TSS) as the total workload number for that day.

This study was conducted before easy to use HRV apps, so HRV was collected using a Polar S810 watch and PC software during 15 minute lying down periods at baseline before the start and during the two rest days (days 10 and 17).

They analysed a number of time and frequency domain HRV parameters, including ithlete used RMSSD.

What did they find?

The TRIMP charts show how the total load varied from day to day, firstly for a multi stage winner:

Image 1

and secondly for a domestique (team helper):

Image 2

The average daily TRIMP load is certainly higher for the domestique, as is the amount of time spent in zones 2 and 3 (white and light grey respectively). To give us non elite readers a reference, the author is a keen amateur cyclist, accumulates fatigue at TRIMP levels >200 per day. Some of these days exceed twice that amount and they do up to 5 days in a row!

From an HRV point of view, there were no clear trends observed from the start to the end of stage 9, but this became a different story between stages 10 and 15:

Image 3

The single * identifies the team leader / multi stage winner, whose RMSSD remained at a level of approx. 50 ms (78 on the ithlete 20x LnRMSSD scale) whereas the domestique (**) had managed to get his down to a mere 20 ms (59 on the ithlete scale). What is also very interesting is to see the relationship between total workload accumulated during the later stages and HRV. An R squared of 0.87 is a very strong relation. Very similar correlations were found for the other HRV parameters used.

What does it mean?

The authors conclude:

“Our data strongly suggest that changes in HRV are directly related to volume and intensity of exercise, as athletes who showed the greatest cumulative physical exertion also showed the largest decrease in supine HRV.”

I love this paper because it brings cycling and HRV, two of the things I am most interested in, together with an insight on how tough the pros really are. My takeaways from this study are:

  1. A 3-week stage race of 4-5 hours per day imposes a massive workload, and this really starts to tell during the 3rd
  2. Professional athletes selected for the Grand Tours are about as fit as human beings can become, but even they have limits, as evidenced by the rapid decline in HRV once accumulated TRIMP exceeded 2000 after the 2nd rest day.
  3. Junior domestique riders work harder than others fetching supplies from team cars and protecting team leaders so they can save their ‘TRIMP budget’ for stages where it really makes a difference to the outcome.
  4. There was essentially no difference between the HRV parameters in terms of their response to the accumulated load, further reinforcing the suitability of LnRMSSD (as used by ithlete) as an easy to use, robust choice of parameter.

Relation between physical exertion and heart rate variability characteristics in professional cyclists during the Tour of Spain

C P Earnest, R Jurca, T S Church, J L Chicharro, J Hoyos and A Lucia

Br. J. Sports Med. 2004;38;568-575 doi:10.1136/bjsm.2003.005140

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