This study was performed on 8 professional cyclists during the 3 week Tour of Spain, by Dr Conrad Earnest (Cooper Institute for Human Performance) and a team of well respected sports scientists. The study aimed to determine how heart rate variability (HRV) reflecting the body’s recovery state would track the high levels of effort performed on successive days by the team leader, and other team members.
HRV (and resting heart rate) was measured on day 0 to act as a baseline, then on two rest days during the 3 week grand tour. Time domain (RMSSD, SDNN) and frequency domain (HF, LF, total power) measures were taken. Training load was measured continuously based on the amount of time spent riding in 3 intensity zones, and added to make a single TRIMP number.
What did they find ?
No significant changes in HRV for the group as a whole were found during the first 9 days. After that they found a very significant relationship (r = -0.95) between training load TRIMP and decline in HRV during the following 6 days. Interestingly, one of the worker bee domestiques went from 86 on the ithlete scale to 59, a drop of nearly 30 points as a result of doing a huge amount of work, whereas the team leader hardly dropped at all over the same period. They found no significant change in resting HR during the course of the race.
Very fit professional athletes pace themselves during longer multi day events such as Grand Tours so that they can recover fairly well day to day until well into the second half of the race, when the continual body stress begins to make itself felt, and HRV declines according the amount & intensity of work performed. Team strategy means that the workers sacrifice themselves to give the leaders an easy time until it’s their turn to give their all in a sprint or hilltop finish.
It’s too simplistic to say that any bout of training will always cause your HRV to drop the next day. If you are able to recover fully from the training overnight, then no reason why morning readings should drop at all, but if you are not fully recovering from day to day, you will surely see changes in your ithlete HRV sooner or later. Pushing yourself continually to the limit will cause large changes in HRV, which reflects the body’s inability to repair itself quickly enough. Since this study was performed, links between HRV and inflammation, such as that caused by muscle damage have been established.
On the other hand, resting heart rate once again showed itself to be at the very least insensitive. I’ve heard comments from professional athletes along the lines that ‘by the time your resting HR rises enough for you to detect, it’s too late’.
To read the paper:
Br J Sports Med 2004;38:568–575. doi: 10.1136/bjsm.2003.005140