Changes in Heart Rate Recovery (HRR) after high-intensity training in well-trained cyclists

Background

It is well understood that effective training involves balancing training load and recovery from this training. Training load is easily controlled by adjusting the frequency, length and intensity of training sessions but appropriate recovery is more difficult to quantify, depending as it does on a multitude of factors such as sleep, nutrition and other ‘lifestyle stresses'. An appropriate metric for quantifying this ‘training status' is important to prevent over-reaching and to enable the prescription of an optimal training-recovery balance.

Methodology

14 well-trained cyclists (VO_2max 60.3 ± 7.2ml.kg^-1 min^-1; relative peak power output (PPO) 5.2 ± 0.6 W.kg^-1) participated in a high-intensity training programme (eight sessions in 4 weeks). Before and after high intensity training, performance was assessed with a peak power output test including respiratory gas analysis (VO_2max) and a 40-km time trial. HRR was measured after every high-intensity training session and 40-km time trial.

The HIT programme consisted of two interval sessions and two 90min recovery rides at an intensity below lactate threshold. The interval sessions involved eight 4 minute intervals at 80% of PPO with a 90s self paced recovery.

HRR was measured as the decrease in heart rate after 60s following exercise. Subjects were instructed to remain seated upright on their bicycles and to not talk during recovery in an attempt to control factors that may influence heart rate and HRR.

Results

The first thing to note is that the HIT program did have the desired effect in improving performance. PPO and 40km TT time were improved as shown by figure 1 but there was no increase in VO_2max.

Figure 1: Improvements in performance following HIT

This increase in performance was accompanied by an improvement in HRR. Between the first and last HIT training session HRR improved by 7 ± 6 beats and following the 4 week training block, HRR at the end of the 40km TT improved by 6 ± 3 beats. Moreover, HRR improved continuously throughout the HIT training protocol, this improvement reached statistical significance after the 5^th training session.

What does this mean?

The big problem with the application of this study is similar to that faced with all heart rate based measures. The sheer number of factors that can affect HR have to be carefully controlled in order to get meaningful data. The authors of this paper acknowledge that previous work has shown day to day variation in sub-maximal HR and HRR to be 5-6 and 7-8 beats.min^-1 with a standard deviation of 3 beats.min^-1. The average improvement seen in HRR is clearly within this level of day to day variation.

Any athlete wishing to explore the use of HRR would be advised to devise a standardised protocol for its measurement. This protocol would need to ensure that recovery body position, timing and duration of measurement are kept as constant as possible. For example make an effort to remain seated on the bike, without talking or being otherwise distracted and measure the reduction in heart rate after 60s. The most useful comparisons will likely be between the same sessions performed over an extended period of time so making an extra effort to accumulate data on sessions that are regularly repeated will likely provide the greatest insight.

The authors expressed the aim of assessing HRR as a measure of ‘fatigue' but actually tested HRR against existing measures of ‘fitness'. It is difficult to recommend the use of HRR as a means of tracking training status on the basis of only this study, what might be useful is an individual case study. If an athlete were to collect a large body of data, controlling for body position, talking etc during recovery, it might be possible to assess the usefulness of HRR as a means of tracking training status.