The art of effective training is maintaining a training load sufficient to produce steady improvement while avoiding the damaging effects of over-training. In my preceding post, I described a test designed to help achieve these goals by assessing improvement in aerobic fitness while providing a sensitive indication of the early signs of over-training. The first key principle in the design of the test was measurement of heart rate (HR) and heart rate variability (HRV) under various circumstances, thereby assessing multiple aspects the way that the autonomic nervous system regulates the heart, and avoiding dependency on a single potentially erratic measurement. The second design principle was that the test should fit within the framework of a warm-up preceding training, making it practical to perform it frequently within only minor interference with a training program.
At the time I was doing much of my training on the elliptical cross trainer so I designed the first version of the test for use on the elliptical. The protocol started with measurement of HR and HRV while standing in a relaxed state. Then after very brief warm-up to allow initial stabilization of the cardio-vascular system, HR was measured at three different levels of work intensity: easy, mild and moderate; followed by an assessment of heart rate recovery (HRR) during a minute of standing and finally HR was assessed again in the final minute of a short easy-paced recovery. The evidence accumulated during a 10 week period of aerobic base-building indicated that the first version of the test provide a sensitive measure of improved aerobic fitness, while also quantifying stress levels during a period when life-events were challenging, and in addtion it proved also to be a sensitive indicator of impending over-training.
The consistency of beats/Km
More recently I have developed a version of the test for use while running. The structure of the test is similar, but the biggest practical challenge to overcome was that fact that it is less easy to maintain a constant work rate over a period of several minutes when running compared with exercising on an elliptical cross-trainer with a power meter that allows regular monitoring of work-rate. The key thing that provides the solution to this problem is the observation that the number of heart beats per Km changes only slowly with changing effort across the aerobic range. Therefore, absolute stability of pace is not essential if the measurement of interest is heart beats per Km at each work-level. Furthermore, it is not essential to achieve the same pace at each of the three work levels on different occasions. Small discrepancies in pace from session to session have a minimal effect on the measured beats per Km at each level, and larger discrepancies can easily be dealt with by simple correction.
I do not have access to a track, so I developed the test on a 230m loop of woodland path – slightly undulating and laced with treacherous tree roots, but on the other hand, an inspiring environment in which to run. At each of the three work-rates, I do three laps at approximately constant pace. During the first two laps, HR stabilises. Heart rate in the final lap at each level is used to estimate beats/Km at that level. The final lap should cover the same terrain on each occasion, and preferably should be a closed loop so that variations in wind speed from day to day have little effect. If you have access to a track, 2×400 m would probably work as well. The first 400 m lap allows stabilization. Beats/Km in the second lap is the measurement of interest.
Easy, mild and moderate levels
The easy, mild and moderate work levels correspond to 75%, 82% and 88% of maximum heart rate. The highest level (88%) is near the top of the aerobic range. The subjective effort required to maintain this pace increases quite markedly when over-training occurs, so for the purpose of early identification of over-training, it is desirable to have a level as high as this, though 3-4 minutes at this pace is perhaps a little more demanding than an ideal warm-up. Perhaps this level could be omitted on days when you want to perform the test before a demanding training session, though I find the full version of the test works well as a warm up for moderately intense interval sessions. The HR measured during the final lap of the recovery (performed at a subjective effort similar to that of the easy first phase of the test) reveals a substantial increase in beats/Km at that effort, demonstrating substantial mobilization of adrenaline during the test.
Target HR or pace
At least on irregular course, it is more practical to aim for a particular HR than a particular pace, though it is necessary to allow for the fact that it takes a few minutes to reach a near equilibrium state. If you have a foot pod that provides a continuos display of pace, using it to maintain a constant pace might be preferable. Nonetheless, I find that at least at mild and moderate effort levels I can maintain pace such that time per lap is constant to within less than 2% without using the foot pod.
Figure 1 shows the time course of heart rate during the full test.
Figure 2 shows the beats/Km in the final lap at each of the three effort levels on tests performed prior to an interval session in three consecutive weeks of my current phase of training, in which I have introduced interval training after a phase of low intensity, moderately high volume base-building. On all three occasions, subjective effort during the final lap at the third level was either 11 or 12/20. During this time I have not experienced over-training, though past experience indicates that effort level would rise to 14 or 15/20 at this pace during the early phase of over-training.
The amount of improvement over the three weeks is surprising, though it did correspond to a marked improvement in my fitness observed during other sessions in the same weeks. I will describe my current training program in greater detail in a subsequent post. Note that beats/Km decreases gradually as effort level increases. From the slope of the line a correction factor can be estimated if the intensity at any of the levels on a particular occasion is appreciable different from the intended level.
Standing HR, HRV and HRR
The other measurements of interest (standing HR and high frequency HRV during standing at the beginning , and heart rate recovery while standing for one minute after the final lap at the highest intensity level) are performed as in the elliptical version of the test described previously. Interestingly, in the three weeks depicted in figure 2, initial standing HR was 52, 57 and 52 beats/min while the three values of RMSSD (a measure of high frequency HRV that reflects ‘restful’ parasympathetic activity) were 51, 30 and 57 milliseconds. Thus both standing HR and high frequency HRV indicated reduced parasympathetic activity in the second week, possibly indicative of a somewhat increased stress level. In general, high standing HR and low high frequency HRV provide a sensitive indication of general level of stress. But neither standing HR nor HRV provide a consistent and sensitive measurement of improved fitness because they are too sensitive to various sources of stress.
The interpretation of HRR is complex, though the earliest phase (in the first 30-40 sec) is largely determined by the ability to re-engage the parasympathetic system, which is a good indicator of healthy cardiac regulation. One feature I attend to closely is the development of strong beat to beat variation within 45 sec of stopping running (illustrated as the fuzziness of the trace in figure 1) confirming strong parasympathetic re-engagement. Although I have not experienced an instance of over-training since I began the development of the running version of the test, the preliminary evidence acquired with the elliptical version revealed low HRR during over-training. Furthermore, during the over-trained state, HRR was low despite moderately large high frequency HRV during the initial period of relaxed standing, suggesting that high initial parasympathetic activity but reduced ability to re-engage the parasympathetic system might be a marker for over-training, but this is only a tentative interpretation.