Target heart rates

I used a metronome on my last run, which is suggested by several coaches as a way of monitoring turnover or cadence, that is to say the number of steps taken in a given time. The idea is that for maximum efficiency, we should run at around 180 steps per minute. This enables us to make use of energy stored in the muscles and tendons of the foot and lower leg, which would otherwise be lost. It also discourages overstretching and heavy pounding, both of which can lead to injury. I was surprised to find last night how much slower than 180 I was running without the metronome to keep me in time.

On the other hand, my pace was a bit slower than I expected, and it occurred to me that I did not know whether this was because of altering my cadence, or just because I was putting less effort in. In short, I don't have a good way of judging how hard I am working from one run to the next.

One way of solving this problem is to use a heart rate monitor, and to try to keep the heart rate within some predetermined range. As it happens I do have such a monitor, so I dug it out of a bottom drawer today.

Target HR ranges are normally worked out as some percentage of your maximum heart rate (HRmax). Runners World have some ranges in their training plans for different distances, namely: 93-97% of HRmax for 5km, 90-94% for 10km, 87-91% for half-marathons and 79-84% for marathons. There are several formulas for working out HRmax, usually based on age. The most well-known is:

HRmax = 220 - Age

although this study found that this formula, while simple, is not really very accurate. It suggests that of the formulas most commonly used, the one that is the least objectionable is:

HRmax = 205.8 - (0.685 x Age)

and I also found another study, which came up with a non-linear formula of:

HRmax = 191.5 − (0.007 × Age²)

Based on all these formulas, my own maximum heart rate would be 177, 176 and 178 respectively. Taking the middle of these values and applying the Runners World percentages, I get the following ranges:

5K      164 - 171
10K    159 - 166
20K    153 - 160
40K    139 - 148

My runs at the moment are less than 5K, so I will wear my HR monitor on my next run, and try to stay in the range 164-171. By sticking to this range for all runs, I should be fairly sure I am working at roughly the same level every time. I can then be more certain that any improvements in pace are down to improving fitness, rather than just a higher level of effort. This approach should have the added benefit of ensuring that I always have enough left in me to complete the required distance without collapsing with exhaustion.