We can determine the answer by asking three telling questions:
- How many kilometres of running, cycling or swimming did you log this week?
- What was your time on your feet for your running sessions? (Coaches call that TOF).
- What was your average and maximum intensity for each session?
Chances are that you will be able to answer the first two easily enough, but you might come unstuck on the third question. The three variables to assess your training are distance, time and speed (or intensity). It is quite easy to monitor time and distance, but intensity leaves even the most educated confused. Many of us use a heart rate monitor or watch the speedo on the bike, but what do the figures actually mean and are we getting the most out of our training?
Beginning at the beginning
Let’s start with the old-fashioned methods of measuring intensity. Speed is easily assessed by knowing the distance of your route and dividing that by the time spent exercising. Distance on land can be measured with a cycle speedo or by using a pre-set loop such as a running or cycle track. Distance in the water might need a GPS system or a friendly boat-driver to measure your route. Keeping track of your time (and therefore speed) for set routes is a very useful way of assessing progress throughout a training programme.
The limitation for speed as a measure of intensity is that unless you are exercising flat-out, you can’t assess the amount of effort that was required to create the speed. The majority of your training is sub-maximal, so it is also helpful to know how hard your body is working. For example, last month you did a hard 10km run in a time of 40 minutes. This month you ran 30 seconds faster. Can you say that you have actually become fitter? Your intensity was higher this time, but your effort might also have been more.
The next step
Enter the Rate of Perceived Exertion (RPE) – whether they knew it or not, this was the method that all athletes used to assess their effort prior to the invention of heart rate monitors. The art of ‘feeling’ your intensity forms the basis of pace-making and helps you to understand your body’s responses to exercise no matter how many electrical gadgets you use! The table shown above uses a scale of 6-20, which is thought to roughly follow your heart rate (multiplied by 10). There is also a 1-10 scale in use. If both times that you ran the 10km, your average RPE was around 16, you can probably say that you have become fitter from one month to the next. Another use for RPE is to check if you are having an off-day or are possibly overtraining. If you are normally able to do a set of 10 x 400m track reps in 70 seconds each at an average RPE of 18 and one particular evening you are doing 71-72 second reps with an average RPE of 19, then it might be time for a rest.
Matter of the heart
Despite my opening thought that exercise intensity is under-monitored, heart rate monitors may be over-used, while not fully understood. What are the numbers that you use to set your training? Is heart rate max measured as 220-age or assessed by an exercise-specific max test? Do you monitor %age max HR or %age HR reserve? Did you learn about the heart rate zones from a credible source or was it from a popular article in the media focused on the virtues of fat burning?
If you are going to use a heart rate monitor, it is really important to know your actual maximum heart rate (HRmax). It can be hugely variable from one individual to the next.
It also doesn’t decrease by a beat per minute (bpm) for every year of natural age as the 220 minus your age formula would have us believe. A way of finding your max is to do a ramped VO2 max-type test to exhaustion or to exercise flat-out for two minutes, followed by a one minute rest and then another flat-out two minute bout, after a thorough 20+ minute warm-up.
Complete the test in the discipline in which you will be training because HRmax will vary between running, cycling, swimming and paddling. You then need to use the appropriate HR zones based on the type of fitness that you aim to bolster – aerobic, anaerobic or lactate threshold.
The final straw of measurement
Power meters are the last intensity measure currently available. Although they are expensive, they are now commercially available for cyclists and are popular for monitoring of training programmes. Power means the amount of work performed in a given time and is an excellent assessment of intensity of effort applied to the bike. Like speed, in a time-trial situation, the rider with the highest average power (assuming similar bike components and aerodynamics) will be the winner. Power has the advantage over speed in that speed will be affected by hills and wind whereas power will always reflect the work rate of the rider.
Additionally, power gives a far more accurate indication of effort than heart rate when doing interval sessions. Power will immediately change when the interval is started and stopped, whereas heart rate will have a significant lag-time in its adjustment. Like speed, however, one limitation of power monitoring is not knowing whether an increase in power is due to improved fitness or simply an increase in effort. Combining the use of heart rate or RPE with power readings will give a truer picture of effort versus fitness.
Summary of Intensity Assessments
If you are training or racing on/in a surface that is very consistent and free from significant wind resistance (such as a swimming pool, a running or cycling track), speed is a very fair indication of intensity. In order to understand physiological effort, heart rate and/or RPE complements the information nicely.
If you are training or racing on/in a surface that is inconsistent such as a rolling terrain with gusts of wind, power is a more reliable indication of intensity. Just like speed though, in order to understand physiological effort, it is best to also assess heart rate and/or RPE. Even if you have chosen to use up-to-date technology though, it does generally pay to master the ‘art’ of intensity by being able to interpret the signals emanating from your own body.
(B.Sc., M.Sc., CSCS),
Originally published in Go Multi November/December 2009 issue