If it was a choice, we would, of course, say Power Meter, over Heart Rate Monitor as we are slightly biased.
Historically we have progressed from using Breath Intervals, to RPE, to Heart-rate, to Power-meters; the snag with Breath Intervals and RPE is that these systems are based on the ‘psychological’, not the ‘physiological’. Both Breath Intervals and RPE (Rated Perceived Exertion) are used to measure the intensity of your exercise. Basically you, the athlete, has to give feedback, as to how hard you think you are working. The RPE scale in particular, runs from 0 – 10, so you grade yourself. As you can imagine, different people perceive ‘zero – moving with not a chance of sweating’, to the top of the scale, ‘ten – when you’ve emptied the tanks’ – very differently.
Heart rate monitors are more scientific as they measure the physiological; ‘you exercise, your heart rate goes up’ but the flaw is ‘the human factor’. Monitoring heart rate for training purposes, you’ll need to appreciate that your stats can be affected by poor hydration, energy levels, muscle fatigue and temperature. Alternatively a Power Meter, for training purposes, will give you real-time stats, you can use for Pacing.
Pacing is used to gauge improvement. So for example, you can set a distance as part of a four week training plan and increase the intensity in following rides to gauge improvement. Doing an FTP test will allow you to set up Training zones ensuring you are pushing hard enough during intervals, and pedalling gently enough on recovery and endurance rides.
Put simply a Power Monitor can:
Unlike heart rate, there is no lag in feedback so the intensity can be maintained for the full duration of the interval. Also for those who participate in races, knowing your threshold will enable you to gauge the power you have available to complete the race.
The absolute ideal though, is surely to use both a Power Meter and a Heart rate monitor together, as the Heart rate monitor can warn of overtraining. Stats from both will help you see your improvement over the weeks of training – The most simple gauge would be that your heart rate lowers over time, this means you’re getting fitter.
Learning to pace effectively means you won’t slip into training that makes you tired but not fitter. Having real-time stats can pre-empt overtraining, but keep you on track, so that you can achieve personal goals, and improve, not plateau.