Interval Training - Power vs. Heart Rate

Intervals are the key to breaking through training plateaus and achieving new levels of speed and fitness. At Two Wheels, we prescribe lots of interval workouts for our clients, based on their current fitness level and training goals. We have seen dramatic increases in performance for clients who are using power-based (wattage) training for their interval work over clients who are using HR or RPE (rate of perceived exertion). I want to briefly address the differences and touch on a few FAQ’s we receive.

- Measuring power for an interval workout gives near instantaneous information concerning the intensity of the effort. Measuring HR is practically worthless for most intervals unless they are 5 minutes or more and your HR has a chance to catch up to your effort and level.
- Repeating the interval effort is critical to increasing fitness. If wattage numbers are not available, speed can be used on the trainer or on the road (assuming the terrain and wind are identical). Speed/pace is how we will prescribe intervals for runners. A wattage based workout interval is hard to mess up – work for 30 sec. at x watts and recover for 30 sec. at x watts. No trying to guess at the RPE, either you hit the wattage or you don’t.
- How to determine when you have done enough? Typically we recommend the end of an interval session when you can no longer be within 10% of the target wattage for a work piece. If the goal is 60 sec work pieces at 300 watts and you only hit 270 after doing 5 intervals at 300, time to stop.
- What we find is most people tend to stop early (they could have hit 300 a few more times) because the effort seemed too difficult or they did not feel as though they recovered enough. Even more common is for someone to thrash themselves well beyond the point where they should stop. They typically do more intervals (because more is better right?) at intensity slightly lower than they need for maximum benefit. Repeated sessions of this type can quickly lead to overtraining.

The bottom line is if you are serious about making gains with a minimum amount of training time; get a power meter and a coach to help you utilize the data. As an alternative, leave the HR monitor at home on your interval days and go by feel (RPE) or use your speed.

Good riding – Coach Kevin