By now, there is no dispute that training with power on the bike yields a ton of valuable information. The tricky part is the interpretation of the data and putting it to good use via your training plan. The end result....faster bike splits, of course. Lost in all the variable power metrics though is the oft forgotten grand daddy of all training metrics, heart rate.
As you employ your power numbers and see your average wattage start to climb, remember to gauge your power output against your heart rate. For example, if on your long ride you push an average of 200 watts and maintain an average heart rate of 130 bpm, what happens when your wattage jumps to 230? Is the increase in watts a significant jump in fitness, or is it the fact that you are hammering the ride with your training buddies? Are you having a great day, are you feeling the effects of dropping some off season weight, or is it some combination of effects?
A very effective way of measuring fitness is to not only watch the watts produced but keeping an eye on your heart rate numbers too. In the example above, if the average watts jump from 200 to 230 and the heart rate remains around 130bpm, the rider has indeed experienced a nice gain in fitness. Conversely, if he is now pushing 230 watts and his heart rate jumps to 145bpm, chances are, he is just pushing harder. Over the long haul, that spells trouble.