German scientists have collected data from six professional road cyclist´s during a multi stage race. The riders used the SRM system to measure power outputs and heart rate monitors to record heart rates. This study got my attention, because it shows the benefits of using a power meter in the races instead of just a heart rate monitor. It was published in Medicine and Science in Sports and Exercise, January 2006. Before I start advertising more for using a power meter system, I will tell you a little about the study setup.
Before the stage race the six riders performed an incremental cycling test in the laboratory. Peak power output, power output, and heart rate at the lactate threshold and at a lactate increase of 1mM above the lactate threshold were assessed. Based on the test results there were made 3 different intensity zones for both heart rate and power output. Zone 1 was below LT, zone 2 was LT to LT+1mM and finally zone 3 was above LT +1mM. After the testing session the riders were ready to compete in the stage race.
Time spent in power meter zones
The scientists analyzed the time spent in the three target zones during the 6 stages. There were five mass-starts where the riders averaged 220 Watts and one uphill time trial with an average power output at 392 Watts. This is not breaking news for experienced power meter users. In an uphill time trial riders prefer to ride with a slower cadence and are therefore able to maintain a higher average power output and they have to go fast all the time which also adds Watts to the average power output. In the mass-starts the heart rate monitors over-estimated the time spent in Zone 2, and I am not surprised at all.
Heart rate monitor and power meter should go hand in hand
The heart rate monitors recorded that the riders spent 38% vs. 14% recorded with the power monitor. Heart rate monitors are still valuable, but it is important to know the physiology behind to understand how it works. There is a delay in the heart rate due to oxygen deficit or repayment of oxygen debt. A professional cycling race is either slow or very fast, there is almost nothing in between. But when they ride this stop and go way, the average heart rate will be somewhere in between, in this case this will say Zone 2. This could lead to the wrong conclusion that training in heart rate target zone 2 is optimal for preparation to stage races. Listening to the power meter makes more sense to me, since it tells me instantly what the power output is and therefore gives a much more precise description of the effort.
Vogt S, Heinrich L, Schumacher YO, Blum A, Roecker K, Dickhuth HH, Schmid A.
Power output during stage racing in professional road cycling.
Med Sci Sports Exerc. 2006 Jan;38(1):147-51.