In the last two posts I wrote about one of my favorite topics – race pacing. In the first I once again described the issue I’ve written about so many times. In the second I briefly discussed the issue of pacing when fast starts are necessary to race strategy. In this post I want to comment on how heart rate monitors affect pacing. Bottom line: they teach you to pace the start of the race poorly and finish weakly.
Why is that? Well, it’s simply because heart rate responds relatively slowly to sudden changes in intensity. It can take several minutes for heart rate to catch up with your output intensity (power, pace, speed). And that’s good for cardiovascular health. We really wouldn’t want it any other way. But if you rely on heart rate to pace yourself in workouts and races then you have a dilemma: How do you pace during those few minutes when heart rate is “low” but catching up?
I’ll come back to this dilemma and its solution shortly. But let’s first establish what the problem looks like. In the accompanying graphic (click to enlarge) you see a bike interval workout done by a real athlete. What you see here is the interval portion of the workout that was 5 x3-minutes at power zone 5 with 3-minute recoveries – a hard workout intended to boost aerobic capacity (VO2 max). The black line is power (it could just as easily be speed or pace for running). The red line is heart rate. The 5 work intervals are highlighted in green. The dashed lines indicate the general slope of heart rate and power within each interval.
Notice that the slope of power in each of the first four intervals is fairly flat. That means the athlete was holding a steady output. On the last interval, power output slopes up slightly after starting at about the same power as the previous four (I like to see this as it means the athlete was holding back early in the workout and so was able to finish strongly).
Also notice how heart rate slopes upward quite steeply for each interval not reaching a peak until near the very end. Heart rate at the end of each interval was zone 5b, the same as the power zone. But how they got to their zones was greatly different. While heart rate took more than half of each interval to reach the zone, power was there in about 5 pedal strokes.
Now if the athlete only had a heart rate monitor and not a power meter for this workout he would not have a clear indication of how intensely he was working until about the last minute. So how do athletes typically manage this conundrum? They push themselves at a higher level than is called for in each interval in order to force heart rate up sooner. If we were to cover up the power data on the athlete’s handlebar head unit so he could only see heart rate we probably find that his power was zone 6 or even 7 in the first half of each interval. This would create considerable fatigue so it’s unlikely he would have been able to finish the workout so strongly.
So relying on heart rate for pacing, in any type of workout, teaches the athlete to start too fast and then finish weakly. That’s exactly the opposite of what we want in most steady-state races. So it’s no wonder that races; such as 10km runs, 40km bike time trials, and even the bike portion of a triathlon; start overly fast. Not only is the athlete emotionally excited by starting line or transition enthusiasm, but he or she has also been trained to start too fast due to the heart rate monitor. Thus, trying to teach athletes to pace themselves early on in races is very challenging.
So if you don’t have output equipment (power meter or speed-distance device) and all you have is a heart rate monitor (shame on you!) you have to learn to ignore it in the early portions of higher-intensity workouts like intervals. Instead, learn to use a Rating of Perceived Exertion (RPE) to rate how hard you are going on a 1 (low) to 10 (high) scale. To do this in a race takes considerable practice. It won’t be mastered in a single workout. It could take you weeks of constant practice to become good enough to do it precisely at the start of a race when your emotions are telling you to go faster.
Well-paced races are signs of an emotionally strong athlete.