I use a
heart rate monitor with my Garmin computer. Before I got a power meter, my
heart rate monitor was the only equipment I had to gauge my intensity. We also
use heart rate monitors in my spin class, and so I’ve gotten very familiar with
the levels of effort associated with the various heart rate zones. This guide was developed by fitness expert Joe
Friel:
Level Name Maximum
Duration
Level 1 Recovery
Level 2 Endurance All day
Level 3 Tempo 1-5 hours
Level 4 Subthreshold 45-120 minutes
Level 5a Superthreshold 15-60 minutes
Level 5b Anaerobic Endurance 3-7 minutes
Level 6 Power 1 minute
Level 7 Sprint 15 seconds
These zones
correspond with a percentage of your threshold level, i.e., the highest power
that you can maintain for one hour. With training you can increase your
threshold level, which indicates better fitness. Threshold level can be assessed quite
accurately as 95% of average power in a 20-minute test.
It’s
important to note that your threshold level is different from your maximum
heart rate, which is genetic. Furthermore,
although the various zones are calculated as percentages of threshold power, they
commonly are correlated to heart rate because heart rate is cheaper to measure
than power. (A heart rate monitor costs
a lot less than a power meter.) Evaluating
intensity with heart rate works well, but it’s not foolproof, as I have
discovered in recent weeks.
In spin
class and at Tuesday Worlds, we ride a lot at Level 3 and Level 4 with
occasional forays to Level 5a or even 5b. Additionally, in spin class I’ve
learned to assess my effort level pretty accurately just by perceived exertion,
which I can confirm with my heart rate monitor.
This ability has translated fairly well to riding on the road, too.
In the last several
months it’s gotten harder for me to get my heart rate level up in spin
class. My 10-minute warm-up often isn’t
enough even to get me to Level 2; only jumps or sprints will start elevating my
heart rate. I haven’t thought too much about it, simply attributing it to the
huge amount of endurance riding I’ve been doing for the last couple of
years. However, I’ve only just realized
how this manifests itself on my road bike.
On a typical
solo road ride in the 30-mile range, I usually spend most of my time in the
upper endurance/low tempo zone, around Level 2.8 to 3.5. In the last few weeks, however, I started
noticing that my heart rate zone was usually around 0.7 to 1.8 – even though my
perceived effort seemed much higher. I
told Robert that I thought my heart rate monitor was broken! He asked if I had
looked at actual heart rate, not just the heart rate zone. Aha! Why didn’t I
think of that? (That’s why I pay him the big bucks.) Sure enough, my heart rate
has also been much lower. My heart rate monitor is working correctly after all.
Robert
pointed out that when I’m riding my bicycle for 8 to 13 hours, as I do when I
ride a 200-or 300-km brevet, there’s no
way my heart can sustain a high heart rate for that long. Although that should be obvious from the zone
chart above, it still doesn’t quite explain why my heart rate is lower even on
the 30-mile rides. I was intrigued and decided to do a little research.
The average
adult resting heart rate is about 70 beats per minute (bpm). Although I was
already well aware that endurance athletes usually have a much lower resting
heart rate (as low as 40 bpm or sometimes even less), I didn’t know that
endurance training also decreases the submaximal heart rate. In other words,
with a lot of endurance training, your heart is also going to beat more slowly
while exercising. One reason is because
your body adapts to utilize more oxygen (VO2max increases). Also, the stoke volume of the heart (the
amount of blood pumped per beat) increases.
These processes allow the heart and body to work more efficiently for a
given effort.
Now I better
understand the difference between power and heart rate. While training with intensity increases threshold
power, endurance training lowers the heart rate during exercise. Doing both
types of training is important and results in better performance, whether
you’re a sprinter or a randonneur. For
the past couple of years I’ve been very happy with the effectiveness of my
training mix: the intensity of Worlds and interval training as well as long,
slow centuries and brevets. I think I’m just now really seeing pronounced
effects from my endurance training.
Yesterday I
was glad to find that I still can get my heart rate up even during a shorter
ride. I did one of my favorite routes, which is 31.3 miles. A typical ride on
this route will yield data approximately as follows:
Average
speed = 17 mph
Average
power = 135 W
Intensity
factor (= normalized power/threshold power) = 0.70 to 0.75 (Normalized power is
slightly higher than average power.)
Now check
out yesterday’s data:
Average
speed = 18.4 mph
Average
power = 176 W
Intensity
factor = 0.884
I had already planned to do a longer than usual
lunchtime ride yesterday because of an atypical schedule. Little did I know how
therapeutic it would prove to be. In the
morning I went to a meeting that made me sick to my stomach (politics triumphed
over science). I worked out my
frustration on the bike. Maybe I should use this training strategy more often:
get mad before I ride.