Question:
I just completed a maximal treadmill graded exercise stress test at the U.Cal
- Davis Performance Lab that clearly indicated my maximum heart rate was 173,
exactly on the norm for an age 47 male.
However, I've worn a Polar Pacer and Accurex II for the past year and I
routinely get readings in the mid-180's during interval workouts. My max
heart rate on both monitors is 190 BPM doing 1/2 miles. The test
administrators suggested my monitors were wrong and I should do a manual
count. So today I ran a fast 1/2 mile at 183 BPM and backed up the monitor
with a manual count of 186. I also backed up the monitor reading with manual
counts at 140, 150, 160, and 170 and it was always within a couple of beats.
What gives here? I thought the treadmill test was supposed to be the
definitive measure of max heart rate, VO2 max, etc., and Cal Davis tests
many pro football and basketball players. Yet the measurements were way off on
me! Are there any exercise physiologists on this list who could shed some
light on this situation? I'm wondering if the other data - VO2 max - is off as
well.
Answer:
While it is not uncommon for competitive athletes to achieve maximum heart
rates in the field that are 1-3 bpm higher than that seen during a
laboratory treadmill (or cycle) VO2max test, the difference of 17 bpm you report
(190 vs 173) is so large that there must be an error somewhere. The Polar monitors
tend to be quite accurate and also quite resistant to intereference, and you also
backed up that data with manual counting, so your max heart rate probably really is
190. Thus, although I can't say anything for certain, my guess is that it is the lab
data that are incorrect. The most likely explanations is that you simply didn't push
yourself as hard on the treadmill as you do in "real life". This is often a problem
in performing VO2max tests, esp. in subjects who are naive to the experience - the
mouthpiece, narrow treadmill, etc. can be a major distraction. (Of course, there is
also the possibility that the test was stopped early due to some medical reason, but
since you didn't mention any I assume that you were give a clean bill of health.)
You might try playing with the data yourself, to see if your effort was truly
"maximal". On a graph, plot the measured VO2 on the Y axis and the treadmill speed
and/or grade (depending on which was increasing) on the X axis. If you really
reached a true VO2max, then your VO2 should increase and then level off (less than,
say, a 1.5 mL/min/kg increase) over the last minute(s). If it does, then the
measured VO2max is probably correct, even if the heart rate is not (in some
individuals, stroke volume decreases at higher exercise intensities, so that VO2
doesn't rise despite the increase in heart rate). If not, then the measured VO2max
is probably too low...(usually a test will be accepted as maximal, even w/o a
leveling off of VO2, if two other criteria are met, i.e., a heart rate w/in 10
beats/min of age-predicted maximum, AND and a respiratory exchange ratio (RER or RQ)
of greater than 1.10. But, it already seems clear that you didn't reach max heart
rate, so unless your VO2 plateaued, I wouldn't call the test a true max).
If you REALLY want to know the answer, you might see if you can schedule a
retest in the lab...that is what we would do with a research subject who we were
uncertain had pushed themselves to max.
I would expect the problem would lie in the test protocol. Testing labs often
use the Bruce protocol, the Balke or some variation thereof. Both test
protocols are primarily walking based and use substantial elevations to
increase intensity, rather than running speed. (Example: the Bruce protocol
has the following stages: 1) 1.7 mph/10% elevation 2) 2.5/12% 3) 3.4/14%
4) 4.2/ 16% 5) 5.0/18% 6) 5.5/ 20%). Because most people do not
specifically train at those types of workloads, it is possible to "max out"
before reaching a true VO2 max, probably due to localized muscle fatigue. It
is not as big a deal with untrained subjects, because they will hit their peak
doing just about anything, but for a trained runner, it will probably stop you
short. (I'm assuming there was no handrail support, otherwise that's another
confounding factor). The best thing for runners is to get them up to a running
speed that is near their AT and then increase the grade a little at a time, so
that they max out at an elevation of 2%--6%.
I too have a major difference in maximum heart rate from
pulmonary stress tests and two different heart rate monitors.
The stress tests were two years apart and showed a maximum
heart rate of 148. The monitors hit 168. I have confidence in
both figures because they reflect different "training"
protocols. The stress tests forced me to failure rather quickly
(ten minutes?) whereas my maximum heart rate on the monitors
comes from sprinting after a long training run. I have assumed
that if I do not gradually raise my heart rate by starting and
maintaining a slow speed that I will max out very quickly. At
least that is how I have explained the difference. Is my theory
possible? If it makes a difference my age is 52 and I have mild
emphysema.
