Personal Fitness Professional - Summer 2017 - 21
Figure 1: Error example of the 220-age formula for estimating MHR in a 20-year old
high-intensity exercise can promote greater
carbohydrate storage and utilization 24-7), genetics (e.g., ectomorphs - tall and slim favor
carbohydrates over endomorphs - heavier who
favor fats), medications and more.
So then, how can we define a zone by some
generic range? Here too, we need to understand the limitations to exercising heart rate
which is also influenced by many events that
} Blood volume - a dehydrated body
generally decreases blood volume, subsequently increasing HR responses above
normal. Does that mean you are rewarded
with more points for being dehydrated?
} Simulants (e.g., caffeine) - they can activate the sympathetic nervous system
which accelerates HR responses above
normal. Again, is one rewarded with more
points for taking a stimulant?
} Stress and lack of recovery - a body not
afforded adequate recovery from exercise
or life stress may demonstrate elevated HR
responses above normal.
Fitness improvements - As mentioned
previously, training adaptations lower HR responses due to improved cardiorespiratory
efficiency. Attaining pre-set intensity ranges
can become more difficult over time (i.e., a
person finds it harder to earn zone points
due to improved fitness). Why should they
be penalized for becoming more fit?
We should therefore ask; If tracking time or
attainment in zones is so inconsistent when derived from %MHR, is it really a valid indicator of
adherence, progress or improvement?
Anaerobic training and heart rate
Any time exercise intensity changes, the body's
cardiopulmonary system adapts to meet the
new demands, but unfortunately this takes
time - anywhere from 30-45 seconds up to
several minutes, depending upon the intensity
change. The ability of the body to meet current
energy demands is known as attaining steadystate (SS), often referred to as getting the 'second wind.' It essentially represents HR responses matching work demands. Why do we care
about SS-intensity exercise? SS-HR responses
during sub-maximal work (i.e., outside of resting HR or MHR) correlate decently with oxygen
consumption (VO2), from which calories can
be estimated consistently. But, this correlation
only applies to SS-HR responses during exercise and not to non-SS exercise. Considering
the popularity of many of today's workouts
where work intervals are generally performed
for less than three minutes (e.g., HIIT-type
training, resistance training sets), they mostly
involve non-SS HR response, rather than SSHR responses. Subsequently, the HR response
measured does not necessarily reflect the ac-
tual work performed by the body. As proof of
concept of this HR-response lag or to demonstrate the non-SS nature of interval-type training, conduct the following simple test:
} Perform a SS, light-to-moderate intensity
bout of exercise for four minutes while monitoring and recording HR response (by four
minutes, your HR should ideally level off,
attaining a SS-response). Next, perform an
all-out 60-75 second bout of high-intensity
exercise before returning to an easy pace to
recover. Complete the following tasks:
1. How long did it take for the HR response
to start climbing? Had it increased much by
10 seconds? How about at the 30-second
mark? In fact, it may still be climbing by the
end of the work interval.
2. Monitor HR response during the first 30
seconds of recovery. Did HR continue to
climb higher during the early phase of recovery, or did it being to drop immediately
following the end of the exercise bout?
What this translates to is that HR measured
during interval-type training cannot be used
to estimate true work performed by the body
or calories, given its delayed response time.
Therefore it is only a number. But, as a number,
it can still hold some value if the same work intensity is performed consistently at lower nonSS HR responses or if HR during the recovery
phase decreases more rapidly (i.e., both imply
improved cardiopulmonary efficiency).
We agree that mathematical formulas, especially 220-age, are flawed, as are zones using
arbitrarily defined ranges. Aiming to score or
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