Owner’s Manual
22
should be measured after two minutes of exercise at a given workload and again
after the third minute of exercise at that workload. These two HR’s should then
be compared. If a difference of more than five beats per minute between the
two is found, the subject should continue to exercise at one-minute intervals at
the same workload until two successive HR’s differ by less than five beats per
minute.
It is also important that the sub-maximal HR obtained be between 115 and 150
BPM, because it is within this HR range that a linear relationship tends to exist
between HR and oxygen uptake or workload for most adults. When the HR is less
than 115, many external factors (e.g. talking, laughing, apprehension, etc.) can
greatly influence HR. Once the HR reaches a level between 115 and 150, external
factors no longer influence HR, and a linear relationship exists. As the HR rises
above 150, the HR/oxygen uptake relationship becomes curvilinear.
The third assumption involves maximal HR. Maximal HR is the greatest HR that
can be measured when an individual is exercising to the point of volitional fatigue
(i.e. exhaustion) during a graded exercise test. The SC916 StairClimber uses the
most current published equation developed to estimate the average maximal HR
as follows:
Max Heart Rate = 215 – (Age * .75)
Maximal HR can, however, vary greatly among different individuals of the same
age. One standard deviation is ±12 BPM, which means that two-thirds of the
population varies an average of plus or minus 12 heart beats from the average
given by a prediction equation. If an individual’s age-predicted maximal HR is
higher than that person’s true maximal HR, then his/her estimated VO
2 MAX
will be
an overestimation of the correct or actual value.
The final assumption addresses the issue of mechanical efficiency. Oxygen
uptake at any given work rate can vary by approximately 15% between different
individuals. Therefore, individuals vary in the amount of oxygen they require
to perform a certain exercise workload. Some individuals are more efficient
at performing a given task than others. As a result, the average oxygen
consumption associated with a given workload may vary significantly from one
person to another. Thus, VO
2 MAX
predicted by sub-maximal exercise tests tends
to be overestimated for those who are mechanically efficient and underestimated
for those who are inefficient.
The point to remember is that sub-maximal exercise testing, though not as precise
Operation
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