Exercise And Heart
Intensity is an essential part of the
traditional cardiovascular exercise recommendations. An optimal exercise
prescription for competitive training as well as for fitness improvement is a
balance between the frequency, intensity and duration of exercise and an
exercise mode. The latest recommendations for health-related exercise, however,
are emphasizing the frequency and the total amount of exercise, e.g. adding
daily steps or accumulating 1000 kcal a week (Physical Activity and Health
The basic variable in the intensity of the
exercise is maximal aerobic power or maximal oxygen uptake (VO2max). It is the
highest rate of oxygen consumption measured during maximal exercise and a
"golden standard" of the cardiorespiratory fitness. Maximal aerobic power is a
product of the cardiac output and arterial-venous oxygen difference. The
cardiac output is a product of stroke volume and heart rate and it is
constantly changing due to changes in stroke volume and heart rate. Stroke
volume reaches its maximum at a relatively low intensity during exercise and
the rest of the oxygen uptake increase is due to an increase in heart rate.
Thus, heart rate is an important index of heart's work and an indicator of the
functions of cardiovascular system during exercise. The heart rate-oxygen
uptake relationship is linear within an individual at least up to so called
"anaerobic threshold" (Wilmore and Costill 1994). Because heart rate is easily
and noninvasively obtainable, e.g. on-line during exercise with modern
telemetric heart rate monitors, it is more practical and useful for exercise
intensity determination than oxygen uptake, cardiac output or stroke volume.
Resting and maximum
heart rates and heart rate reserve
Heart rate at rest is determined by vagal
tonus (parasympathetic nervous system). It averages between 60 and 85 bpm
(beats per minute) in an adult person. Measured resting heart rate is needed
for the Karvonen-formula (Karvonen 1957) for the heart rate reserve calculation
(based on Karvonen 1957) and the target exercise heart rate determinations.
Maximum heart rate is the highest heart rate achieved in an all-out effort. It
is very individual due to heredity, fitness level and age. Endurance training
has not, however, been shown to influence maximum heart rate on the population
level (Wilmore et al. 1996). Maximum heart rate can be predicted using age,
e.g. maximum heart rate for adults equals to 220 - age (ACSM 1990) and for
11-16-year-old children 220 bpm (Armstrong 1991). However, the standard
deviation (SD) of any prediction equation published is at least 8-12 bpm
(Miller et al. 1993, Whaley et al. 1992).
Exercise heart rate
Exercise heart rate is regulated by
increased sympathetic activity. It varies within an individual according to
heredity (size of the left ventricle in heart), fitness level, exercise mode
and skill (economy of exercise). Body posture, environmental variables
(temperature, humidity, altitude), state of mood and hormonal status also alter
the heart rate response. Heart rate is also affected by drugs, stimulants and
According to the goal of the exercise, however, the
target heart rate and heart rate zones can be calculated as a percentage of the
maximum aerobic power or heart rate. ACSM´s latest recommendation (1998)
for developing and maintaining cardiorespiratory fitness in healthy adults
gives 55/65%-90% of maximum heart rate (HRmax) or 40/50%-85% of oxygen uptake
reserve (VO2R) as the intensity limits. Percentages of VO2max (being about 10%
less than %HRmax at the same intensity) can be changed to the %HRmax with the
following formula: %HRmax = (%VO2max + 28.12) / 1.28. Typically, 50-60% of the
maximum heart rate represents light, 60-70% light to moderate, 70-80% moderate
to heavy, 80-90% heavy and 90-100% very heavy intensity. Combining the rating
of perceived exertion, e.g. Borg-scale (Borg 1982) with heart rate, makes the
intensity to better meet the individual target intensity. For the most accurate
exercise intensity (heart rate) determination (also for the Karvonen-formula)
the measured maximum heart rate is needed.
Heart rate variability
(HRV) has been shown to provide an individual method for target heart rate
determination. Polar OwnZone (in Polar SmartEdge and M-series HR monitors) is
based on a decrease in HRV during incremental exercise (Tulppo et al. 1996,
1998). The target heart rate determination by the OwnZone results limits
corresponding to 62-84% HRmax on healthy men and women (Laukkanen et al. 1998)
and 68-86% HRmax in obese adults (Byrne et al. 1999). Reproducibility of this
method has been shown to be good (Kinnunen et al. 1998).
rate in exercise is difficult and confusing for many individuals, e.g. when
participating aerobic classes, if they do not know their maximum heart rate.
Adding beats/subtracting beats to the resting/pre-exercise heart rate helps
them to better control the intensity (Laukkanen et al. 1997). This method is a
new reading approach to the target heart rate charts reported also by
In typical resistance training (targeting to muscle
power and strength increase) heart rate does not play very important role
during exercise bouts, but may be helpful in controlling the recovery time
needed between the work out sessions. However, recently a heart rate guided
low-resistance circuit training program has been shown to be beneficial for
both aerobic and muscular fitness (Kaikkonen et al. 1999).
Other heart rate based
Heart rate recovery period (time) can be
used to detect recovery after the exercise. The time it takes for the heart to
return to its resting rate is decreased as a consequence of regular endurance
training (Wilmore and Costill 1994, Gilman 1996).
Heart rate can also
be used as an indicator of overstrain. Comparison between the resting heart
rate and "the standing up heart rate" (body posture and venous return change)
is the idea in the orthostatic test (Piha 1988). Polar Overtraining Test in
Polar Precision Performance SW2.1 is the latest application in overtraining
detection and is based on HRV measure during orthostatic test (Uusitalo 1998).
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