Dateline, World Gym, Tuesday afternoon. Chest and triceps day. While taking a 10-second break to grab some water, I heard the following exchange between two rather skinny
individuals who were furiously pedaling away on Lifecycles:
Person 1: "So, you gonna do some lifting when you're done on the bike?"
Person 2, shaking his head vigorously: "Naw. 1 hear lifting is bad for your heart."
Incredible! I'm not sure what somebody who believes that was doing at World, but it got me thinking that even those who don't believe it may be interested in what heavy
lifting does to the old ticker and related systems.
All forms of exercise, when pursued vigorously, result in physiologic changes to the body. The type and extent of these changes depend on the type of exercises performed and
the vigor with which they are pursued.
Weight training is no exception. Whether as the main focus or as an adjunct to other forms of exercise, weight training results in characteristic changes in the body. The
type and extent of these changes depend on the type of weightlifting and the vigor with which the weights are lifted.
What changes occur? How do they differ from changes seen in aerobic training? What happens to heart rate, blood pressure and oxygen consumption? Are these changes good or bad?
The Aerobic Heart
The cardiac changes seen with weight training are considerably different from those seen with aerobic conditioning. In aerobic conditioning (running, bicycling and swimming,
for example) the demand for oxygen delivery is increased. This translates into a demand for the heart to pump more blood per minute in order to deliver more oxygen. If the
demand for increased oxygen delivery is high enough over a long enough period of time, the cardiac tissue changes by increasing ventricle cavity size; that is, increasing the
diameter of the heart's main pumping chambers.
A bigger ventricle can pump more blood with every stroke (increased stroke volume); therefore, at a given heart rate more blood gets pumped per minute (increased cardiac
output), and more oxygen gets delivered to the tissues. (To keep a big-chambered heart from pumping too much blood at rest, the resting heart rate goes down. That's why highly
aerobically trained athletes often have resting heart rates in the 40s.)
The Anaerobic Heart
For the bodybuilder the demands on the heart are quite different. Instead of needing to increase oxygen delivery for prolonged periods of time, the heart needs to increase its
ability to pump against high resistance for very short periods of time.
During a lift your blood pressure may go as high as 280/350. While your heart needs to sustain such incredibly high pressures for only short periods of time, these high pressures
still place considerable demand on the heart. If this demand occurs repeatedly over a long-enough period of time, the cardiac tissue changes by increasing ventricle wall thickness
without changing chamber size. A thicker ventricle pumps the same amount of blood with every stroke but can generate a much greater pressure when needed.
These heart changes, both in aerobically trained and in weight-trained athletes, come on fairly quickly- measurable differences have been noted in as little as one week. It appears,
however, that these changes persist only as long as the training continues. If training is stopped, the heart thickness and chamber sizes eventually return to pre-training dimensions.
As mentioned above, during a lift blood pressure can reach very high levels. Blood pressure is related to the amount of weight lifted and the muscle mass involved, and it increases
with every rep, reaching the highest levels when submaximal lifts are repeated to failure. The rise appears to be significantly less in experienced bodybuilders than in inexperienced
bodybuilders. Other than the momentary increases during a lift, however, weightlifting does not seem to increase baseline blood pressure. In fact, there is some evidence that
weightlifting may actually decrease baseline blood pressure. Chalk up another one for iron!
Resting heart rate is unchanged in weight-trained athletes. This contrasts with aerobically trained athletes, who show a decrease in their resting heart rates. During a 10-to-12-rep
max set a trained lifter's heart rate increases to 80 to 85 percent of the maximum heart rate attainable during aerobic activity. This increase is a result of a combination of neural
and hormonal influences, but the heart rate quickly returns to normal once the exertion is stopped.
When trained lifters lift to exhaustion, they have higher heart rates and lactate levels than untrained subjects, but they recover more quickly. This is attributable not only to the
fact that by the time they reach exhaustion trained weightlifters have performed more work, but also that they have well-developed fast glycolytic systems. This means that by training
they have geared up the muscle glucose-metabolism machinery so that their muscles can metabolize a greater amount of glucose in a shorter period of time. This is similar to
glucose-metabolism changes seen in aerobically trained athletes.
Trained weightlifters and body-builders also show an increase in VO2 max, the maximum rate they can consume oxygen under aerobic conditions. This increase, however, is only proportional
to the increase in muscle mass. If the increase in VO2 max is corrected for the increase in muscle mass, weightlifters show no increase in VO2 max. Weight training is not an efficient
way of increasing VO2 max; traditional aerobic-type exercises are much better for this.
The Bottom Line
Are the heart changes seen in body-builders good or bad? Although in the strict scientific sense the jury is still out, there is no solid evidence that these changes are detrimental
and some evidence that they may in fact be beneficial. The increased ventricular wall thickness and momentary increases in blood pressure do not appear to be harmful or injurious to
otherwise healthy athletes. Resting heart rate remains at normal levels and resting blood pressure may decrease slightly. There is evidence to suggest that weight training may improve
serum cholesterol and lipid (fat) profiles in steroid-free bodybuilders comparably to aerobic training, thus decreasing the risk of heart disease. That's a pretty good score-card, if
you ask me!