Workout routines that don’t deliver what you expect may be a waste of energy.
Most workout routines designed to improve your aerobic fitness involve exercising for 20 minutes or longer at a percentage of your maximum heart rate — known as your training zone.
Quite apart from the fact that the formula traditionally used to calculate your maximum heart rate is extremely inaccurate, some workout routines can elevate your heart rate without having any effect on your cardiovascular fitness. In other words, it's possible to raise your heart rate, keep it there for 20 minutes or more several times each week, and it won't improve your fitness in the slightest.
Most aerobic workout routines are based on the relative stress they impose on your body. For example, the general rule for establishing a suitable training intensity is to measure your VO2max. To improve your aerobic fitness, you then follow a training program that corresponds to a percentage of this maximum.
However, most people don't have access to the equipment needed to measure their VO2max. Instead, they use their heart rate to establish a suitable training intensity.
This is because during some forms of exercise, there's a link between oxygen consumption and heart rate. During aerobic exercise, such as running or walking for example, oxygen consumption and heart rate tend to rise together. Yet the relationship doesn't hold true for all forms of activity.
Some evidence for this comes from a study carried in Medicine and Science in Sports and Exercise. Researchers from Washington University measured the effect of four months of strength training using Nautilus exercise machines.
A group of 13 untrained males aged 40-55 took part in the study. During each workout, which was carried out 3-4 times per week, test subjects performed one set of each of 14 exercises.
• There was no change in body fat levels. • Upper-body strength increased by an average of 50%. • Lower-body strength increased by 33%.
During Nautilus exercise, the heart was working at 155 beats per minute, which was approximately 80% of its maximum. However, despite training in this way for up to four times each week, there was no significant change in aerobic fitness.
This is because the large rise in heart rate was partly caused by an increase in the production of hormones known as catecholamines (pronounced cat-a-coal-a-meens). Adrenaline, for example, was roughly 4.5 times higher during Nautilus exercise than treadmill walking at a similar oxygen consumption.
This doesn't mean that training with weights isn't a suitable way to improve your aerobic fitness. After all, compound exercises such as the squat and the deadlift place a large stress on your cardiovascular system. What it does mean is that measuring your heart rate isn't always the best way to gauge the effectiveness of your workout routines.