Understanding Volume and Intensity in Weight Training

woman preparing to do a deadlift
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In weight training, volume is the term used to describe how much work you do, such as the number of repetitions (reps) you perform of an exercise. Intensity describes the difficulty of an exercise, typically based on the amount of weight you lift.

Take deadlifts as an example. If you do five reps with a 100-pound barbell and increase to 10 reps with the same barbell, you have increased the volume. If you do five reps but increase the barbell weight to 150 pounds, you have increased the intensity.

These two scenarios do not deliver the same results. The outcomes in terms of muscle growth and fitness are actually very different.

How Volume and Intensity Serve Your Fitness Goals

Broadly speaking, increasing your exercise volume improves fitness and endurance. Increasing intensity builds lean muscle mass and strength.

This is not a cut-and-dried rule. Any exercise you do will improve your fitness, endurance, muscle mass, and strength to varying degrees. But, ultimately, you cannot grow your muscles simply by increasing reps, or improve your endurance if you don't increase your reps.

In this case of deadlifts, for example, a higher volume forces your heart and lungs to work harder. As you adapt to the changes in volume, your cardiovascular fitness and endurance will improve. You may gain a little extra strength and bulk, but not enough to significantly increase muscle size.

On the other hand, if you increase the weight of the lift and keep the reps the same, you will build muscle faster but do little to improve your lung and heart function. Endurance is developed by forcing your heart to work harder than it is accustomed to. Keeping the reps the same will do little to change this.

Measuring Volume and Intensity

Volume can be measured by the hours and minutes you train at the highest level (such as on a treadmill) or the number of sets and reps you do in a workout. If you do hybrid training, such as includes circuits or intervals, volume might involve both duration and reps.

By contrast, intensity is measured by either the weight you lift or the pace in which you perform an exercise (such as running). The rate of perceived exertion (RPE) can be used as a general guide to intensity levels. RPE is often measured on a scale of 1 to 10, with 1 for no activity and 10 for maximum exertion. Intensity may also be measured on a Borg scale of 6 to 20.

Measuring Fitness Levels

While muscle mass is relatively easy to measure, your actual fitness level is based on multiple factors, such as how well your heart and lungs respond to intense physical exertion. As a general rule, the intensity of a workout is described as a percentage of your maximum heart rate (MHR). The MHR is the maximum number of heartbeats you experience during one minute of intense effort.

To improve your cardiovascular fitness, you should aim for 65% to 75% of your MHR. At this level, you are improving your aerobic fitness (your body's ability to use oxygen to fuel workouts).

You can estimate your maximum heart rate by subtracting your age from 220. However, if you have a heart condition or are older and haven't exercised in a while, check with your doctor to determine a safe maximum heart rate for you.

For a more accurate assessment, you can take a treadmill stress test under the supervision of doctor or sports physiologist. The same test can also ascertain your VO2 max (the maximum amount of oxygen your body can utilize during intense exercise). Increases in VO2 max confer to increase in lung capacity and endurance.

Ultimately, your heart's response to the intensity and volume of a workout will establish your fitness level. Whatever your baseline MHR, you can improve your overall fitness by increasing the duration and intensity of an activity.

If you are exceptionally fit, you can train to between 80% and 90% of your MHR. This will place you in an anaerobic state in which your body utilizes glycogen stored in your muscles rather than oxygen to fuel exercise.

While in an anaerobic state, you not only improve your heart and lung function, but you also stimulate muscle growth better than aerobic exercise alone. It is this combination of volume (measured by duration) and intensity (measured by pace) that can help you achieve muscle growth and cardiovascular health all at the same time.

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