Moderate vs Vigorous Exercise: How to Tell

The weekly target only works if you can classify what you just did. The Physical Activity Guidelines for Americans give three ways to do it, and they answer slightly different questions.

The talk test: the one you can use mid-workout

This is the guidelines’ own rule of thumb, quoted from the sidebar in Chapter 4:

“As a rule of thumb, a person doing moderate-intensity aerobic activity can talk, but not sing, during the activity. A person doing vigorous-intensity activity cannot say more than a few words without pausing for a breath.”

No equipment, no arithmetic, and it self-adjusts to your fitness. It is the test to use when the question is “does this session count.”

The MET scale: how the guidelines define the categories

Intensity is defined by energy cost, in multiples of the rate of energy expenditure while sitting at rest. One MET is that resting rate.

Intensity	METs	Walking speed given as the example
Light	under 3.0	slow or leisurely, 2 mph or less (3.2 km/h)
Moderate	3.0 to 5.9	briskly or with purpose, 2.5 to 4 mph (4.0 to 6.4 km/h)
Vigorous	6.0 or more	walking very fast, 4.5 to 5 mph (7.2 to 8.0 km/h)

Those speeds are from the Glossary on page 105, and the third row is the one that surprises people: walking very fast is not a milder form of jogging in this scheme. At 4.5 mph it sits in the same intensity class as running, shoveling snow and carrying heavy loads upstairs.

The examples in Table 4-1 fill out the picture. Moderate: recreational swimming, cycling slower than 10 mph on level ground, doubles tennis, ballroom or line dancing, water aerobics, general yard work. Vigorous: jogging or running, swimming laps, singles tennis, cycling faster than 10 mph, jumping rope, hiking uphill or with a heavy pack, high-intensity interval training, kickboxing.

The 0-to-10 scale: relative intensity

The third method adjusts for the person rather than the task. On a scale where sitting is 0 and the greatest effort possible is 10, moderate intensity is a 5 or 6 and produces noticeable increases in breathing and heart rate; vigorous intensity begins at 7 or 8 and produces large increases in both.

The difference between the absolute and relative views is not academic. The same 3-mph walk can be moderate for one adult and vigorous for another, and the guidelines are explicit that for older or less fit adults, relative intensity is the better guide — activities such as tai chi, classified as light on the absolute scale, may be moderate or vigorous in practice. If you would rather judge by pulse, the heart rate zone calculator and the target heart rate for exercise chart cover that route, though heart rate has its own confounders.

Why the classification changes the arithmetic

Vigorous minutes are worth double: “2 minutes of moderate-intensity activity counts the same as 1 minute of vigorous-intensity activity.” Hence the two weekly ranges — 150 to 300 moderate minutes, or 75 to 150 vigorous — and hence the freedom to mix them. Sixty minutes of running plus 60 minutes of brisk walking equals 180 moderate-equivalent minutes.

Work out your own weekly total in how much exercise per week, check whether your walk clears the brisk threshold with the walking pace calculator, and see the daily walking version in how many minutes of walking per day.