METS, watts or heart rate: What is the best way to measure your workout?

Winter means moving most of your cardio workouts indoors to your favourite exercise machine. With a view limited to the console in front of you, have you ever wondered about watts and METs and whether you should pay more attention to these unfamiliar sets of numbers flashing across your screen?

Choosing which metric to gauge exercise intensity is largely related to your goals. If your goal is to burn as many calories as possible during a workout, keeping an eye on caloric expenditure is your best bet. But if your workout is based on spending all or part of it in a specific heart rate zone, then heart rate is your go-to metric. METS is a good choice if you want an easy measure of how long you spend at various exercise intensities (light, medium or vigorous) and watts is a favourite of cyclists who adjust speed and resistance based on reaching and/or sustaining a certain wattage.

Still confused about which metric best measures your efforts? Here’s a quick guide to watts, METS and heart rate. Just remember, all metrics generated from a piece of exercise equipment are based on the information you provide before the workout starts, like age, sex and weight. Even then, the values are an estimate at best, with the data only as good as the algorithms the manufacturer uses and the ability of the machine to factor in accurate measures of speed, resistance and/or heart rate.

Watts is an expression of power

A popular measure of intensity for cyclists, watts is an expression of power determined by a combination of how fast you’re turning the pedals (speed or revolutions per minute) and the gear you’re using (force on the pedal). If you want to increase watts, you need to maintain pedal speed in a high gear versus increasing either speed or resistance on their own.

Why do cyclists prefer measuring intensity by watts versus heart rate? Watts don’t lie. Heart rate fluctuates based on sleep, stress, hydration status, temperature and how much coffee you drink. There’s a lag between an increase in intensity and an increase in heart rate. Not so with watts, which offer a consistent measure of how fast you can push against resistance no matter how late you stayed up or the number of coffees you consumed to get ready for your day.

Watts-based training sets goals based on sustaining a certain wattage for a specific amount of time, be it for the length of the ride or for a short interval. The key to using watts as a training tool is to establish the number of watts you can sustain for at least 20 minutes. Use that as your baseline, then select intervals based on maintaining watts 25, 50, 75 or 100 per cent greater than your baseline.

METS is a matter of intensity

METS (metabolic equivalents) represent the amount of energy it takes to do any type of physical activity. The higher the MET count, the greater the intensity of the workout. One MET is considered baseline and is equivalent to the energy expended while at rest. One to three METS qualifies as light intensity activity (it requires up to three times more energy than being at rest). Moderate intensity activity is three to six METS and vigorous physical activity is anything over six. Exercise physiologists have given METS designations to thousands of different types of physical activity, which helps you choose the type of exercise that best matches your desired level of intensity.

Using the METS numbers on your exercise machine console, you can easily determine when your walk turns into a workout and when your workout goes from moderate to vigorous. If your goal is to maintain a moderate intensity workout, you can move from a jog to a walk and back to a jog, controlling the degree of incline and speed so that your METS stay between three and six.

Heart rate can be trickier

During exercise, your heart rate is a reflection of how much oxygen is needed to meet the demands of your working muscles. The harder the intensity of the workout, the more heart rate increases (more beats per minute). Intensity is expressed by a percentage of maximum heart rate, which is universally set at 220 bpm but adjusted based on age (220–your age). Heart rates sustained between 50 to 70 per cent of your age-predicted MHR are considered moderate intensity. Seventy to 85 per cent of MHR is a vigorous workout. Anything less than 50 per cent of MHR is light intensity exercise.

The challenge is that it’s tough to take your pulse (and do the math) on the go. Unless you have a smart watch or use the sensors on your exercise machine to measure heart rate (a traditionally finicky feature on most cardio machines), heart rate is a less-than-practical means to guide exercise intensity in real time. Some medications can lower your heart rate and its response to exercise, making it a less accurate measure of your efforts. That said, heart rate zone training is becoming increasingly popular, especially as smart watches make it easier to track and record heart rate over the course of your workout.