How to Tell if You're Exercising Hard Enough
Nearly every fitness plan includes some prescription for exercise intensity. Even the CDC’s recommendations — arguably the simplest and most straightforward — mandate 150 minutes per week of moderate-intensity exercise.
But, considering every individual’s physical abilities and fitness goals are different, how can you measure exercise intensity? And why does it even matter?
Why Is Exercise Intensity Important?
There are two factors that determine the effectiveness of a workout: duration and intensity. And the truth is, if your workout doesn’t reach the level of intensity necessary for a specific goal, all the duration in the day won’t be enough to achieve it.
Jackie Wilson, CPT, founder and CEO of NOVA Fitness Studios in New York City, explains: “When you perform lower-intensity exercise movements, your body will use fat as the predominant fuel source. This is what is meant when people refer to the ‘fat-burning zone.’ As you increase the intensity of a workout, your body will start to use carbohydrates as the [primary] fuel.”
Sounds from Wilson’s explanation like someone interested in losing weight or improving their physique should stick to gentle walks. But he’s not finished.
“The net caloric expenditure is larger after higher-intensity bouts of training,” Wilson continues. In other words, you’ll burn way more calories overall running for 20 minutes than you will walking for the same amount of time, even though fat isn’t your primary fuel source.
In practice, amping up your intensity and venturing into higher heart rate zones yields exponentially greater results. But that’s not all!
Revving your heart rate additionally results in an “after-burn” effect known as excess post-exercise oxygen consumption (EPOC). This causes your body to continue burning calories hours after you’ve wrapped up your workout.
“After strenuous activity, there is a measurable elevation in oxygen intake and usage. This increased oxygen consumption is how the body adapts to the training and restores homeostasis, but is also accompanied by an increase in energy expenditure,” explains Wilson.
To reach your desired heart rate zone for a specific goal, you must first calculate your target heart rate.
How to Find Your Target Heart Rate
Your target heart rate is determined by your maximum heart rate (MHR) and your goal (fat loss, strength, endurance, etc.). An exercise physiologist with access to a testing facility can accurately determine your MHR, but if you’d rather forgo the stress test (and the expense), you can calculate a rough estimate using the Tanaka equation:
MHR = 208 – (0.7 x your age)
For example, if you’re 30 years old, your estimated max heart rate is 188.
208 – (0.7 x 30) = 187
Jesse Abend, doctor of osteopathic medicine, certified personal trainer, and founder of Middleman Coaching, explains how to use your MHR to find your target heart rate. “A heart rate that is 50 to 70 percent of your max is considered low intensity, 70 to 80 percent is moderate intensity, and 80 to 100 percent is considered high,” he says.
Once you’ve identified your MHR, you’ll then use that number to calculate how many beats per minute (BMP) are needed to reach the heart rate zone that corresponds with your objective.
How Do I Know If I’m Exercising Intensely Enough?
Heart rate monitoring is a standard feature for most wearable fitness trackers, so you can likely use your smartwatch to track your heart rate throughout a workout. Or opt for a compatible chest strap, which will provide more accurate metrics.
But, if you’ve entered a sweat session sans gear and want to make sure you get in some legitimately intense exercise (or keep your effort on the moderate or lighter side), you can use these general guidelines to stay in your cardio lane.
Associated goals: (Re)introduction to fitness, active rest, warm-up/cooldown
A stroll in the park, leisurely bike ride, or meditative gardening session are all examples of low-intensity exercise. If you can sing a song or conduct a conversation during the activity, you’re exercising at low intensity, explains Wilson.
“Low-intensity workouts are great for people who are new to working out, rehabilitating an injury, fatigued, older populations, or anyone taking an ‘active recovery day,’” he says.
Associated goals: General fitness, weight loss, cardiorespiratory/muscular endurance
During moderately intense exercise, talking is still possible, but it’s harder to have a conversation, and singing is definitely out. When most of us hop on a treadmill for a 30-minute jog or participate in a group exercise class, we tend to exercise at moderate intensity.
“This range is good for most of the population,” Wilson says. “It’s challenging enough to get consistent (weight-loss and cardiorespiratory fitness) results, yet manageable for those who aren’t performing at competition levels.”
Associated goals: Fat loss, increased strength, improved cardiorespiratory capacity (VO2 max)
The all-out sprint at the end of your spin class or the 20-second intervals during a tabata session are considered high-intensity exercise. Talking is nearly impossible during highly intense exercise (you may manage to sputter a few words between labored breaths).
“High-intensity exercise is great for performance athletes, well-conditioned gym-goers, and those looking to ignite their metabolism over a shorter period of time,” Wilson says.
How to Choose Exercise Intensity
The typical, uninjured person should aim for a well-rounded fitness routine that includes a mix of low-, moderate-, and high-intensity exercise, but with an emphasis on moderate-intensity exercise.
Dr. Nicole Lombardo, PT, doctor of physical therapy at Back Intelligence, explains that the average 30-minute workout should include around 18 minutes of moderately intense exercise, 5 to 10 minutes of high-intensity exercise, and 2 to 5 minutes of low-intensity exercise during the warm-up and cooldown periods.
“This will work on improving overall cardiovascular fitness and speed up metabolism following the workout, but not overstress your system,” she says. “If you overstress your system, your body recognizes this is a fight-or-flight situation which can actually slow your metabolism down.”