How to measure the effectiveness of your workout

“The challenge is that determining how hard we’re working is often a subjective thing,” says UW Health senior exercise physiologist Jude Sullivan. “And our bodies don’t always tell us what’s happening in real time.”

A common measurement of how hard you should be working is your target heart rate. Essentially, your target heart rate is around 50-85 percent of your maximum heart rate. But it has its limitations, explains Sullivan. He uses the example of working out in hot and humid conditions. Our heart rate tends to accelerate because our bodies are trying to compensate for the hot temperatures. If you’re relying on your target heart rate to tell you how hard you’re exercising, it’s going to be off.

“In hot and humid conditions, you may not actually be working any harder because of your effort, but your heart rate is higher because it is also helping regulate your body’s core temperature,” he says.

Another common scenario Sullivan encounters with clients at UW Health’s Fitness Center is when medications affect heart rate. Certain medications control blood pressure by lowering the heart rate. If someone is taking that kind of prescription and monitors their workout based on heart rate – they will not get an accurate reading. No matter how hard they work, their rate won’t go over a certain amount because the medication is keeping it low.

Rating of perceived exertion

“Judging exertion by heart rate can be woefully inaccurate,” he says and points out that even so, many wearable fitness trackers are centered around the target heart rate. That’s why you need to be aware of the limitations. And it’s one reason why the Fitness Center encourages the use of the Borg Rating of Perceived Exertion (RPE).

“It marries the concept of the subjective – ‘I can trust myself to know how hard hard feels to me’ – with the calculations of a tool like the target heart rate,” he explains.

Sullivan points out that there are a number of benefits to using the scale, including that it allows for good days and bad days. “Sometimes you wake up and don’t feel great. Your wearable may tell you your heart rate is right where it should be, but you may feel exhausted compared to other days. On the flipside, there may be days where it feels incredibly easy.”

Sullivan admits the RPE uses an odd numbering system – it starts with 6 and goes up to 20. However, he explains, the system works because it relates to an individual’s phyiology – or how a person’s body functions. For perspective, he explains, 6 is the feeling of sitting down, having a conversation or reading a book. Twenty on the other end is a level so physically intolerable, you need to stop. And the important thing to remember is that it will be different for every individual.

“We’re not defining what an exercise ‘should’ feel like to you,” says Sullivan. “Who am I to tell you what very, very hard feels like? I’m there to coach you to be honest about how it feels.”

Because how hard an exercise feels is such an individual experience, the RPE scale offers the benefit that it evolves with your fitness progress. When you start an exercise routine, you may feel like a work level (for instance, walking 3 miles per hour on a level treadmill) is really challenging and you rate it as a 13 or 14 ("somewhat hard") on the RPE scale. But over the course of time, this same work level will begin to feel easier — you may rate the effort at a 10 or 11 ("fairly light"). That's when you know it's time to pick up the pace or introduce new challenges.

Print your own RPE (pdf)

“Over time we expect that you will have to work harder to feel the same level of intensity,” explains Sullivan. “Hard will always feel hard to you, but over time it will begin to take more effort and energy to feel it.”

He notes that it’s human behavior to create blind spots of sorts when it comes to admitting how hard or easy something is. Our personalities may lead us to say something is easy no matter how hard it may be. But Sullivan stresses that it’s important that we’re honest if we want to get the most out of our exercise routine.

Another challenge Sullivan sees is that people can get into the habit of judging their workouts based on past experiences. They may think that after 10 reps they shouldn’t be tired, but in Sullivan’s words “every day is a new day.” He encourages his clients and anyone who exercises to be curious — what does difficult feel like? How am I feeling today and does that change what feels difficult?

“Explore your limits and get to know your body,” he says, adding that is one reason the RPE scale can be so beneficial. While it takes a little bit of practice to use it, it can be used for any activity – whether that’s yoga, swimming, running or exercising at the gym. Over time, you’ll begin to see how you’re progressing and find new ways to challenge yourself.

But no matter what method you use to monitor your progress, there’s one assessment according to Sullivan that’s the most important of all — “Are you having fun while being active?”

For a discussion of the RPE scale, watch Jude Sullivan and Dan Wanta's Facebook Live recording.