“Insulin sensitivity is down to an interaction between the hormones. Cortisol and insulin are almost inverse; cortisol breaks down while insulin builds,” explains NHS GP and personal trainer Dr Amos Ogunkoya. “We know that cortisol levels are higher in the morning and cortisol tends to hold onto fat. That means exercising later might allow you to actually do a better workout – especially as most of us have time limitations in the morning but more time in the evening.”

We know exercise has stress-relieving properties and further studies link evening exercise to falling asleep faster and spending more time in deep sleep. So, knowing how good it is for me, could I, a sworn morning person – who frequently goes to sleep in full daylight and to the sound of young children playing outside – switch my routine around? Could I become a fitness owl?

Monday evening yoga class

Not wanting to throw myself into anything too brutal straight off the circadian bat, I opted for a Monday evening yoga class. To get there involved a short bike ride in the setting sun. Which was picturesque until an enormous brown rat ran across my path. That’s one problem with being out and about in the evening – so are the rodents. 

Somehow, the slowness of yoga – all that breathing and stretching and listening to your body – can feel frustrating to me in the morning. But after a full day of work, childcare, unpaid domestic labour and the news, I relished the idea.  As a beginner, I found my muscles shaking like a Polaroid picture after even just a few seconds of downward facing dog.

Verdict

Yoga’s seriously good for you. One 2016 study by the Rockefeller University in New York showed that participants doing yoga three times a week significantly improved bone mineral density in their spine, hips and thigh bones. The slow breathing has been shown to have a calming effect on our nervous system and reduce our stress levels too – both conducive to getting eight hours of sleep, which also happens to be linked to good heart health. 

Tuesday evening run

With my metabolic processes in mind, I had an extremely early dinner on Tuesday with my son to be ready for a run after his bedtime. It felt completely bizarre, bordering on scandalous to be pulling on a pair of Lycra shorts at 8pm.

But, honestly, how else are parents to small children supposed to capitalise on all this evening insulin regulation? I may have provocatively suggested to my partner that “vigorous physical activity in the evening is widely acknowledged as a therapeutic strategy for improving cardiometabolic risk factors,” but I’m not sure it was quite the seductive line I’d hoped. So, I was stuck with running.

The problem with something as high adrenaline as a jog down the towpath, at night, is that by the time I got home a little over an hour later, sweaty and with my pupils dilated, I was in no fit state to fall asleep. 

Verdict

Despite a hot shower and cup of chamomile tea, I lay in bed for at least an hour and a half, completely unable to switch off. Indeed, studies show that in order for evening exercise to improve sleep it needs to be moderate intensity, not vigorous and end at least an hour before bedtime. Lesson learned.  

Slower exercise definitely seems more conducive to good sleep but I don’t want to give up my running. Thankfully, Dr Ogunkoya reassures me that doing something is always better than nothing – whatever the time. “The biggest contributor to diabetes, cardiovascular disease and cancer is a sedentary lifestyle,” says Dr Ogunkoya. “So, if you find cardiovascular exercise in the morning easy then go with that. And maybe do weights in the evening.”

A handy health and fitness feature with watchOS and iOS is the ability to see your heart rate zones on Apple Watch and iPhone. Read on for what they mean, how to see your max heart rate, manually edit your zones, and more.

Apple Watch and iPhone – with watchOS 9/iOS 16 and later – automatically create your five heart rate zones based on the Heart Rate Reserve method. Max and resting values are updated automatically on the first day of each month.

Here’s how Apple describes the feature:

“Heart Rate Zones are a percentage of your maximum heart rate and are automatically calculated and personalized using your health data. On Apple Watch, Heart Rate Zones are presented in five segments—effort levels from light to increasingly harder. By monitoring your Heart Rate Zone, you can make your workout more efficient and challenge yourself to improve your fitness.”

How to see heart rate zones on Apple Watch and iPhone

See heart rate zones during a workout

• Make sure you’re running watchOS 9 or later on Apple Watch and also have your birthdate entered in the Health app on iPhone
• Start a cardio-focused workout like a walk, run, or cycling (Apple hasn’t shared exactly which workout types include heart rate zones except for “cardio-focused” ones)
• Swipe down on the first Workout screen to see your heart rate and which zone it’s in

See heart rate zones after a workout

• After a workout, head to the Fitness app on iPhone to see heart rate zone data
• Choose a workout from the main Summary screen or tap the rings or Show More to pick a different date/workout
• Once you’ve picked a workout, swipe down until you see Heart Rate, tap Show More

Now you’ll see the breakdown of how much time you spent in each heart rate zone:

How to manually edit your heart rate zones

While the heart rate zones are automatically added based on your age, height, and weight, you can manually change them (usually for advanced athletes).

• Head to Settings > Workout > Heart Rate Zones on your Apple Watch and choose Manual at the top
• Or on iPhone go to the Apple Watch app > Workout > Heart Rate Zones then choose Manual at the top

How to see your max heart rate?

Going beyond your max heart rate is considered unsafe by medical professionals. To see your recommended maximum:

• Head to Settings > Workout > Heart Rate Zones on your Apple Watch, swipe down to find your max heart rate
• Or on iPhone go to the Apple Watch app > Workout > Heart Rate Zones, swipe down to find your max heart rate

What do heart rate zones mean?

Understanding your heart rate zones can be useful in a variety of ways. But some of the most practical applications are using heart rate training (properly rest or push yourself), targeting fat-burning or carb-burning heart rate zones, and awareness for those who have health conditions.

The Cleveland Clinic has a helpful article on understanding what kind of calories you’re burning in different zones. This won’t map directly to the five heart rate zones with Apple Watch, but is a good starting point.

Use your max heart rate (details on finding above) to figure out the numbers from the below calculations:

• Lower-intensity zone: You’re exercising at 50% to 60% of your max heart rate. At this point, 85% of the calories you burn are fat. The downside? You’re burning fewer calories overall than you would if you were exercising at a higher intensity. You’re generally able to sustain this zone the longest amount of time.
• Temperate zone: You’re exercising at 60% to 70% of your max heart rate. Roughly 65% of the calories you burn are fat.
• Aerobic zone: Working at 70% to 80% of your max heart rate puts you in the aerobic zone. About 45% of the calories you burn are fat. But you’re burning a higher number of overall calories compared to the other heart rate zones. You generally sustain this zone the shortest amount of time. 

For heart rate training, the big idea is to “train your aerobic system without overstressing your skeletal and muscular systems, explains personal trainer Erin Carr.” Check out this article from Runner’s World for all the fine details:

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