You’ve had a cold or the flu and your symptoms have begun to subside. Your nose has stopped dripping, your cough is clearing and your head and muscles no longer ache.

You’re ready to get off the couch. But is it too early to go for a run? Here’s what to consider when getting back to exercising after illness.

Exercise can boost your immune system – but not always

Exercise reduces the chance of getting respiratory infections by increasing your immune function and the ability to fight off viruses.

However, an acute bout of endurance exercise may temporarily increase your susceptibility to upper respiratory infections, such as colds and the flu, via the short-term suppression of your immune system. This is known as the “open window” theory.

A study from 2010 examined changes in trained cyclists’ immune systems up to eight hours after two-hour high-intensity cycling. It found important immune functions were suppressed, resulting in an increased rate of upper respiratory infections after the intense endurance exercise.

So, we have to be more careful after performing harder exercises than normal.

Can you exercise when you’re sick?

This depends on the severity of your symptoms and the intensity of exercise.

Mild to moderate exercise (reducing the intensity and length of workout) may be OK if your symptoms are a runny nose, nasal congestion, sneezing and minor sore throat, without a fever.

Exercise may help you feel better by opening your nasal passages and temporarily relieving nasal congestion.

However, if you try to exercise at your normal intensity when you are sick, you risk injury or more serious illness. So it’s important to listen to your body.

If your symptoms include chest congestion, a cough, upset stomach, fever, fatigue or widespread muscle aches, avoid exercising. Exercising when you have these symptoms may worsen the symptoms and prolong the recovery time.

If you’ve had the flu or another respiratory illness that caused a high fever, make sure your temperature is back to normal before getting back to exercise. Exercising raises your body temperature, so if you already have a fever, your temperature will become high quicker, which makes you sicker.

If you have COVID or other contagious illnesses, stay at home, rest and isolate yourself from others.

When you’re sick and feel weak, don’t force yourself to exercise. Focus instead on getting plenty of rest. This may actually shorten the time it takes to recover and resume your normal workout routine.

I’ve been sick for a few weeks. What has happened to my strength and fitness?

You may think taking two weeks off from training is disastrous, and worry you’ll lose the gains you’ve made in your previous workouts. But it could be just what the body needs.

It’s true that almost all training benefits are reversible to some degree. This means the physical fitness that you have built up over time can be lost without regular exercise.

To study the effects of de-training on our body functions, researchers have undertaken “bed rest” studies, where healthy volunteers spend up to 70 days in bed. They found that V̇O₂max (the maximum amount of oxygen a person can use during maximal exercise, which is a measure of aerobic fitness) declines 0.3–0.4% a day. And the higher pre-bed-rest V̇O₂max levels, the larger the declines.

In terms of skeletal muscles, upper thigh muscles become smaller by 2% after five days of bed rest, 5% at 14 days, and 12% at 35 days of bed rest.

Muscle strength declines more than muscle mass: knee extensor muscle strength gets weaker by 8% at five days, 12% at 14 days and more than 20% after around 35 days of bed rest.

This is why it feels harder to do the same exercises after resting for even five days.

But in bed rest studies, physical activities are strictly limited, and even standing up from a bed is prohibited during the whole length of a study. When we’re sick in bed, we have some physical activities such as sitting on a bed, standing up and walking to the toilet. These activities could reduce the rate of decreases in our physical functions compared with study participants.

How to ease back into exercise

Start with a lower-intensity workout initially, such as going for a walk instead of a run. Your first workout back should be light so you don’t get out of breath. Go low (intensity) and go slow.

Gradually increase the volume and intensity to the previous level. It may take the same number of days or weeks you rested to get back to where you were. If you were absent from an exercise routine for two weeks, for example, it may require two weeks for your fitness to return to the same level.

If you feel exhausted after exercising, take an extra day off before working out again. A day or two off from exercising shouldn’t affect your performance very much.

Ken Nosaka, Professor of Exercise and Sports Science, Edith Cowan University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

It’s that time of year when many people are getting started on their resolutions for the year ahead. Doing more physical activity is a popular and worthwhile goal.

If you’re hoping to be more active in 2024, perhaps you’ve invested in an activity tracker, or you’re considering buying one.

But what are the benefits of activity trackers? And will a basic tracker do the trick, or do you need a fancy one with lots of features? Let’s take a look.

Why use an activity tracker?

One of the most powerful predictors for being active is whether or not you are monitoring how active you are.

Most people have a vague idea of how active they are, but this is inaccurate a lot of the time. Once people consciously start to keep track of how much activity they do, they often realise it’s less than what they thought, and this motivates them to be more active.

You can self-monitor without an activity tracker (just by writing down what you do), but this method is hard to keep up in the long run and it’s also a lot less accurate compared to devices that track your every move 24/7.

By tracking steps or “activity minutes” you can ascertain whether or not you are meeting the physical activity guidelines (150 minutes of moderate to vigorous physical activity per week).

It also allows you to track how you’re progressing with any personal activity goals, and view your progress over time. All this would be difficult without an activity tracker.

Research has shown the most popular brands of activity trackers are generally reliable when it comes to tracking basic measures such as steps and activity minutes.

But wait, there’s more

Many activity trackers on the market nowadays track a range of other measures which their manufacturers promote as important in monitoring health and fitness. But is this really the case? Let’s look at some of these.

Resting heart rate

This is your heart rate at rest, which is normally somewhere between 60 and 100 beats per minute. Your resting heart rate will gradually go down as you become fitter, especially if you’re doing a lot of high-intensity exercise. Your risk of dying of any cause (all-cause mortality) is much lower when you have a low resting heart rate.

So, it is useful to keep an eye on your resting heart rate. Activity trackers are pretty good at tracking it, but you can also easily measure your heart rate by monitoring your pulse and using a stopwatch.

Heart rate during exercise

Activity trackers will also measure your heart rate when you’re active. To improve fitness efficiently, professional athletes focus on having their heart rate in certain “zones” when they’re exercising – so knowing their heart rate during exercise is important.

But if you just want to be more active and healthier, without a specific training goal in mind, you can exercise at a level that feels good to you and not worry about your heart rate during activity. The most important thing is that you’re being active.

Also, a dedicated heart rate monitor with a strap around your chest will do a much better job at measuring your actual heart rate compared to an activity tracker worn around your wrist.

Maximal heart rate

This is the hardest your heart could beat when you’re active, not something you could sustain very long. Your maximal heart rate is not influenced by how much exercise you do, or your fitness level.

Most activity trackers don’t measure it accurately anyway, so you might as well forget about this one.

VO₂max

Your muscles need oxygen to work. The more oxygen your body can process, the harder you can work, and therefore the fitter you are.

VO₂max is the volume (V) of oxygen (O₂) we could breathe maximally (max) over a one minute interval, expressed as millilitres of oxygen per kilogram of body weight per minute (ml/kg/min). Inactive women and men would have a VO₂max lower than 30 and 40 ml/kg/min, respectively. A reasonably good VO₂max would be mid thirties and higher for women and mid forties and higher for men.

VO₂max is another measure of fitness that correlates well with all-cause mortality: the higher it is, the lower your risk of dying.

For athletes, VO₂max is usually measured in a lab on a treadmill while wearing a mask that measures oxygen consumption. Activity trackers instead look at your running speed (using a GPS chip) and your heart rate and compare these measures to values from other people.

If you can run fast with a low heart rate your tracker will assume you are relatively fit, resulting in a higher VO₂max. These estimates are not very accurate as they are based on lots of assumptions. However, the error of the measurement is reasonably consistent. This means if your VO₂max is gradually increasing, you are likely to be getting fitter.

So what’s the take-home message? Focus on how many steps you take every day or the number of activity minutes you achieve. Even a basic activity tracker will measure these factors relatively accurately. There is no real need to track other measures and pay more for an activity tracker that records them, unless you are getting really serious about exercise.

Corneel Vandelanotte, Professorial Research Fellow: Physical Activity and Health, CQUniversity Australia

This article is republished from The Conversation under a Creative Commons license. Read the original article.