Both new joggers and marathon fanatics can benefit from 30 minutes of running. It’s a short enough period to fit easily into a busy schedule, but long enough to work up a sweat and burn some calories. But what actually happens to you during a 30-minute run?
In the race to figure out which is the best fitness tracker to use, what the best phone holders for running are, or which of the best running shoes best serve your gait, we can forget to consider the most vital aspect of all: what is happening to our bodies as we run?
Tom’s Guide spoke to the University of East London’s Richard Avery, a running specialist in sports and exercise physiologist, to find out more.
What happens to your body after 10 minutes of running?
When you first start running, you’ll notice a rapid surge in your breathing and an increased heart rate. This is all down to your body’s need for oxygen.
“As the muscles start to move the body,” explains Avery, “there is an increased demand for oxygen. Breathing rate increases, so that oxygen can pass into the bloodstream via the lungs, and heart rate increases, to pump the blood to the working muscles more quickly.”
As anybody who struggles through that first couple of kilometres will know, eventually things ease up: “Within a few minutes of running the body adapts, with heart rate and breathing frequency following a more regular pattern,” says Avery, “you can tell you have settled into a comfortable running pace, if you are slightly out of breath, but still able to hold a conversation.”
What happens to your body after 20 minutes of running?
Generally, it’s seen as desirable to keep yourself in an ‘aerobic state’, where your body is taking in enough oxygen to keep everything running smoothly. Push too hard, by sprinting mid-run or maybe taking on a giant hill, and you could find yourself in an ‘anaerobic state’, where your body produces lactate, fatigue sets in and you’re burning too much energy.
“There are different ways to measure your exercise intensity to make sure you are exercising aerobically,” adds Avery. “A common method of predicting maximum heart rate is 220 minus your age. The British Heart Foundation recommends keeping your heart rate within 50 to 70% of your age-predicted maximum during moderate-intensity exercise.” (Here's more on how to measure your heart rate).
Don’t forget that other conditions play into performance too. Even on a shorter run, external factors can have a huge sway over your performance. As Avery puts it: “Your perceived effort will vary depending on several factors, so it is important to account for these when running. This can include weather conditions, terrain, and levels of fatigue. Remember, your heart rate will be significantly higher running uphill in the heat when you’re tired!”
Heat or no heat, don’t be afraid of sweat. This is simply the body’s way of venting heat, rather than a sign of overexertion. “After 10 minutes of running at a steady pace,” explains Avery, “the body starts to rely on thermoregulation to prevent overheating. Heat is generated within the working muscles, so sweat is produced to release excess heat through evaporation. The body generates more heat with higher intensity exercise, which is why you tend to sweat more when running faster.”
What happens to your body when you run past 30 minutes?
If it’s fat-burning you’re looking for, then running past the 30-minute mark should be your target. “The body will start to get more efficient at burning fat for fuel during longer runs,” Avery elaborates. However, as with all aspects of fitness, the benefits should be weighed up against the drawbacks.
While pushing your body into the fat-burning zone may be desirable, you may find yourself facing a longer recovery time. Longer recovery can mean fewer runs, which in turn means fewer opportunities to burn fat. “If intensity stays the same and you run for longer, the body will have a proportionally longer recovery time,” explains Avery. “There should always be a balance to make sure you are not overtraining. If you are not a regular runner and you push beyond 30 minutes, your heart rate tends to gradually increase at the same intensity of exercise, as the body and mind start to fatigue.”
So just how much should you run to find that balance between pushing yourself and avoiding overtraining? (Here are all the signs you might be overtraining). “The American College of Sports Medicine (ACSM) physical activity guidelines suggest that all healthy adults, between 18 and 65 years old, should perform moderate aerobic activity for 150 minutes each week, spread over 4 to 5 days,” states Avery. “Even exercising just once or twice a week can reduce the risk of heart disease or a stroke, and can help reduce your resting blood pressure.”
What happens to your body when you stop running?
When you cease running, the body begins to return to its natural state. Breathing and heart rate slow, although how quickly depends on the intensity and duration of the workout, not to mention your fitness level. The more running you do, the quicker your recovery time. “As fitness levels increase, and your body adapts over time, your heart rate will recover more quickly, following a run at the same pace,” says Avery.
The benefits don’t stop there either. Strengthening your cardiovascular system won’t just net you a new personal best in your midweek run, it also grants a host of physical health benefits, not to mention reduced levels of anxiety, better moods, and improved overall wellbeing.
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Dan Cooper is an experienced fitness writer who firmly believes in the power of running. The hardest race he has completed so far was Tough Guy, the world’s oldest and most demanding OCR event. There he learned that you may be able to outpace opponents, but outrunning hypothermia? That's a different race entirely.