And that’s actually totally normal, as it should feel hard. "The first mile is the hardest because it leads to a rapid increase in oxygen demand to your entire body," says Sadi Raza, MD, FACC, a board-certified cardiologist in Dallas, Texas. As your heart works to keep up with your whole body, its cardiac output—aka the blood that pumps through the body in one minute—changes dramatically. "Your cardiac output is a direct product of your heart rate and stroke volume, where the stroke volume is the amount of blood pumped out by the heart in one contraction," explains Dr. Raza. Basically, it’s the amount of blood the heart pushes out in each heartbeat.
So, what’s going on during that first mile, exactly?
Early in a run, you'll feel your heart rush to meet the body's needs. "When you first start to exercise, your muscles' metabolic requirements may increase up to 50-fold," says Edo Paz, MD, a cardiologist and Vice President of Medical at K Health. To increase cardiac output during that first mile, the heart rate and stroke volume both increase quickly to better meet the new (and greater) oxygen demands.
Early in a run, you'll feel your heart rush to meet the body's needs.
As your heart pumps more blood (faster, stronger!) your blood vessels deliver more oxygen to your muscles. At the same time, blood flow to other organs, such as those in your gastrointestinal tract, decreases. As a result, the workout feels most challenging at first, before these organs have fully caught up. "Your lungs exchange more oxygen by increasing the rate of breathing, and exchanging more gas with each breath," says Dr. Paz. "In other words, your heart, lungs, blood vessels, and muscles work harder to support your exercise."
This is where cardiac output and stroke volume come in again. "The first mile is harder because of the mismatch," Dr. Raza says. "The heart rate and stroke volume haven't caught up to the cardiac output required by your muscles during that first mile."
You should feel better as you continue running
A mile is an abstract thought—it’s just a distance. You can consider that first mile to be the toughest, rather than thinking in terms of how many minutes until you’ve adjusted. "The heart 'catches up' pretty quickly, but how quickly depends on your baseline level of conditioning," Dr. Raza says. In other words, a regular runner will acclimate sooner than someone just starting out. Most people, though, should feel adjusted by halfway into the first mile. Phew.
Which warm-up ideas make the first mile easier?
A few warm-up tricks can make that first mile less grueling. "Make it easier by hydrating yourself well, which helps ensure a good stroke volume," says Dr. Raza, who recommends having a glass of water 30 minutes before you exercise.
You can also increase your heart rate ahead of time. Try raising your resting heart rate prior to that first mile through a warm-up such as stretching, flexing, or jogging in place.
A few warm-up tricks can make that first mile less grueling.
A warm-up doesn’t need to be longer than five minutes, but your goal is to get your heart rate close to 100, says Dr. Raza. Then you can hit that first mile strong. You can use an Apple Watch or any other fitness device to track your heart rate.
Lastly, be consistent and keep running regularly to improve your cardiovascular health. "Exercising consistently will help even more," says Dr. Paz. "As your body adapts over time, [it] is better able to meet the metabolic requirements of exercise."
Need some serious motivation? Think about the long-term benefits. “Doing regular exercise has also been shown to reduce the risk of all-cause mortality for most individuals, and may be beneficial in preventing cardiac issues, diabetes, obesity, and even some cancers,” Dr. Paz adds. There are other perks, too, such as improvements in mood. So, it’s a win-win all around. Just keep pushing!
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