What’s the absolute hardest part of your workout?

My mom says (HERE) that for her it’s putting on her tennis shoes.  “Once you get your tennis shoes on,” she says, “you know you’re going.  ‘Okay, this is what I’m fixin’ to do,’ you say to yourself.”

For me it’s the first few minutes of endurance activity that are the hardest. I’m sucking wind, my legs are burning, my arms are fatigued. Good grief, I’m thinking, what’s wrong with me!

Actually, though, lots of people experience that heavy sensation of exhaustion at the start of a workout. Even elite athletes. Why? Because there’s lag time between when you start a high-intensity, full-body endurance exercise and when your body starts delivering the fuel your working muscles need.

At the start of your run (or swim, bike, etc.) your body can deliver about two to three minutes of fuel to your muscles through its anaerobic energy system. After that two to three minutes, your body has to switch to an aerobic system, which uses oxygen to convert stored glycogen, fat and lactic acid into energy.

If you’re pushing pretty hard from the get-go, switching from anaerobic to aerobic can create an oxygen deficit. That’s when the heavy breathing, burning sensation and muscle discomfort hits.

Once your body jumpstarts its aerobic energy pathway, that’s when you start settling down into steady breathing and heart rate.

This phenomenon is why, when I was seven playing freeze-tag on the playground, the start of the game was always the hardest. That’s when I’d sometimes slow down, get tagged, clutch my knees and start panting.

Nowadays I don’t have a fast friend who comes to unfreeze me and get me moving again. I just have to push past that challenging phase. But it helps to know it’s a phase.

A few weeks ago I was running with my youngest son Jacob, who’s decided to compete in his first marathon next year.  When that initial burning and fatigue hit both of us, I shared with him my “mind over matter” visualization of what’s going on physically:

Body:  “Whoa, wait a minute, I was doing just fine a second ago. Cut it out! I don’t wanna do this!”

Mind:  “I know you don’t. But you’re gonna have to get used to it.”

Body:  “I said, I don’t wanna do this!”

Mind:  “You’ll get used to it.”

Body: “… … Hmm, okay, I guess if I have to.”

If those first five or so minutes feel too insurmountable, or you’re new to exercise, you can lessen this uncomfortable phase by gradually warming up to your workout pace, which will also help with injury prevention and help the rest of your workout feel more enjoyable.

The more you exercise, the faster and easier your body will transition from anaerobic to aerobic energy delivery because:

  • Your heart muscles will grow stronger, which means they’re able to pump more blood with each contraction.
  • Your lungs will grow more efficient, which means your breathing reserve increases.
  • Your blood vessels will grow wider and more elastic, which means oxygen transfer to muscles increases.

Next time you feel that initial discomfort, remember you’re in good company, visualize what’s happening in your body, breathe, and keep going.


Jenny Pruitt Cleveland is a Content Creator in Nashville, Tenn. She swims, bikes, and runs a lot. In former lives she’s been a middle school teacher, magazine reporter and editor, cycling tour guide, and underwater photographer.