A professional trainer reveals 5 facts about getting into shape that may surprise you

Spring seems to have come early in much of the world, and that's motivating many people to go outside and get back in shape.

Training for a competition to get fit — a triathlon, 10K, mud-and-obstacle run, or something else fun — is an excellent way to stay motivated.

But if it's your first time preparing for that kind of physical challenge, you're likely to learn a few unexpected things along the way.

Business Insider spoke with Dan Arnett, a professional triathlon coach, to see what surprises people encounter while getting into shape.

Here are his top five: