In recent years, Denver has established itself as one of the fittest cities in the United States. In fact, according to the 2015 American Fitness Index, the Mile High City checks in as the country’s sixth fittest by excelling, especially, in outdoor activities. But whether you take part in early-morning hikes or pump iron after work at one of the many Denver gyms, one thing is certain: warming up is in your best interest.

That’s because the consequences of not stretching have the potential to sideline you for days or even weeks with a pulled muscle—also called a distraction rupture or strain—which happens when muscle fibers are stretched beyond their limit. Doctors divide muscle strains into three categories:

• First-degree strains are generally what athletes talk about when they say they’ve pulled a muscle. It’s a very slight tear damaging less than 5% of the muscle, causing discomfort and swelling but little loss of function.
  
• Second-degree strains produce a much more noticeable tear and pain when trying to contract the muscle.
  
• Third-degree strains, or ruptures, are complete tears across the muscle’s width that take the muscle completely out of commission and may even require surgery. Many people confuse strains with sprains, though a sprain can only refer to damage done to ligaments, not muscle.
  

Muscles most often get pulled because they’re stretched too quickly, whether by a burst of speed on the track or a too-sudden lift of the family mastiff. Warming up creates more flexibility by literally raising the tissue’s temperature, optimally by 1–3 degrees. That’s why dynamic, cardio-based warm-ups are preferred.

So if you’re at the Denver Athletic Club, take a few laps in the 25-meter indoor pool before engaging in more strenuous exercise. If you’re at the Cherry Creek Athletic Club, get your heart pumping on one of more than 100 pieces of cardio equipment. Whatever the case, just make sure you’re sufficiently stretched out before diving into your workout and doing your part to push Denver to the top of the American Fitness Index.