As people hop into a new year of workouts, one common issue regularly crops up: dealing with old injuries and ongoing tweaks – pain in backs, knees, shoulders, etc. The easy solution is to just ‘play it safe,’ completely avoiding any even slightly painful movements. But, in the long run, that’s an ineffective approach.

Pain is complex – it’s not just a physical sensation, but the mental interpretation of that sensation. In other words, while the muscle you pull in your back may be the initial negative stimulus, it’s your brain that turns the stimulus into the experience of pain. You’ve probably experienced that directly – perhaps you cut yourself accidentally, but didn’t feel pain until you looked down and realized what you’d done.

In the days and even weeks after an injury, the physical stimulus and mental response are usually pretty tightly coupled. But, often, even after the physical damage heals, the pain response persists. It’s kind of like the ‘check engine’ light in your car – once it’s on, regardless of any fixes to the engine itself, the light will only turn off if you reset it directly.

And, in the case of muscle or joint pain, the best way to ‘reset’ is through movement. Repeatedly move safely through a range of motion that previously caused damage, and your brain will update its map of the situation in the sensory cortex, no longer signaling the movement as painful.

But for that reset to work, the key part is moving safely. Moving through injury too much or too soon can actually make things work.

So, how can you tell if you’re helping or hurting? If the feeling in your shoulder as you press, or in your knee as you lunge, is a sign that you should pull back, or just something you should live with temporarily as you keep going and rebuild pain-free health?

When I’m working with athletes, I have four rules – four questions you can ask about the nature of the pain caused by any specific exercise or movement.

1. On a scale of 1 to 10, is the pain a 4 or less?

2. Does the pain remain the same or improve as you repeat the movement, rather than getting worse rep by rep?

3. Does the pain stop once you stop doing the movement?

4. Does the joint or muscle feel better or about the same 6-24 hours after the movement as it did before?

If you can answer yes to all four, you’re good to go.

As the physical therapists say, ‘motion is lotion.’ If you have musculoskeletal pain, get moving. Just follow the four rules along the way, and you’ll be back to feeling excellent sooner than you think.

Despite fifteen years in the fitness industry, I’m pretty sure I look more like a gym’s accountant than a trainer or coach at one. Even the most flattering descriptions I’ve ever gotten in the press — “a lean, athletic build developed from years of working out regularly—picture Bruce Lee, not Arnold Schwarzenegger” — make clear I’m not exactly intimidatingly large. So perhaps it goes without saying that I’ve never before taken steroids.

It was from that place of ignorance that I was so surprised by some recent anabolic steroid usage facts:

Surveys indicate that between 1-3 million Americans use steroids. For context, there are about 60 million people with gym memberships in the country, and 2/3 of those people never go to the gym, taking the number of actual gymgoers down to about 20 million. If we assume that the people using steroids are actually working out, that means that between 1 in 20 and 1 in 6 people you see in the gym are on steroids.

Especially given that survey response data tends to underestimate illegal activity —which people are understandably reluctant to report — it seems waaaaay more people are juicing than I would have assumed.

Years ago, when I lived in Manhattan’s Hell’s Kitchen, I was a member at Mid-City Gym, an institution in the bodybuilding world. (If you’ve ever watched the classic documentary Pumping Iron – and I highly recommend it, regardless of your interest in fitness — all of the New York scenes were filmed there.) Though I was mostly doing weird functional fitness stuff in the corner, rather than leg pressing and bicep curling with the gigantic regulars, I was still offered steroids by some random dude in the locker room at least once a week. Still, in my CrossFit NYC days, and now at Equinox, I tend to assume almost nobody is on drugs. Yet based on the numbers, it looks like I’ve been naive.

Fortunately, given my own fitness goals, I don’t think I’m much missing out. I’m not looking to get huge, nor do I have any pro sports pennants I’m gunning for. Though, as one colleague here pointed out, if I do decide to do a cycle one day, I’m in the clear. At my advancing age, I can just call it “testosterone replacement therapy,” and pick up prescriptions legally from any number of overpriced and slightly sketchy anti-aging medical practices here in NYC.

As I said, I don’t have any immediate plans to that end. But if, years from now, I’m the only guy in the nursing home with 18-inch biceps and a six pack: you heard it here first.