I am a distance runner. My time at the gym or in the streets before sitting down at my job, in the world defined by three and a half shoulder-height walls of my beige cubicle, is sacrosanct to me. Therefore, when I wake up more tired than usual at 4:30 a.m., or if I drag through free weight reps or the first few miles, I usually choose to power through it. And most of the time, my body eventually decides to join the party with a little energy.

But not this morning. This morning, at barely 7:30 a.m., I stopped exercising, and hit the showers.

Our bodies send out danger signals for a variety of reasons, and the plain truth is that most of the time, it's mental fatigue rather than overexertion that halts our exercise efforts. Learning to overcome mental barriers (and sometimes physical ones like excess body fat or a sedentary lifestyle) is just part of the deal if you're an athlete, or aim to get fit. But sometimes, like mine did this morning, your body sends certain signals that you shouldn't ignore.

Heading Under the Weather

For gym rats and anybody who exercises more than two times a week, a change in your performance on the track or at the gym will be among the first signs that you're getting sick. Here are some preliminary signs that you're about to hit some turbulence:

1. Warming up doesn't give you that warm, fuzzy feeling. Warming up is probably the most crucial period of cardiovascular exercise and is critical for injury prevention and sustained performance. It's also supposed to be easy.

But if your power-walk fades into a power-shuffle, or your limbs feel leaden or sluggish instead of limbering up, take note: Your body might be infected with something other than pre-exercise enthusiasm.

2. You sweat excessively. Your body generally develops fevers to fight infections, and if you run a fever and exercise, the results could be uncomfortable, and possibly hazardous to your health. If you're sweating like you've run a marathon and you're only on mile three, it might be time to slow down and re-evaluate your condition (and remember to re-hydrate!).

3. Your heart is pounding. One of the foundational scriptures of exercise science is that elevating your heart rate is critical to the pursuit of fitness. If your heart is pounding in rhythm to how hard you're running, how much weight you're lifting, or how vigorously you're kickboxing or Spinning, fear not: Your heart rate is probably normal. However, if you get dizzy, or you take a break and your heart seems to be pounding out of proportion to your effort, pay attention. Your body is telling you to cease and desist, as the added stress of exercise may lower your body's ability to fight an infection that you may not otherwise notice.

Cruising for a Bruising

One other way our bodies quietly beg us to knock it off with that exercise stuff is by direct pain. Delayed Onset Muscle Soreness (DOMS) is common to any exercise program, especially in the beginning stages, but there's a bright line between the microscopic tears in muscle that constitute DOMS and a muscle strain or sprain. Runners and other endurance athletes are especially prone to exercising through any pain, but here's how to tell between DOMS and a real injury:

1. You can exercise through a lot, but this particular pain is distracting. If you find yourself losing form or limping during exercise because of pain, stop the movement or move on to some exercise that leaves the painful area alone.

2. It's growing. A minute ago, your knee was the usual size, and when you look down 10 minutes later, it's grown to the size of a navel orange. Stop exercising. If swelling persists even after ice and rest, see a sports physician.

3. You find your other muscles compensating for the painful spot. Are you stiffening your shoulders because one elbow has grown painful to bend? Stop exercising or move on to a different part of the body. When one part of your body compensates for the injury of another part, you risk further and more serious damage.

If you are especially sore after a workout or you think you are injured, see a doctor who specializes in sports medicine. Also, the RICE method (Rest, Ice, Compression, Elevation) can help you with minor injuries. Check out this helpful Runner's World primer on applying RICE to any sports injury.

If you entertain thoughts of quitting during exercise sometimes (OK, a lot of the time) that's probably normal. But be careful not to ignore the more serious signs of distress that can occasionally come from illness or injury. Take some time off.

You'll thank me later.

This post was included in the latest edition of The Homesteading Carnival.