When the weather finally warms, spring is a time when many people think of dusting off their sneakers and taking up running.

And why not? Running is pretty simple. Not much to master, really; just put one foot in front of the other and you're off and running.

But while springtime is a great time to hit your fitness stride, it's also a time when many winter couch potatoes-turned-wannabe marathoners get hurt -- or just plain sore. Just ask Toronto-based sports medicine physician Dr. Grant Lum. He's seen hundreds of running injuries at his clinic, Athletic Edge Sports Medicine.

"We see a lot of sprains and strains in the areas of their bodies that are not ready for the rigourous activity that they're plunging into," he tells CTV.ca. "So that is usually knee pain, back pain and foot pain. Those are probably the three most common injuries."

The classic mistake novice runners make is trying to run too far, too hard or too often, in too short a period of time.

The injuries that can result have fancy names -- IT band syndrome, medial tibial syndrome or patella-femoral syndrome -- but they all come from forcing muscles and tendons to do work they're not used to doing. That causes muscle tightening and joint friction, which can then develop into tendonitis or bursitis.

The worst of these overuse injuries is a stress fracture. That's a tiny crack typically in the foot and shin bones of runners, which often cannot even be seen on x-ray. But the pain they cause is pretty hard to miss.

For most injuries, the treatment is to simply slow down. "Frequency, intensity and duration -- If you cut down on one of them, that may be enough to settle your problem," says Lum. But with a stress fracture, "the only solution would be to keep the patient from running for six weeks." So long, marathon.

Dr. Douglas Stoddard, the medical director, of the Sports & Exercise Medicine Institute (SEMI) in Toronto, says runners should always pay attention to any injury that doesn't get better in a short period of time.

"If you experience a new ache or pain that hasn't settled down in 10 days of modifying activity, or with more attention to stretching or icing or with over-the-counter anti-inflammatory medicines, then it's time to get it checked out," he tells CTV.

To help new runners avoid injury, Lum suggests they begin with a walk/run routine, one that might look like this:

After Week 5, you could increase your running and reduce the number of cycles so that your workout stays at around 30 to 40 minutes.

The walking element of the routine is crucial. In fact, Lum thinks all runners should incorporate some walking in their routine, as a way to incorporate stretching.

"Stretching cold is never a good idea," he says. "So the whole idea of putting on your shoes, standing on your porch and stretching and then taking off on a run - that actually increases your risk of injury. But a lot of people still do that.

"What they should do is start by walking and then walking briskly with long strides to get blood into your muscles and heat them up a little bit. The medical literature isn't clear on why this works, but it seems to decrease injuries."

Changing terrain

Even those runners who have kept up their runs over the winter using the treadmill are still at risk of injury in the spring. That's because running outdoors is quite different from running indoors. For one thing, there is the aspect of the cold.

"Cold, wet spring days can lead to reduced muscle flexibility, as compared to the controlled climate of a gym or your basement where your treadmill might be," he says. So again, he stresses the importance of limbering up thoroughly.

Springtime is also the season for slips and falls from indoor runners who misjudge the terrain of the great outdoors.

Last summer in Toronto was particularly bad, Lum says. The soggy start to the summer made for muddy trails and wet grass, where slips can happen easily. Then as the summer dried out, so did all that mud. The result was bumpy fields and trails -- perfect for tripping up and spraining ankles.

The best running surfaces are trails designed for runners and walkers. They are usually properly cleared and well-lit and are softer than asphalt roads. The worst surface of all, ironically, is a concrete sidewalk. As all runners eventually learn, it's simply too hard to absorb the impact of pounding feet.

"The harder the surface, the more force from landing is transmitted up into your feet and legs, even all the way up to your back, potentially increasing injuries like stress fractures or shin splints," says Lum.

The shoes you choose

While running is pretty cheap compared to other sports, there is one essential piece of equipment required: the proper running shoe.

It's a good idea to have your shoes fitted at a store that specializes in running shoes to determine what kind of feet you have. Lum explains that our feet roll in towards the instep while running, in a movement called pronation. Flatter feet tend to over-pronate, putting additional stress on the inner half of the ankles and knees, and also tilting the pelvis and increasing injuries in the back. They need stability shoes to give some control of over-pronation.

Those who have high arches supinate, or under-pronate, and may need cushioning shoes. Custom foot orthotics can also help to reduce pronation problems.

Finally, it's important to replace running shoes every 800 kilometres or so, since old shoes lose shock absorption, cushioning and stability over time. Heavier runner should consider replacing them more often, as should those who run on rough terrain.