With more than half a million runners finishing a marathon in 2015 according to Running USA, the 26.2-mile distance is becoming increasing popular. But how do you run it safely with the greatest chance of success?

The truth is that most runners prepare poorly (and the annual injury rate hovers around 50-75% - higher than professional football). Because of the sheer distance of the marathon, the race is daunting.

Racing a marathon results in a lot more than simply sore muscles:

Muscle strength is reduced (inflammation and cell damage can persist for two weeks)

The immune system is suppressed (which is why marathoners often get sick the week after the race)

Coordination and "muscle memory" are compromised, making it more likely to get injured in the weeks after the marathon

Even the heart may be damaged (it's more common in beginner runners but remember that the heart is a muscle and will heal just like your leg muscles!)

Most of these issues are far less serious or non-existent for shorter races, making adequate preparation for the marathon critical.

Follow these three guidelines and you'll run your best marathon with the least risk of injury.

#1 Give Yourself Time to Prepare

Too many runners rush into marathon training without first ensuring they're even ready to start!

First, allow yourself at least 16 weeks to train. It takes time for the body to adapt to the increasing mileage, longer workouts, and long runs that help you complete 26.2 miles. Trust that adaptation process and schedule about four months of specific training before the race.

Next, make sure your long run is at an appropriate starting point. If the longest run you've ever done is 5 miles, then you simply won't be ready to run a marathon in 16 weeks.

Instead, aim to comfortably be able to run a 10-12mi long run at the start of your marathon training program. This allows yourself a safe, gradual progression of increasingly longer long runs.

#2 Prioritize Injury Prevention

Most runners get hurt because they succumb to the "three too's" - too much mileage, too soon before they're ready, at too fast a pace.

But if you give yourself enough time, you'll avoid most of that problem. The next step is to bake injury prevention directly into your training plan to maximize your chance of staying healthy during the high mileage training weeks.

A helpful strategy is to "sandwich" each run between a dynamic warm-up and a runner-specific strength routine.

A series of warm-up exercises help the body prepare for a run by elevating heart rate, warming up the muscles, lubricating joints, "waking up" the nervous system, and opening capillary beds in the extremeties like your feet.

A runner-specific strength routine doesn't have to take long. Just 10-15 minutes are all you need to build strength, particularly in the hips and glutes which are particularly important for runners.

Finally, make sure to run your easy runs at a truly easy pace. You won't get much fitness out of running a short run really fast - and instead, you'll only compromise recovery.

Instead, make your easy days really easy by making the shortest mileage days of the week your slowest. By polarizing your training this way, you'll maximize recovery on easy days.

#3 Run Appropriate Workouts

SO many runners run workouts that don't help their marathon goals (and even set their fitness back)!

Rather than running too many workouts geared toward increasing VO2 Max (like repeat 400's on the track at 5k pace or a similarly intense session), it's best to focus on aerobic workouts that will increase your endurance.

There are three that work particularly well:

Tempo runs of 2-6 miles in length done at a "comfortably hard" effort or roughly 85-90% of maximum heart rate Goal marathon pace runs of 3-10 miles (advanced strategy: run marathon pace at the end of long runs for a race-specific stimulus) Progression runs where you gradually speed up over the final 2-4 miles so the last 3-5 minutes is at your tempo pace.

Since the marathon is over 99% aerobic, that's what to focus on during training. You'll get the most out of your training, the race itself, and have the least risk of injury.

By planning your season properly and focusing on the right workouts and strategies, you'll have a very successful marathon.

And successful marathons are usually fast marathons!