As with any workout regimen, running puts you at risk for muscle injury. When you do sports or rigorous physical exercise, it's important to take preventive measures to ensure an injury-free session. Even more so than choosing the right shoes and equipment for running, it's advisable to do a warm up before you run. To make sure that your muscles are prepped for the long workout ahead, stretching should be included in your warm ups. There are two types of stretching exercises: static and dynamic. Static stretches are good for loosening up your muscles for the workout ahead after you warmed them up already. You should be careful not to overstretch, or go beyond the point where it's comfortable. Dynamic stretching requires you to move about more, and is a great way to get your heart beating and your blood flowing while you stretch. This allows you to break into a sweat and get more pumped up for your running session. Here are a few key stretching exercises to help avoid muscle injury for runners.1. Calf Stretch
This is a type of static stretching that you can do standing up or against the wall. Put one leg forward, and stretch your other leg behind you. Make sure that the leg behind you is stretched straight. You can push against the wall to stretch it further. Count to 10, and do the same with the other leg. You can repeat this several times.2. The Flamingo
This is another kind of static stretching that works on your quadriceps. You can do this standing or leaning against a wall. You raise your right leg behind you at the knee, and grab your foot with your right hand. Now you pull back slowly while you feel your quadriceps stretch. Repeat this several times for each leg.3. Heel Drops
This static stretching exercise is key to preventing Achilles tendinitis, or injury to your heel tendons. Stand on a curb with the frontal part of your feet. Now you drop your heels slowly towards the ground and count to 10 and lift them back up. Do this a few times.4. Walking Lunges
This is a type of dynamic stretching that works your calves, hamstrings and knees. Take one giant step forward, as in a lunge, and keep your back leg straight. Then do the same with another leg. Do this until you've taken about 20 lunges or giant steps. Be sure to do this slowly, especially if you're a beginner or your muscles are still cold.5. Leg Pendulum
This is a dynamic stretching exercise that's good for your hips. You stand on one leg, and lift the other leg to the side. Now you swing that leg in front of you like a pendulum, and swing it back. Do this 10 times for each leg.6. Hamstring Stretch
Here's another important dynamic exercise that's targeted to your hamstrings. You lie flat on your back, and wrap a rolled-up towel or rubber tubing around your right foot. Then you pull at the towel or tubing as you raise your leg, all the while keeping your knee straight, then bring it back down to the ground. Repeat this 10 times for each leg.