Running generally makes up the majority of your movement in Parkour. When getting from one place to another, you use various movements (vaulting, climbing, rolling, etc), but in between all of that you are running.
Considering this, it is a good idea to consider the way you run and attempt to make it as effective as possible, as bad technique can cause long lasting damage.
Most importantly when running, you should be touching the ground on the balls of your feet or mid-foot (between your toes and the arch of your foot). This means no heel striking!
If you are intent on heel striking and believe it’s the ‘correct’ or ‘natural’ way to run, try this experiment:
Take off your shoes, and run barefoot for a little while. 50 metres will do.
It is highly unlikely that by the end of it, you are touching your heel to the ground first. It hurts. Your body absorbs the impact by passing the shock of landing through the ball of the foot, the arch, then the ankle and muscles of the leg. When landing on your heel, your body can’t do this, and the shock gets taken more in the joints than the muscles. Over time this will likely lead to injury.
It is important to develop the ability to strike forefoot first correctly. When running with a forefoot striking technique it is important not to land with the heel inches above the ground.
When the foot lands on the ball of the foot you do not want the heel to be any more than an inch from the ground, with the foot rolling from ball to heel, so the heel contacts the ground when you are running over longer distances.
Be aware of the foot rolling from side to side when running, you should aim to land with the foot square to the ground, avoid landing on the inside or outside of the foot and rolling.When running try and be as silent as possible, noise is a good indication that you are doing damage to the joints. By focusing on keeping out landings silent you use your muscles more effectively to absorb impact, rather than using the bone structure, which damages joints
Use of the arms – The rate and power at which you swing your arms has a direct relation to the power from your legs and the overall speed at which you run. The arms are not simply there for balance, but to help propel you forward.
Unless you have professional coaching, running is much like any other skill for Parkour. It involves a lot of experimentation, trial and error on your part. Play with it; find ways to run as fast as possible (sprinting), and also how to comfortably run for long periods without becoming out of breath, and without using too much energy.