INJURIES: True to Form

Phases of Flight

The running gait cycle is broken down into: the pushoff, the swing or flight phase and the stance or support phase, which is sometimes broken down into early, mid and late stance or support phase.

The Pushoff:

While standing, the gravity line passes behind the ears down through the front of the shoulder, down through the front of the hip joint then knees, finishing just in front of the ankle joint. When you start the forward lean to run, the gravity line should remain relatively straight. In order to do this you need flexible ankles and good core strength. As your centre of gravity starts moving forward and you push off with your support foot, your knee should remain slightly bent. One study found that the most economical runners had a forward lean of 5.9 degrees, which was greater than the less economical runners.

Swing Phase:

The swing phase starts when both feet are off the ground. This is actually a time when you get some rest. The longer you’re in the swing phase the more rest you get, but there is also an optimum time, too, for airtime, based on your overall speed so that you maintain your forward momentum and minimize the ground resistance when your lead foot hits the pavement.

Stance Phase:

Early

The stance phase begins the moment the lead foot hits the ground. As far as biomechanical efficiency is concerned, this is a critical point in the running cycle. If your foot contact is close to or under your centre of gravity, your momentum along with the gravitational force will continue to pull you forward like a line of dominos. If your foot contacts the ground too far forward, your foot will tend to break the forward motion and you’ll need more energy to pull your centre of gravity back over your support foot.

Mid

As the gravity line of the body passes directly over the ankle, which is considered mid-stance, your foot pronates (rolls inward), allowing the arch to act as a shock absorber and adapt to the terrain. While the foot is pronating, the lower leg internally rotates, pulling the knee and the upper leg with it. If there is too much pronation, the structures in the leg, pelvis and lower back are subject to stress and strain. Injuries are most likely to occur during this phase of the gait cycle.

Late

As the leg gets ready to shift into the pushoff phase, the knee and ankle are flexed and the centre of gravity is at its lowest point. If there’s too much flexion in these areas, the knee, quadriceps, Achilles and calf muscles will all be stressed. Over-flexion also tends to make the pushoff angle too vertical, wasting precious energy.

Dr. John De Finney is a Markham, Ont. chiropractor and one of the founding members of the College of Chiropractic Sports Sciences. He has won national titles as an age-group runner.