So you want to do a gait analysis? Part 1
From casual observation to a computer driven model, before you can know what may be wrong with a gait, you need to know what is right. Knowing what is happening at each phase of the gait cycle is essential. This series will explore just that and provide you with an overview of what should be happening.
Let’s begin with a typical walking gait cycle. There are two phases: stance and swing. It comprises approximately 62 percent of the gait cycle.1 Jaqueline Perry2,3 uses this descriptive classification to describe stance phase:
- Initial contact: When the foot first touches the floor.
- Loading response: Weight bearing on the loaded extremity from initial contact and continues until the opposite foot is lifted for swing.
- Midstance: The first half of single-limb support, beginning when the opposite foot is lifted until weight is over the forefoot.
- Terminal stance: Begins with heel rise and continues until the opposite foot strikes the ground.
- Pre-swing: When initial contact of the opposite extremity begins and toe-off ends.
Swing phase is divided into 3 parts
- initial (early) swing: when the extremity is being accelerated just after pre swing; this action initiates supination in the opposite, stance phase leg
- mid swing: largely passive
- terminal (late) swing: when the extremity is being actively decelerated, largely through eccentric action of the muscles
How about we start with initial contact, commonly called “heel strike”.
Heel strike, a traumatic deceleration event with the transfer of weight from one extremity to the other, creates shock, which must be attenuated. This is accomplished by four distinct mechanisms:
- Ankle plantar flexion: At heel strike, followed by eccentric contraction of the pretibial muscles to decelerate foot fall.
- Subtalar pronation: As the coefficient of friction between the calcaneus and the ground increases, the talus slides anterior on the calcaneus while plantar flexing, adducting and everting. This motion causes concomitant internal rotation of the lower leg. Both these actions cause a time delay, allowing force to be absorbed over a longer period of time.
- Knee flexion: This is a reaction to the heel rocker, forward motion of the tibia, and passive tension in the posterior compartment. It is slowed by eccentric contraction of the quadriceps, with the abdominals acting as a primary anchor.
- Contralateral pelvic drop: This is decelerated by the ipsilateral hip abductors (primarily gluteus medius) and lateral chain, as defined by Myers.4 It occurs as weight is suddenly dropped on the contralateral limb.
What is happening biomechanically? Lets look at the major anatomical areas:
the foot should be supinated at this point, as it should be from preswing. It is dorsiflexed, inverted and adducted.
The ankle should be neutral or slightly dorsiflexed
the knee is usually neutral or slightly flexed and the thigh and leg externally rotated approximately 4-6 degrees
The heel strike hip should be flexed 20-30° and the lumbar spine neutral; the opposite hip should be extended 20-30° and equal to the amount of flexion present in the initial contact hip.
Today, look for aberrances at initial contact in your clients and patients. Knowing what is normal is the 1st step toward knowing what isn’t. Got it?
Next post in this series (not necessarily our next post) will cover loading response.
Ivo and Shawn
- Root MC, Orion WP, Weed JH. Normal and Abnormal Function of the Foot. Los Angeles: Clinical Biomechanics, 1977.
- Perry J. Gait Analysis: Normal and Pathological Function. Thorofare, NJ: Slack 1992.
- The Pathokinesiology Service and the Physical Therapy Department. Observational Gait Analysis. Rancho Los Amigos National Rehabilitation Center, Downey, CA, 2001.
- Myers TW. Anatomy Trains: Myofascial Meridians for Manual and Movement Therapists. Elsevier: 2001.