4.2 Gait

Big ideas

• A gait cycle (one stride) runs from one foot’s initial contact to that same foot’s next contact; a step is from one foot’s contact to the other’s. At normal walking speed, stance ≈ 60% and swing ≈ 40% of the cycle, with two double-support periods of about 10% each.
• Stance phases (Rancho Los Amigos): initial contact, loading response, midstance, terminal stance and preswing. Swing: initial swing, midswing and terminal swing. Older terms: heel strike, foot flat, midstance, heel off and toe off.
• Muscles: in loading response, tibialis anterior lowers the foot and the quadriceps control knee flexion (both eccentric), gluteus maximus and the hamstrings extend the hip and gluteus medius steadies the pelvis. From midstance, the calf controls the tibia moving forward, then pushes off. In swing, the hip flexors advance the leg, the dorsiflexors clear the toes and the hamstrings slow the leg in terminal swing.
• Typical walking ranges: the knee flexes about 15–20° in loading response and about 60° in swing; the ankle reaches about 10° dorsiflexion in stance and 15–20° plantarflexion at toe-off; the hip moves from about 30° flexion at contact to about 10° extension in terminal stance.
• Walking speed = step length × cadence. Running adds a flight phase and loses double support, and stance falls below half the cycle. Deviations: Trendelenburg gait (weak gluteus medius), foot slap or steppage gait (weak dorsiflexors), antalgic gait (short stance on a painful leg), backward trunk lean (weak gluteus maximus) and circumduction or vaulting (a functionally long leg).

Key formulas

Worked example

Common mistakes

• Mixing a step (one foot to the other) with a stride (the same foot twice, one full cycle).
• Giving running a double-support phase. It has a flight phase instead.
• Saying tibialis anterior works concentrically at heel contact. It lowers the foot eccentrically.