Gait Cycle

Overview

One gait cycle is measured from heel-strike to heel-strike
- consists of
  - stance phase
    - period of time that the foot is on the ground
    - ~60% of one gait cycle is spent in stance
    - during stance, the leg accepts body weight and provides single limb support
  - swing phase
    - period of time that the foot is off the ground moving forward
    - ~40% of one gait cycle is spent in swing
    - the limb advances
Stride
- is the distance between consecutive inital contacts of the same foot with the ground
Step
- is the distance between initial contacts of the alternating feet

Stance Phase

Initial contact (heel strike)
- definition
  - occurs when foot contacts the ground
- muscular contractions
  - hip extensors contract to stabilize the hip
  - quadriceps contract eccentrically
  - tibialis anterior contracts eccentrically
Loading response (initial double limb support)
- marks the beginning of the initial double limb stance
- definition
  - occurs after initial contact until elevation of opposite limb
  - bodyweight is transferred on to the supporting limb
- muscular contractions
  - ankle dorsiflexors (tibialis anterior) contract eccentrically to control plantar flexion moment
  - quads contract to stabilize knee and counteract the flexion moment (about the knee)
Mid-stance (single limb support)
- initial period of single leg support
- definition
  - from elevation of opposite limb until both ankles are aligned in coronal plane
- muscular contractions
  - hip extensors and quads undergo concentric contraction
Terminal stance (single limb support)
- definition
  - begins when the supporting heel rises from the ground and continues until the opposite heel touches the ground
- muscular contractions
  - toe flexors and tibialis posterior contract and are the most active during this phase
Pre-swing (second double limb support)
- is the start of the second double limb stance in the gait cycle
- definition
  - from initial contact of opposite limb to just prior to elevation of ipsilateral limb
- muscular contractions
  - hip flexors contract to propel advancing limb

Swing Phase

Initial swing (toe off)
- start of single limb support for opposite limb
- definition
  - from elevation of limb to point of maximal knee flexion
- muscular contractions
  - hip flexors concentrically contract to advance the swinging leg
Mid-swing (foot clearance)
- definition
  - following knee flexion to point where tibia is vertical
- muscular contractions
  - ankle dorsiflexors contract to ensure foot clearance
Terminal swing (tibia vertical)
- definition
  - from point where tibia is vertical to just prior to initial contact
- muscular contractions
  - hamstring muscles decelerate forward motion of thigh

Variables Affected During Gait Cycle

Pelvic rotation
- pelvis rotates 4 degrees medially (anteriorly) on swing side
  - lengthens the limb as it prepares to accept weight
Pelvic tilt
- pelvis drops 4 degrees on swing side
  - lowers COG at midstance
Knee flexion in stance
- early knee flexion (15 degrees) at heel strike
  - lowers COG, decreasing energy expenditure
  - also absorbs shock of heel strike
Foot mechanisms
- ankle plantar flexion at heel strike and first part of stance
Knee mechanisms
- at midstance, the knee extends as the ankle plantar flexes and foot supinates
- restores leg to original length
- reduces fall of pelvis at opposite heel strike
Lateral displacement of pelvis
- pelvis shifts over stance limb
  - COG must lie over base of support (stance limb)
Center of gravity (COG)
- in standing position is 5cm anterior to S2 vertebral body
- vertical displacement
  - during gait cycle COG displaces vertically in a rhythmic pattern
    - the highest point is during midstance phase
    - lowest point occurs at the time of double limb support
- horizontal displacement
  - COG displaces 5cm horizontally during adult male step

Muscle Activity