Gait Cycle - Foot & Ankle

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
    
    gluteus medius and calf muscles undergo eccentric 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
- Figure showing muscle activity through different phases of gait cycle