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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
  • Figure showing muscle activity through different phases of gait cycle  
 

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