Evolution of Upright Gait

Study Notes

Upright gait evolved many times, suggesting a strong selective advantage
Advantages of bipedalism:
- Energetically efficient
- Improved vision
- Display and warning abilities
- Allows tool use, carrying, hunting, and gathering
- Improved thermoregulation
Disadvantages of bipedalism:
- Less stable
- Makes one more visible to predators
- Exposes vulnerable body parts
- Slower than quadrupedal running (over short distances)
- Single limb injuries are more disabling
- Energetically expensive blood circulation
- Increased loading on spine, pelvis, hips, knees, and ankles
- Makes climbing more difficult
Anatomical adaptations to bipedal locomotion:
- Change in position of foramen magnum: Shifts from the back of the skull in early hominoids to directly under the vertex in humans
- Change in spinal curvature: Development of additional lumbar curvature to allow pelvic alignment
- Change in pelvic shape: Adaptations for weight-bearing and muscle attachment
- Change in leg structure: Increased femur angle for foot placement under the pelvis
- Change in mass distribution: Reduced mass above the waist for balance
- Change in foot structure: Reduced size of primary toe, elimination of opposable digits, and development of raised arches

Phases of the gait cycle:
- Stance phase (60-65%): Foot is on the ground
- Swing phase (35-40%): Foot is off the ground
- Double support phase (22%): Both feet are in contact with the ground
Distance and temporal variables for quantifying gait:
- Stride length: Distance between two successive events by the same lower limb
- Step length: Distance between two successive points of contact of opposite extremities
- Stride duration: Time to complete one stride
- Step duration: Time to complete one step
- Cadence: Steps per minute
- Speed: Cadence x step length, or stride length x stride length
- Width of base of support: Distance between feet
- Degree of toe out: Angle of feet relative to the direction of motion
Joint angles for quantifying gait:
- Ankle, knee, and hip angles are measured relative to neutral anatomical posture
Ankle motion during walking:
- Plantarflexion during contact, dorsiflexion during swing and pre-contact.
Knee motion during walking:
- Flexion after contact, extension during support, flexion for propulsion and ground clearance, and extension pre-contact.
Hip motion during walking:
- Extension during loading, flexion for propulsion, and slight extension pre-contact.
Motion beyond the sagittal plane: Involves pelvic rotation in frontal and transverse planes.

To minimize vertical CoG movement:
- Lateral pelvic tilt (pelvic drop), knee flexion, and complex joint interactions work together
To minimize drop in the CoG:
- Lateral pelvic tilt and forward/backward pelvic rotation help maintain a more extended leg position
To minimize lateral CoG movements:
- Physiologic valgus at the knee reduces the width of the base of support
Trunk and upper extremity motion:
- Rotations around the vertical axis contribute to forward motion

Ten critical elements in gait assessments:
- Step length asymmetry
- Ankle and knee angles at contact
- Stance phase knee flexion
- Duration of single-limb support
- Ankle and foot angles during push-off
- Swing phase knee flexion
- Trunk angle
- Frontal plane hip drop
- Transverse plane posture
Requirements for normal walking:
- Each leg supporting body weight without collapse
- Maintaining balance during single limb stance
- Swinging leg advancing to a support position
- Sufficient power for limb movement and trunk advancement
Factors affecting gait: Age, injury, fitness, environment, clothing, footwear, and disease