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chapter 12. Ambulation and Ambulation Aids. Gait. = A series of rhythmical, alternating movements of the limbs and trunk that causes a forward progression of the center of gravity (CoG).
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chapter12 Ambulation and Ambulation Aids
Gait • = A series of rhythmical, alternating movements of the limbs and trunk that causes a forward progression of the center of gravity (CoG). • Involves a repetitive loss and recovery of balance through displacing and controlling the motion of the CoG in the most efficient manner
Gait Cycle • = The series of events that occur between the heel strike of one limb and the next heel strike of the same limb.
Gait Components • Step length: the distance covered between heel strike (HS) of one limb and HS of the other limb • Stride length: The distance covered between the successive HS of one limb and HS of the same limb (continued)
Gait Components (continued) • Cadence: The speed of gait. It can be measured in the number of steps for a period of time (usually steps/min). • Cadence and time for gait cycle are related: The longer the period of time for the gait cycle, the slower the cadence. • As cadence increases, the time of double support decreases.
Terminology • HS: heel strike = IC: initial contact • FF: foot flat = LR: loading response • MS: midstance = MS: midstance • HO: heel-off = TS: terminal stance • TO: toe-off = PS: preswing • ES: early swing=IS: initial swing • MSw: midswing = MSw: midswing • LS: late swing = TSw: terminal swing
Gait Cycle Phases • Stance phase: • 62% of the gait cycle • From HS of one limb to toe-off (TO) of same limb • Some or all of the body’s weight borne on the limb • Swing phase: • 38% of the gait cycle • Time the limb is non-weight bearing • From TO to HS • Double support: • 20% of the gait cycle • Both limbs in contact with the ground • One limb in late stance, other in early stance
Stance Phases • Heel strike (HS): • When the heel strikes the ground • Sometimes called foot strike • Foot flat (FF): When entire sole of foot contacts ground • Midstance (MS): When body is directly over the limb (continued)
Stance Phases (continued) • Heel-off (HO): When heel leaves the ground but ball of foot remains in contact • Toe-off (TO): • When toe leaves the ground • Final phase of gait
Swing Phases Early swing (ES): • Immediately following TO • Limb CoG begins accelerating forward to move in front of the body’s CoG • Sometimes called acceleration phase (continued)
Swing Phases (continued) • Midswing (MSw): • Limb passes directly beneath the body. • Tibia is perpendicular to the ground. • Late swing (LS): • Limb passes in front of the body in preparation for HS. • Sometimes called deceleration phase.
CoG and Gait • Purpose of gait is to move the CoG. • CoG is located approximately anterior to S2. • During gait, CoG moves from side to side and from superior to inferior. (continued)
CoG and Gait (continued) • Vertical displacement: • CoG is displaced to vertical peak twice in gait cycle. • Highest point occurs at MS. • Lowest point occurs at double support. • CoG follows sinusoidal path in the vertical direction. • Total vertical displacement is ~2 in. (~5 cm). • Horizontal displacement: • CoG is moved from side to side once in gait cycle. • CoG follows sinusoidal path in the horizontal direction. • Total side-to-side displacement: ~1.75 in. (~4.5 cm).
Determinants of Gait • Six determinants • Pelvic rotation • Pelvic tilt • Knee flexion at early midstance • Foot and ankle • Ankle and knee • Lateral pelvic motion • Work together to increase gait efficiency
Determinants of Gait: Pelvic Rotation • Pelvic rotation: ~4° to each side • Pelvis rotates left to right and vertically. • Left-to-right rotation depends on swing limb (e.g., right limb leads pelvis rotates to left) • Amount of swing varies with cadence and step length. (continued)
Determinants of Gait: Pelvic Rotation (continued) Effect of some rotation occurs at both hips • Amplitude of sinusoidal wave crest • Severity of deflections between wave arcs • Severity of impact with the ground • Force needed to change direction of CoG from trough to crest wave • Smoothes out deflection points
Determinants of Gait: Pelvic Tilt • Pelvic tilt: ~5°to either side • Pelvis drops inferiorly opposite to weight-bearing (WB) limb. • Some motion occurs at both hips. • Adduction on WB side • Abduction on non-weight-bearing (NWB) side • Effects: • Amplitude of sinusoidal wave • How does this effectiveness of hip abductor mechanism?
Determinants of Gait: Knee Flexion in Early Midstance • Knee begins to flex immediately after HS and continues to flex (~15°) until FF. • Effects: • Amplitude of sinusoidal wave crest • Severity of deflections between sinusoidal wave arcs
Determinants of Gait: Foot and Ankle • Talocrural joint • CoG is falling and WB limb shortens to dampen impact: Talocrural joint dorsiflexes. • Plantar flexes immediately following HS to FF. • Dorsiflexes in MS. • Begins to plantar flex immediately after MS. (continued)
Determinants of Gait: Foot and Ankle (continued) • Foot • Pronated by FF. • Begins to supinate immediately after FF. • Talocrural center of rotation (CoR) position changes: high at HS, low at MS, high at TO.
At HS: Knee flexes. Ankle CoR moves high to low. At FF Knee begins extension. Ankle CoR remains low. At HO Knee begins flexing to shorten the limb for swing. Ankle CoR rises, then knee flexion increases as ankle CoR continues to rise. (continued) Determinants of Gait: Ankle and Knee
Determinants of Gait: Ankle and Knee (continued) • Effects: • Severity of the deflections between wave arcs • Smoothes out the reversal of motion of the CoG at the low point of its course • Combinations of knee and ankle motions gradual change in functional limb length throughout gait
Determinants of Gait: Lateral Pelvic Motion • Lateral displacement of CoG toward stance limb could be as much as 6 in. • Effect: produces lateral movement of CoG • Hip-knee angle lateral movement to 1 in. each side
