12.2.2 Trunk and Lower Extremity Joint Motion in Normal Gait
The center of gravity (CG) of the walking person is located in the pelvic area. During walking the CG moves both up and down, and right and left. The maximum upward excursion occurs at mid-stance and from there the CG drops to its lowest position during the phases of double support. The lateral displacement is towards the stance leg. Energy consumption during walking is partially controlled by the amount of CG movement. The most efficient motion is less than 10 cm (3 inches) of vertical and lateral motion.
Trunk and pelvic motions are also very important for an efficient gait pattern. During swing phase the ipsilateral pelvis rotates 4° forward and drops down just before the initial contact. By the end of stance the ipsilateral pelvis has rotated back by the same 4°. The rotation of the shoulder and the arm swing is opposite to the direction of rotation of the pelvis. Suppression of this counter rotation results in increased energy consumption and an inability to increase the velocity (Inman et al. 1981).
At heel strike the ipsilateral pelvis is rotated forward, the hip is in 25-30° flexion. The knee is extended and the ankle is in neutral. For shock absorption at heel strike, eccentric contraction of the ankle dorsiflexor muscles lower the forefoot to the floor and the knee moves into 15-20° flexion.
By mid-stance the hip, the knee and the ankle have moved into neutral (0°). As the body continues to progress forward the hip reaches a relative 15-20° extension, due partially to the backward rotation of the pelvis. During the terminal stance and pre-swing, the hip and knee flex to prepare the swing. At the same time the ankle moves from 15° dorsal flexion at the start of heel-off to 20° plantar flexion at toe off.
Swing (O Fig. 12.1 e-g, 12.2 e-g, 12.3 e-h) Just before mid-swing the knee is in its maximum flexion of 65°, the hip is in 20° flexion and the ankle is in neutral. During the deceleration of the leg in terminal swing, the pelvis is rotated forward and is descending, the hip reaches 25° of flexion, the knee fully extends and the ankle remains in neutral.
12.2.3 Muscle Activity During Normal Gait (Perry 1992)
Muscle activity during forward walking works largely either to stabilize or decelerate the body segments. The momentum of the body as it moves forward provides most of the work for motion.
The trunk flexor and extensor muscles work throughout the gait cycle both to stabilize the trunk and to give the hip muscles a secure base for their work. The abdominals and the back extensor muscles stabilize the trunk in all planes. The trunk extensor muscles are more active after heel strike to stabilize the trunk during weight acceptance. The erector spinae are also active during the push off. The abdominals help to introduce the swing phase.
1 Drawing by Ben Eisermann, Hoensbroek, muscle activity based on Perry J. (1992)
The hip extensor muscles are most active from the end of the swing phase, to decelerate the moving limb. Their activity continues through the initial contact and loading response as shock absorbers. There is essentially no activity of these muscles during mid-stance as the momentum of the body over the fixed foot provides the extension of the hip. The gluteus maximus is most active during heel strike and acts as a shock absorber by controlling the hip and knee extension and external rotation. During terminal stance these hip extensor muscles become active again to assist the propulsion.
The hip abductor muscles are active to stabilize the pelvis in the frontal plane (prevent excessive pelvic drop on the swing side). The abductor group is primarily active during heel strike and the early stance phase. The tensor faciae latae contracts more during the second part of stance.
The quadriceps and hamstring muscles also do most of their work at the end of swing through the beginning of stance. The hamstrings contract to assist in knee flexion at the end of the stance phase and to decelerate the lower leg (shank) at the end of the swing phase. They also assist the gluteus maximus in hip extension. The quadriceps are active at the end of swing and through the period of loading response as shock absorbers and to counteract the flexion torque during the loading response. Neither the hamstrings nor the quadriceps are active during mid-stance. Knee control during this time is managed by the calf group. The rectus femoris becomes active at the end of the stance phase together with the iliopsoas to introduce the forward swing of the leg.
The pre-tibial muscle group (dorsi-flexors) works during swing to raise the foot to neutral (0°) and then switch to eccentric work to lower the forefoot to the floor after heel strike. The plantar flexor muscles begin to work as soon as the foot is flat. First the soleus acts to control the tibia's forward motion. The tibial control provides passive knee extension and assists in hip extension. As the body continues its motion forward over the fixed foot the gastrocnemius contracts along with the soleus. At the end of stance all the plantar flexor muscles work to stabilize the ankle and allow the heel to rise up. This ankle restraint also aids the hip and knee flex ion motion. During push off they act to propel the body forward.
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