312


PART IV THE LOWER EXTREMITY


maximus continues to contract throughout the stance phase, supporting the body weight. The muscle is mainly inactive during the swing phase until late swing, when it increases its activity to slow the fl exing hip and begin active hip extension.





  Frontal plane Subtalar joint angle


Figure 14.8 The inversion and eversion angle of the calcaneus during walking can be measured using the lines bisecting the lower leg and the calcaneus. The calcaneus typically moves from 3° of eversion to 2° of inversion during the gait cycle.


(see Fig. 13.16D). The toes then lift off the ground, and the joint fl exes slightly. Restricted toe extension during heel off can decrease the effi ciency of push off during the gait cycle.


TRUNK AND UPPER EXTREMITIES


During normal walking, the arms swing in a rhythmic pattern that is opposite the pattern of the lower extremi- ties. As the hip moves into fl exion, the ipsilateral arm moves into extension. Conversely, as the lower extremity extends, the ipsilateral arm fl exes. Although the magni- tude of arm swing between fl exion and extension varies among individuals, the pattern of movement is fairly con- sistent. The function of the arm swing balances the small rotational components of the trunk that occur during walking. This small amount of trunk rotation in the horizontal plane places the shoulder girdle in a rotated position opposite to the pelvis. Both arm swing and this small amount of trunk rotation contribute to an effi cient gait pattern.


MUSCLE ACTIVITY DURING GAIT


HIP AND KNEE MUSCLE ACTIVITY Both the hamstrings and the gluteus maximus start to activate at the end of late swing to extend the hip and prepare the leg to accept the weight at the beginning of initial contact and in stance phase. The hip exten- sors prevent uncontrolled trunk fl exion as the trunk is displaced forward over the supporting limb. The gluteus


During the gait cycle, the hip fl exors lift the lower extremity during toe off and help the foot clear the ground during initial swing phase. During the second half of swing phase, the limb swings forward as a result of the momentum gained by the leg during initial swing, without needing activation of the hip fl exor muscles. The hip abductor muscles are activated during the gait cycle on the stance leg to eccentrically lower the contra- lateral pelvis on the side where the leg is in swing phase of the cycle. The hip abductors work concentrically in late stance to control the frontal plane alignment of the femur.


The components of the quadriceps play different roles during normal walking speeds. The vasti muscles begin to activate during the fi nal components of swing phase and assist with shock absorption at initial contact. They eccentrically control knee fl exion as the body weight transfers to the standing limb. The quadriceps then con- tract concentrically to extend the knee and support the body weight during mid-stance. As the lower extremity transitions from stance to swing phase, the rectus femoris assists with hip fl exion and eccentrically controls knee fl exion.


ANKLE AND FOOT MUSCLE ACTIVITY


At initial contact of the heel with the ground, the tibialis anterior, extensor digitorum longus, and extensor hal- lucis longus activate eccentrically to decelerate plantar fl exion of the ankle as it lowers to the ground. During swing phase, these same muscles produce enough ankle dorsifl exion to clear the toes from the ground. The plantar fl exor muscles, including the gastrocne- mius, soleus, and secondary muscles that contribute to plantar fl exion (see Chapter 13), are active throughout stance phase to eccentrically control forward move- ment of the tibia and fi bula over the ankle. Without this control, the knee can move into excessive uncon- trolled knee fl exion during the stance phase. The plantar fl exors provide a push off action as they increase their activity near heel off. They produce a plantar fl exion torque that assists in the forward propulsion of the body. The activation of the plantar fl exor muscles decreases to nearly zero as the toes leave the ground during the toe off phase.


In addition to its contribution as a plantar fl exor, the tibialis posterior is an important supinator of the foot during the fi rst half of the gait cycle. As the foot makes contact with the ground, the tibialis posterior decelerates and controls foot pronation. The muscle then begins to concentrically supinate the foot from mid-stance to toe


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