Previous studies have identified differences in gait kinetics between healthy older and young adults. However, the underlying factors that cause these changes are not well understood. The objective of this study was to assess the effects of age and speed on the activation of lower-extremity muscles during human walking. We recorded electromyography (EMG) signals of the soleus, gastrocnemius, biceps femoris, medial hamstrings, tibialis anterior, vastus lateralis, and rectus femoris as healthy young and older adults walked over ground at slow, preferred and fast walking speeds. Nineteen healthy older adults (age, 73 ± 5 years) and 18 healthy young adults (age, 26 ± 3 years) participated. Rectified EMG signals were normalized to mean activities over a gait cycle at the preferred speed, allowing for an assessment of how the activity was distributed over the gait cycle and modulated with speed. Compared to the young adults, the older adults exhibited greater activation of the tibialis anterior and soleus during mid-stance at all walking speeds and greater activation of the vastus lateralis and medial hamstrings during loading and mid-stance at the fast walking speed, suggesting increased coactivation across the ankle and knee. In addition, older adults depend less on soleus muscle activation to push off at faster walking speeds. We conclude that age-related changes in neuromuscular activity reflect a strategy of stiffening the limb during single support and likely contribute to reduced push off power at fast walking speeds.

This study introduces a framework for co-simulating neuromuscular dynamics and knee joint mechanics during gait. A knee model was developed that included 17 ligament bundles and a representation of the distributed contact between a femoral component and tibial insert surface. The knee was incorporated into a forward dynamics musculoskeletal model of the lower extremity. A computed muscle control algorithm was then used to modulate the muscle excitations to drive the model to closely track measured hip, knee, and ankle angle trajectories of a subject walking overground with an instrumented knee replacement. The resulting simulations predicted the muscle forces, ligament forces, secondary knee kinematics, and tibiofemoral contact loads. Model-predicted tibiofemoral contact forces were of comparable magnitudes to experimental measurements, with peak medial (1.95 body weight (BW)) and total (2.76 BW) contact forces within 4-17% of measured values. Average root-mean-square errors over a gait cycle were 0.26, 0.42, and 0.51 BW for the medial, lateral, and total contact forces, respectively. The model was subsequently used to predict variations in joint contact pressure that could arise by altering the frontal plane joint alignment. Small variations (62 deg) in the alignment of the femoral component and tibial insert did not substantially affect the location of contact pressure, but did alter the medio-lateral distribution of load and internal tibia rotation in swing. Thus, the computational framework can be used to virtually assess the coupled influence of both physiological and design factors on in vivo joint mechanics and performance.

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Study Design Cross-sectional laboratory study. Objectives To assess differences in hip strength, iliotibial band length, and hip and knee mechanics during running between male runners with iliotibial band syndrome and healthy controls. Background Flexibility, strength, and running mechanics are commonly assessed in patients with iliotibial band syndrome (ITBS). However, these variables have not been evaluated concurrently in this population. Methods Thirty-four males participated (17 healthy, 17 ITBS). Hip strength was measured with a hand held dynamometer and iliotibial band flexibility was assessed using an inclinometer while performing the Ober’s test. Kinetic and three-dimensional kinematic data were obtained during running. Kinematic variables of interest included frontal and transverse plane hip and knee joint angles at the time of early stance. Independent sample t-tests as well as effect sizes were used to assess group differences. Results Compared to the control group, persons with ITBS had a significantly lower Ober’s measurement (1.2°), weaker hip external rotators (1.2 Nm/kg), greater hip internal rotation (3.7°), and greater knee adduction (3.6°). However, only hip internal rotation and knee adduction exceeded the minimal detectable change score. Conclusions Our results suggest that intervention strategies that target neuromuscular control of the hip and knee may be indicated for males with iliotibial band syndrome.

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