changes in muscle strategies duringlanding task in subjects with and without knee genuvarum

Introduction: onset and offset activation of lower limb and trunk muscles may change the knee withgenu varum during landing. these motor control strategies can be different from those in healthysubjects and contribute to more injuries in lower extremities. this study aimed to compare the delaytime of the onset activity of the abdominal and lower limb muscles in the specific landing task.materials and methods: ten females with genu varum deformity and ten females with normalknee participated in this case-control study. genu varum deformity was measured by a cameracapturing goniometer. the subjects were informed to land by preferred lower limb from a table (30cm high) on a force plate. vertical ground reaction force (vgrf) was measured to clarify theonset of the landing task. surface electromyography (semg) of transverse abdominal/int. oblique(ta/io), vastus medialis (vm), vastus lateralis (vl), lateral gastrocnemius (lg), and medialgastrocnemius (mg) muscles were recorded during landing. the difference between the onsetactivity of the above muscles and onset of vgrf was calculated as delay times and comparedbetween muscles and between two groups. also, the offset of activities and the intensity of muscleactivation (normalized rms) were compared between the two groups.results: lower limb and trunk muscles showed significantly different onset of activities in the genuvarum group (p<0.05), whereas there was no significant difference in the onset of muscle activitiesin the healthy group. results indicated significant differences between two groups in ta/io, lg, andmg muscles and the genu varum group had longer delay time for motor control strategy (especiallyankle strategy) in the landing task. offset time of all muscles in the genu varum and healthy subjectshad a significant difference between muscles, especially in gastrocnemius muscles (p<0.05). also,there were significant changes between the two groups in lg and mg muscles (p<0.05). normalizedmuscle activities (nrms) generally indicated an increase in muscle activation of genu varum subjects(ta/io, lg, mg) compared with the normal subjects (p<0.05).conclusion: motor control strategies in landing task is different in the genu varum group due tochanges in biomechanics and properties of the knee joint. this variation may be due to changes inproprioception afferent pathways around the knee joint. an increase in muscle activation, delay, andoffset time of muscle activities in these subjects, indicated that an increase in the degree of freedommay change motor control strategies. internal anticipation and postural adjustment of the landing taskin these subjects need more motor unit recruitment (an increase in nrms). this deformity in the kneejoint might affect some activities and possibly cause knee changes such as osteoarthritis.