Bi-articular muscles and their control of activity at the knee

This thesis addresses the role of biarticular muscles in the control of the knee joint during a static isometric and a dynamic balance task, and the question of whether these can be affected with training. Thirty-nine healthy participants participated in this study (F=17, M=25.46yrs±4.15): 17 in the static task (F= 8, M=24.29yrs±2.62), and 22 in the dynamic task (F = 9, M=26.23yrs± 4.69). Surface EMGs were recorded from multiple muscles at the knee and ankle of the right leg. The prevailing assumption during these tasks is that the anatomical position of the muscle underpins its activity, so its contribution to control is welldefined at all times. The agonist-antagonist interactions at the joint, aid maintenance of an upright posture. For example, at the knee joint it is the interaction between the flexors (semitendinosus (ST) and bicep femoris (BF)) and extensors (rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM) and vastus intermedius (VI)), together with the ankle flexors (tibialis anterior (TA)) and extensors (soleus (SL), lateral gastrocnemius (LG) and medial gastrocnemius (MG)). During a dynamic task, used to examine and restore balance, muscles at the ankle and trunk are assumed to be most involved in maintaining balance. My findings suggest that the biarticular muscles of the knee are involved significantly in both static and dynamic tasks, as well as when balanced, although there was an overall increase in activity in the ankle muscles. With training, these were found to be more involved, suggesting rehabilitation focussed on the knee muscles may speed recovery of balance. My data suggests further research is necessary to not only establish the role of the muscles acting at the knee during common tasks such as sit-to-stand, posture and walking but also in rehabilitation.