| Abstract: | Hypotheses advanced concerning the functions and advantages of the two-joint (and multi-joint) muscles in the lower limb include transferring energy, ease of control, muscle bulk reduction and decreased velocity of contraction. The aim of this investigation was to assess quantitatively the generality of one such suggestion seen in the literature. It was hypothesized that two-joint muscles would be recruited preferentially when they produced appropriate moments at the joints they crossed. This organizing strategy was used to partition the sagittal plane joint moment at the hip, knee and ankle between the one- and two-joint muscles crossing those joints. If the conditions of the strategy were not met, the moment was considered to be producted by one-joint muscles only. Ten representative muscles were modelled: tibialis anterior, soleus, gastrocnemius, short head of biceps femoris, vasti, rectus femoris, long head of biceps femoris, sartorius, gluteus maximus and iliopsoas. A number of static loading and walking conditions were recorded and then compared to simultaneously measured linear envelope EMG records of each activity. The joint moments were determined from a sagittal plane kinetic analysis using cinematography and measurements of the ground reaction force. Overall, the strategy partitioned the moment between the one- and two-joint muscles in accordance with the EMG records. The strategy tended to underestimate the contributions of the one-joint musculature, implying the existence of other important control strategies, such as cocontraction of antagonists for joint stability, or of synergistic activation to share the joint moment. It was, however, observed that predicted activity of two-joint musculature did agree well with recorded EMG activity. |
