C-35 Free Communication/Poster - Motor Units and EMG: MAY 28, 2009 7:30 AM - 12:30 PM ROOM: Hall 4F
Force transmission from muscle to bone may occur in a more complex manner than previously appreciated. For example, it has been shown in animals that force transmission between synergists and antagonists muscles may take place, and further, that lateral force transmission may occur within the load bearing tissues such as tendons and aponeuroses. The mechanisms that underlie tendon injury are elusive, however, heterogenous muscle activation and non-uniform force transmission between muscles and/or within tendons may potentially play a role.
PURPOSE: To determine if lateral force transmission occurs within and between superficial and deep plantarflexor muscles in humans in vivo.
METHODS: Seven subjects performed 4 types of either active contractile tasks or passive joint manipulations with the limb positioned in two different joint configurations (extended and flexed knee): 1) voluntary plantarflexion, 2) voluntary hallux flexion, 3) passive hallux extension and 4) selective percutaneous stimulation of one superficial plantarflexor muscle (medial gastrocnemius (MG)). Muscle displacement during manipulations were determined by ultrasonography obtained at a proximal and distal site for 3 muscles (MG (proximal site), soleus (SOL) (proximal and distal site), flexor hallucis longus (FHL) (distal site)). Neural activation of muscles was assessed by EMG.
RESULTS: During passive hallux extension the FHL tendon underwent 5±1 mm (mean±sem) displacement in distal direction without any movement in the adjacent SOL muscle. The FHL tendon moved 4±1 mm in proximal direction during selective FHL contraction without any movement in SOL. During full plantar flexion SOL and MG displacement was similar in the proximal direction (∼7±1 mm) while FHL only displaced 2±1 mm. Percutaneous stimulation of MG generated 3±1 mm of displacement of GM and 2±1mm in SOL in the proximal direction while FHL remained fixed.
CONCLUSIONS: The present data suggest that lateral force transmission occurs between the superficial plantarflexor muscles (GM and SOL), and that the deep flexor muscle FHL, which is also a strong plantar flexor muscle, seems to be an independent actuator.
This work was Supported by the Danish Medical Research Council