Triceps surae force, length and velocity during walking.

Individuals with neuromuscular conditions may develop muscle contractures that limit joint motion. Decreased muscle length is clinically obvious, but deviations in other functional characteristics of muscle, such as underlying weakness or decreased shortening velocity are more obscure. Therefore, a more comprehensive assessment of muscle characteristics may be required to fully restore function in these individuals. To provide normative comparison data on the force, length and velocity of the triceps surae during walking, 20 adults free from neuromuscular and orthopedic problems were assessed using instrumented gait analysis. Kinematic and kinetic data were used to calculate gastrocnemius and soleus length and velocity, and plantarflexor force during walking. Gastrocnemius length was shortest in early swing and longest in terminal swing and again in midstance. Soleus length was longest throughout the period of single limb stance and was shortest at foot-off. Gastrocnemius shortening velocity was greatest in early swing phase whereas soleus shortening velocity was greatest in pre-swing. Plantarflexor force increased steadily throughout stance phase and peaked in terminal stance at 33.8+/-3.6 N/kg bodyweight. These data provide target levels on the functional parameters of plantarflexor force, length and velocity in order that therapeutic and surgical interventions could be focused on the deviations observed, and the outcomes of these interventions more objectively assessed.