- Medial Head
- Lateral Head
- Plantar Flexion [1, 2 ]
- Flexion [1, 2 ]
- Medial Condyle (Posterior) [1 ]
- Lateral Condyle (Posterior) [2 ]
- Achilles Tendon [1, 2 ]
The biarticulate gastrocnemius muscle [1, 2 ] enters passive insufficiency through the completion of ankle dorsal flexion when the knees are more extended or through the completion of knee extension when the ankles are more dorsal flexed. The biarticulate gastrocnemius muscle [1, 2 ] enters active insufficiency through the completion of knee flexion when the ankles are more plantar flexed (hamstrings become more active) or through the completion of ankle plantar flexion when the knees are more flexed (soleus becomes more active). In the seated calf raise (knees flexed to 90º), the gastrocs are virtually inactive while the load is borne almost entirely by the soleus.
In moderate force, the soleus is preferentially activated in the concentric phase, whereas the gastrocnemius is preferentially activated in the eccentric phase. The gastrocnemius becomes even more activated at higher lengthening velocities (Nardone & Schiepatti, 1988). During hopping, the gastrocnemius, with its greater proportion of fast twitch motor units, is preferentially activated over the soleus (Moritani et al., 1990). During stationary cycling, the gastrocnemius is also preferentially activated at higher pedaling speeds (Duchateau et al., 1986).