To describe changes in the VL and BF muscle tendon unit using US after a long-term stretching program to identify which structures are responsible for ROM increase.

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Recently, Eng et al. (Eng et al., 2008) presented a study that examined muscle architecture and fiber type in the rat hindlimb to define the functional specialization of each muscle. Nevertheless, a literature search for studies quantifying skeletal muscle architectural parameters of rats in vivo was unsuccessful. Studies with animals related to the degeneration-regeneration process subsequent to muscle injury are restricted to in vitro analysis and do not permit longitudinal follow-up. SUMMARY This work describes the use of ultrasound biomicroscopy (UBM) to follow up the degeneration-regeneration process after a laceration injury induced in the lateral gastrocnemius (LG) and soleus (SOL) muscles of rats. UBM (40MHz) images were acquiredand used for biomechanical characterization of muscular tissue, specifically using pennation angle (PA) and muscle thickness (MT). The animals were distributed in three groups: the variability group (VG; N5), the gastrocnemius injured group (GG; N6) and the soleus injured group (SG; N5). VG rats were used to assess data variability and reliability (coefficients of variation of 9.37 and 3.97% for PA and MT, respectively). GG and SG rats were submitted to the injury protocol in the LG and SOL muscles of the right legs, respectively. UBM images of muscles of both legs were acquired at the following time points: before and after injury (immediately, 7, 14, 21 and 28days). We observed an increase in PA for the non-injured leg 28days after injury for both GG and SG rats (GG10.68 to 16.53deg and SG9.65 to 14.06deg; P<0.05). Additionally, MT presented a tendency to increase (GG2.92 to 3.13mm and SG2.12 to 2.35mm). Injured legs maintained pre-injury PA and MT values. It is suggested that a compensatory hypertrophic response due to the overload condition imposed to healthy leg. The results indicate that UBM allows qualitative and quantitative muscle differentiation among healthy and injured muscle at different stages after lesion.