A comparison of iEMG activity between the medial and lateral heads
of the gastrocnemius muscle during partial weight bearing plantarflexion
contractions at varying loads
Affiliations: [a] University of Miami School of Medicine, Division of
Physical Therapy, Coral Gables, FL 33146-2406, USA
Note: [] University of Miami School of Medicine, Division of Physical
Therapy, 5915 Ponce de Leon, Plumer Building 5th Floor, Coral Gables, FL
33146-2406, USA. Tel.: +1 305 284 4535; Fax: +1 305 284 6128; E-mail:
ldingley@miami.edu
Abstract: The purpose of this study was to determine the differences between
iEMG activity of the medial head (MH) and lateral head (LH) of the
gastrocnemius of normal right legs during partial weight bearing isometric
plantarflexion contractions under varying percentages of body weight (BW) and
maximal contractions. Fifty-three healthy volunteers ranging in age from 18 to
35, with no history of right lower extremity injury or disease volunteered for
this study. Each subject's age, height, weight, and medical history were
recorded. A chronaximeter was used to identify the motor points of the MH and
LH. After performing a 5-minute warm-up, surface electrodes were placed just
distal to the motor point, and subjects were positioned on the sliding board of
the Total Gym Therapy System. The percentage of BW used as resistance was
determined by the angle of inclination of the slide board. The subjects were
then directed to plantarflex to 20 degrees, with 8 second iEMG recordings, with
a proprioceptive cue, under four conditions: 30%, isometric (1 trial). Paired
t-tests concluded the MH consistently demonstrated a larger
percent of total iEMG activity than the LH in the 30, 50, and 70% difference
between iEMG activity of the MH and LH during the maximum isometric trial was
not statistically significant (p= 0.2958). A repeated
measures ANOVA and post-hoc analysis demonstrated the percent of total iEMG
differences to be greater at the lighter loads (D30 > D50
> D70; p< 0.0001). These findings
strongly suggest separate but complementary functions of the two heads of the
gastrocnemius muscle.
