Vol. 94, Issue 1, 171-178, January 2003
Expression of the bilateral deficit during reflexively evoked
contractions
N.
Khodiguian,
A.
Cornwell,
E.
Lares,
P. A.
DiCaprio, and
S. A.
Hawkins
Department of Kinesiology, California State University, Los
Angeles, California 90032
During maximal contractions, the sum
of forces exerted by homonymous muscles unilaterally is typically
larger than the sum of forces exerted by the same muscles bilaterally.
This phenomenon is known as the bilateral deficit (BLD), and it is
suggested that this deficit is due to neural inhibition. It remains
unclear, however, whether such inhibition is mediated by supraspinal
mechanisms or by reflex pathways at the level of spinal cord. To
further study the origin of likely neural influences, we tested for the presence of BLD under the condition of reflexive force generation. Force output and integrated electromyogram (iEMG) (quadriceps femoris)
were measured in 17 male participants after initiation of the myotatic
patellar reflex under unilateral and bilateral conditions. A
significant BLD of 9.26 ± 1.19 (P = 0.004) and
16.76 ± 4.69% (P = 0.001) was found for force
and iEMG, respectively. However, because similar findings were not
evident during maximal isometric knee extensions, it is difficult to
predict the contribution of a spinal mechanism to the BLD under the
condition of maximal voluntary activation.
myotatic reflex; reflexive force generation; maximal voluntary
contractions; cross-inhibition
