| The flexion-relaxation phenomenon consisting of an erector spinae
silent period occurring with trunk flexion can place considerable
stress upon tissues. Since individuals often flex their trunks while
unstable, the purpose of the study was to examine the effect of an
unstable base on the flexion-relaxation response. Fourteen participants
flexed at the hips and back while standing on a stable floor or an
unstable dyna-disc. Hip and trunk flexion were repeated four times
each with one-minute rest. Electromyographic (EMG) electrodes were
placed over the right lumbo-sacral erector spinae (LSES), upper lumbar
erector spinae (ULES), lower abdominals (LA), biceps femoris and soleus.
In addition to the flexion-relaxation phenomenon of the ES, a quiescence
of biceps femoris and a burst of LA EMG activity was observed with
the majority of stable trials. There was no effect of instability
on the flexion-relaxation phenomenon of the ULES or LSES. The incidence
of a biceps femoris silent period while stable was diminished with
an unstable base. Similarly, the incidence of a LA EMG burst was curtailed
with instability. Soleus EMG activity increased 29.5% with an unstable
platform. An unstable base did not significantly affect LSES and ULES
EMG flexion-relaxation, but did result in more persistent lower limb
and LA activity.
KEY
WORDS: Electromyography, erector spinae, hamstrings, trunk flexion.
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