muscles to be tested should be tested in functional
positions when possible. If the muscle is mainly
used in a closed chain manner, it should be tested in
a closed chain manner. If the muscle is activated in
different planes of motion, it should be tested in
various planes of motion. If muscles are used primarily
in an eccentric manner, they need to be tested in
an eccentric manner. Often, to assess all of the
different muscles that function together to provide
core strength, evaluation of specific motion patterns
and quality of movement may be done.[39,40] This
method of analysis is harder to quantify, but is more
similar to actual three-planar core function. There is
no consensus regarding the most reliable or reproducible
evaluation system.
Fig. 5. Frontal plane evaluation. One option to assess core strength that incorporates
many of these variables is to look at one-leg
Alteration of knee flexion has also been associat- standing balance ability, a one-leg squat, and a
ed with increased stresses in the arm. Tennis players standing, three-plane core strength test. In a standing
who did not have adequate bend in the knees, break- balance test, the patient is asked to stand on one leg
ing the kinetic chain and decreasing the contribution with no other verbal cue (figure 1). Deviations such
by the hip and trunk, had 23–27% increased loads in as a Trendelenburg posture or internally or externalhorizontal
adduction and rotation at the shoulder and ly rotating the weightbearing limb indicates inability
valgus load at the elbow.[37] A mathematical analy- to control the posture and suggests proximal core
sis of the tennis serve showed that a decrease in 20% weakness (figure 2).
of the kinetic energy developed by the trunk resulted A one-leg squat would be the next progressive
in a requirement of 34% more arm velocity or 80% evaluation if the standing balance test is done well.
more shoulder mass to deliver the same energy to Assuming the same starting point as the standing
the ball.[23] balance test, the patient is asked to do repetitive
Weakness or tightness at the hip can also affect
the arm. Decreased hip flexibility in rotation or
strength in abduction (positive Trendelenburg) was
seen in 49% of athletes with arthroscopically proven
posterior-superior labral tears.[38]
6. How is Core Strength Evaluated?
There is no standard way that has been described
to measure core strength. Different investigators
have used different techniques to try to gauge the
relative strengths of specific core muscles via electromyogram
data[39] and isometric dynamometer
values.[40,41] These data can give an approximate
estimate of core strength. Firing of numerous muscles
in task-specific patterns to provide core strength
makes evaluation of any specific single muscle as a
reference point questionable. Any evaluation technique
will need to take into consideration that the