The objective of the present study was to establish test-retest reliability of isokinetic
hip torque and prime mover electromyogram (EMG) through the three cardinal planes
of motion. Thirteen healthy young adults participated in two experimental sessions,
separated by approximately one week. During each session, isokinetic hip torque was
evaluated on the Biodex Isokinetic Dynamometer at a velocity of 60 deg/s. Subjects
performed three maximal-effort concentric and eccentric contractions, separately,
for right and left hip abduction/adduction, flexion/extension, and internal/external
rotation. Surface EMGs were sampled from the gluteus maximus, gluteus medius, adductor,
medial and lateral hamstring, and rectus femoris muscles during all contractions.
Intraclass correlation coefficients (ICC - 2,1) and standard errors of measurement
(SEM) were calculated for peak torque for each movement direction and contraction
mode, while ICCs were only computed for the EMG data. Motions that demonstrated high
torque reliability included concentric hip abduction (right and left), flexion (right
and left), extension (right) and internal rotation (right and left), and eccentric
hip abduction (left), adduction (left), flexion (right), and extension (right and
left) (ICC range=0.81-0.91). Motions with moderate torque reliability included concentric
hip adduction (right), extension (left), internal rotation (left), and external rotation
(right), and eccentric hip abduction and adduction (right), flexion (left), internal
rotation (right and left), and external rotation (right and left) (ICC range=0.49-0.79).
The majority of the EMG sampled muscles (n=12 and n=11 for concentric and eccentric
contractions, respectively) demonstrated high reliability (ICC=0.81-0.95). Instances
of low, or unacceptable, EMG reliability values occurred for the medial hamstring
muscle of the left leg (both contraction modes) and the adductor muscle of the right
leg during eccentric internal rotation. The major finding revealed high and moderate
levels of between-day reliability of isokinetic hip peak torque and prime mover EMG.
It is recommended that the day-to-day variability estimates concomitant with acceptable
levels of reliability be considered when attempting to objectify intervention effects
on hip muscle performance.