Abstract: One of the most important assumptions of the passive method of
gravity correction in isokinetic dynamometry is that subjects are relaxed
during the test. The purpose of this study was to examine the validity of the
passive gravity correction method in pubertal children. Fifteen pubertal males
performed passive knee extensions and flexions at
30°·s^{-1}. The electromyographic (EMG) activity
of the vastus medialis (VM), vastus lateralis (VL) and biceps femoris (BF) was
recorded using bipolar surface electrodes. The GM was estimated using five
different methods: the recorded GM during knee extension and flexion, the
estimated GMs from the recorded knee extension and flexion GMs at 30° of
knee flexion and the GM estimated using anthropometric data. The results
indicated that the passive knee movements resulted in significantly (p<0.05)
higher GM compared to those estimated using anthropometric data or
mathematically using the GM at 30°. The GM in the range of 31--90° was
significantly (p<0.05) higher during knee extension compared with knee
flexion. The VM and VL raw EMGs were significantly (p<0.05) higher during
knee extension compared to knee flexion movement, reaching 40% of the their
maximum EMG values. The BF EMG ranged from 7% to 10% of the maximum, but it was
not significantly different between extension and flexion phases. It can be
suggested that the recorded dynamometer moment during passive gravity
correction tests is affected by forces exerted by musculotendinous structures
which are activated during the test. The application of passive gravity
correction techniques in pubertal children demonstrates significant problems
and should be applied with extreme caution.
