Article

Changes in hamstring and quadriceps activity are well known in individuals with
anterior cruciate ligament deficiency (ACLD) to potentially compensate for knee
joint instability. However, few studies have explored gastrocnemius activity or
its relationship to knee stability. The purpose of this study was therefore to
examine the activation characteristics of medial gastrocnemius (MG) in ACLD
subjects and relate any changes to knee joint laxity. Two subject cohorts were
assessed: those with unilateral ACLD (n=15) and uninjured control subjects
(n=11). Surface EMG of the left and right MG were recorded during a controlled
single leg hop on each limb. Onset and offset of MG activation relative to
take-off, during flight and landing were calculated as well as muscle activity
(RMS). Passive antero-posterior knee laxity was measured with a KT1000
arthrometer during a maximal manual displacement test. Medial gastrocnemius
activity on the injured side of ACLD participants demonstrated significantly
prolonged activation in preparation to hop, minimal muscle inactivity prior to
take-off, and increased duration of overall muscle activity when compared to the
uninjured side and control subjects (p<0.05). Significant positive correlations
were found between passive knee joint laxity and prolonged activation prior to
knee bend. RMS of the muscle signal was not significantly different between
limbs. Overall, MG on the ACLD side demonstrated longer activation, with minimal
rest during the hop test, which may be an attempt to maintain knee stability.
Furthermore, the strong relationship between knee laxity and prolonged muscle
activation suggests that individuals with a loss of knee stability are more
reliant on active control of the gastrocnemius muscle.
CI - Copyright (c) 2012 Elsevier Ltd. All rights reserved.

Langue : ANGLAIS