The effect of an inclined landing surface on biomechanical variables during a jumping task
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The relative stress on the Achilles tendon during ambulation in an ankle immobiliser: implications for rehabilitation after Achilles tendon repair
by
Akizuki KH, Gartman EJ, Nisonson B, Ben-Avi S, McHugh MP.
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last modified
2009-10-09 15:16
Br J Sports Med. 2001 Oct;35(5):329-33; discussion 333-4.
BACKGROUND: After Achilles tendon repair, immediate weightbearing and
immobilisation closer to neutral plantarflexion are thought to limit atrophy and
stiffness, but may place deleterious stress on the repair. OBJECTIVES: To estimate
the relative stress on the Achilles tendon during weightbearing with
immobilisation in varying degrees of plantarflexion. METHODS: Electromyographic
(EMG) activity from the plantarflexors was recorded during walking in 10 subjects
(six men, four women) without ankle pathology. Four walking conditions were
examined: (a) normal walking; (b) immobilised (cam-walker) in neutral
plantarflexion; (c) immobilised with a 0.5 inch heel lift; (d) immobilised with a
1 inch heel lift. EMG activity relative to plantarflexor torque was determined
for each subject during isometric contractions at 25%, 50%, 75%, and 100% of
maximal voluntary contraction (MVC). EMG activity during walking was calculated
as a percentage of MVC based on the EMG-torque relation during graded isometric
contractions. RESULTS: During normal walking, the plantarflexor torque was
estimated to be 30 (12)% (mean (SD)) of MVC, compared with 21 (15)% MVC for
immobilisation in neutral (p<0.05), 17 (15)% MVC with the addition of a 0.5 inch
heel lift (p<0.01), and 12 (12)% MVC with the addition of a 1 inch heel lift
(p<0.01). The 1 inch heel lift resulted in less than 10 degrees plantarflexion in
all subjects. CONCLUSIONS: When the ankle is immobilised, stress on the Achilles
tendon is determined by the degree of plantarflexion and the contractile activity
of the plantarflexors. In the immobilised ankle, the addition of a 1 inch heel
lift was sufficient to minimise plantarflexor activity during walking.