Abstract
Ongoing motor deficits are routinely present following anterior cruciate ligament
(ACL) reconstruction, including the ability to regulate muscle force. While such deficits
are known, it is unclear why this occurs. The goal of the current study was to investigate
the potential influence of muscle spindle input on submaximal force regulation and
muscle activity at the knee in people following ACL reconstruction. Fourteen participants
(8 female) who were 6−24 months post-ACL reconstruction and 15 control participants
(8 female) undertook submaximal force matching and force modulation tasks before and
after 20 min of vibration applied to the patella tendon. Across all tasks, the ACL
reconstruction participants were poorer at force matching (P=0.007). The effect of vibration was not significant in either group for the force
matching tasks (P=0.06), although there was a reduction in maximum voluntary contraction post-vibration
in the control group (P<0.001). The ACL reconstruction group also showed evidence of greater activation of
the medial hamstring muscles in comparison to controls (P=0.04). Individuals who have undergone ACL reconstruction have a diminished ability
to accurately match and regulate submaximal muscle force, but this does not appear
to be related to impaired muscle spindle input. Neuromuscular retraining programs
that involve force regulation tasks may be necessary to optimize rehabilitation after
ACL reconstruction.
Key words
anterior cruciate ligament - electromyography - force matching - muscle spindle -
gamma loop
