Background: Anterior cruciate ligament (ACL) reconstruction, using hamstring auto-graft is a common surgical
procedure, which often leads to persistent hamstring muscle-strength deficiency and reduced function. The purpose of
this randomized controlled trial (RCT) is to investigate the effect of a combined, progressive, strength and neuromuscular
exercise intervention on knee muscle strength, functional capacity and hamstring muscle-tendon morphology in
ACL-reconstructed patients with persistent hamstring muscle-strength deficiency compared with controls.
Methods/design: The study is designed as a multicenter, parallel-group RCT with balanced randomization (1:1) and
blinded outcome assessments (level of evidence: II) and will be reported in accordance with the CONSORT Statement.
Fifty ACL-reconstructed patients (hamstring auto-graft) with persistent limb-to-limb knee-flexor muscle-strength
asymmetry at 12–24 months’ post surgery, will be recruited through outpatient clinics and advertisements. Patients will
be randomized to a 12-week progressive, strength and neuromuscular exercise group (SNG) with supervised training
twice weekly or a control intervention (CON) consisting of a home-based, low-intensity exercise program. Outcome
measures include between-group change in maximal isometric knee-flexor strength (primary outcome) and knee-extensor
muscle strength, hamstring-to-quadriceps strength ratios of the leg that has been operated on and Knee injury and
Osteoarthritis Outcome Score (KOOS) (secondary outcomes).
In addition, several explorative outcomes will be investigated: The International Knee Documentation Committee Subjective
Knee Form (IKDC), the Tegner Activity Score, rate of force development (RFD) for the knee flexors and extensors, tendon
regeneration and potential muscle hypertrophy at graft harvest site evaluated by magnetic resonance imaging (MRI),
postural control, kinetic/kinematic gait characteristics and knee-related functional capacity.