Functional Resistance Training Improves Thigh Muscle Strength after ACL Reconstruction: A Randomized Clinical Trial

Abstract

Purpose: Quadriceps weakness is common after anterior cruciate ligament (ACL) reconstruction, resulting in prolonged disability and increased risk for reinjury and osteoarthritis. Functional resistance training (FRT) combines resistance training with task-specific training and may prove beneficial in restoring quadriceps strength. The primary purpose of this study was to determine if a walking-specific FRT program (e.g., resisted walking) improves knee strength in individuals after ACL reconstruction.

Methods: Thirty participants were randomized into one of three groups: 1) FRT with a customized knee BRACE applied to the ACL leg, 2) FRT with elastic BAND tethered to the ankle of the ACL leg, or 3) a TARGET MATCH condition where no resistance was externally applied. Participants in all groups received training while walking on a treadmill 2-3 times per week for 8 wk. Isometric knee extension and flexion strength were measured before the start of the intervention, after the intervention (POST), and 8 wk after intervention completion (POST-2).

Results: The BRACE group had greater knee extensor strength compared with the TARGET MATCH group at POST and POST-2 ( P < 0.05). The BRACE group had greater knee flexor strength than the TARGET MATCH group at POST and POST-2 ( P < 0.05) and the BAND group at POST ( P < 0.05).

Conclusions: FRT applied via a customized knee brace results in improvements in knee extensor and flexor strength after ACL reconstruction. FRT is a beneficial adjuvant to ACL rehabilitation and leads to better strength compared with standard of care.

FIGURE 1.

CONSORT (Consolidated Standards of Reporting Trials) diagram illustrating the flow of participants through the study. FRT = Functional Resistance Training

FIGURE 2.

Schematic illustrating the testing and training visits associated with the study. *indicates the timeline of the training session for weeks 1, 3, 5, and 7. + indicates the timeline of the training session weeks 2, 4, 6, 8. TB = training block; Eval = Evaluation

FIGURE 3.

Schematic showing a participant training with the BRACE (left) and the BAND (right). The BRACE provided bi-directional resistance across the knee requiring activation of the quadriceps and hamstrings, while the BAND provided uni-directional resistance during knee extension.

FIGURE 4.

Average OMNI scores for each training session for all three study groups. The OMNI score was used to scale the resistance applied for the BAND and BRACE groups and was adjusted every two weeks. We aimed for BRACE and BAND groups to train between a 5–7 (somewhat difficult) on the OMNI scale. Participants (N=17; BRACE = 6; BAND = 5; TARGET MATCH = 6) completing two sessions a week had resistance adjusted after the second session of weeks 1, 3, 5, and 7. Participants (N = 11; BRACE = 4; BAND =4; TARGET MATCH = 3) completing three sessions a week had resistance adjusted after the third session of weeks 1, 3, 5, and 7. Arrows indicate training sessions during which the resistance was adjusted and increased.

FIGURE 5.

Knee extensor strength (A) and knee flexor strength (B) for the BRACE, BAND, and TARGET MATCH groups prior to intervention (PRE), immediately post-intervention (POST), and approximately 8 weeks after the intervention (POST-2). *indicates that the BRACE group was significantly different than the TARGET MATCH group. † indicates that BRACE group was significantly different than the BAND group.