This study is withdrawn due to a lack of available recruitment within the researchers' timeframe.

After rehabilitation completion, there remains large deficiencies between the operative (OP) and non-operative (NOP) limbs in lower-limb outcomes (e.g., size, strength, and function) and these deficits can persist for years. Therefore, further specialized training protocols, such as the ones in the present study, are required to determine if these deficits can be lessened. The proposed project will evaluate the effect of 8-weeks of single-leg and double-leg lower-body resistance training on musculoskeletal function in individuals with a previous anterior cruciate ligament (ACL) reconstruction (ACLR) in a randomized control trial. The study will recruit 30-40 males and females between 18-35 years of age that have undergone a previous ACLR. Participants will be randomized to either the single-leg/unilateral (UL) or double-leg/bilateral (BL) training groups. Training will occur three times per week for 8-weeks. The UL group will participate in exercises such as split squats, single-leg deadlifts, or single-leg squats. The BL group will utilize exercises such as double-leg squats, conventional deadlifts, and leg presses. One week prior to (PRE) and one week after (POST) the training program, all participants will undergo a testing battery. Musculoskeletal ultrasound will measure quadriceps and hamstrings muscle cross-sectional area (mCSA), fascicle length (FL), and pennation angle (PA) of both OP and NOP limbs. Strength will be assessed through maximal voluntary isometric contractions (MVIC) for the quadriceps and hamstrings, and one-repetition maximum tests for single-leg leg extensions, leg curls, and leg press. Lower-limb function will be assessed through single-leg and double-leg jumps on a dual force plate system for jump height, impulse, rate of force development, and peak force. Data will be analyzed via separate mixed-factorial analyses of variance for the within-subjects factor of leg (OP vs. NOP) and time (PRE vs. POST) and the between-subjects factor of biological sex (male vs. female) and group (UL vs. BL). Post-hoc analyses will include lower-order ANOVAs and t-tests as pairwise comparisons when significance is detected. Significance will be established at p≤0.05. The results of this study will assist practitioners, coaches, sport scientists, and most importantly, the athletes, in the development of post-rehabilitative strength training protocols designed to reduce between-limb discrepancies.

Inclusion Criteria:

1. Participant has provided written and dated informed consent to participate in the study
2. Participant is 18-35 years of age, inclusive
3. Participant is in good health as determined by a health history questionnaire
4. Participant has been medically cleared to return to sport after primary ACLR in the previous two years

Exclusion Criteria:

1. Participant has a history of other lower-body related injuries in the past 6-months.
2. Participant has undergone more than one ACLR or has injured the ACL of both legs.
3. Participant has implants, hardware, devices, or other non-removable metal material in the body that would limit the accuracy of skeletal muscle size and body composition assessments within the measurement area.
4. Participant has a cardiovascular, metabolic, or neuromuscular disorder that contraindicates their ability to participate in an exercise program.