rehabilitation programs typically recommend incorporating these exercises earlier after surgery in controlled manners (Adams et al., 2012; Capin, Behrns, et al., 2017). Executing strengthening exer- cises throughout the entire knee flexion ROM early after ACL re- construction may place tension on the new graft, although some tension is needed for graft maturation. Therefore, clinicians may consider having patients begin performing WB training in a limit- ed ROM of knee flexion (0° to 40°). Early after ACL reconstruction, patients may perform NWB eccentric training on a limited knee flexion ROM (90° to 45°). At 6 weeks following surgery, patients may perform both WB and NWB eccentric exercises at larger knee flexion ROM (0° to 90°) to maximize quadriceps strength (Lorenz & Reiman, 2011).
Clinicians should therefore implement gradual, progressive load- ing of the lower extremity musculature and the ACL graft dur- ing the rehabilitation process while respecting the healing times of concomitant injuries and surgical considerations (see above). Open kinetic chain (NWB) exercises are both safe and essential to restoring quadriceps strength (Noehren & Snyder-Mackler, 2020). Closed chain (WB) are also safe and generally more functional. Both WB and NWB exercises should be incorporated throughout the recovery process in controlled, progressive manners. The 2017 updated clinical practice guidelines for knee ligament sprains suggests implementing both WB and NWB exercises within 4 to 6 weeks of injury (Logerstedt et al., 2017). Progressive
Figure 8: Non-weightbearing (Open kinetic chain) Exercise Example
Note . From Western Schools, © 2018.
Eccentric muscle strengthening In an ACL rehabilitation program, the goal of eccentric training is to resolve muscular impairments by providing interventions that can safely and effectively overload the quadriceps muscle to in- crease the muscle size and strength. Particular consideration is given to the type, frequency, and magnitude of strength training due to concern for increasing the anterior tibia translation and shear force that is applied to the healing graft (Beynnon, Johnson et al., 2005). In addition to the NMES and WB/NWB exercises, ec- centric exercises are used to improve the quadriceps strength and force generation after ACL injury and reconstruction surgery. Gen- erally, muscle force production is greatest when an external load exceeds a muscle’s force capacity and when the muscle fibers are lengthening eccentrically. Eccentric contraction occurs when the muscle fibers are lengthening, as in lowering a weight through a range of motion. During eccentric training, the contractile forces generated by the muscle are less than the external load, which causes the muscle to lengthen. The tension developed in the muscle fibers during the lengthening phase of muscle contraction is considerably greater than the tension developed when muscle fibers are shortening, as in a concentric contraction (Lorenz & Rei- man, 2011). Eccentric training for the quadriceps muscles is considered safe and effective (Beynnon, Johnson et al., 2005; Gerber et al., 2007b). Application of eccentric resistance training as early as 3 weeks af- ter ACL reconstruction surgery increases the cross-sectional area and strength of the quadriceps muscle without compromising the tissue of the new graft. (Gerber, Marcus, Dibble, Greis, & LaStayo, 2006; Gokeler et al., 2014; Kruse, Gray, & Wright, 2012). Evidence suggests that incorporation of eccentric resistance train- ing into ACL rehabilitation programs during the first 15 weeks fol- lowing ACL reconstruction induces greater increases in muscle volume, strength, and knee functional measures when compared to ACL rehabilitation without eccentric resistance training (Ger- ber et al., 2006). A meta-analysis study comparing eccentric to concentric training reported that eccentric training is more effec-
tive than concentric training in increasing muscle strength, muscle mass, and rate of force development (Faulkner, 2003). Eccentric training elicits greater changes in neural activation and muscle hypertrophy (LaStayo et al., 2003). Lepley, Wojtys, and Palmieri- Smith (2015) studied the effectiveness of combined NMES and eccentric exercises on the recovery of quadriceps activation and strength after ACL reconstruction surgery. These findings indicate that patients who receive eccentric exercises alone or eccentric and NMES improve quadriceps activation and strength after re- construction surgery. The results of Lepley’s study were related to the improvement in the quadriceps’ activation and strength to the eccentric exercise (Lepley et al., 2015). Eccentric training may be incorporated into WB or NWB activities. Therapists instruct the patient to initiate eccentric training at low- er intensities and progress to high-intensity exercises that involve exercise-specific machines, such as the leg press and squats (Lo- renz & Reiman, 2011). During squats, patients lower themselves down on the reconstructed limb and then raise themselves back up with the assistance of the non- operated limb. In the leg press, patients straighten the non-operated knee concentrically and fol- low by flexing the reconstructed knee eccentrically. The ultimate goal of strength training is to restore quadriceps (and other lower extremity musculature) strength symmetry be- tween limbs, and thus to minimize the potential risk of reinjury of the reconstructed limb and contralateral limb. Once patients finish their rehabilitation programs, they are encouraged to start strength training at a gym (and/or with their athletic trainer, strength and conditioning coach, or personal trainer) to improve and maintain their quadriceps and other muscle strength. In ad- dition, patients are instructed to expand their strength exercises to include strengthening of the uninvolved limb when symmetric quadriceps strength has been achieved. Continuing to do uni- lateral strengthening exercises performed separately with each limb may be a prudent recommendation to facilitate long-term strength symmetry.
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