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 increase 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, eccentric exercises are used to improve the quadriceps strength and force generation after ACL injury and reconstruction surgery. Generally, 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 & Reiman, 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 after 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 training into ACL rehabilitation programs during the first 15 weeks following ACL reconstruction induces greater increases in muscle volume, strength, and knee functional measures when compared to ACL rehabilitation without eccentric resistance training (Gerber et al., 2006). A meta-analysis study comparing eccentric to concentric training reported that eccentric training is more effective 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 reconstruction 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 lower intensities and progress to high-intensity exercises that involve exercise-specific machines, such as the leg press and squats (Lorenz & 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 follow by flexing the reconstructed knee eccentrically. The ultimate goal of strength training is to restore quadriceps (and other lower extremity musculature) strength symmetry between 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 addition, 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 unilateral strengthening exercises performed separately with each limb may be a prudent recommendation to facilitate long-term strength symmetry. Neuromuscular training Rehabilitation programs that focus only on restoring joint motion, increasing quadriceps muscle strength, and improving agility skills do not optimize return to all previous activity levels. Rehabilitation programs should emphasize treatment techniques that facilitate appropriate neuromuscular strategies for participation in high-level activities that involve jumping, cutting, and pivoting maneuvers. Patients with ACL deficiency or ACL reconstruction exhibit poor proprioception resulting from damage to the mechanoreceptors that are embedded in the articular structures of the knee and the ACL (Lephart, Pincivero, Giraido, & Fu, 1997). Neuromuscular training increases neuromuscular awareness and improves dynamic stability of the knee joint (Cooper, Taylor, & Feller, 2005; Fitzgerald, Axe, & Snyder-Mackler, 2000b; Fitzgerald, Axe, & Snyder- Mackler, 2000c; Fu et al., 2013; Gerber et al., 2009; Gerber et al., 2007; Risberg, Holm, Myklebust, & Engebretsen., 2007). Therefore, neuromuscular training should be integrated into the ACL rehabilitation to improve patients’ outcomes (Gokeler et al., 2014; Kruse et al., 2012; Logerstedt et al., 2017). Neuromuscular training programs include balance exercises, dynamic stabilization exercises, plyometrics, agility drills, and perturbation training. The therapist progresses the exercise difficulty from low-intensity to high-intensity maneuvers and decreases patients’ base of support by progressing from two-limb support to one-limb support. As balance improves, squatting or sport-specific activities – such as dribbling a basketball, kicking a football, or throwing a baseball – may be implemented during balance training. Examples of dynamic knee-stability exercises include the Star Excursion Balance training and single-limb squat. In the Star Excursion Balance training, patients stand on single-limb support in the center of an eight-line grid (Figure 9). Patients are asked to reach with the free foot as far as possible along each of the eight lines. Although balance exercises have been shown to improve patients’ functional outcomes and are often used in rehabilitation programs, the guidelines for the balance exercises are not well established (Herrington et al., 2009). Perturbation training, described earlier, may be incorporated into the postoperative rehabilitation program as soon as patients are pain free, knee joint effusion is trace or less, and full knee ROM is restored. A randomized clinical trial investigated the effect of a progressive quadriceps strengthening training augmented with perturbation training compared to only progressive strengthening training administered preoperatively (Hartigan et al., 2010). The results of that randomized clinical trial revealed that functional outcomes were not different between the two treatment programs, except that more patients who received perturbation training achieved a higher score on a global rating scale that allowed them to pass the return-to-sport criteria at 6 and 12 months postoperatively (Hartigan et al., 2010). Other studies shown that perturbation training was effective to mitigate abnormal gait pattern prior to the reconstruction surgery (Di Stasi & Snyder-Mackler, 2012), and preoperative perturbation training was effective to restore normal limb-to-limb biomechanical symmetry at 6 months after surgery (Hartigan et al., 2009). Resolving the abnormal movement pattern is of high importance, because this was found to predict a second ACL injury after reconstructive surgery (Paterno et al., 2010). Another randomized clinical trial found no difference in clinical, functional, or biomechanical outcome measures or second injury rates between an extended, postoperative ACL rehabilitation program that included strengthening, agility, plyometrics, and secondary prevention exercises compared to a rehabilitation program that included the same training plus perturbation training in men or women immediately after program completion
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Book Code: PTNJ0824
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