INTRODUCTION AND EPIDEMIOLOGY
Lateral epicondylalgia (commonly referred to as tennis elbow) is a musculoskeletal condition characterized by repetitive microtrauma to the common extensor tendon of the lateral epicondyle (Figure 1) (4,17). Peak incidence occurs between 35 and 55 years of age (14). Prevalence of this condition has been estimated at 1–3% in the general population (4,14,18,19), with the dominant arm affected in more than 70% of cases (4). In a review of elbow tendinopathies, Donaldson et al. (7) found that 9% of tennis players are affected, with novice players affected more than professional players. Furthermore, a systematic review by Bisset et al. (3) found that 15% of workers in highly repetitive hand task industries experience symptoms.
Researchers have consistently documented the extensor carpi radialis brevis tendon to be most commonly affected, with one-third of patients having involvement of the extensor digitorum tendon (2,8). Classified as an overuse disorder, lateral epicondylalgia can be a frustrating injury that substantially impacts function and presents challenges to the health care industry (3,4). Current conservative treatment methods found in the literature demonstrate poor efficacy and relapse on return to the offending activity (4). Eccentric-based exercise has gained considerable attention for managing this condition (11). Recent literature has emphasized the importance of eccentric exercise as a key component of tendinopathy rehabilitation (10,12). Moreover, a randomized control trial by Svernlov and Adolfsson (16) found that regardless of the duration of symptoms, the most effective therapeutic intervention for lateral epicondylalgia is eccentric training.
Eccentric exercise can be a key component of tendinopathy rehabilitation if integrated at the appropriate stage of injury. Nirschl has defined an ordinal 0–4 staging system for tendon injury, which delineates the clinical manifestations and proposed histological findings of each stage (6). A tendon in stage 0 is defined as healthy and composed of organized collagen in a noninflammatory state. Stage I is the first symptomatic stage, and it is defined by the clinical presentation of acute pain, swelling, local tenderness, warmth, and minimal dysfunction. Stage II is hallmarked by purposeful unloading of the tendon. Clinically, chronic tendinopathy often seen in this stage yields increased dysfunction compared with stage I, in addition to microtears and degenerative changes. Stage III is when chronic structural changes occur including palpable tendon enlargement from increased collagen disorientation and edema, and focal necrosis resulting from vascular compromise. Increased levels of dysfunction are present in stage III, which may or may not yield pain. Stage IV is defined by the complete rupture of the tendon. Gradual eccentric loading to the tendon may counteract the degenerative sequelae at stage III as it has been shown to improve collagen type I synthesis and decrease overall tendon thickness (11,13). Bigland-Richie and Woods (2) found that eccentric exercise results in more force production, less oxygen consumption, and less energy requirements compared with concentric exercise, thus improving remodeling potential of aberrant tendon structure (1). Remodeling occurs through the process of mechanotransduction; a physiologic, cellular response to mechanical loads to promote favorable structural changes (10). Considering eccentric actions are more energy-efficient mechanical stimuli than the concentric counterpart, we can impose more mechanical stimulus per unit of intensity, which may allow the user to work pain free and still be efficacious toward their recovery.
Despite a variety of conservative treatment approaches, relapses of lateral epicondylalgia are quite frequent with a recurrence rate of 24% (9). An eccentric treatment intervention initially performed for achilles tendinosis has shown promising results for lateral epicondylalgia. This may be a hypothesized extrapolation as similar changes are noted in both achilles tendinosis and lateral epicondylalgia. In 2007, Croisier et al. performed an intervention study on 92 patients. Two groups of 46 subjects were established with both groups participating in a training program 3 times a week for a 9-week period (4). The control group underwent a passive approach with an emphasis on palliative care, stretching, and deep friction massage. The experimental group performed isokinetic eccentric focused exercise for the wrist extensor and supinator muscle groups in addition to the treatment received by the control group. Pain intensity, strength, tendon integrity, and improvement of disability status were recorded to objectively measure potential and substantial change. The visual analog scale, Cybex Norm Device (Cybex International, Inc.; Medway, MA, USA), a 10 question disability questionnaire, and an ultrasonographic examination were utilized to detect the respective changes. At the conclusion of the experiment, the eccentric group had significantly less pain, mitigated bilateral strength deficits, improved homogenous tendon integrity (e.g., showed evidence of pathology resolution), and improved disability status when compared with the control group. These beneficial correlations may be extrapolated (and modified based on equipment availability) into the clinical setting, and with proper form and technique as described in the practical applications section, and may be useful in improving outcomes.
In a 1998 prospective study, Alfredson et al. investigated eccentric training on athletes diagnosed with chronic Achilles tendinosis. Unlike Croiser et al., they used a treatment protocol consisting of eccentric exercise twice per day, 7 days a week, for 12 weeks (1). Both treatment protocols found similar positive results. The optimal dosage for eccentric training regimes has yet to be delineated, and the effectiveness of various doses remains unclear (11). Croiser et al. chose to perform the exercises 3 times per week to give the tendon a sufficient rest period between successive sessions and subsequently obtained excellent results (4). Therefore, it seems logical that if fewer exercise sessions have similar positive effects in terms of outcome, lower frequency/intensity eccentric exercise protocols should be used (12).
There are multiple injuries outside of lateral epicondylalgia that may present with lateral elbow pain; therefore, before performing any treatment protocol, it is prudent that the participant be screened and cleared by a qualified health care practitioner. Recommendations for eccentric exercise interventions that may be used in the treatment of lateral epicondylalgia are listed below and adapted from the aforementioned research evidence. It should be noted that the original study used isokinetic machinery, and the following exercises have been adapted to be performed in the clinic or household settings without the demand of expensive equipment. With that being said, in the best effort to emulate the original evidence, there should be no concentric load and each eccentric repetition should be performed in a slow and controlled manner. Ideally, all range achieved with these exercises will be pain free. Some protocols may suggest working within a painful range (15); this, however, may result in decreased compliance or additional injury. Since the mechanism of injury is still only theoretical, it is our evidence-informed recommendation that pain be avoided. Specific exercise parameters are described in Figures 2–5.
Exercise parameters—Perform eccentric exercises 3 times per week with 24–48 hours between bouts of eccentric work to allow for proper recovery. As stated previously, the Alfredson protocol suggests performing exercise twice daily, however, the Crosier et al. study had similar outcomes with a much lower frequency. Therefore, we propose using the lower intensity protocol to prevent the user from potentially exercising through a painful stimulus such as delayed onset muscle soreness. The study from Crosier et al. was performed for 9 weeks, however, a benefit may be derived from incorporating this routine into one's typical regimen for greater durations given the tendency for recurrence. Each exercise session should consist of 1 wrist supination and 1 wrist extension exercise for 2 sets of 10 repetitions each. Exercise intensity should originally equate to 30% of the users eccentric 1 repetition maximum and progress gradually per the participant's tolerance to 80% 1 repetition maximum toward the end of the 9 weeks. Each eccentric contraction should endure approximately 4–6 seconds without variation in speed throughout the repetition.
The current literature has shown great promise for the rehabilitation specialist to use eccentric exercise to restore function, decrease pain, and improve performance (4,5,14). Eccentric exercise should be an integral component of any lateral epicondylalgia rehabilitation program (11), not only because evidence suggests eccentric work to be superior to conventional interventions but also because it is based off sound physiological principles (3,4,13,14,16,17). Although isokinetic, eccentric training has been shown to be an effective treatment option, it may be too expensive or impractical for many facilities. Therefore, the aforementioned protocol based off the Crosier et al. study is a practical treatment option to incorporate in the lateral epicondylalgia rehabilitation program for use by the health care professional (17).
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