BRINGING SCIENCE TO TREATMENT

Case Report: James Harden’s Hamstring Hardships

Hamstring strain injuries are one of the most common soft tissue injuries. Persistent neuromuscular deficits in eccentric strength and fascicle length increase the risk of reinjury. Cameron Gill explores exercise selection to mitigate the nonmodifiable risk factors and return athletes to performance safely.

Brooklyn Nets shooting guard James Harden (13) sits on the court after an injury at the end of the second quarter against the Washington Wizards at Barclays Center. Mandatory Credit: Brad Penner-USA TODAY Sports

Across an eight-season stretch with the Houston Rockets, James Harden cemented himself as an all-time great while scoring over 18,000 regular-season points. But unfortunately, his time as a dominant superstar has ended after a series of hamstring strain injuries (HSIs) in the second half of the 2020-2021 season. Hamstring injuries are one of the most common non-contact injuries in multiple sports and are particularly prevalent in the NBA(1–5). Typically, athletes return to play within three weeks after experiencing an HSI. Still, the associated tissue capacity reductions and complex musculoskeletal effects can persist dramatically longer, thereby increasing the injury risk for months after(6–8).

Harden’s hamstring history

On March 31, 2021, Harden suffered an HSI while playing for Brooklyn Nets. At the time, this injury did not appear to be a significant cause for concern. Previously, Harden experienced two HSIs with the Rockets, one during the 2017-2018 season and another during the 2018-2019 season, which together sidelined him for just ten games. However, by April 5, 2021, Harden returned after missing only two games but experienced a subsequent HSI four minutes into the game, which sidelined him for the next 18 games.

During the first round of the 2021 playoffs, Harden returned to performance without any apparent challenges. However, less than one minute into Game one of the Eastern Conference Semifinals against the Milwaukie Bucks, Harden suffered another HSI. Despite having an offseason to recover, persistent hamstring issues continued into the 2021-2022 season, sidelining Harden for several games and likely contributing to the notable decline in his performance relative to the past six seasons when he received MVP votes each year.

Hamstring strain injuries

Hamstrings generate hip extension and knee flexion torque and play a pivotal role while running at high speeds. During the second half of the swing phase, they act eccentrically to decelerate the flexing hip and extending knee(9). Most running-induced HSIs affect the biceps femoris long head. This injury most likely occurs during the terminal swing phase when the biarticular hamstrings experience peak activation, eccentric loading, and strain (see figure 1)(10).

Figure 1: Phases of gait

Multiple neuromuscular deficits, such as shorter biceps femoris long head fascicles and lower eccentric knee flexion strength, exist well after athletes return to play(11–16). Therefore, a history of a prior HSI increases the injury risk(17). As Harden experienced his second HSI in 2021, during the initial RTP weeks, he was at the greatest risk for reinjury, and recurrent HSIs are often more severe(6,18,19). Furthermore, HSI risk increases as an athlete’s age increases, and this relationship exists independently from someone’s prior injury history(17,20). While athletes can still be in their prime in their thirties, they are at a noticeably greater HSI risk than those in their early twenties or even mid-twenties(21,22).

Reducing Risk

Athletes and practitioners can do nothing to reverse an athlete’s age or undo a previous HSI. Still, practitioners can mitigate the effect of these two “nonmodifiable” risk factors on an athlete’s probability of sustaining a new injury. For example, researchers at the Australian Catholic University in Melbourne, Australia, demonstrated that age and prior HSI history no longer significantly increase an athlete’s injury risk when athletes have high eccentric knee flexion strength(23). On the contrary, low eccentric knee flexion strength, previous HSI, and relatively older age increase HSI risk(22,23).

The same trend occurs when measuring the biceps femoris long head fascicle lengths. For example, longer fascicle lengths mitigate age and a prior HSI, but these two variables affect injury risk when fascicles are very short(22). Given the relationship among these nonmodifiable and modifiable variables, increasing eccentric knee flexion strength and biceps femoris long head fascicle lengths should be critical objectives for athletes as they approach their thirties.

Fascicles are bundles of muscle fibers composed of myofibrils that include sarcomeres (see figure 2). Therefore, the number of sarcomeres in a series determines fascicle length. For a given degree of myofibril lengthening, each sarcomere will experience a lower change in length and consequently a lower magnitude of strain. The addition of sarcomeres in series, termed sarcomerogenesis, is an adaptation that can be induced by certain types of resistance training depending upon the type of muscle action utilized and the peak muscle length loaded. For yielding the most significant increase in fascicle length, eccentric training is superior to concentric training, and loading a muscle at long peak lengths is superior to loading a muscle at short peak lengths(24–31).

Figure 2: Skeletal muscle anatomy

Eccentrically loading a muscle at long peak lengths is highly effective at enhancing eccentric strength. Although concentric or isometric resistance training may increase eccentric strength, strength gains still demonstrate some degree of muscle action type specificity. Therefore, eccentric resistance training yields the greatest magnitude of eccentric strength gains(32,33). In addition, strength gains also exhibit muscle length specificity, so training a muscle at long lengths can yield greater improvements in the torque produced at long lengths than training a muscle at shorter lengths(29,34–41). Terminal swing phase, while running, lengthens the biarticular hamstrings beyond their resting lengths. Therefore, eccentric resistance training through this lengthened position will be optimal for enhancing eccentric hamstring strength at the joint angles where HSIs are most likely to occur.

Rehabilitation

Practitioners typically prescribe Nordic hamstring curls to mitigate HSI risk (see figure 3). Nordic curls provide high-intensity eccentric hamstring training, increase eccentric knee flexion strength, lengthen the biceps femoris long head fascicles, and reduce HSI risk(42–48). However, good does not equate to optimal. There is little reason to believe that Nordics are the most efficient tool for inducing these desirable effects because they never load the biarticular hamstrings beyond their resting lengths.

Figure 4: Nordic hamstring curl

Alternatively, a machine seated unilateral knee flexion exercise or a multi-hip machine unilateral hip extension exercise performed with a minimal angle of knee flexion eccentrically loads the biarticular hamstrings at long peak muscle lengths (see figures 5 and 6). A partner can manually perform the concentric phase for either exercise while the athlete exclusively trains the eccentric phase until achieving peak biarticular hamstring stretch.

Figure 5: Machine seated eccentric knee flexion

Figure 6: Multi-hip machine eccentric hip extension with minimal angle of knee flexion

Athletes unaccustomed to these exercises may experience muscle damage and soreness, so practitioners should gradually progress the volume and intensity. After an acclimation period, practitioners can prescribe supramaximal loads (i.e., exceeding concentric one rep maximum) to provide the most potent stimulus to increase eccentric strength and fascicle lengths. Practitioners can prescribe both exercises concurrently to train the primary functions of the hamstrings and strengthen their synergists.

 Conclusion

James Harden is a prime example of how the typical RTP timeframes do not capture how long full recovery may require. Despite the challenges, athletes can take meaningful steps to restore hamstring function and reduce the risk of recurrent injury. Exercise selection is just one facet of rehab and injury risk mitigation programs, and practitioners should carefully select exercises based on their ability to influence eccentric strength and fascicle length. Therefore, exercises that eccentrically train the biarticular hamstrings at long peak muscle lengths with a supramaximal load merit inclusion in a plan designed to address HSI risk factors.

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