Muscle injuries are highly prevalent in sports such as soccer, basketball, hockey, and athletics, accounting for more than 40% of total injuries in some disciplines .1 Groin pain accounts for up to 10% of sports injury clinic visits with a higher prevalence in males aged 26–30 .2,3 In soccer specifically, adductor-related groin injuries represent 64–69% of all groin injuries4,5 and are the second most common muscle injury among soccer players .1 These injuries result in an average absence of 15 days, and up to 40% of affected players miss more than 28 days of competition .5 The most common injury mechanisms in soccer involve kicking and changes of direction, which impose high eccentric demands on the adductor muscles .4

Several studies have identified low eccentric hip adduction strength (EHAD) as an intrinsic risk factor for groin pain, especially in soccer players with a history of injury .4,6 As a result, prevention and rehabilitation programs have incorporated adductor strengthening exercises to reduce injury incidence and time loss .1 However, commonly used protocols such as the FIFA 11+ lack specific exercises targeting hip adduction strength, which may limit their effectiveness in preventing groin injuries .6 In this context, the Copenhagen Adduction Exercise (CAE) has gained attention for its ability to improve EHAD and reduce the risk of adductor-related injuries .4

The CAE is a dynamic, high-intensity partner exercise that requires no equipment and can be easily performed on the field or in any training facility .1,6 The CAE is usually performed by side-lying on the floor with the upper leg supported in the air by a teammate or a bench. The hip is adducted until the body forms a straight line from the ankles to the shoulders (concentric phase). Then the player is instructed to lower the body slowly (eccentric phase) until reaching the floor to start the next repetition .7 EMG studies have shown that the CAE produces very high levels of activation, reaching 108% of maximal voluntary isometric contraction in the adductor longus of the dominant leg .4

Scientific studies have demonstrated significant improvements following CAE interventions. For instance, Ishøi et al.5 reported a 35.7% increase in EHAD after an 8-week program, and Harøy et al.6 observed a 36% increase in U19 sub-elite soccer players. A recent systematic review and meta-analysis confirmed a significant effect size in favor of the CAE (mean difference = 0.61 Nm/kg; p = 0.003) .1 However, Dawkins et al.4 found that low-dose interventions (e.g., twice weekly for six weeks) did not significantly improve EHAD, although they increased peak adductor squeeze strength. Moreover, most studies have focused on young male athletes, limiting the generalizability of the results to other populations.

Given this background, the aim of the present systematic review was to evaluate the influence of the CAE on groin pain management in athletes and physically active individuals. By synthesizing the available literature, this review seeks to offer practical recommendations on CAE implementation, optimal training parameters, and expected benefits in prevention and rehabilitation programs. Considering the high prevalence of groin injuries and the simplicity of the CAE, the results may serve as a valuable guide for coaches, clinicians, and sports professionals aiming to apply evidence-based strategies in real-world training settings.

The aim of this systematic review was to evaluate the influence of the CAE on the management of groin pain in athletes and physically active individuals. The main findings indicate that CAE interventions generally lead to improvements in several outcomes related to groin pain.

Beyond imaging-based assessments such as ultrasound and, in some studies, surface EMG, the included trials employed a wide range of clinical and functional evaluations that provide a broader understanding of groin function. These measures included strength-related assessments such as maximal EHAD and isometric adductor squeeze tests; range-of-motion assessments, primarily hip abduction ROM; functional performance tests, such as dynamic balance assessments using standardized protocols; and pain- and symptom-related outcomes, including HAGOS subscales, self-reported pain scores, and weekly prevalence of groin problems during training and competition. The use of such heterogeneous outcome measures reflects the multifactorial nature of groin-related dysfunction and supports a more comprehensive interpretation of how the CAE influences strength, symptoms, and neuromuscular performance across different athletic contexts.

Among the ten studies included in this review, seven reported improvements in at least one outcome related to groin pain management following CAE interventions. In contrast, three studies4,11,15 did not report significant changes in the assessed variables. These studies shared several characteristics, such as shorter intervention durations, fewer weekly sessions, or a lower total training volume, which may have limited the effectiveness of the intervention. Taken together, these findings suggest that studies using longer intervention periods (around ≥8 weeks) and higher cumulative exposure (approximately >200 total repetitions) tended to report more consistent improvements. However, this apparent threshold should be interpreted with caution, as it arises from indirect patterns observed across heterogeneous study designs rather than from trials explicitly comparing different CAE volumes or durations. Higher training doses may enhance outcomes through increased neuromuscular activation, repeated eccentric loading stimulus, improved motor control of the hip and pelvic stabilizers, and progressive architectural adaptation of the adductors. At the same time, several studies have reported substantial delayed-onset muscle soreness (DOMS) and reduced adherence during higher-volume protocols, particularly in the early weeks or when implemented in-season, indicating that the relationship between training volume and effectiveness is not linear. Consequently, although greater exposure appears to favor more robust adaptations, optimal dosing should be tailored to athletes’ tolerance, clinical presentation, and timing within the competitive calendar rather than applied as a fixed threshold.

This finding aligns with the dose-response relationship proposed by Quintana-Cepedal et al.7 who showed that a high-volume CAE protocol produced significantly greater improvements in adductor squeeze strength compared to a low-volume approach, with the effects persisting even after detraining period. Additionally, O’Connor et al.18 found that integrating external load into isometric CAE (i.e., weighted CAE) led to superior gains in the adduction/abduction strength ratio compared to the unweighted version, suggesting that both volume and intensity are key parameters for maximizing adaptations.

Notably, Dawkins et al.4 observed increases in peak adductor squeeze strength despite the absence of changes in EHAD, a pattern that echoes the low-dose findings in the O’Connor study. This may indicate partial neuromuscular adaptations even with minimal stimulus, though potentially insufficient to elicit eccentric strength gains, an important consideration given the established association between EHAD and injury prevention.

Strong evidence from randomized controlled trials also supports the use of CAE for injury prevention. Harøy et al.17 and Fujisaki et al.13 demonstrated reductions of 30–41% in groin injury incidence among male soccer and high school athletes compared to standard training protocols. These findings are further supported by both earlier and more recent meta-analyses6,19,20, which highlight the consistent strength gains achieved following CAE interventions. The high neuromuscular demand and eccentric nature of CAE likely play a key role in enhancing adductor resilience.

Regarding dynamic balance, one study included in this review16 reported positive effects, and these results are corroborated by the RCT by Al Attar et al.16 with over 200 participants, which showed significant improvements in balance metrics when CAE was performed either alone or in combination with NHE. This suggests potential broader neuromuscular benefits of CAE beyond adductor strength alone.

Although the included studies comprised a combined sample of approximately 1,099 participants, all were conducted exclusively in male athletes. This represents an important limitation, as groin injuries also affect female athletes, and recent evidence indicates that women may exhibit different baseline hip adductor strength profiles, neuromuscular activation strategies, and adaptation patterns to eccentric loading. These sex-related differences suggest that the responses to the CAE observed in male cohorts cannot be assumed to generalize to female populations. Therefore, the applicability of the present findings is limited, and future research should prioritize the inclusion of female athletes to determine whether CAE-related adaptations differ across sexes.

Although this review focuses on the CAE as a strengthening exercise for the hip adductors, it is important to acknowledge that the movement is not functionally isolated. EMG-based studies have shown that the CAE requires substantial coactivation of trunk stabilizers and pelvic musculature to maintain alignment and control the long-lever position, as well as contributions from upper and lower limb muscles across the kinetic chain .11,21 These synergistic muscular demands may influence performance and adaptation outcomes, suggesting that improvements attributed to the CAE may also reflect broader neuromuscular engagement rather than isolated adductor activation. Similarly, studies using ultrasound imaging have reported that hypertrophic adaptations may reverse after short periods of detraining, highlighting the need for program continuity .15

Few studies were found that evaluated and used CAE as the only exercise in the IG, which makes it difficult to guarantee that the observed effects can be attributed exclusively to the CAE, particularly because most interventions were performed alongside regular sport-specific training. Nevertheless, as shown in this review, studies that implemented the CAE as the primary or isolated component generally reported improvements in strength, function or symptom-related outcomes, suggesting that the CAE may provide meaningful benefits even when not embedded within comprehensive prevention programs. However, the scarcity of trials using CAE as a stand-alone intervention likely reflects both methodological and practical constraints. In real-world settings, the CAE is typically integrated into broader prevention or rehabilitation programs, together with other neuromuscular, strength and sport-specific exercises, rather than being implemented in isolation. Recent reviews have noted that most CAE-based protocols are combined with additional training elements, limiting the ability to isolate its independent effects .1,19 Likewise, current recommendations for hip and groin injury prevention favor multifactorial approaches that include adductor strengthening, trunk and pelvic stabilization, load management and movement control strategies .3,17 From a methodological and ethical perspective, isolating the CAE would require substantial restrictions or modifications to athletes’ usual training routines, which is often infeasible in applied sport environments.

Distinguishing prevention- and rehabilitation-oriented applications of the CAE is essential for accurate interpretation and clinical translation of the findings. The two injury-prevention trials included in this review17,13 primarily assessed the incidence of groin problems over a competitive season and implemented high-volume, progressive CAE protocols integrated into team training. In contrast, the rehabilitation-focused studies12,11 evaluated symptom severity, pain, hip adduction strength, and functional capacity in athletes with established groin pain, typically using lower weekly volumes and closer supervision. Strength- and architecture-focused trials4,5,7,14–16 further differ in design, as they targeted neuromuscular adaptation rather than injury risk or symptom resolution. Importantly, the parameters used in preventive programs, characterized by higher volume and longer duration, may not be directly transferable to rehabilitation contexts, where pain irritability and tissue tolerance require more cautious progression. Conversely, the lower volumes used in rehabilitation studies may be insufficient to achieve the exposure thresholds associated with injury-preventive effects. Therefore, while the CAE appears beneficial across domains, the optimal volume, frequency, and progression are likely context dependent, and clinicians should tailor the prescription according to whether prevention, symptom reduction, or structural adaptation is the primary target.

Furthermore, several of the included trials combined the CAE with additional training components, such as the Nordic Hamstring Exercise, general strength routines, or regular team training .13,16,19 This makes it even more challenging to isolate the specific contribution of the CAE to the observed outcomes. When multiple exercises targeting related neuromuscular capacities are administered simultaneously, improvements in strength, balance, or injury prevalence may result from cumulative or synergistic effects rather than from the CAE alone.

The substantial methodological heterogeneity across the included studies further limits the strength of the conclusions drawn from this review. The trials differed markedly in CAE progression parameters (sets, repetitions, weekly frequency, and use of external load), participant characteristics (age ranges, competitive levels, and baseline symptom status), and the extent to which the CAE was combined with other exercises such as the NHE or general strength routines .4,5,12,11,14,13,15,16 This variability complicates direct comparison of effects and reduces confidence in identifying optimal training parameters for specific clinical contexts. Moreover, the diversity in outcome measures and intervention designs precluded the pooling of data for a meta-analysis, as combining such heterogeneous protocols would risk producing misleading or clinically uninterpretable estimates.

To facilitate clinical application of the present findings and in line with reviewer recommendations, we provide a set of practical guidelines summarizing frequency, volume, progression strategies, and typical duration of CAE-based interventions according to their intended purpose. These recommendations are derived from the parameters used in the included randomized trials and should be interpreted as evidence-informed guidance rather than prescriptive protocols.

This potential injury-preventive effect is supported by evidence showing that increases in EHAD enhance the tissue’s ability to tolerate high mechanical loads and reduce adductor–abductor strength imbalances, both of which are recognized risk factors for groin injuries. In addition, recent meta-analyses have consistently reported substantial gains in adductor strength following CAE interventions19, which are closely associated with reduced injury risk.

Future research should include more diverse populations (e.g., women and non-athletes), isolate CAE’s effects, standardize protocols, and assess long-term outcomes to improve real-world implementation and guide clinical practice.

The CAE appears to be an effective intervention for improving and managing groin-related outcomes in male athletes. Evidence from randomized trials supports its preventive potential, while its rehabilitative applicability is suggested by consistent improvements in strength and symptom-related variables across studies. Given that all included studies examined only male athletes, the generalizability of these findings to female populations remains limited, and future research should determine whether CAE-induced adaptations differ across sexes. Although further research is needed to confirm these effects in broader populations, the current body of evidence supports its inclusion in conditioning and injury-prevention programs.

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“This work was supported by Faculty of Physical Activity and Sport Science, Europan University of Madrid”

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