Effect of US-Guided PNM in CrossFit With Nonspecific Shoulder Pain

CrossFit is a high-intensity physical training program that combines exercises from various disciplines, such as weightlifting, track and field, running, and gymnastics. The three main characteristics of this sport discipline are as follows: first, the execution of functional movements; second, performing them at high intensity; and lastly, constant variation. This training model has shown improvements in strength, power, balance, flexibility, and cardiorespiratory capacities.

There are various risk factors described in the literature that may lead to injuries in CrossFit athletes. It has been suggested that demanding training programs increase this risk, especially when performed incorrectly (poor technique). Additionally, excessive training load and frequency can lead to early fatigue, greater perceived effort, and risky movement execution.

On the other hand, older age, male sex, and previous injuries also appear to be relevant risk factors, as well as performing stretches prior to CrossFit practice. Several studies have shown that the shoulder is the joint with the highest prevalence of injury in this sport, surpassing other commonly affected joints such as the lumbar spine or the knee.

Among the wide variety of injuries related to the shoulder, the diagnosis of "nonspecific shoulder pain" has a high prevalence in the adult population. This term is used to describe clinical cases where it is not possible to identify the specific cause of the pain, and is justified by its multifactorial etiology, which is associated with several risk factors. These include: imbalance in the strength ratio between internal and external rotators, limitations in rotational mobility of the glenohumeral joint, deficits in motor control of the scapular musculature, shoulder muscle fatigue, and the repetitive execution of overhead exercises.

This last factor is especially relevant in the CrossFit population, as such movements are frequent in the discipline. Repeated overhead exercises have been associated with a deficit in glenohumeral internal rotation. From a biomechanical perspective, this movement is more efficient when accompanied by external rotation, so internal rotation limitation can compromise the motion. This deficit has been linked to modifiable musculoskeletal factors such as posterior capsule stiffness, shortening of the infraspinatus or teres minor muscles, and scapular mechanics alterations, as well as non-modifiable factors like bone torsion observed in young athletes. These conditions can lead to pain and/or glenoid labrum pathology.

Regarding the clinical management of nonspecific shoulder pain, conservative physiotherapy treatment is the most common approach. This is based on manual therapy and therapeutic exercise. However, in recent years, invasive physiotherapy has gained popularity in the treatment of musculoskeletal disorders through techniques such as ultrasound-guided percutaneous neuromodulation (US-guided PNM). This technique involves delivering electrical stimulation through an acupuncture needle placed near the nerve (epineurium) or the motor point of the target muscle, aiming to restore proper functionality of pathological neuromuscular structures.

US-guided PNM, applied to both the lower and upper limbs, has shown effectiveness in both healthy individuals and subjects with various musculoskeletal disorders, improving pain, strength, flexibility, and normalization of neural excitability.

Currently, there are therapeutic exercise protocols used for both evaluation and treatment of nonspecific shoulder pain in CrossFit athletes. Additionally, there are US-guided PNM protocols that have been applied to healthy CrossFit athletes and have demonstrated improvements in shoulder rotational strength. However, US-guided PNM has not yet been studied in a population of CrossFit athletes with nonspecific shoulder pain. Therefore, this randomized clinical trial aims to evaluate the effectiveness of two different US-guided PNM protocols, analyzing which methodology is most appropriate for reducing the risk factors associated with the development of nonspecific shoulder pain in CrossFit athletes.