Ultrasound-Guided Percutaneous Neuromodulation in the Strength of CrossFit Athletes

The origin of CrossFit (CF) dates back to 1995 when Greg Glassman opened the first facility dedicated to the sport he named CF in Santa Cruz, California. However, the dissemination and promotion of this sport began in 2000 with the creation of the CF brand alongside his wife Lauren Jenai. Today, the brand generates around 100 million euros annually and has a market valuation of approximately 4 billion euros. CF boasts 14,000 boxes in 155 countries, with over five million users. Spain ranks as the fifth country with the most CF centers.

CF training focuses on constantly varied functional movements, including gymnastics, weightlifting exercises, and cardiovascular activities (e.g., running or rowing). Variety is one of the main attractions for participants, as the workouts are short, intense, and diverse.

Within invasive physiotherapy, there is the technique of ultrasound-guided percutaneous neuromodulation (US-PNM), which enhances muscle function, muscle recruitment patterns, and motor control. This minimally invasive intervention involves the application of percutaneous electrical stimulation through an electrode similar to an acupuncture needle, placed in close proximity to the nerve or motor point of the target muscle under ultrasound guidance. Performing this technique under ultrasound guidance is recommended as it makes the procedure safer and more effective, allowing real-time visualization of needle positioning and technique application.

Most studies on US-PNM have focused on pain treatment in patients, but some studies have explored its benefits in healthy individuals. For instance, De-la-Cruz-Torre et al. demonstrated that applying this procedure to the sciatic nerve can increase hamstring flexibility; De-la-Cruz-Torres et al. also reported an increase in the performance of the flexor hallucis longus muscle in dancers; Álvarez-Prats et al. showed an improvement in quadriceps muscle strength after performing electrical stimulation on the femoral nerve; and Gallego-Sendarrubias et al. suggested an enhancement in performance skills in soccer players by applying the neuromodulation procedure to the femoral nerve before specific strength training.

Overall, the literature suggests that US-PNM intervention improves strength levels, but the results should be confirmed with future research due to sample size limitations and short-term evaluations. Additionally, there are currently no studies on the application of US-PNM in a sample of CF athletes. Therefore, the objective of this study is to analyze the effectiveness and duration of the effects of two US-PNM protocols applied to the axillary and suprascapular nerves on shoulder rotation strength in healthy CF athletes.

The study aims to:

* Analyze whether 3 sessions of ultrasound-guided percutaneous neuromodulation (US-PNM) are more effective than 1 session of US-PNM for shoulder rotation muscle strength in healthy CrossFit athletes.
* Analyze whether the US-PNM intervention has a positive effect on the ability to perform a one-repetition maximum (1RM) in a functional CF movement, such as the "Shoulder Press," in healthy CrossFit athletes.

To achieve this, a randomized clinical trial is proposed with three study groups:

* Control group: no intervention will be performed.
* Experimental group 1 session US-PNM: will receive 1 session of US-PNM.
* Experimental group 3 sessions US-PNM: will receive 3 sessions of US-PNM, with one week of separation between each session.

Eligibility Criteria:
Inclusion Criteria:

* Be between 18 and 65 years old
* Have at least 1 year of experience in CrossFit training

Exclusion Criteria:

* Have not undergone any previous surgeries
* Have no pathology that causes any type of pain
* Have no physical impairment that would hinder dynamometry measurements (muscle injuries, joint instability, joint inflammation, etc.)
* Have no contraindications for the application of Ultrasound-Guided Percutaneous Neuromodulation (US-PNM) such as trypanophobia, pregnancy, epilepsy, or pacemakers.