The goal of this pilot clinical trial is to evaluate whether the ultrasound-guided percutaneous peripheral nerve stimulation through a needle results in greater gains in strength and power compared to the administration of current through surface electrodes in patients undergoing strength and power assessments. The main questions it aims to answer are:

Does percutaneous stimulation of the superior and inferior gluteal nerves using ultrasound-guided needles enhance strength and power more effectively than transcutaneous stimulation through electrodes?

Is the effectiveness of current delivery significantly different between percutaneous and transcutaneous methods when assessed with a linear encoder in a standarized hip extension exercise?

Participants will:

Be randomized into two groups: one undergoing ultrasound-guided percutaneous stimulation of the gluteal nerves (experimental group) and the other undergoing transcutaneous stimulation through electrodes (control group).

The same stimulation protocol at 10 Hz frequency with the maximum muscle contraction evoked without pain will be performed in both groups. Then, the participants will undergo strength and power assessment before and after therapy administration using a linear encoder in a hip extension exercise.

Researchers will compare the experimental group to the control group to see if the method of current delivery (percutaneous vs. transcutaneous) has a significant impact on the gains in strength and power. This comparison is based on the hypothesis that percutaneous delivery of current, guided by ultrasound, is more effective than simply positioning a surface electrode for transcutaneous stimulation. The evaluation of strength and power will be performed through a linear encoder that measures peak strength and concentric power in each repetition, conducted by a blind operator unaware of the patients' group allocations.

This study delves into the comparative efficacy of two modalities of nerve stimulation for enhancing muscular strength and power: the percutaneous application of electrical current via acupuncture needles versus traditional transcutaneous electrical nerve stimulation (TENS). The overarching objective is to discern whether percutaneous peripheral nerve stimulation (pPNS), guided by ultrasound, facilitates superior gains in muscle strength and power in the gluteal muscles compared to conventional TENS.

Participants, suffering from chronic knee pain, were systematically randomized into two cohorts: the experimental group underwent ultrasound-guided pPNS targeting the superior and inferior gluteal nerves, whereas the control group received TENS. The experimental setup was meticulously designed to ensure the sole variable of distinction between groups was the method of electrical stimulation applied. pPNS was delivered using a biphasic asymmetric electric current, set to a frequency of 10 Hz, a pulse width of 240 microseconds, and an intensity tailored to achieve maximal muscle contraction without inducing pain, based on a protocol of ten 10-second stimulations interspersed with 10-second rest periods. This regimen was predicated on prior findings demonstrating its efficacy in augmenting isometric strength following femoral nerve stimulation. The control group was subjected to a parallel protocol, differing only in the application technique, wherein electrodes replaced needles, adhering to the same stimulation parameters.

The therapeutic efficacy of both interventions was assessed through a rigorous evaluation of strength and power before and after the administration of therapy. This assessment employed a linear encoder to measure peak strength and concentric power during the Hip Thrust exercise, a method chosen for its reliability in quantifying these parameters. The procedure entailed performing the exercise under three different loads (30%, 50%, and 70% of the participant's maximum capacity, 1RM), with the evaluation aimed at capturing the concentric peak power in each repetition until a noticeable decline in performance was observed.

The hypothesis posits that pPNS, by virtue of its targeted and invasive nature, will yield greater improvements in muscle strength and power than TENS, attributed to its more direct stimulation of the nerve fibers and the encompassing muscle groups. The underpinning rationale is that pPNS's ultrasound-guided approach allows for a more precise delivery of electrical current to the nerves, potentially overcoming limitations associated with the superficial and diffuse application of TENS.

For the analysis of the collected data, an initial evaluation of distribution characteristics will be performed utilizing visual tools such as Q-Q plots and density plots, complemented by statistical measures of kurtosis and skewness to understand the data's underlying structure. The Shapiro-Wilk test will be applied to assess the normality of residuals, ensuring the validity of subsequent statistical tests. Descriptive statistics, including the mean, median, mode, and standard deviation of the collected quantitative measures, will be thoroughly examined to summarize the data effectively. Additionally, the homogeneity of these variables across the dataset will be scrutinized.

Regarding inferential statistics, an exploratory approach will be adopted to estimate confidence intervals and discern trends in the data, particularly focusing on pre- and post-treatment differences both within individual subjects and between the groups. Due to the anticipation of non-normal data distribution and the structure of the study design (pretest-posttest control group), non-parametric statistical tests will be employed for the analysis. Specifically, the Mann-Whitney U test will facilitate between-group comparisons, while the Wilcoxon test will be used for related measurements to detect changes within groups over time.

Data analysis and visualization efforts will be supported by SPSS 23.0 software (SPSS Inc., IBM Chicago, IL, USA) and/or GraphPad Software (San Diego, CA, USA). For the interpretation of results, a 95% confidence interval and an alpha level of 0.05 will be established as thresholds for statistical significance. The creation of figures and graphical representations of the findings will be executed using Adobe Illustrator (San José, CA, USA), ensuring that the visual presentation of data is both clear and informative. This comprehensive approach to data analysis and visualization aims to elucidate the potential differences in efficacy between percutaneous peripheral nerve stimulation and transcutaneous electrical nerve stimulation in enhancing muscle strength and power, guiding future research and clinical applications in the field.

Inclusion criteria:

• Adult athletes above the legal age threshold
• Amateur athletes
• Experiencing chronic knee pain
• Possessing a prior diagnosis related to their knee condition
• Competent in the execution of the hip thrust exercise

Exclusion criteria:

• Underage or elderly
• Significant co-existing medical conditions and/or comorbidities
• Professional athletes
• Sedentary lifestyle
• Lack of familiarity with the hip thrust exercise
• Needle phobia or rejection to peripheral stimulation techniques
• Considerable contraindications such as a history of knee surgery, current pregnancy, or issues related to blood clotting.

In line with the commitment to share Individual Participant Data (IPD), the plan encompasses disseminating all collected IPD that underlie the results reported in a forthcoming scientific publication. This effort is designed to promote transparency and facilitate further research by providing comprehensive access to detailed datasets. To ensure adherence to ethical standards and protect participant privacy, all shared data will undergo an anonymization process.

Data will be available after the publication of the main results, allowing sufficient time for the primary research team to complete additional analyses.

Access to the anonymized datasets will be granted upon request to researchers who provide a methodologically proposal.

In the study, blinding will be implemented to minimize bias. The evaluating clinician will be blinded to participant group assignments, ensuring assessments are unbiased. Similarly, the data analyst will also be blinded, analyzing data without knowledge of group allocations to maintain impartiality. Data will be handled objectively, with statistical methods applied blindly to compare treatment groups. Despite challenges in completely blinding participants due to the distinct nature of interventions, every effort will be made to minimize potential bias.