The Effect of PNF Stretching on Knee Extension Range of Motion and Bike-Fitting Kinematics in Adult Male Cross-Country Mountain Bikers with Hamstring Tightness: A Randomized Controlled Trial

To determine the effect of a six-week proprioceptive neuromuscular facilitation (PNF) stretching program on knee extension range of motion, posterior thigh pain, lower-limb and trunk pedaling kinematics assessed by bike fitting, and pedaling efficiency in adult male cross-country mountain bikers with hamstring tightness.

Randomized, controlled, parallel-group clinical trial with outcome assessor and data analyst blinding, involving 40 cross-country mountain bikers (20 per group). Randomization was performed in blocks of four using a random sequence generated with Randomizer.org.

This study will be conducted in cycling clubs in Tabriz on 40 cross-country mountain bikers with hamstring tightness. Participants will be randomly allocated to an intervention group or a control group. Knee range of motion, posterior thigh pain, bike-fitting pedaling kinematics, pedaling efficiency and squat strength will be assessed after the intervention.

Inclusion criteria: Male cross-country mountain bikers aged 18–35 years at club level, with at least two years of regular training, hamstring tightness (inability to reach less than 15° of knee flexion in the Active Knee Extension test), and mild to moderate posterior thigh pain (VAS 3–7). Exclusion criteria: Hamstring strain within the past six months, lower-limb fracture or surgery within the past year, spinal disorders, posterior thigh pain of non-muscular or neural origin (positive Slump test), knee flexion contracture, and cardiovascular or metabolic disease contraindicating exercise.

Intervention group: PNF stretching using the hold-relax technique for the hamstring muscles for six weeks. Control group: No intervention.

Active knee extension range of motion; posterior thigh pain intensity; maximum knee extension angle during pedaling

Participants will be allocated to the PNF stretching group or the control group using block randomization with a fixed block size of four and a 1:1 allocation ratio. Each block will assign two participants to the PNF group and two to the control group, keeping group sizes balanced throughout recruitment and reaching 20 participants per group. The unit of randomization is the individual, and no stratification will be used, as all participants are male cyclists of the same discipline and training level. Before recruitment begins, a person not involved in the study’s assessments or intervention will generate a random sequence for 40 participants, comprising ten blocks of four, using an online program (Randomizer.org). The group assignment for each number will be written on a separate card and placed in an opaque, sealed envelope numbered sequentially from 1 to 40. To ensure allocation concealment, the envelopes will be kept by the same independent person. Once a participant has been confirmed as eligible, has signed the consent form and has completed the baseline assessment, the next envelope in sequence will be opened to reveal his group. Researchers who enroll participants and perform baseline testing will therefore remain unaware of group allocation until baseline assessment is complete.

The de-identified individual participant dataset of the PNF stretching and pedaling kinematics trial will include all primary and secondary outcome variables recorded at the individual level at baseline and follow-up. These variables comprise active knee extension range of motion, posterior thigh pain intensity, pedaling kinematic angles (maximum knee extension and maximum knee flexion angles, hip angle at the top and bottom of the pedal stroke, torso angle, foot and ankle angles, knee tilt, and the width and length of the knee path), mean heart rate during constant-intensity pedaling, and the estimated one-repetition maximum in the single-leg squat. The dataset will also include baseline demographic variables, namely age, height, weight, body mass index, leg length and training experience, as well as test-condition control variables, namely mean power output and cadence. The correlation analysis between changes in knee angle and changes in heart rate will also be included as an exploratory analysis, but will be explicitly labelled “exploratory”. All direct and indirect participant identifiers, including video files, will be removed before release. In addition to the dataset, the full study protocol will be shared. It includes the inclusion and exclusion criteria, a detailed description of the intervention and stretching protocol, the randomization and allocation concealment procedures, the assessor blinding method and the pre-specified outcome measurement schedule. The statistical analysis plan will also be shared, providing full specifications of the pre-specified statistical models: analysis of covariance with the baseline score as a covariate, Quade’s non-parametric analysis of covariance if residuals are not normally distributed, the Wilcoxon test for within-group changes, and Pearson or Spearman correlation coefficients. The plan also specifies the assessment of assumptions using the Shapiro-Wilk and Levene tests and homogeneity of regression slopes, the reporting of effect sizes as partial eta squared, the per-protocol analysis approach, and the method for assessing attrition bias. The complete SPSS syntax file to reproduce all primary, secondary and exploratory analyses reported in the article, and a blank, de-identified copy of the informed consent form used in this study (the form template only, not participants’ completed forms), will also be made available.

The access period for de-identified data, analysis scripts, and supplementary materials will begin immediately upon final acceptance of the manuscript for publication. These materials will be accessible via a Digital Object Identifier (DOI), included in the published article, hosted in the public Zenodo repository, and this access will continue for a minimum of 10 years from the date of publication. During the peer review process (prior to final acceptance), materials will be made available through the corresponding author upon reasonable request.

Because the data and documents from this study will be deposited publicly and without access restrictions in the Zenodo repository, they will be available to any researcher — whether affiliated with academic institutions, research centres, or industry — whose intended use is legitimate scientific research, replication of findings, or meta-analysis, without requiring specific permission from the authors. The only requirement will be appropriate citation of the original data source (the published article and repository DOI).

In addition to the criteria described above regarding who is eligible to request access, the following conditions will govern the use of data and documents from this study: 1. Purpose of use: Data may be used solely for non-commercial research purposes; any commercial use will require separate written permission from the corresponding author. 2. Permitted types of analysis: No restrictions will be placed on the type of statistical analysis or research methodology applied to the delivered data; researchers may use any analytical approach appropriate to their research objectives. 3. Request process: Applicants must submit a written request to the corresponding author, including the project title, research objectives, proposed methodology, and a written commitment to adhere to research ethics principles. 4. Data delivery mechanism: Upon approval of the request, data will be provided to the applicant either through the public Zenodo repository (using the dedicated DOI) or via direct file transfer. 5. Citation requirement: Researchers will be required to properly cite the data source, including the DOI and reference to the original article, in any publication resulting from secondary use of the data. 6. Participant privacy protection: Applicants will be required to commit to using the data solely for the purposes stated in their request and to refrain from any attempt at re-identification of participants.

First priority (direct public access): All de-identified data, analysis scripts and supplementary materials will be uploaded to the Zenodo public repository and made available through a digital object identifier (DOI) included in the published article. Interested users can download the data free of charge, without direct contact, by following the DOI link provided in the article. Second priority (request to the corresponding author): If additional information or documents not uploaded to the public repository are required (such as the informed consent form), applicants may send a written request to the corresponding author, including the project title, research objectives, proposed methodology and a written commitment to adhere to research ethics principles. Corresponding author contact details: Name: Sina Najafpour Affiliation: Department of Sports Injuries and Biomechanics, Faculty of Sport Sciences, Bu-Ali Sina University, Hamedan, Iran Postal code: 65178-38695 Email: sina.student15@gmail.com Phone: +98 914 630 1771

Applicants should first access the public Zenodo repository via the Digital Object Identifier (DOI) provided in the article and download the data directly and free of charge, a process expected to take less than 5 minutes. If access to the repository is not possible, the applicant must submit a written request — including the project title, research objectives, proposed methodology, and a commitment to adhere to research ethics principles — by email to the corresponding author. The request will be reviewed within 3 to 7 business days, and if approved, the data will be provided to the applicant within 1 to 3 business days via an access link, email, or secure file-sharing platforms. The total time required, in cases where the public repository is not accessible, will be approximately 1 to 2 weeks.