Does nervous system function predict rehabilitation outcomes in people with patellar tendinopathy?

12-weeks contemporary progressive exercise rehabilitation program: Participants will complete a 12-week progressive exercise rehabilitation program that closely follows a contemporary, evidence-based protocol. This will progress through four 'levels': isometric exercise, isotonic exercise, stretch-shorten cycle (energy-storage) exercise, and return to sport exercise. Progress is based on strict pain and function criteria. Following the initial assessment, participants will be provided with thorough, standardised education by the chief investigator, covering: • The benefits of exercise therapy; • How to monitor pain irritability using pain provoked by prescribed exercises; • The structure and application of progressive-exercise rehabilitation, including: o Program stages and progression criteria; o Detailed descriptions of gym-based resistance exercises and home-based alternatives; o Guidelines for modifying activity (e.g., training and competition) based on pain irritability. Participants will be provided access to gym facilities required to complete the rehabilitation program, with an agreement in place for 12-weeks membership with a gym chain, who have sites locations situated throughout east and south-east Melbourne to maximise accessibility for the targeted recruitment region. Additionally, home-based alternate exercises will be provided to improve feasibility of adherence to the exercise program. The intervention will be delivered by experienced physiotherapy clinicians who have undergone comprehensive training in key intervention components, including progressive-exercise rehabilitation. Intervention delivery will be supported and monitored using PhysiApp (Physitrack, London, UK), a freely available, HIPAA-compliant, cloud-based mobile phone application. Clinicians will access the corresponding clinician-facing software (Physitrack). Participants will be supported to install PhysiApp on their personal mobile device and to navigate functions required for this trial (e.g., logging exercises). Individualised exercise programs, matched to their rehabilitation 'level', will be delivered via the application. This will include written exercise details, in addition to videos demonstrating appropriate exercise performance/technique recorded for this trial. Exercise mode, frequency, and durations per level: • Level 1 (isometric stage): Primary exercises include the single-leg isometric knee extension using a leg extension or leg press machine (or a double- or single-leg isometric wall sit as a home alternative). Sessions are completed every second day. The starting dosage is 5 sets of 45-second holds, which gradually progresses within the level to 5 sets of 20-second holds as weight is increased. Each session is anticipated to take approximately 20 minutes to complete. • Level 2 (isotonic stage): Primary exercises include the single-leg isotonic knee extension (or a walking lunge or step-up as home alternatives). Level 1 exercises are also continued on the same day (completed after isotonic movements). Sessions are performed every second day. The starting dosage is 4 sets of 15 repetitions, which progresses by reducing repetitions and increasing load until 4 sets of 6 repetitions are achieved. Each session is anticipated to take approximately 30-45 minutes to complete. • Level 3 (energy-storage stage): Exercises consist of stretch-shorten cycle movements such as jump squats, split jump squats, and box jumps, alongside continued Level 1 and 2 maintenance exercises. Sessions are performed every third day. The dosage starts at 3 sets of 6 repetitions and progresses up to 6 sets of 6 repetitions. Each session is anticipated to take approximately 45-60 minutes to complete. • Level 4 (sport-specific stage): Exercises involve an individualised approach matched directly to the participant's recreation or sport (e.g., jumping, dribbling, and cutting drills for a basketball player). Level 1 and 2 exercises continue on the first day post-sport-specific training. Sessions are performed every second to third day. The starting duration is approximately 30 minutes per session, building gradually until full training duration is reached. Exercise intensity targets and assessment: Exercise intensity is formally evaluated following the completion of each exercise using a modified Rated Perceived Exertion (mRPE) scale ranging from 1 to 10. • For Levels 1 and 2, the target level of exercise intensity is vigorous to very hard, explicitly aiming for a target mRPE of 8/10 or higher by the end of each set (indicating near-fatigue). • For Level 3, intensity is judged by movement velocity and power rather than muscle fatigue. It starts at a target velocity rating of 7/10 (high velocity/70% of perceived maximum speed) and aims to progress to a target of 9/10 or higher (extremely high velocity) with no velocity loss by the final repetition. • For Level 4, exercises begin at a self-perceived moderate intensity, targeting approximately 70% of match intensity (corresponding to a mRPE rating of 7/10 [hard]), before gradually progressing to 'full' maximum athletic intensity. Participant app interaction and review format/timing: Participants are not required to interact with PhysiApp for a designated minimum daily duration; instead, they use the app at their own discretion to guide their prescribed workout sessions and must log their exercise data (sets, repetitions, load, mRPE, and pain scores) immediately following each completed session. Clinical review and progress assessments do not follow a fixed bi-weekly or tri-weekly timeline. Instead, data logged by participants is monitored remotely by clinicians on a continuous basis. Clinicians formally evaluate individual progress once a week via the Physitrack desktop portal to determine if within-level progression criteria are met. When a participant successfully satisfies the strict pain and functional criteria required to advance to the next overarching rehabilitation 'level' (e.g., maintaining pain = 3/10 on the Numeric Rating Scale for an entire week at the maximum level dosage), a progression review is triggered. While the initial physical examination screening is conducted face-to-face to confirm diagnosis and eligibility, subsequent level-progress reviews are conducted remotely. Clinicians will utilise the Physitrack system’s integrated video-conferencing function to review the participant when ready to progress from one level to the next, confirm readiness, and provide detailed technical instructions for this upcoming exercise level. All updated program details (when progressed within a level, or between levels) are immediately reflected on the participant's PhysiApp mobile app interface. Clinicians will monitor adherence via the exercise sessions logged on PhysiApp; if participants miss more than one planned session in a week-period, the clinician will follow up via the Physitrack system’s secure messaging function. This function will also be used to alert participants to weekly within-level program updates, and for feedback or urgent enquiries, and will be checked daily by clinicians. Automatic reminders will be sent via PhysiApp for each exercise session to encourage adherence.