This study investigates how simulated knee injury-via artificial joint effusion or deafferentation-affects quadriceps motor unit behavior in healthy young adults. Participants will complete neuromuscular testing during a single 2-hour lab session. This research seeks to improve understanding of muscle inhibition and inform interventions after real-world knee trauma.

Using a controlled laboratory model, the investigators will simulate knee injury through two methods: (1) intra-articular saline injection to induce effusion, and (2) intra-articular lidocaine injection to induce sensory deafferentation. Healthy participants aged 18-30 will undergo surface and decomposition EMG, isometric strength testing, and reflex measurements before and after the intervention. The primary outcome is motor unit recruitment characteristics, with secondary outcomes including quadriceps inhibition (Hoffmann reflex) and isometric peak torque. The findings will inform future neuromodulatory approaches in rehabilitation.

Inclusion Criteria:

1. Age 18-30 years
2. Physically active (Tegner ≥ 5)
3. No prior lower-limb surgery or major injury

Exclusion Criteria:

1. Lower limb surgery or significant injury in past 2 years
2. Cardiopulmonary, neurological, or psychiatric disorders
3. Needle/electrical stimulation anxiety
4. Medications affecting neuromuscular or psychological function
5. Pregnancy
6. Allergic to lidocaine
7. Inability to elicit Hoffmann reflex

De-identified individual participant data (IPD) related to primary and secondary outcomes, including motor unit recruitment characteristics, quadriceps strength, and Hoffmann reflex measurements, will be shared with qualified researchers upon reasonable request.

The IPD and supporting documentation will be available beginning 6 months after publication of the primary manuscript. Data will remain available for 5 years following that date.

Qualified researchers with appropriate data use agreements in place may request access. Requests should be submitted to the Principal Investigator via email and will be reviewed by the study team. Data will be shared via secure file transfer protocols.