The purpose of this small, pilot study is to evaluate a novel device that uses neuromuscular electrical stimulation to assist quadriceps muscles as a user walks. This study will involve use of this device on individuals with patellofemoral pain, a relatively common injury among active people, to see if quadriceps stimulation could mitigate disparities in quadriceps activation timing that may indirectly lead to knee pain.

The interventional device will be tested with 20 women aged 18-40 with evidence of patellofemoral pain syndrome (PFPS) and without any co-morbidities that would confound data or contraindications for NMES use. All participants will be enrolled at a single site (Developmental Motor Lab at the University of Texas), and all of a single participant's testing will be complete within a single day with no requirement for follow-up or long-term participation. Participants will have their gait and quadriceps muscle activation patterns evaluated through four six-minute walk tests (6MWT). The first 6MWT will be without a device, second with a device worn but not activated, third with a device activated and stimulating quadriceps musculature, and the fourth without a device.

Primary Objective: The purpose of this study is to investigate whether electrical stimulation of the vastus medalis (VM) and/or vastus lateralis (VL) to establish coactivation of these muscles during terminal swing phase impacts severity of PFPS symptoms

Secondary Objectives: Secondary purposes for this study include evaluating KneeStim and seeing if there is any evidence of proof of concept in two main areas:

KneeStim as a therapeutic device that may assist individuals with joint rehabilitation KneeStim's on-board operating system and motion tracking system as an effective way to monitor joint kinematics.

This pilot study has a prospective, controlled, single-center design. Participants and investigators will not be blinded to the treatment. Individuals who evaluate the motion-tracking data between VICON and KneeStim will not be informed which data set aligns with which treatment.

Inclusion Criteria:

• Aged 18-40 years
• Symptomatic PFPS on Patella Glide Test, Patella Tilt Test, and Patellar Apprehension Test.

Exclusion Criteria:

• Rheumatoid arthritis or inflammatory arthritis as assessed by licensed physician
• Use of walking aids other than a cane more than 50% of the time in ambulation
• Diagnosed knee disorder other than patellofemoral syndrome
• Pacemaker use, unstable angina, or decompensated heart failure
• Knee replaced in preceding 12 months or replacement planned within 6 months
• Moderate to severe dementia
• Pregnancy (self report)
• Altered sensation at the knee such that the patient is unable to perceive the presence of pinprick.
• Use of intra-articular viscosupplementation or steroid injection within preceding 2 months.
• Use of chronic anticoagulation medication.
• Movement-limiting pain in the back, hip, ankle, or foot of either lower limb.