Trial of Neurostimulation and Blood Flow Restriction for PFPS in Active Duty

Strength of knee extension muscle groups will be measured using the Nicholas Manual Muscle Tester (NMMT). The participant will be positioned with a small towel roll placed distally to support the femur in 90-degree hip flexion. The participant's knee will be placed in 70º knee flexion using a goniometer. The distance from the tibial tuberosity (TT) to the superior aspect of the medial malleolus will be measured.

For knee extension, the first measurement will be taken using standard NMMT protocol (0.6 X the distance from the tibial tuberosity to the superior aspect of the medial malleolus). Participants will perform three maximal efforts holding contractions for 4 seconds, separated by 30-sec rest; the highest value of the will be accepted (kg).

Strength of knee flexion muscle groups will be measured using the Nicholas Manual Muscle Tester (NMMT). The participant will be positioned with a small towel roll placed distally to support the femur in 90-degree hip flexion. The participant's knee will be placed in 70º knee flexion using a goniometer. The distance from the tibial tuberosity (TT) to the superior aspect of the medial malleolus will be measured.

For knee flexion, the NMMT will be positioned 0.6X distance from TT to superior border of medial malleolus on the dorsal limb side. Participants will perform three maximal efforts holding contractions for 4 seconds, separated by 30-sec rest; the highest value of the will be accepted (kg).

Strength of hip posterolateral stabilizer muscle groups will be measured using the Nicholas Manual Muscle Tester (NMMT). The hip stability isometric test (HipSIT) will be measured using the NMMT as described by Almeida et al. Participants will perform three maximal efforts holding contractions for 4 seconds, separated by 30-sec rest; the highest value of the will be accepted (kg).

Tests the activity of stair climbing. The test will begin with participants ascending up four steps (6-inch rise, 11.5-inch run) to a 30-inch square platform, and then descending to the bottom of the stairs. Participants will climb the stairs at a self-selected pace using the handrails if necessary.

Each participant will complete two complete rounds, if possible, and the two times will be averaged to produce one score.

This is a specific function test for PFPS, putting weight bearing stress during a movement that mimics stair descent. The test is performed from a 20 cm (8 inch) high platform. The participant steps forward and down toward the floor from a single-leg stance with a straight knee (hands on hips). The knee of the stance leg bends until the opposite foot lightly touches the floor with the heel and then returns to full knee extension. The heel touching the floor is not to be used to accelerate back onto the platform. This counts as one repetition; the number of repetitions performed in 30 seconds is recorded. Both legs are tested separately.

This assesses lower-body strength mimicking squatting. The participant completes as many full stands as possible in 30 seconds. The participant sits in the middle of the chair, feet flat on the floor with arms crossed at the wrists and held against the chest. When instructed, the participant rises to a full stand, and then returns to a fully seated position. The number of completed rises will be recorded.

This is a submaximal test of functional capacity and measures the distance a participant walks at a "fast" pace over a 6-minute period. Participants will "walk as quickly as you can" with the opportunity to stop and rest if required. This test measures functional capacity of walking.

Physical activity will be measured using the Fitbit Charge (San Francisco, CA). The Charge is a wrist-worn, three-axis accelerometer that measures steps walked, distance traveled, energy expenditure and floors climbed. Steps walked will be assessed as the number of steps walked in 24 hours.

Baseline data will be ascertained by wearing the Charge for 3 days while maintaining a typical activity pattern. Subsequently, the device will be worn daily for 9 weeks.

Physical activity will be measured using the Fitbit Charge (San Francisco, CA). The Charge is a wrist-worn, three-axis accelerometer that measures steps walked, distance traveled, energy expenditure and floors climbed. Energy expenditure will be assessed as the calories expended in 24 hours.

Baseline data will be ascertained by wearing the Charge for 3 days while maintaining a typical activity pattern. Subsequently, the device will be worn daily for 9 weeks.

Pain associated with activity limitations will be measured by the Kujala Anterior Knee Pain Scale, a 13-item knee specific self-report questionnaire. Scores range from 0 to 100 with higher scores indicating better performance.

The Visual Analog Scale (VAS) of pain will be used to assess pain at rest and after activity. Participants will complete this scale following the stair climb, step down test, 6-minute walk and the chair rise test. This VAS pain subscale is a 100-mm horizontal line index with descriptive anchors at each end. At the far left (0.0cm) is "no pain" and at the far right (10 cm) is "worst possible pain". The participant is instructed to place a vertical line at some point between the anchors to describe his/her level of pain. The VAS pain scale shows high correlations with acute pain levels.

Knee Injury and disability will be measured by the International Knee Documentation Committee (IKDC) subjective knee form, a well standardized outcomes questionnaire that is knee-specific and assesses patients with various knee disorders. The 18-item instrument assesses symptoms, function and level of sports participation for those with an injured knee.

The Short Form Health Survey Version 2.0 (SF-12v2) Health Survey will be used to determine each participant's overall health-related quality of life. The SF12v2 has two summary scores for physical (PCS) and mental health (MCS). Raw scores for each subscale are computed using the scores of 12 questions ranging from 0-100. Zero score indicates the lowest level and 100 indicates the highest level of health. The PCS and MCS subscales are norm-based for different age groups because of the variance in PCS and MCS scores over the life span.