The purpose of this feasibility study is to determine the initial efficacy of early combined Neuromuscular Electrical Stimulation (NMES) and Blood Flow Restriction (BFR) in addition to standard rehabilitation in 15 subjects after Total Knee Arthroplasty (TKA). The second aim is to determine the feasibility and patient perceptions of combined NMES and BFR by assessing: 1) adherence, 2) satisfaction and 3) safety.

It's estimated that almost 3.5 million Total Knee Arthroplasties (TKA) will be performed annually by 2030. Despite initiating rehabilitation within 48 hours of surgery, up to a 60% strength loss is noted in the quadriceps one month after TKA. This weakness persists for years after surgery and is associated with decreased gait speed, balance, stair climbing ability and is associated with an increased risk for falls. Approximately 85% of the strength loss after TKA is explained by the combination of voluntary muscle activation deficits and muscle atrophy. Immediately postoperatively, strength loss is primarily due to activation deficits, and as time progresses, muscle atrophy becomes the major contributing factor. Early in the postoperative period, Neuromuscular Electrical Stimulation (NMES) has been shown to diminish activation deficits and improve function after TKA. Blood Flow Restriction (BFR) is a proposed strength training alternative for people who are unable to tolerate traditional strength training at 70-80% of their 1 repetition maximum (1RM), such as those who have just had surgery. Performing low intensity exercise (20-30% of 1RM) with BFR has been shown to achieve similar muscle mass and strength gains when compared to high intensity resistance training. BFR has been studied in people with TKA, but it has been used later in the recovery period (>6 weeks postoperative) when the greatest strength losses have already occurred. The goal of this study is to address both factors of postoperative quadriceps weakness, activation deficit and atrophy, through the use of early NMES and BFR in addition to standard postoperative rehabilitation in an attempt to minimize strength loss and improve functional outcomes.

AIM 1: To determine the initial efficacy of combined neuromuscular electrical stimulation and blood flow restriction training (COMBO) on strength (primary outcome), activation, pain, range of motion, and function compared to historical controls.

Hypothesis 1.1: The COMBO group will have greater attenuation of early postoperative strength losses and improved pain, ROM, and function compared to historical controls.

AIM 2: To determine the feasibility of COMBO by assessing 1) adherence, 2) satisfaction, and 3) safety

Hypothesis 2.1: An 80% adherence rate to the intervention will be observed.

Hypothesis 2.2: Study participants will indicate acceptability of COMBO with a satisfaction survey median score of at least 4/5 ("somewhat satisfied").

Hypothesis 2.3: There will be no intervention-related Adverse Events or Serious Adverse Events during the 8-week protocol.

Inclusion Criteria:

• Scheduled to undergo primary unilateral total knee arthroplasty secondary to end-stage osteoarthritis

Exclusion Criteria:

• BMI > 40 kgm2
• Current smoker or history of drug abuse
• Comorbid conditions that substantially limit physical function or would interfere with the participant's ability to successfully complete rehabilitation (e.g. neurologic, vascular, cardiac problems, or ongoing medical treatments)
• Unstable orthopedic conditions that limit function
• Uncontrolled diabetes (hemoglobin A1c level > 8.0)
• Pregnancy
• Preoperative ROM less than 10-120 degrees
• Demand cardiac pacemaker or unstable arrhythmia
• Prior history of DVT/PE
• Thrombophilia or other clotting disorders
• Sickle cell trait/anemia
• History of peripheral vascular disease
• Patient report of easy bruising