• Numeric pain rating scale [ Time Frame: 12 months ]
  change in score on 0-10 pain rating scale with 0 being no pain, and 10 being worst pain.
• Pain free grip strength [ Time Frame: at final therapy visit up to 12 weeks after enrollment ]
  Change in pain free grip strength on dynamometer
• Maximum grip strength [ Time Frame: at final therapy visit up to 12 weeks after enrollment ]
  Change in maximum grip strength on dynamometer
• Other treatments received [ Time Frame: 12 months ]
  We will collect data on whether the patient sought or received treatments beyond physical/occupational therapy over the 12 months of enrollment in the study

Patients will be randomized to one of two groups, and treatment will be open label and unblinded. A target of 44 patients for enrollment has been set for 80% power. Treatment will last for 6 visits with physical therapy with recommended visit intervals of 1 week :

Intervention Group: Evidence based physical/occupational therapy, with the addition of therapeutic exercises using a blood flow restriction tourniquet.

Control Group: Patients will receive standard evidence based physical therapy

The primary outcome (Patient-Rated Tennis Elbow Evaluation [PRTEE]) will be collected at enrollment, 3, 6, and 12 months.

Secondary outcomes will be collected at the beginning and end of physical therapy interventions (change in: numeric pain rating scale, maximum pain free grip strength, pain free grip strength). We will collect treatments received after the end of physical therapy and before final follow up.

• Device: Blood flow restriction tourniquet
  A blood flow restriction tourniquet, which impedes arterial flow to extremity at 50% of usual flow.
  Other Name: Delfi personalized tourniquet system
• Other: Evidence based physical/occupational therapy
  Up to date physical/occupational therapy for lateral epicondylitis

• Experimental: Blood flow restriction with physical/occupational therapy
  physical/occupational therapy including use of blood flow restriction tourniquet over 6 visits (within a twelve week period).
  Intervention: Device: Blood flow restriction tourniquet
• Active Comparator: Evidence based physical/occupational therapy
  evidence based physical/occupational therapy program over 6 visits (within a twelve week period) without use of blood flow restriction tourniquet
  Intervention: Other: Evidence based physical/occupational therapy

Inclusion Criteria:

• The diagnoses included are lateral elbow pain, lateral epicondylitis, or lateral epicondylalgia, more general diagnoses elbow tendinitis or elbow pain will be included if their clinical picture at physical therapy meets criteria for lateral epicondylitis.
• If the inclusion diagnosis is other than lateral epicondylitis or tennis elbow (such as elbow pain), we will confirm the diagnosis at the first therapy visit with tenderness at the lateral epicondyle and/or pain with resisted wrist/long finger extension at the lateral epicondyle.
• Pain for 4 weeks or more.
• All participants must be between the age of 18 and 70 years old and have had pain for 4 weeks or more.

Exclusion Criteria:

• Ligamentous elbow sprain, osteoarthritis of elbow and cervical radiculopathy in the affected limb will be excluded from the study.
• Any history of ligamentous, bony or other soft tissue reconstruction surgery at the affected elbow,
• Vascular disorders to include: history of DVT, history of endothelial dysfunction, peripheral vascular disease
• Injection therapy (corticosteroid, platelet rich plasma, or other injection therapy) in the prior 3 months to the affected site
• Current fracture in affected arm
• History of crush injury to affected arm
• Any surgery on affected arm in last 1 year
• Surgical procedure on their contralateral extremity (Changed 9/2019 to surgery within last year on contralateral upper extremity).
• History of lymphectomy (such as axillary exploration with breast surgery, lymph node biopsy in the affected axilla/arm)
• Pregnancy
• Active infection
• Current cancer diagnosis/treatment
• Sickle cell anemia or trait
• Kidney dialysis
• History of syncope/passing out with pressure to body (such as massage, or blood pressure cuff).
• inability to consent