Effect of Blood Flow Restriction Training on Quadriceps Muscle Strength, Morphology, Physiology, and Knee Biomechanics Before and After Anterior Cruciate Ligament Reconstruction: Protocol for a Randomized Clinical Trial

Abstract

Background: Despite best practice, quadriceps strength deficits often persist for years after anterior cruciate ligament reconstruction. Blood flow restriction training (BFRT) is a possible new intervention that applies a pressurized cuff to the proximal thigh that partially occludes blood flow as the patient exercises, which enables patients to train at reduced loads. This training is believed to result in the same benefits as if the patients were training under high loads.

Objective: The objective is to evaluate the effect of BFRT on quadriceps strength and knee biomechanics and to identify the potential mechanism(s) of action of BFRT at the cellular and morphological levels of the quadriceps.

Design: This will be a randomized, double-blind, placebo-controlled clinical trial.

Setting: The study will take place at the University of Kentucky and University of Texas Medical Branch.

Participants: Sixty participants between the ages of 15 to 40 years with an ACL tear will be included.

Intervention: Participants will be randomly assigned to (1) physical therapy plus active BFRT (BFRT group) or (2) physical therapy plus placebo BFRT (standard of care group). Presurgical BFRT will involve sessions 3 times per week for 4 weeks, and postsurgical BFRT will involve sessions 3 times per week for 4 to 5 months.

Measurements: The primary outcome measure was quadriceps strength (peak quadriceps torque, rate of torque development). Secondary outcome measures included knee biomechanics (knee extensor moment, knee flexion excursion, knee flexion angle), quadriceps muscle morphology (physiological cross-sectional area, fibrosis), and quadriceps muscle physiology (muscle fiber type, muscle fiber size, muscle pennation angle, satellite cell proliferation, fibrogenic/adipogenic progenitor cells, extracellular matrix composition).

Limitations: Therapists will not be blinded.

Conclusions: The results of this study may contribute to an improved targeted treatment for the protracted quadriceps strength loss associated with anterior cruciate ligament injury and reconstruction.

Trial registration: ClinicalTrials.gov NCT03364647.

Figure 1.

Flowchart of the clinical trial. ACL = anterior cruciate ligament; BFRT = blood flow restriction training; MRI = magnetic resonance imaging.

Figure 2.

Rating of perceived effort. The scale begins at 0, which is defined as no physical effort is taking place. This can be likened to the perception of effort sitting on an exercise machine but not having to exert any effort to complete the activity. The scale ends at 10, which is described as the maximum perceivable effort. This can be likened to the perception of effort when, despite putting forth as much exertion as you can, you cannot physically complete the activity being attempted.

Figure 3.

Flow of adverse event reporting.