The goal of this study is to compare quadriceps muscle activation in patients recovering from lower extremity injury, such as an ACL tear. Specifically, the main objectives are as follows:

• Determine the effects of ankle positioning on quad muscle activation during straight leg raise exercises performed while the patient is lying on his or her back
• Determine if there is a difference between ankle positioning on quad muscle activation during straight leg raise exercises performed while the patient is lying on his or her back, comparing healthy versus post-operative participants

Returning quadriceps neuromuscular control and preventing atrophy is an area of intense current interest in orthopedic rehabilitation and recovery science. It is clear that returning full autonomous control of the quadriceps, including the vastus medialis obliqus (VMO), at full knee extension is an important factor in rehab and dysfunction of the quadriceps leads to a loss of physical performance and self-reported function. Quadriceps function is critical for optimal ambulation patterns and eccentric control is essential for the weight acceptance phase of gait.

Quadriceps atrophy is one of the most common post-operative side effects of anterior cruciate ligament (ACL) reconstruction, total knee arthroplasty, and many other surgeries including meniscal repairs, patella realignment procedures, and microfracture procedures. Due to the swelling within the joint after injury or surgery to the knee, the joint inflammation cascade occurs and leads to the quadriceps being arthrogenically inhibited by spinal neuron inhibition as a protective mechanism. These neural changes usually lead to decreased voluntary quadriceps contraction. Additional contributions of inhibition from post-operative pain, patient apprehension, and surgical procedure requiring protection of the repaired tissue. The sooner one regains control of the quadriceps muscles the less atrophy occurs, reductions in strength are minimized, and the more optimal the outcome is achieved for patient recovery.

Studies have shown that neuromuscular electrical stimulation (NMES), Transcutaneous electrical nerve stimulation (TENS), and biofeedback techniques can limit post-operative quadriceps atrophy and can return strength of the quadriceps back to normative values faster than without those techniques and traditional therapeutic exercise and have better long-term outcomes based on pain, functional outcomes, and return to sport participation rates.

Irradiation effect is a proprioceptive neuromuscular facilitation technique that causes an overflow of neuronal energy from distal to proximal muscles to increase muscle activity of a targeted muscle. This technique can be used to selectively recruit weaker motor units through the application of resistance or stimulation. By inducing a stronger contractile force of the quadriceps, our hope is to return quadriceps function to normal quicker with less atrophy and greater strength.

The investigators hypothesize that ankle positioning in maximal dorsiflexion (DF) changes the quantity of contraction as a percent of the reference voluntary contraction when performing a supine straight leg raise compared with having the foot in neutral (0°), relaxed, and plantarflexed (PF) positions. This may help provide insight into proper instruction and cuing for patients to return quadriceps neuromuscular control sooner and thus limiting quadriceps atrophy.

(All Participants)

Inclusion Criteria:

• Males and females ages 18-55

Exclusion Criteria:

• History of diagnosed cancer, neurological disorder, peripheral nerve injury affecting the lower limb or injury to the lower spine with radicular symptoms, which may affect quadriceps activation
• History of musculoskeletal injury to the quadriceps that may affect ability to maintain muscle contractions without excessive fatigue or discomfort

(Healthy Participants)

Exclusion Criteria:

• Injury to the knee or quadriceps muscle group within the past 12 months to the tested side
• History of lower extremity orthopedic surgery in the past 12 months to the tested side

The study population consists of two groups of 50 individual participants each. These groups are healthy participants and participants who have recently undergone knee arthroplasty.