The purpose of this study is to determine the effects of one week of knee-joint immobilization on muscle size, strength, neuromuscular function, and brain function. In addition, the effects of two different interventions (i.e., neuromuscular electrical stimulation and action observation/mental imagery) throughout immobilization will be determined. Following the immobilization period, participants that have lost strength will be rehabilitated with twice weekly resistance training sessions, and sex-based differences in rehabilitation timelines will be examined.

This study will utilize a repeated measures design in healthy adults aged 18-40 years. After a thorough familiarization visit, muscular size, strength, neuromuscular responses, and corticospinal excitability/inhibition will be measured before (PRE) and after (POST) one week of unilateral knee joint immobilization of the left leg. Four groups will be examined: 1) immobilization only, 2) immobilization + daily neuromuscular electrical stimulation, 3) immobilization + daily action observation/mental imagery training, 4) a control group. Throughout the immobilization period, participants will be in a leg brace locked at 90 degrees knee flexion. They will perform daily range of motion exercises and wear a compression sock at all times to mitigate the risk of blood clots. Following completion of the immobilization period, participants that have lost strength will complete a supervised rehabilitation program of twice weekly lower body resistance training sessions until they have returned to baseline levels of strength. Group assignment will be randomized and blocked on sex to ensure an equal number of participants within each group consisting of a relatively equal number of males and females.

Inclusion Criteria:

• Healthy men and women between the ages of 18-40 years
• Body mass index >20 kg/m2 or < 35 kg/m2

Exclusion Criteria:

• Body mass index <20 kg/m2 or > 35 c
• Experience of major joint pain/discomfort of the upper or lower limbs, back, or neck within the previous six months.
• History of major musculoskeletal injury or surgery
• Neuromuscular disease (e.g., Parkinson's, MS, ALS)
• Metabolic disease (e.g., diabetes, thyroid disorder, metabolic syndrome)
• Personal or family history of blood clots
• Trouble using or controlling one's muscles
• History of cancer
• History of stroke
• History of heart attack
• History of arthritis
• Use of an assistive walking device or mobility aids within the past six months
• Use of anabolic steroids within the past six months
• History of convulsions, seizures, or syncope
• History of concussion as diagnosed by a physician
• Certain medications (e.g., muscle relaxants, benzodiazepines)
• Very thick hair or certain hairstyles that would impede the TMS coil from making direct contact with the scalp
• Allergy to rubbing alcohol
• Lack of transportation to and from the laboratory
• Implant of any kind
• Pregnancy
• Allergy to silver
• Diagnosis of any psychiatric condition

Participants enrolled in this study must self identify with their biological sex at birth

IPD will be shared by the PI upon reasonable request. Personal identifiable information will not be shared; however, physiological data and outcome measures may be shared if requested.

Data will be made available upon reasonable request after the time of study completion and manuscript publication

To access IPD, please contact the study PI.