Which of the following factors has most likely contributed to the atrophy of the patient’s muscle cells?

A nurse practitioner employed in a hospitalist notices that a patient is experiencing muscle atrophy following 2 weeks in traction after a motor vehicle accident. Which of the following factors has most likely contributed to the atrophy of the patient’s muscle cells?
High levels of insulin and IGF-1 in the patient’s blood during immobilization
Denervation of the affected muscles during the time of traction
A reduction of skeletal muscle use secondary to the traction treatment
Reduced oxygen consumption and cellular function that ensures muscle cell survival