what are the names of the "subunits" within the myofibrils that run the length of skeletal muscle fibers?

Sarcomeres

Explanation:

A muscle fiber is composed of many myofibrils, A sarcomere is the basic unit of a myofibril.

Sarcomeres are arranged in a stacked pattern throughout the muscle tissue, giving it a striped pattern. Sarcomeres are composed of thick and thin filaments. The thin and thick filaments interact  initiate the movement of muscle.

a 20-cm-long, cylindrical graphite (pure carbon) rod is inserted into an oxidizing atmosphere at 1145 k and 1.013 x 105 pa pressure. the oxidizing process is limited by the diffu- sion of oxygen counterflow to the carbon monoxide that is formed on the cylindrical surface.