Final answer:
To assess the brachialis muscle strength accurately after an injury, the forearm should be placed in a neutral position. This position allows for isolated contraction of the brachialis, away from the involvement of the biceps brachii which also aids in supination.
Step-by-step explanation:
To assess muscle action in the lever system, one principle used is the function of muscles in their role as prime movers or synergists. The brachialis muscle is responsible for providing power when flexing the forearm and is deep to the biceps brachii. The proper position to assess the brachialis muscle strength is with the forearm in a neutral position, meaning neither fully pronated nor fully supinated, as this facilitates isolated contraction of the brachialis without the assistance of the biceps brachii, which is also involved in supination of the forearm.
Understanding the function of the forearm flexors, such as the biceps brachii, brachialis, and brachioradialis, is essential. The biceps brachii is a two-headed muscle that assists in flexing the forearm and supinating it, while the brachialis provides additional power in flexing the forearm. The brachioradialis is capable of flexing the forearm quickly or aiding in lifting a slow load. These muscles work together in a coordinated manner to perform forearm flexion.
Therefore, the correct assessment of brachialis muscle strength following an injury like Alex's requires the forearm to be in a neutral position to accurately measure its power and ensure its proper rehabilitation.