腕 and 肘: the arm and the elbow
Distinguish an arm from its elbow and recognize contexts in which 腕 refers to skill.
Moving the arms
腕, read うで, means arm. 両腕を広げました。 says that someone spread both arms. 両 prevents a reading involving only one arm.
右腕を上げたまま待ちました。 says that someone waited with their right arm raised. まま marks the posture maintained during the wait.
Locating the elbow
肘, read ひじ, means elbow. 肘を曲げました。 means that someone bent their elbow.
机に肘をつきました。 says that someone rested an elbow on the desk. The desk provides the support; do not replace the elbow with a palm.
腕 as skill
料理の腕を磨いています。 describes honing one's cooking skills. It is not the physical action of cleaning an arm.
腕のいい職人 means a skilled craftsperson. Do not treat every occurrence of 腕 as an anatomical reference; use the surrounding words to choose its meaning.
What is being improved in 料理の腕を磨いています?
Show the answer and why
Cooking skill. Here, 腕 refers to ability rather than the physical arm.