Ergonomic standards for home management and kitchen planning dictate that general manual tasks should be performed at elbow height (or about $1$ to $3$ inches below elbow level). This posture keeps the upper arms relaxed, minimizes strain on the shoulder and back muscles, and prevents fatigue during extended periods of standing or seated work.

Option analysis:

• at height of shoulders: Incorrect. Causes severe shoulder fatigue and trapped trapezius tension.
• above elbow height: Incorrect. Forces excessive abduction and flexion of arms and shoulders.
• at elbow height: Correct. The biomechanically ideal height for standing or seated manual labor.
• at eye level: Incorrect. Unsuitable for manual hand tasks, leading to rapid muscle exhaustion.