Goniometry is the measurement of:

Goniometry specifically refers to the measurement of joint angles and the range of motion at specific joints. This technique involves the use of a goniometer, which is an instrument designed to quantify the degrees of motion available in a joint. Understanding joint range of motion is essential in fields such as physical therapy, rehabilitation, and fitness, as it helps assess the function of joints and identify any limitations or deviations from normal movement patterns.

While muscle strength, flexibility, and posture are important aspects of physical fitness and health assessments, they are distinct from goniometry. Muscle strength assesses the force that a muscle can produce, flexibility evaluates the ability of a muscle or muscle group to lengthen, and posture refers to the alignment of the body in space. None of these elements are specifically measured using goniometry, which focuses solely on the range of motion of joints. Thus, the correct answer, representing the specific definition of goniometry, is the measurement of joint range of motion.