Which of the following is closest to the estimated number of muscles in the human body?

The estimated number of muscles in the human body is closest to 650. This figure is derived from the human muscular system's complexity, which includes both the major skeletal muscles that are commonly recognized and many smaller muscles that play roles in fine motor control and other functions.

The muscular system is comprised of approximately 640 to 750 muscles in adults, depending on various factors, such as how one categorizes certain muscles (for example, individual muscles versus muscle groups) and anatomical differences among individuals. This total encompasses muscles of various types, including skeletal, smooth, and cardiac muscle, but the focus typically on skeletal muscles leads to the most widely accepted estimate of around 650.

The figures associated with the other choices do not align as closely with this understanding, as they are either too low or too high given this range. Recognizing the significance of the 650 estimate aids in further discussions of muscle function, biomechanics, and corrective exercise practices in the context of overall human physiology.