Which method is commonly used to assess muscle strength?

One-repetition maximum (1-RM) testing is considered a standard method for assessing muscle strength, as it determines the maximum amount of weight a person can lift for a single repetition of a given exercise. This method is widely recognized in strength training and exercise physiology because it provides a clear and quantifiable measure of an individual's strength capabilities. It is particularly useful for quantifying progress in resistance training programs, allowing trainers and physiologists to tailor individual workout regimens appropriately based on an athlete's strength levels.

The other options do not focus primarily on muscle strength assessments. The Cooper test, for instance, is primarily a measure of aerobic fitness and endurance rather than muscle strength. The vertical jump test measures explosiveness and lower body power, while flexibility tests assess the range of motion in joints rather than outright muscle strength. Therefore, the one-repetition maximum testing stands out as the most relevant method for evaluating muscle strength.