Which test best determines an athlete's upper body muscular endurance?

The test that best determines an athlete's upper body muscular endurance is conducting push-ups to failure. This test specifically measures how many repetitions of the push-up the athlete can perform before fatigue sets in. Push-ups require repeated engagement of the muscles in the chest, shoulders, and triceps, which directly assesses muscular endurance, as the athlete must maintain strength over multiple repetitions rather than just performing a single maximum effort.

In contrast, while a plank hold is excellent for assessing core stability and endurance, it does not specifically target the upper body in the same way. The bench press maximum primarily gauges an athlete's maximal strength, not endurance, as it focuses on the heaviest load an individual can lift for a single repetition. The lat pull-down repetition test is more oriented toward back and shoulder strength rather than overall upper body endurance, which is less applicable to overall upper body muscular endurance in the same context as push-ups.

Therefore, the push-ups to failure provide the most comprehensive measure of upper body muscular endurance due to their emphasis on repetitive motion over a sustained period until fatigue, making it the most effective choice for this purpose.