Nà wèi yùndòngyuán zhèng chǔyú diānfēng zhuàngtài.
That athlete is at the peak of their form.
Tips
usage
巅峰 vs 高峰: 高峰 is more general (rush hour, peak season), while 巅峰 implies the absolute highest point and is more dramatic. 巅峰对决 (diānfēng duìjué, 'summit showdown') is a popular phrase in sports and gaming for a clash between the very best.