Maybe if his arm is exhausted he depends on the curve a lot more. Or any hook. Appears lifeless arm would demonstrate up nor prominently on rapid ball velocity, not everything hooking. Authorities Chatting with DailyMail.com said the signs or symptoms were being 'non-particular' and so they needed more details. https://www.dailypioneer.com/2015/sports-bytes/no-excuses-for-wilting-in-heat-says-federer.html