For players , 9.7 % ( 95 % CI 6.1 % to 13.3 % ) , 4.7 % ( 95 % CI 2.1 % to 7.3 % ) and 4.7 % ( 95 % CI 2.1 % to 7.3 % ) believed a warm-up would prevent muscle , knee and ankle injuries , respectively .