ok so my DD tonight was doing drills with the pc. and shes been working out with weights now for about 2 weeks to build up some strength anyway they were swapping between reg 12" balls and tennis balls she maxed out on reg balls at 57mph and tennis balls at 67mph the pc says she really should be throwning in the 60s with the reg balls I checked there isn't a ton of weight difference between the too (he thinks its in her head somewhat) true or not true?