Low Tone

When our son was diagnosised w/ ASD we were told he had low tone.  Not really asking questions since it didn't at the time seem like he was having any issues because of it I'm starting to notice he is having trouble doing certain task.  Like using a fork or crayon.  He has the basis of what he's suppose to do with it but seems to not have the "strength" to use it properly.  Does anybody have suggestions on how help with this?  Any information would be great.