In reply to Sib81: He said a twinge in his arm, not in his finger.
>Sound's like it might be a pulley injury! As mentioned above - your finger flexor tendon's - which run across your palm to the end of each finger may not have had the time to adapt to the increased muscle strength.
that's a bizarre mixed diagnosis, whether your flexor tendons are strong enough doesn't affect whether your pulleys are going to get injured, how strong your pulleys are does.