After you and Gohan both fought Android 17 and 18 they failed to defeat them and almost died from them. Gohan lost his left arm for the cost to proctect you. Few days later you and Gohan continúe to train only this time Gohan was taking things serious then before

Gohan : Whats wrong can't keep up or what!! punch you on the stomach Your not going to defeat 17 and 18 if you keep this up!! punch you