The invention discloses a protective training device for muscle training in a sports classroom, one end of a support frame is provided with an adjusting mechanism, and the adjusting mechanism comprises a sliding groove, a guide rod, a connecting block, a connecting belt, a mounting block, a rotating rod, a guide hole, an auxiliary rotating shaft, a support block, a clamping groove, a clamping plate, an extension spring, an embedded plate, an embedded groove, a support rod and a bearing frame; according to the structure, the adjusting mechanism is arranged, the connecting block is conveniently driven to move through the connecting belt, the extension spring is conveniently installed through the cooperation of the clamping groove and the clamping plate, when an exerciser is a beginner, the exerciser is assisted to do pull-up through the action of the extension spring, muscle strain caused by forced upward stretching is avoided, in addition, through the cooperation of the clamping groove and the support rod, the bearing frame can be conveniently installed, and therefore by placing a heavy object in the bearing frame, the exerciser can add the proper weight according to the situation of the exerciser, and the exercise effect is improved.