In order to encourage people who are playing an electronic games machine (12) also to take exercise, and to encourage users of exercise machines (76) who simultaneously play a games machine to exercise at a particular rate, an interrupter system (34) is added to an existing connection (18,20,22) between the games machine and its controller (14) so as to provide a modified connection. Operation of the exercise machine is detected, and the interrupter system is used selectively to enable and interrupt the modified connection between the game controller and the games machine to enable and interrupt normal operation of the games machine in dependence upon the detected operation of the exercise machine. The normal operation of the games machine may be interrupted if the rate of operation of the exercise machine is detected as being below a predetermined threshold and/or above a pre-determined threshold. Accordingly, a parent can arrange it such that their child cannot play normally on a games machine unless the child also exercises on the exercise machine. Also, a user of an exercise machine and games machine can be encouraged to exercise in a particular manner, otherwise their game will be interrupted.