Fit
When working your way through a circuit-training course, challenge your friend to a game of Fit. The game is very similar to the basketball game Horse. Player 1 steps up to the first activity in the circuit, perhaps chin-up exercises, and does as many as he can. Player 2 must meet the challenge, and perform as many chin-ups as player 1 did. If player 2 cannot complete the task, he is penalized with the first letter in the word Fit. Next, Player 2 moves on to the next activity, maybe sit-ups, and does as many as he can. Player 1 must then copy that activity. If he can't, he is penalized with the letter F. Whoever gets all three letters first, loses the challenge.
"Simon Says Bicep Curls"
If you still have energy left for another game, a round of Simon Says in the gym is a little less strenuous, but just as challenging. Choose a piece of equipment like hand weights. Select a player to be the leader. All the other players must line up in front of the leader. The leader does a series of weight lifting exercises, and as she does them, she calls them out. She must begin each command with "Simon says..." For example, "Simon says bicep curls, Simon says hammer curls, Simon says triceps push-downs..." If the leader doesn't say "Simon says" and the players follow, they are out. The last player standing wins.
Crunch Ball Toss
Finally, find a bouncy ball, a mat and a friend and get ready to do your crunches. Lay down on the mat facing your friend. Player 1 holds the ball in their lap. Both players begin doing standard crunches. They should call out the repetitions as they go. When player one crunches upwards, she tosses the ball to player 2. Player 2 crunches back and up and tosses the ball back. Pass the ball back and forth until you get to 20. The game makes the repetitions go by much faster.