This training minigame can be played at the gym in the morning by selecting the weight bench once you convinced Kevin to spot you. To do so, talk to Kevin in the school cafeteria, he requests the main character to find him a replacement for his duty. Meet Erik who agrees if you bring him a new video game.
How to play
Tap the screen or press Space as fast as possible until you fill the bar on the left side of the screen. You succeed if you fill the bar completely before the gauge reaches the top. It will climb faster in higher difficulties.
Successful completion provides +1 to Strength.