I Open A Fitness Gym In An Alternate World

Mike transmigrated into a world with swords and magic. Immediately, he acquired a fitness gym.
He was invincible in the gym. The stronger he grew, the size of the area in which he was invincible grew larger too.
However, the prerequisite of him becoming stronger was to have more people working out in his gym.
Mike came up with all sorts of ways to gradually increase the visitors coming to his gym.
The people in this alternate world realized that compared to other gyms, the result of their exercise was more prominent when they worked out in Mike’s gym. On the other hand, Mike also realized that he gained something every time someone worked out in his gym.
[Ding! Someone is training their muscles using the machines. Strength +1]
[Ding! Someone is running on the treadmill. Speed +1]
[Ding! Someone is doing yoga. Tenacity +1]
As more and more people worked out in his gym, Mike was slowly on his path of becoming invincible!