A dream or vision in which you are playing sports tells you about learning rules, having talent and achieving your goal. Another explanation is the importance of cooperation, harmony and working in a team, which is the key to a balanced life. An alternative explanation is that sports tell your feelings about sex, aggressive acts, expressions and social problems.
You can experience gym dreams both positively and negatively, this completely depends on whether you come out as a winner or not. You are your opponent as well as the competitor and the trainer. Another explanation is that it also represents learning and studying - you will not be an expert by experience tomorrow, you have to prepare for this.
Patience, practice and try, wait great masters take all the time in the world before coming out. It is both the victory and the failing (ego) way to get where you want to be in life.
Yet another explanation is having fun working together, teaming up and attracting like-minded people - at the right time, all the pieces of the puzzle fall into place. A spiritual explanation is that a gym also reflects the connection with the higher, dimensions, universe, gods and/or that with which you are connected. Higher spiritual experiences and soul growth from the source, your base and life purpose