You can for example add this to your gym script to get stronger.
[ Functions ]
Skills displays in a nui menu using the command /skills and/or ESC → Stats → Skills
All the skills that is added by default have a unique “function”, for example if you run your stamina will increase by the time.
Depending on the skill level your character will perform the skill better, for example if your stamina is high you can run longer without getting exhausted.
Every Config.UpdateFrequency (seconds) it will remove the current RemoveAmount for that skill.
The original code is from gamz-skillsystem originally converted to QBCore by other contributors on the repo and I. Attached is my request for permission to post per forum rules, I have yet to get a reply if you have contributed or have any inquiries please contact me here or more contact info is available on the GitHub Screenshot
Well the idea is to add more + skill stuff to usual stuff in your scrips so it is easier to get skill but the default is 600 seconds which is 10 minutes you can double it or totally remove the feature if you so choose, the idea around the feature is to keep players going to gyms and improving there skill while also adding realism (like for example if you stop going to the gym you and then return after a while IRL you will not be able to lift as much) play around with the numbers and find a good medium ground for your server.