What qualifications does this job require? Or can I just go apply at 24 hr fitness?

I think that what you might mean is, "personal trainer." Do you?

I found something on the following site that might be of use and/or interest to you. The following information is from a site in the U.K. But, if in the U.S. I would think that the job description would be similar. Also, in the U.S. to be employed working on things concerning people's health and fitness, you most certainly would need to have some relative schooling, training and also maybe a license. Hopefully, some others will also come along to address your question.

Link: Personal trainer: Job description and activities (http://www.prospects.ac.uk/cms/ShowPage/Home_page/Explore_types_of_jobs/Types_of_Job/p!eipaL?state=showocc&idno=677)



Personal trainer: Job description and activities

Personal trainers provide physical fitness instruction and fitness and lifestyle assessments. Due to increasing public interest in health and fitness, there are opportunities to work in a range of settings: personal trainers are either employed by or work on a freelance basis at fitness centres, health clubs and hotel leisure centres. Some also work in corporate fitness, offering services to employers. Experienced trainers who have built up a reputation may also work privately with individuals.
Typical work activities include:

working closely with clients to develop personalised health and fitness plans;
providing information and advice on nutrition and stress management;
measuring and assessing blood pressure, heart recovery rate, body fat ratio, etc.;
monitoring client development;
maintaining and updating client records;
providing practical feedback and support.Employers may require a qualification in sports science, exercise and health studies, leisure studies, sports studies, recreation management or human movement studies, but qualifications approved by the Register of Exercise Professionals (REPs) (http://www.exerciseregister.org/) are the preferred industry-related standard. There are four levels of entry onto the register, and graduates with a relevant degree and six months' current work practice will usually be given provisional entry at level 3.

For more information see Sports coach/instructor (http://www.prospects.ac.uk/cms/ShowPage/Home_page/Explore_types_of_jobs/Types_of_Job/p!eipaL?state=showocc&idno=477)