Begin with the End in Mind
Many people go to the gym without and move around without a particular end in mind.
This is okay if you’re only trying to enjoy yourself or meet people (a common event at gyms).
Toward a Definition of Fitness and Exercise
But, if you want to become fit, then you have to know what fitness is. Lon Kilgore says that to be fit one must have:
“Possession of adequate levels of strength, endurance, and mobility to provide for successful participation in occupational effort, recreational pursuits, familial obligation, and that is consistent with a functional phenotypic expression of the human genotype.”1
What this means is that fitness is relative to the needs of the individual, but objective precisely because one’s optimal fitness is not actualized if they experience unnecessary struggle in work, fun, and family.
So much for fitness, but what is exercise? Exercise can be defined as training undertaken for the purpose of obtaining and maintaining fitness. For instance, sport training is not designed for fitness per se, as one can be fit without being good at a sport. And one can be pretty good at a sport while still being incredibly unhealthy otherwise.
Now that you have a definition of fitness, I suggest that you make a plan to achieve it. Any good exercise plan should make provision for improving or maintaining:
Include some form of resistance training with weights, bands, and/or calisthenics. Also, certain explosive activities like sprinting and jumping have utility here, but they do come with an increased safety risk.
Endurance exists at several levels. For instance, if you can dead lift 350 pounds, then your endurance for light weight lifting is probably quite remarkable. Cardiovascular endurance is another level, but it is important to remember that while general physical fitness is real, activities still improve in specific ways.
Mobility can be enhanced by stretching, running, walking, lifting weights through a full range of motion, jumping, etc.
1 Kilgore, Hartman, and Lascek, Fit: An Unconventional Guide to using conventional methods for creating fitness for the real world (Killustrated, 2011), 5.