Foundations
What "fitness" actually means
The word covers at least five unrelated qualities, and confusing them is why most people train for years without getting what they wanted.
Contents — three sections
Ask ten people what it means to be fit and you will get ten answers: being able to run a long way, being strong, being lean, not getting out of breath on the stairs, looking a certain way. All of these are real. None of them is fitness, because there is no such single quality.
Fitness is a set of separate capacities that are trained differently and, past a point, trade off against each other.
The capacities
Strength — how much force you can produce. Trained with heavy resistance and long rests.
Muscle size — how much muscle tissue you carry. Related to strength but not the same thing, and trained with somewhat different methods.
Endurance — how long you can sustain effort. Cardiovascular, and largely independent of the two above.
Body composition — the ratio of muscle to fat you carry. Mostly a nutrition outcome, not a training one, which surprises people.
Health markers — blood pressure, insulin sensitivity, bone density, how well you will move at seventy. Quietly the most important one, and the one nobody photographs.
Why the distinction matters
These are separate dials. Turning one up does not turn the others up with it, and turning one up hard will sometimes turn another down.
The person who runs 50km a week is extremely fit by one measure and may be quite weak. The powerlifter is enormously strong and may be winded climbing four flights of stairs. Neither is doing anything wrong. They are training different capacities, on purpose.
Where this becomes a problem is when someone trains for one capacity while wanting a different one. Years of steady-state cardio, undertaken because someone wanted to change their body composition, is the most common version of this. The training is fine. It just is not aimed at the thing they said they wanted.
What to do with this
Before choosing a method, name the capacity. Not a mood, not an aesthetic — a capacity.
“I want to be stronger” is a usable goal. “I want to get in shape” is not, because it does not tell you what to do on Monday.
Most people, when they push on it, want some combination of: more muscle, less fat, and enough general capacity that ordinary life is easy. That combination has a well-understood answer, and it is mostly resistance training plus a deliberate approach to food. The rest of this series is about that.
The next piece covers why resistance training specifically, and why it does more than the obvious.