At 16 years old, I was extremely fit. I was playing football at least once a day, I was going to the gym at least four days a week, I sometimes ran the 4x100m relay, 400m and did shot put for school athletic meets. I ran a 18 minute treadmill 5km. I was strong, fast and had good endurance and tended to excel at most physical tests. I remember some basic ones that didn't fit this category.
My girlfriend at the time lived near a small train station that connected her to her local city. To travel into the city, we had to go up some steps, over a bridge and down another set of steps to get to the platform. Sometimes we would have to rush for a train...and she would do the stairs nearly twice as quickly as me.
It baffled me for years. I was extremely fit. She was in aesthetically good shape but apart from occasional dance classes, the fitness demands she placed on herself were practically nil. When we had to run on flat ground, the pattern would be reversed but on steps, she was in a different league to me. She left me in the dust.
It was the same with swimming. Neither of us were avid swimmers and yet she swam like a fish compared to my brick-like efforts.
Fast forward 10 years and the same type of thing happens. My current girlfriend is generally active and in good aesthetic shape but has no real sporting background. She occasionally jogs and goes for gentle bike rides. She prances up steps compared to me. At a obstacle course we did a few years ago, she cleared the balance beams under perfect control in around the quarter of the time it took me. When we hike on uneven ground, she is probably 50% quicker than me over short distances (where fatigue doesn't play a part). Fitness doesn't put me on a level playing field in some activities.
When does fitness fail?
When function is suboptimal. Ranges of motion that are much smaller than the mechanical potential in combination with muscular firing patterns that are riddled with compensations lead to and come from suboptimal function. When I look at athletic performance through the filter of function rather than fitness, I can easily how I performed so poorly at these very elementary activities. These girls were/are much more functional than me. They are much more mobile than I am and it is this that separates our abilities. My lack of mobility (I am improving daily) comes from a muscular system that is generally overactive. To do something simple like run up a step, I am fighting against my own generalised, elevated muscle tone before I even perform the movement. My looser counterparts had less of this issue. Their joints could move freely and their muscles were more available for and more harmoniously organised to carry out these basic actions. This freedom shines through in unpredictable environments and in activities where the environment place limits on your movements due to its shape and size (in running up and down steps, stride length is fixed by the size of the steps and not your size and strength).
Forgetting fitness for a minute, how well do you function? Where do you find you act clumsily? Are there basic movements you can't perform with ease?
Squatting and running make you fit but this fitness will always fail in certain circumstances in the underlying function is not currently operating.
Find your function first to forget those fitness failures.