One of the rules of product design is to focus on a Main Metric. Using this approach, a design team will isolate a single measure of quality or fitness and continually assess the product against that metric throughout the product’s life cycle. The benefit of a Main Metric is that it tends to focus your efforts which results in a more coherent product. A good example of this would be the iPad. The iPad is only good for one thing, but at that one thing the iPad is truly remarkable.
Here’s the important bit. The designers of the iPad were not focused on aesthetics as the main metric. Nevertheless the iPad is quite beautiful. How did that happen? The iPad is beautiful because its designers carved away everything that didn’t support the main functional metric. Imagine what the iPad would look like with a CD expansion bay, or even a USB port. The iPad is such a uniquely satisfying user experience because it doesn’t try to do everything.
In the context of fitness isolating a main metric is quite tricky. What is that single measure which can justify the sweat and tears you shed in the gym? What is that unique point of satisfaction that keeps you coming to the gym, even when you’re sore and tired?
In my years as a trainer I estimate that 90% of my clients start with a goal of body composition. In other words, for that 90% the initial main metric is primarily aesthetic. However not a single client has ever thanked me for losing weight or leaning out or fitting into smaller pants. When clients thank me, it always goes to something deeper: a stronger connection to their body; being a better parent or partner; longer life; a bigger lift; a higher jump; a marathon PR, etc. In their gratitude, these people have identified their main metric.