In the most simple terms: through measurement and records. Without these two practices, we have no objective way of knowing how, or even if or whether we are progressing. The more rigorous and detailed our measurements, the more we can learn about our progress. And through measurement, we can further determine which aspects of our training are most effective and which, for example, may be causing us to stagnate or languish.
This implies that our pursuit must be measurable, objective, and definitive, which might therefore appear to be problematic for sports such as bodybuilding, which are inherently subjective. It similarly presents challenges for sports in which our performances are mutually exclusive, such as racquet sports, the various football codes, or the martial arts. Nevertheless, there always exist underlying dependencies in these sports that are objective. The key is to avoid chasing goals such as “I want to get fitter” or “I want to look good,” since such goals are implicitly unachievable or immeasurable. That is, either the bar is perpetually moving, or it is unclear where indeed the bar lies.
Competitive bodybuilding is the expression of lean mass, size, balance, and proportion—the latter of which includes elements of subjectivity, but which can nevertheless be described in objective terms if we know what the judges are looking for. Hence, periodic measurement of body mass, body composition, and muscle girth at different sites provide all the information required to see how training is altering our physique. And of course, the training itself—strength, endurance, and recoverable volume (MRV)—is entirely measurable too, and hence comparable.
For mutually exclusive performance sports, it is necessary to identify the skills and qualities that influence our performances. Our competitor/s can always prove to be better, or better ‘on the day’, as it were, but if we are measuring objective improvements in our physical performances in training, they will eventually translate to corresponding improvements in our competitions. For how long do we compete? What types of speed or agility do we require? What are the force and power characteristics of our sport? Are we being limited by flexibility, efficiency, or economy? And what of technical elements? If we can answer these questions, we can design a battery of tests around those skills and qualities, and hence track our progress.
Sports that are based on extrinsic measurements of time, distance, force, and power are most easily tracked, of course. We can measure our time at distance intervals, distance covered at time intervals, or our average and maximum speed, power, and force output. At the very least, we should measure one primary performance metric against time. (See below.) Physiological factors such as temperatures, heart rates, respiration rates, and sweat rates can be equally important. And secondary performance characteristics such as stride rates, stroke rates, or cadence further allow us to interpret these results—for example, how are we to explain the sudden fall in performance at the end of this graph? Was it a change in distance, a different type of training, or following a bout of sickness?
Together, these data allow us to put together a ‘picture’ of how we are progressing and, most importantly, what we need to do or change in order to reach our goals. And as both an analytical and motivational tool, it helps to programme long-term and interim performance goals which allow us to ‘see’ our achievements. The simple example below describes actual energy consumption per bout, as well as showing the target energy output—in this case, the distance of the course.
The bottom line is that, whatever your goal, you must have some way of assessing how you are improving. For you, it would most aptly be measured in terms of strength (loads), muscular endurance (repetitions), recovery (MRV), and muscular girth (cross-sectional area), which is associated with strength and endurance. Without objective evidence of physiological and/or functional adaptation, it is unsurprising that you might feel as though you are not progressing. And that is always going to be demotivating, as you have found.
I hope that helps.