When people are working without the guidance of a coach or the structure of some objective markers, there is a tendency to fall into a very specific intensity of training: comfortably uncomfortable. In other words, they are pushing just hard enough that they feel they are being challenged and “working” – but ironically, it is this sweet spot that can mean little to no progress. It may be either too hard for certain endurance or stamina adaptations or not hard enough to improve strength and power. The unfortunate result is that despite all the time spent training, progress and forward momentum fail to occur, and they wind up essentially running at a standstill.
Objective vs. Subjective Measurements
While research in the field of self-assessment seems to have firmly established the inherent inaccuracy in our ability to evaluate our own performance and abilities, this doesn’t mean we should disregard our observation of the training intensity. Instead, we are better off overlaying this subjective evaluation (“Rating of Perceived Exertion”, or “RPE”) with objective and measurable data to better calibrate the gauge. There are several different scales and ways to interpret and record this RPE, but I have found that keeping it simple with a 1 to 10 rating has been the easiest to score.
In terms of objective measures, there are several different types, all with different degrees of accuracy and reliability. Furthermore, for every physiological measure that can be evaluated, there are even more products available. Different brands and companies offering everything you can imagine. From basic heart rate monitors and training logs to advanced recovery assessment tools that analyze sleep quality, heart rate variability, and direct-current electroencephalography (DC-EEG) to determine your training readiness. Your personal choice will depend on numerous variables, but it’s best to select ones that are easy to implement and that have a relatively proven track record.
Once you have a couple of these objective and trackable measures (i.e., a heart rate monitor and a detailed training log), ensure you record your RPE within approximately ten to fifteen minutes of your training session. This process needs to be done consistently over a period of time (longer than a week or two) as you need to be able to step back and consider your recent history from a couple of different vantage points: are there variations in the intensities from workout to workout, week over week; what does the measured data look like when compared to how you rate your effort; and are all of the intensities unfailingly falling within the same range regardless of the session?
Why You Need to Train at Different Intensities
Let’s speak in broad terms and simplify our definition of intensity to three levels: low, medium, and high. The lower zones provide active recovery and allow for skill development (during both aerobic and resistance training) and, when done for a longer duration, help to develop endurance by improving the efficiency of energy uptake and increasing mitochondrial density (this is specific to cardiovascular training).  The high zones are where you develop top-end absolute strength, power, and speed (during both aerobic and resistance training).
There can be a lot of opposition from athletes of all levels to train in the low zones, though it tends to be more notable when they are at the recreational level. This is due to the fact that we have been programmed to believe that if we don’t feel the effort, nothing’s happening – and with this lowest intensity level of training, none of the physiological markers that we use to define effort are going to be elevated: our heart rate has to stay low, our breathing rate isn’t elevated and the weights we are using are 40-70% below our maximum. Given that a lot of the adaptations we’re deriving from training at this intensity are occurring at a cellular level and over a long period of time, it’s no wonder that we don’t “feel” the results of the training session in the traditional sense. Furthermore, the more time that an athlete has been training without a plan that targets these varied intensities, the more set their body is physiologically due to this decreased efficiency. They jump into the middle zone very quickly, and to pull back; they must slow down/decrease the weight early in the session to such a degree that they feel they aren’t accomplishing anything. In response, they often ignore the training session’s parameters because it’s “too easy” or they “can’t go that easy/light” – and as a result, they wind up back in the same middle zone where they always are.
Alternatively, the high or top-end zones are about short, maximal output exertions that tap into an energy system requiring a longer relative recovery, both between sets as well as between training sessions. Since working to this scale is often harder than people realize, they either don’t want to (or can’t) produce the degree of effort required, or they fail to make the necessary adjustments (in rest intervals or between session recovery) to train at that intensity properly. Whatever the case, they once again end up back in that middle zone, unable to generate the effort that will develop these maximal attributes.
Without Challenge, There is No Change
Pushing ourselves truly outside our comfort zones can be difficult – even when we think we are, over time, we ironically become accustomed to that specific degree of discomfort. There are two ways to try and overcome this. First off, understand that challenging yourself isn’t always directly related to a high-intensity “burn,” realizing that slowing down or lowering the weight enough to facilitate cellular adaptations or to allow for recovery can be uniquely “challenging” from a mindset point of view (if not a physical one). Secondly, utilizing some form (or forms) of objective tracking or measurement in conjunction with our subjective assessments can increase our awareness of when we are falling into these unproductive areas and allow us to recalibrate our scale. Remember – “if it doesn’t challenge you, it won’t change you” (Fred Devito).
 Validity of self-evaluation of ability: A review and meta-analysis. Mabe, P. A., & West, S. G. (1982). Validity of self-evaluation of ability: A review and meta-analysis. Journal of Applied Psychology, 67(3), 280–296.