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In our last installment, we talked about variability and how periodization is the thoughtful management of different training variables. Variability is incredibly important for the continued development of an athlete as well as in injury prevention. Today we’ll talk about one of the most important program variables: Exercise intensity. 
Exercise intensity can be defined in many different ways: 
From the subjective observer, intensity looks like; sweating; grunting or swearing; chalk flying everywhere; tearing your hands; laying on the ground after your workout and sometimes even crying or throwing up. This is not a reliable metric for defining intensity because it’s all based on perception. It’s easy to look intense but how can we quantify intensity?
From the subjective participant, intensity can be quantified by different scales such as Rating of Perceived Exertion (RPE). RPE is a reliable method used to help individuals with a prescription of intensity based on their own perceptions. RPE is typically a 1-10 scale with 1 being the easiest and 10 being the hardest. You might see this represented as, “5 rep back squat at RPE8.” which means you would do 5 reps and it should feel like an 8/10 effort. Subjective ratings of intensity are great for all athletes from beginner to elite.
Objective measures of intensity would be things like percentage of one repetition maximum (%1RM), percentage of heart rate maximum (%HRM), percentage of VO2 Maximum (%VO2M), or percentage of maximal speed/power (%MS / %MP). Objective measures are the most reliable ways to consistently prescribe intensity based on the ability of an athlete. 
I’m sure you’re thinking, “Which one is best; objective or subjective?” well, there are pros and cons to both. Objective measures are incredibly reliable and accurate, they display only the numbers with little room for interpretation. Where objective measures fall short is when considering things like athlete readiness. Athlete readiness refers to how you are feeling on any particular day. It’s related to how you slept, what you ate, how much activity you have had in the days leading up, and a myriad of other factors. Sometimes athletes have bad days and even with the best-laid plans, objective intensity prescriptions just aren’t appropriate. Objective prescriptions also require more interpretation of how they related to the task being performed. For instance, running for 30 seconds at 90%HRM won’t be that hard for most people. Almost anyone will find running for an hour at 90%HRM to be a difficult task; same intensity, same modality, different tasks. Similarly, if we did 5 sets of 1 in the deadlift at 85%1RM, we have a fairly easy workout. That same workout with 5 sets of 5 at 85%1RM is much more challenging. This shows how intensity needs to be balanced against the task being performed. 
What subjective scales lack in accuracy they more than make up for in simplicity. Subjective scales always account for athlete readiness. If an athlete comes in under recovered, with a plan to hit 95%1RM it is possible that prescription could be too much for that day, leaving the athlete feeling inadequate or worse, exposing them to potential injury. With a subjective scale, you can adjust on the fly and choose the weight based on how you feel. This helps athletes become more in-tune with their bodies and encourages them to practice safety. Subjective scales are also more easily applied to different events. 9/10 for 100m and 9/10 for 5k are totally different events but the athlete intuitively understands this and adjusts accordingly. 
In my opinion, subjective scales are the ideal intensity prescription for group fitness programs like CrossFit. In the next installment, we will look at how we manage and monitor intensity and volume to come up with a training program that allows for optimal adaptations.