CrossFit's®️ method to forge elite fitness is Constantly Varied Functional Movements executed at High Intensity. Despite its proven efficacy for a wide range of athletes, there are many who still refute this claim. Why is it that something that is so observably true is still so widely questioned by so many well qualified people? In my experience, there are two main reasons.
High Intensity is mistaken as Maximum Intensity. And nowhere is this more true than in most CrossFit affiliates. There is an unwritten rule that you have to go as hard as possible, every time you workout. Zoom out a little, and for some this may actually be the case. For example, many members may train several times per week elsewhere for strength, power, speed or some combination of specific results, and simply use CrossFit as a conditioning tool a couple of times per week. In this instance, it may make sense for them to go all in when they are in the box. But for the majority, at least where I have trained, who only train CrossFit and attend 4-6 times per week, emptying the tank daily is likely counterproductive to fitness, health and injury prevention. Sure, once or twice a week, go all in. But high intensity can really be thought of as anything north of about 70% effort and most progress is made for most people across most modal domains (types of activity) in the 70-85% range, nudging over 90% on occasion. Too much time spent above 90% will adversely impact the ability of the nervous system to recover, induce inflammation and soreness and often lead to poor movement patterns becoming ingrained. Couple this with poor sleep, hydration, nutrition and other lifestyle factors and burnout is only a workout away.
High intensity is seen as universal. One standard is applied to all, for example, a 7 minute mile is high intensity, 10 minutes is medium and 12 minutes is low intensity. This simplistic view discounts individual ability, training age and tolerance of load. Those who I coach will sometime see me apply a scale mid workout of advising extra rest in an interval format. For example, if the workout calls for a minute of work and 30 seconds of rest, repeated several times, I might advise a switch to 45 seconds of work, and 45 seconds of rest. The ratio of 2:1 work:rest may be too intense for some people, even though they are only working at the same percentage of maximal effort as the person next to them. Their tolerance to volume is simply lower. You see, CrossFit®️ defines intensity as work done, which can be derived mathematically from measures of load, distance and time. This gives us a quantity of work done, and some people have the ability to produce more or less work in a given timeframe than others. To further complicate this, that capacity will vary depending on the nature of the work. For example, in a simple run one athlete may outwork another, only to see this reversed when deadlifts and box jumps are programmed.
So how can any of this be applied to working out as an athlete, and coaching? As an athlete, pick a day or two each week from the programming where you are going to give 100%, or near to it. Still apply pacing and tactics as required to maximise your performance in those workouts, but aim to finish feeling like you couldn't have gone a second faster, or completed a rep more. The other days, work at between 70 and 85% of your best effort. Remember, this is still high intensity! Select which days you will go extra hard based on there being movements you are competent at and try to pick a couple of different time domains, for example a 6-12 minute workout, and a 20+ minute workout one week, then maybe a 3-4 minute sprint and a 12-20 minute workout the next.
As a coach you can look to optimise scales of workouts as a whole, and movements individually, to allow the athletes to achieve this. They can't go all in if they spend 3 minutes out of 10 staring at a set of rings because they are struggling with muscle-ups. Guide the athlete to appropriate scales which will vary based on total volume, interference from other movements and intended stimulus of the workout.
As a rule, high intensity is a great thing, but just as constantly varied isn't random, high intensity isn't just go as hard as you can until you collapse.