Have not heard about 85% rule, but in this context it sounds like just a spin on Pareto principle or 80/20 rule which in turn has been spun in every possible way with regards to fitness (google 80/20 fitness and see how many articles you find).<p>Anyways, I strongly recommend you listen to Prof. Andy Galpin's six part series (<a href="https://hubermanlab.com/dr-andy-galpin-how-to-assess-improve-all-aspects-of-your-fitness/" rel="nofollow noreferrer">https://hubermanlab.com/dr-andy-galpin-how-to-assess-improve...</a>) which addresses fitness in general term and outlines how to train for different outcomes (adaptation) to achieve a combination of Skill/technique, Speed, Power, Force/Strength, Muscle hypertrophy, Muscular endurance, Anaerobic capacity, Maximal aerobic capacity and Long-duration training. The subsequent episodes goes into all these areas in detail and serves as a knowledge base for further exploration.<p>I've yet to come over a better general approach and foundational knowledge information. There are probably equally good resources out there (e.g. books). This is in stark contrast to the broscience filled internet. Too often, it seems like advice is given without taking into account the individual and what you want to achieve. Fitness forums are great, but they are often concentrated on a niche part of fitness. E.g. people who care about Strength/Power/Hypertrophy don't care about Running etc. and vice versa.<p>Another general tip, which is talked about in the podcast series, is to continuously to work "Agile" (heh). In other words, use a feedback loop every month/ 10 weeks to see if you are progressing towards your goal. If not, see if you stuck to the plan. Check what's missing and reassess.