This is how I currently feel about training as it relates to endurance performance.*
Your strength is the foundation.
Strength training is the most important part of training. Being strong is important, not only for athletic performance, but for health as well. It’s important to lift heavy weights if you want to maximize your strength gains. Remember, strength doesn’t mean getting huge (though it can), as many adaptations to lifting heavy things are neuromuscular. Muscle is a function of the nervous system.
There are lots of different ways to strength train. The way you do so will affect whether or not you’re debilitatingly sore, whether or not your muscles will get bigger, whether or not you will get stronger, whether or not you will get more explosive, whether or not you will become more injury proof, etc. Train smart.
Focus more on movements than muscle-groups. The basic movements are solid — deadlift, squat, pullup, pushup/dip, row, press. Master these before anything else is added.
Focus on strength-to-weight ratio.
I think it’s important to be strong in relation to whatever size you are. Especially for endurance-minded athletes, focusing on improving your strength-to-weight ratio is going to yield a lot of practical benefits.
Each training session should be for a specific purpose.
Training shouldn’t simply be picking something that’s difficult to do and attempt to get through it by any means necessary. Is a long, intense workout of lifting weights and running hard going to benefit you in a way that’s helpful for your goals? Is a tempo run whist sucking down gu’s or gels going to maximally improve your fuel economy during an aerobic event?
Many people judge a training session/workout by the immediate feeling of exhaustion or the soreness they feel either after it’s done, or the next day. It’s understandable that we would want to feel like our training is tough and successful. But judging your training progress over time is a better method for determining whether or not your training is going well, instead of just focusing on how tired you were after a run.
The purpose of training is to cause a specific stress that results in a specific adaptation (or set of adaptations) that’s related to your goal.
Some training sessions should be for psychological improvements.
There’s research that compares one’s willpower to that of a muscle in that flexing said muscle will use up the energy stored within it. Once gone, the muscle can’t do a whole lot until its energy has been restored. The same research suggests that using willpower strengthens willpower, basically.
Training (sometimes) in a way that tests your ability to push yourself through something tough will undoubtedly increase your ability to push through something tough in the future.
A lot of what happens during exercise that makes us want to stop is the result of our brain trying to protect itself from perceived harm. Many feedback mechanisms will play into our brain trying to shut us down in order to protect us from harm — things like muscle soreness, energy depletion, inflammation, fatigue — and this will happen before the point that it’s actually harmful. There’s a built-in safety-boundary that prevents us from digging too deep. And because our thoughts affect chemical reactions in our brain, and chemical reactions in our brain affect our thoughts/emotions, when you feel like exercise is getting tough, it is. Similarly, when you start to get fatigued and sore and inflamed, exercise feels harder.
Sometimes you will need to train in a way that allows you to push further into that safety boundary so that you can push increasingly into that safety boundary (and potentially improve willpower in other areas of life).
Training should be polarized.
Different energy systems will come into play depending on what you’re doing. You should train both anaerobic and aerobic pathways in a way that gets you the most out of each. Volume and intensity should be inversely related.
Different muscle fibers are important for different situations. Type I muscle fibers are definitely important. They are fatigue-resistant and oxidative, storing mostly fat for use as a fuel substrate. They are the “slow-twitch” muscle fibers that allow endurance athletes to go long. They are important, yes, but relatively poor at generating force. But type II fibers are important as well — especially type IIa oxidative fast-twitch fibers. They are involved with strength and power, and they are still oxidative which makes them at least somewhat fatigue-resistant (compared to other type II fibers) allowing them to be of use for endurance athletes.
A polarized model of training would train both aerobic and anaerobic metabolic pathways, and both type I and type II muscle fibers.
*I reserve the right to update this over time as I learn and train.