How can you prevent injury during multi-joint movements?

I totally agree with this. Clients think warming up is a waste of time, especially when late for the session. They just want to get right to it. As a coach, we need to emphasize the importance of it or help them to warm up by telling them their first workout is a dynamic warm-up, trick them into doing the warm-up. I’ve a client who didn’t work up enough and got injured.

Warming up is paramount to most workouts, multi-joint or not. I would argue that a proper warmup is the base for any effective workout, although it's a bit controversial to say they can "prevent" injuries. While warmups can certainly mitigate risk, injury risk will largely depend on a lifter/exerciser's ability to gauge their intensity internally and understand what their nervous system and physiological capabilities are. It's pretty common to "overshoot" because you're feeling good after an energy drink or simply because you've got an important event to train for, so it's hard to make the claim that warming up can prevent anything.

Proper metabolic, dynamic warm-up, and/or exercise specific warm-up is a non negotiable. But your system and structural tolerance changes based on your rest, anthropometry, etc. Biomechanical efficiency in technique is a given. In short: progressive overload: most injuries happen due to overload. Too fast too soon. Aim for 0 to 1 not 0 to 100.

Repetition, repetition, repetition. Having graded exposure to a given activity -- meaning hundreds (or possibly thousands) or reps in your arsenal -- is the most surefire way to mitigate injury. To be fully transparent, training to the point of *actual* injury may be the most fool-proof way to prevent re-injury. It's often the case that in some lifting scenarios, exploring a range of motion or a weight that leads to a tweak or level of discomfort is the necessary learning experience for injury mitigation. (That was scary, won't do that again.)

Form comes before everything else. We should learn to be patient when we start to exercise and as we progress too. Trying to increase the load before we master the form often results in injuries or plateaus. Both force us to go back to the basics sooner or later, so better learn from the beginning and progress step by step.

I think load is a big factor. Too many people try to lift too heavy too fast. In saying that, I also find the opposite to be true. Some (Minority) barely have any load, and therefore is common to compensate through dysfunctional patterns rather than slightly challenging the movement and getting the right things to take load.

Yes, choosing the right load is one way to go. There are times when you did everything right but still injured. It happens sometimes; that is just one scenario. There are also times when there is a catch while doing particular move, and we must know to stop; this sort of situation is something the book will not tell you what to do.

I make my clients learn proper form with either bodyweight exercises or very light weights. Once their technique is right, we do a mix of strength and strength endurance sets and reps schemes. Strength: 5 reps with a heavy weight. If you can only do 3, choose a lighter weight, if you can do 7, pick a heavier one. But make sure form is perfect. Strength endurance: 15-20 reps with a medium weight. If you can only do 12 reps, use a lighter weight, if your form is still perfect at 20 reps, use a heavier one. If you follow the guidelines above, you will know when to increase the weight at the right time.

Variability has its place in most exercise protocols and is certainly one of the aspects of training that can make it fun and safer. Still, for anyone with concrete fitness goals of strength or change in body composition, it is important to keep certain exercises in the fold as "staples" of a functional training program. TOO much variability will result in a "many birds, no stones" approach, where nothing actually gets achieved. Instead, keep a core list of 3-4 exercises you can progress over the course of multiple training programs while giving your accessory (less important moves) exercises some variability to keep things interesting.

If proper form is respected and weight is increased progressively and at the right time (see my previous point), doing the same exercises over and over again shouldn't present more risk than varying exercises. However this can lead to plateaus, in which case it is a good idea to switch your routine for a while.

I don’t agree so much with the single-joint exercises. I think in reality, there’s way too much emphasis on this and it’s one of the reasons people get injured. Take a biceps curl for example. A lot of people try to maximise this muscle for aesthetic purposes, but in doing so, place a lot of strain on the lower back. I suggest looking into exercises where the movement and force start with the spine and then translate to the biceps.

Progress happens during recovery. The number 1 recovery method, and by far, is getting enough sleep. This means 7-8 hours minimum for most people. You might believe you function well on 5 hours of sleep but you are likely fooling yourself. Rest days are mandatory. And unless you are an athlete training for a competition, 5 sessions a week of strength training is already playing with fire. Drink water of course. But you should already be drinking a lot of it for many other reasons than recovery. Every other recovery method is useless if you don't get these right first.

You know your body best. Listening to your body is really important to avoid injury and for long term health. There is a difference between pain and muscle discomfort. Any sharp pains during exercise should be a sign to stop exercising and consider getting the necessary care and recovery to reduce the chances of injury.