HOW OFTEN SHOULD YOU CHANGE YOUR WORKOUT?
There are tons of different opinions on this. All I can do is give you my opinion as well as the reasons behind it. Hopefully it will make sense to you. It certainly does to me, but you'll have to decide.
So to start with, I remember I used to work at a gym where there was this other trainer about the same age as me. He always changed his client workouts every workout. I don't know if I every saw his clients doing the same thing twice. He would justify it by saying that it's for muscle confusion and to keep things fresh and new all the time, thereby relieving boredom and staleness. Then on the other side, there was me where I like to repeat programs for a while (at least a few weeks anyway). These are of course vastly different approaches to training. I'm not going to say flat out that mine is the better way. It depends on the individual, their goals, their regularity of working out, etc. Bu what I can do is explain my reasons.
1. First of all, it takes a while to find your groove with a particular movement. We all know that practice makes perfect, but if you never practice the same thing more than once how can you expect to progress.
2. It's also much easier to measure progress. If you're constantly doing different exercises, it can be very difficult to chart your progress. If you do a Stiff Legged Deadlift one day, a Good Morning the next day, a Prone Hyperextension the next day, a Hip Thrust the next day, etc. I think you can see how tough it would be to measure your progress in one of them. They all train similar muscles, but in different ways. If however, you stick with say the Deadlift for a while and over the course of 4 weeks, you've increased the weight by 30 lbs as well as the reps, that's a very clear way to see your progress. And when it's in that form, it's impossible to argue with it! If you're always doing different exercises, it's easy to just tell yourself that you're training hard. But how do you really know you're progressing? It's easy for your mind to play tricks on you.
3. Confidence Building is another benefit of sticking to a program for a while. When they're always changing, it can be a little intimidating. I mean each time you workout you may be doing an exercise you've never done before. That means each time you workout there is a risk that the exercise won't go well for you or you'll find it awkward and uncomfortable. But with doing the same exercises for an extended period of time, you have a chance to really know the movement. Little things such as how you place your feet, shoulders, butt, etc. will always be improving a bit as your numbers go up. This is extremely important for confidence which is often a goal of people who I train.
4. Quality Over Quantity is another element to repeated workouts. It simply isn't necessary to practice so many exercises. Mastering a handful of exercises and really experiencing their benefits is far superior to learning tons of exercises and not mastering any of them. An old expression I like to use is "A little of everything and a lot of nothing".
As many of you know, I am a longtime martial arts practitioner in the arts of Ving Tsun, Boxing, and Baguazhang. All of them have one thing in common. They stress the importance of the basics and quality over quantity. The first day I walked into Mack's Gym in Toronto many years ago, I learned the Boxing stance (rooted and balanced, hands up, chin down), the basic forward step, and the jab. Many years later I'm still working on it and still making it better. That's one single punch, but it's also the most important punch in Boxing. Very similarly in Ving Tsun, I learned the basic straight punch, stance, and first section of the fundamental form called Sil Lim Tao. No matter how advanced you get in Ving Tsun, these are still the most important parts of the system along with a handful of principles. On the other hand, I met up with some guys who did a martial art style which I won't name, that had what seemed like hundreds of different techniques. Long story short, they couldn't fight their way out of a wet paper bag! They knew lots of moves and honestly looked pretty good when doing their demos, but when push came to shove they had nothing. Seriously they had no rooting and didn't even have their hands up! The point is that focusing on a handful of techniques or exercises will bring the best results and that's an undeniable fact!
Now with that being said, people have different reasons for working out and it isn't up to me to dictate those. For getting the best results, there's no question that workouts should be repeated for at least a period of several weeks. It can also be longer, but that all depends on whether or not you're still progressing on it. And even when you do change you can still do the same exercises but in different set/rep patterns. However some people like the idea of always having fresh workouts. Particularly in a group class which is very social, people collectively look forward to what's in store for them that day. And if that aspect keeps them coming regularly, then that's great!
So in conclusion, while I do believe in repeating workouts for extended periods of time and have given my reasons for doing so, there may be times when more frequent changes will better suit you or the situation. I guess at the end of the day, it depends on you. After all, not everyone is willing to train the same punch for 30 years!