1. Start Slow Many people make the mistake of saying they'll go 5x per week (to make up for their slacking lately), but only have time to go 2. Then they'll go 5 times for a couple of weeks and burn themselves out before seeing any real progress.
Instead of running in circles like this, you're better off being honest with yourself. Can only fit 2 gym sessions in your life right now? Do 2 and keep it up for at least 2 months. 2 times per week should now be a habit to can maintain: this is your baseline.
From here on, you want to push your baseline slightly. Try adding a third session after a couple of months and see if this is something you can fit in. If yes? Don't add a 4th session right away, just follow the same principle you did earlier.
Keep up the 3 sessions per week for a couple of months. You have now expanded your baseline fitness habits and are likely already seeing some improvements in your body composition.
2: Duration If long workouts are not an option for you, you got to adapt your training to be as time-efficient as possible. This way you can still keep up the habit of going to the gym and living healthy, without it costing hours of your time.
How do you do this? By using things like dropsets, supersets and decreasing your resting time slightly. It's also wise to prioritize exercises using machines or your bodyweight, as getting up to working weight on barbell exercises like squat and deadlift can take a lot of time.
3: Recovery You will not make something a habit if you are burning yourself out by doing it. Being able to recover from what you do in the gym, no matter how many (or little) sessions you do per week, is key.
This is where maximum recoverable volume comes into play. Your maximum recoverable volume will vary from person to person, but a good metric to know you're doing too much work is:
- you're regressing (less weights/less reps/ same weight feels heavier) - you're stagnating (you are stuck at the same weight for multiple weeks in a row) - you're still sore in the same muscle group during next session
If these are the case, you are doing too much and you will not be able to recover properly. As a result, you will dread going to the gym and making it a habit will be hard for you.
4: Enjoyment If you hate something, chances are high you're not going to do it with the input it takes to get results. This happens on a micro level (disliking specific exercises) and a macro level (disliking specific types of training). Let's cover both.
First, disliking specific exercises will lead to negative emotions in your brain when you think of the gym/training session that includes that exercise. This adds more dread and as we know, dread makes building habits 10x harder.