In my experience, variety is important in a fitness programme. However, there are no set guidelines for how to switch up your routine. It all depends on a variety of factors and will vary from person to person.
Generally, the basic rule of thumb is: The programme is only as good as the time it takes for your body to fully adapt to it. Our bodies are fairly smart and when we move into different workouts too often we stop producing any results, rather than speed it up.
I personally recommend changing routines every five to six workouts within a specific muscle group (or every three to four weeks, depending on the training frequency). Adding variety to your fitness programme also alleviates the boredom of routine and keeps your body guessing.
The most important point is to make every workout enjoyable and challenging.
Some tips to vary your fitness routine include:
Sets and reps By changing the patterns of sets and reps you can prevent hitting a plateau and adaptation.
Alternating intensity Alternating-intensity exercise can be very effective to prevent adaptation. You can adapt your routine by performing two high-intensity, one medium-intensity and one low-intensity workout per week.
Rest periods Rest periods are very important during work sets, as they can improve efficiency. So make sure to challenge yourself with short breaks between sets.
Range of motion The most common mistake — and one you might not even know you’re making — is not following through a full range of motion, which is crucial to move well and stay flexible. Be sure to incorporate different key elements into your routine such as stretching and squatting.
Tempo training One of the most important elements is to select the right type of tempo during your workout to help spur muscle growth and develop body control. The tempo typically uses three or four digits to describe and alter the different training phases and may look like this: 2-0-1. The first number is used for the eccentric lowering phase of the workout. So, when lifting weights, you would have to lift two seconds on the way down, and then zero with no pause, and then one second on the way up.
The most important point is to make every workout enjoyable and challenging. Having a good coach is important too and can help you to reach your goals effectively.