Time under tension is a commonly used term in gyms and personal training studios up and down the country. Time under tension is used to describe how long a muscle is put under strain/tension during a set.
If you want better gains, increase the time you are under tension or strain. Time your sets so they last between 30 and 40 seconds for ideal muscle growth. This length of time ensures the muscles are receiving enough excitement to trigger the growth. The length of time you’re under strain is important, but how you do the workout is too.
Avoid spending large amounts of time doing the easiest part of an exercise (releasing your muscles during a movement for example). The easiest part of a lift is the part that everybody likes as it puts the least amount of stress on your muscles.
Do you struggle to finish the last few reps when lifting weights? Ask your trainer if you can go down a size and finish the exercise. This way your body will be able to recover slowly throughout the set to get through it.