People who want to increase their muscle mass and build the body of their dreams are always looking for ways to make their workouts more effective. In general, if you would like to build strength and size, you should be doing 3 or 4 sets of 5-10 repetitions of each exercise, depending on the weight you're lifting. However, rather than counting the number of repetitions and sets all the time, you could opt for timed sets instead.
This is where 'time under tension' becomes important. Simply put, time under tension is defined as the amount of time that a muscle is actually being strained during a set. For the purpose of this particular definition, straining a muscle is a good thing- within reason, of course. In theory, the longer a muscle is under tension, the better results you will achieve. This is because your muscles will get broken down as a result of time under tension, which will force them to rebuild, adapt and grow. With that being said, the load that you select must be appropriate for your fitness level in order to avoid injuries.
Time under tension, when implemented properly, enables you to make significant gains. Ideally, regardless of the number of repetitions that you are doing, you should aim to make your set last for anywhere between 30 and 45 seconds.
Some people try to pump out as many repetitions as they can in 45 seconds and that is the wrong way to implement time under tension. If you do your repetitions too fast, instead of activating your muscles, you end up using too much momentum to lift the weight. Therefore, when you do your repetitions too fast, you are cheating yourself out of muscle gains.
On the other hand, some people do their repetitions too slow because they spend too much time 'resting' between their repetitions. For example, they will spend too much time at the top of the pushup or at the top of the dip. Spending too much time on the easiest part or phase of an exercise adds virtually no value to your set. This is because your muscle is not actually spending that much time under tension.
It's also very important to make sure that your form does not get compromised during your set.
In order to get the most benefit from time under tension, you need to stay in control of your lift and really focus on engaging the muscles you are targeting during your lift. Ideally, you want to maintain a consistent tempo during each repetition. Typically, the ideal tempo is approximately 3 seconds during the up phase and 3-4 seconds during the down phase of your lift. If possible, make sure that the eccentric part of your lift is equal to or longer than the concentric part of your lift. For those who don't know, the eccentric phase of your lift is when your muscles are lengthening under tension. For example, it's the downward movement during the bicep curl, bench press or squat. The concentric part of your lift is when your muscle shortens under tension, such as during the upward movement in a bicep curl.
As we can see, time under tension, when incorporated properly into your workout, facilitates muscle growth.