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What is Time Under Tension?

Time under tension, or TUT, is the amount of time that a muscle or group of muscles is under stress. Bodybuilders get so big because they are keeping their muscles under stress for longer periods of time when lifting.

The general consensus is that increasing TUT will maximize hypertrophy.

This means that for hypertrophy it may be better for your client to lift lighter weights for a longer period of time than to use heavy weights for fewer reps.

But, this isn’t the full story. There is a lot more to the concept of TUT than simply increasing workout and lifting time.

Slow Down and Focus

Simply increasing total TUT may not be enough to maximize your client’s workout and to help him or her get the most hypertrophy gains.

Research suggests that paying more attention to the reps, slowing them down, and doing fewer is the more effective way to increase TUT and get the benefits.

For example, instead of powering through 15 to 20 reps for 60 seconds, have your client slow it down and do just four to six reps in 60 seconds. This will increase the window of time during which the muscles are actually under tension, therefore giving you more hypertrophy gains.

It’s All about Hypoxia…

The reason that this TUT concept works may be a result of creating a hypoxic environment in the muscles being worked. Here’s how it happens:

  • When you lift weights the body produces a buildup of metabolites.
  • As this occurs muscular contractions cause blood vessels to condense.
  • This leads to a restriction of blood flow to the muscles that are working.
  • Without proper blood flow oxygen is not present, which creates a hypoxic environment.

Research has shown that hypoxic muscle environments actually enhance muscle strength and hypertrophy.4 Blood flow must be obstructed while time under tension is stressed to create a more anabolic response.

…And Muscle Fiber Recruitment

In addition to the benefits of the hypoxic environment, there is something else at work when you use TUT to achieve hypertrophy:

A muscle under stress for a longer period of time, stressed to total fatigue, will have greater muscle fiber recruitment.

The motor units in the muscle being worked are recruited from smallest to largest. The more time you keep a muscle under tension, the greater chance you have of recruiting fast twitch muscle fibers. Fast twitch muscle fibers produce more force and are larger than slow twitch muscle fibers, so more hypertrophy.1

How to Put TUT to Use

The principles behind using TUT for hypertrophy are grounded in research, but what does that mean practically for you and your clients? Here are some strategies to try:

  1. Increase hypoxia. To restrict blood flow to the muscles being worked and trigger more hypertrophy, aim to train as low as 20 percent intensity. This has been shown to improve hypertrophy in as little as three week.2
  2. Light weights, big fatigue. Using lighter loads may seem like the opposite of what you want to do to train your clients for hypertrophy, but the evidence is there. As long as your client uses lighter weights to fatigue, you’ll get results.3 A good guide is to ensure your client gets to volitional fatigue with those lighter weights.5
  3. Minimize rest. To maximize the hypoxic environment and increase the chance that your client gets to volitional fatigue, minimize the amount of rest you allow between sets.6
  4. Use hormones to your advantage. Another reason to stick with lighter weights and maximum fatigue is that research shows your client is more likely to start producing growth hormones at lower lifting intensities. This in turn, will promote hypertrophy.2

TUT is a concept that bodybuilders may be aware of, but it’s a tool that every trainer should have in his or her back pocket. Taking advantage of time under tension in the right way will help you help your client get to hypertrophy. When you do it right—with lighter weights, longer sets, less rest, and volitional fatigue— your client gets maximum results with shorter workouts.