Weider Principle #26: Iso-Tension

How flexing between sets can enhance muscle growth

Some of these Weider Principles are complicated, and some are easy. Iso-tension falls into the latter category. It’s basically a fancy term for flexing. It’s how and when you do it that turns these weight-free contractions into a method for both focusing and intensifying your workouts. You may have thought flexing was something only champion bodybuilders did regularly, especially in a public place like a gym. But we’re going to tell you why everyone should include iso-tension in their training to easily increase their gains.

This tenet

requires that you fully contract the targeted muscle(s) between sets and hold that contraction for 6–10 seconds. For example, if you’re doing pushdowns, immediately after each set lock your elbows straight and maximally flex your triceps. That example is easy to picture because you’re essentially duplicating the contraction of a pushdown, but do this same tensing regardless of the triceps exercise. Whether you’re doing one-arm dumbbell extensions, close-grip bench presses, or machine dips, straighten your arms and flex your tri’s as hard as possible just after each set.

Here are a few iso-tension tips. First, this isn’t a good technique to do with compound lifts that involve many areas. For example, deadlifts work too many muscles (spinal erectors, trapezius, glutes, quads, lats, etc.) to focus on just one. On the other hand, if the compound exercise has one primary muscle, applying iso-tension there can better direct the stress of your sets. As an example, flexing your chest between sets of bench presses can help you target your pecs (primary muscle) and use less of your delts and triceps (secondary muscles).

When doing iso-tension with sets of arm or leg exercises, you may find you can flex harder and focus better by tensing just one limb at a time. Finally, stretch the targeted muscle(s), too. Follow holds in the fully contracted position with holds in the fully stretched position for the same lengths of time.


Here are the pluses of iso-tension

    CONNECTION: Flexing the targeted muscle(s) between sets lets you know the feeling you want to duplicate during the set. With practice, this will strengthen your focus so you can better work that area.
  • SET CONTINUATION: Doing iso-tension immediately after a set keeps the tension on the targeted area. Effectively, it’s a means of continuing the set without a training partner or even a weight, and it therefore lets you easily and safely push a set beyond failure.


There are two potential pitfalls of iso-tension. Here’s how to avoid them.

  • REDUCED REST TIME: Keeping the tension on your muscle(s) after the set is going to eat into your rest time. Therefore, count the iso-tension time as workout time, not rest time. If you normally rest 90 seconds between sets, maintain that minute and a half but start it after the iso-tension and end it when your next set begins.
    Iso-tension can be difficult to apply to specific areas of muscles. For example, if you do it after sets of incline presses, you’ll likely flex your entire chest and not just your upper pecs. To some degree, this can’t be avoided, but strive to contract primarily the targeted area. With practice, you’ll strengthen your mind-to-muscle connection to that area.


Although iso-tension prescribes that you flex between sets, it’s a training tool you should use outside the gym as well. Competitive bodybuilders know that posing practice is itself a workout. You, too, can benefit from striking mandatory poses, such as the rear-lat spread and the front double biceps. Doing so will teach you to better control your muscles during sets.

Similarly, you can enhance your mind-to-muscle connection by iso-tensing your muscles throughout the day. One of the best body parts for this is abs. Even while seated at a desk or driving a car, you can crunch your chest down and tense your midsection to work your rectus abdominis. You can also pull in your waist as far as possible to hit your frequently neglected transversus abdominis (inner abs). Hold either position for as long as possible up to one minute, and do three to five iso-tension holds per session. FLEX




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