Isometrics Part I: What are they and how we can use them.

Isometrics Defined:

Let’s start with the basics. There are three types of muscle contractions: concentric, eccentric, and isometric. As defined in the Sports Medicine Resource Journal they are broken down as follows:

• Concentric - the total length of the muscle decreases as tension is produced.

  • Ex. The upwards portion of a biceps curl as the elbow bends.

• Eccentric - just the opposite! The length of the muscle increases as tension is produced.

  • Ex. The lowering of the weight during a biceps curl as the elbow straightens.

• Isometric - occurs when the length of a muscle stays about the same (ideally the same but being perfectly still is kinda hard).

  • Ex. When holding the weight of a bicep curl totally still at some point during the raising or lowering portion.

Typically, we see that more force can be produced with an isometric contraction than with a concentric contraction. However, eccentric contractions have the potential to produce the greatest amount of force - but we’ll dive into those weeds another day.

“Types” of isometrics:

I like to break down isometrics into two different types: yielding isometrics & overcoming isometrics. You may see them called different names like “holding” or “pushing”. However, despite the differences in nomenclature the principles underlying the two styles are the same.

In the yielding variation, you are holding a weight and resisting the deformation of a certain position while holding that weight. Using the bicep curl as an example again. This is like stopping mid-range in a bicep curl and holding this position. You are resisting “yielding” to the weight in this case. Oftentimes in these, the external load you are resisting is fixed - whether this is your own body weight like in a split squat iso or holding against a DB curl.

In the overcoming variation, you are pushing into a stable/usually immovable object. To use a different exercise as an example, the most common variation of this would be an Isometric Mid Thigh Pull. In these instances, it is you responsible for producing the force and therefore some more variability is present. Though one value of these is that this can be self-regulated by you and your comfort level with the output rather than a fixed external load.

Uses For Each “Type”

There can be a lot of crossover between the two “types” of isometrics. The adaptations gained from each will be primarily driven by intent and effort put into each. It should be noted that isometrics in a rehab sense are most commonly prescribed for tendon “health” or in early-stage muscle/tendon strains. Given there is (in theory) no change to the tissue length the lack of tensile loading to the fibers limits pain and soreness. Additionally, there is some literature supporting an analgesic effect following long-hold isometrics (of ~75% max effort). With that being said let’s dig in a little on the various applications for each type.

Yielding

Yielding Isometrics - like a split squat iso - it is thought that while the joint angle is not moving and the position appears static, the muscle is actually shortening and the tendon “creeps” and is "lengthening”. This lengthening makes it great for tendon health. This puts tension on the tendon without adding too much tensile force. And at the end of the day, tendons love load. 

Typically, I prescribe the yielding variations for longer holds to allow for that tendon creep and increased blood flow to the muscle belly (not the tendon… they are relatively avascular). Isometrics typically have less impact on DOMs in subsequent days and can be a useful tool for recovery or applying load without too much systemic fatigue.

Overcoming

Overcoming Isometrics - like the IMTP - are about producing as much force as possible. However, you can also perform overcoming isometrics at variation levels of effort given on your goal. For instance, long-hold overcoming isometrics are common post-operatively as a safe way to contract a muscle. A common example of this is after shoulder surgery and doing various isometrics into a wall. These are often the safest entry point to loading a muscle and tendon as there is no joint movement. Similarly, submaximal efforts can be performed in instances like Achilles Tendinopathy and have been found to have a temporary analgesic effect. These are typically longer-hold isometrics given their submax nature but we will get into the prescription of these later.

Returning briefly to the max effort overcoming isometrics. These can be prescribed as a primer for explosive movement or heavy lifts. These are usually shorter bursts of effort and for fewer reps. They are also good testing metrics to measure positional power and competency. In recent years Alex Naterra has put together a full course on the power of these types of isometrics in terms of increasing sprint potential.

Summary…

Isometrics - are a type of muscle contraction where no joint excursion occurs meaning there is no change in net muscle-tendon length

Yielding and overcoming isometrics are two “types” that can be prescribed for various uses. Tendon health, entry point in rehab, power production, etc. The intent in these is everything.

Now that we know WHAT isometrics are as well as the different types we can dive deeper into how they can be prescribed and utilized in an exercise and/or rehabilitation program. Stay tuned for Part II.