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Muscle Mastery 101: Isometric vs. Eccentric vs. Concentric

Muscles have a variety of contraction modes and actions to help us perform every movement we do. This happens unconsciously and in fractions of seconds whether you are walking, putting something on a shelf, or hitting a heavy set of back squats in the gym. Have you ever wondered how these interrelated contractions work to produce movement? And how you can manipulate them to vary your program? No? Maybe that’s just the nerdy PT in us 🤓. 

In the next few blogs, we’re about to get in the weeds of muscle actions. For those who are more visual learners and want a quick reference point to refer to throughout the series, here is a visual: 

This week’s blog is just going to work on outlining the top few bubbles, while the remainder of the series will get more into the nuances and applicability of these concepts to rehab and performance. 

Breaking Down Contractions

Overarchingly, muscle actions or contractions can be bucketed into 2 modes: static mode or dynamic mode (Schaefer 2017).  Static vs. dynamic is pretty intuitive: dynamic mode involves motion, while static mode means without motion. (There is also a semi-static mode which will be touched on in a later blog regarding oscillatory movements). 

From these 2 overarching modes, there is a corresponding muscle action, also known as a contraction. For static mode, the corresponding muscle action is ISOMETRIC. For dynamic mode, the corresponding muscle action can either be CONCENTRIC or ECCENTRIC

A quick summary: 

“Within concentric muscle action, we are able to overcome a resistance. In contrast, the eccentric muscle action enables us to decelerate an object. While isometric muscle action includes no gross joint motion, nevertheless, energy is consumed executing it. During performance of isometric muscle action in pilot studies, we have observed that two types of isometric muscle action can be executed. One can resist an object or one can push against it – although in both cases no motion is carried out” (Schaefer 2017)

Let’s break this down a bit further. 

Isometrics vs . eccentrics vs concentrics

  • Eccentric: An eccentric contraction the muscle is contracting in its lengthened position. In a squat, the eccentric phase happens when you are moving DOWN to the ground. In a bicep curl, the eccentric phase is happening when you lower the weight down to your side. Eccentric muscle actions are one of the factors that play into our ability decelerate: be that on the field, court, or in the weightroom (Schaefer et al. 2017). We are usually stronger eccentrically which is why when you bail on a heavy squat, it is typically during the ascent (the concentric phase), rather than the descent (the eccentric phase) when you are lowering to the ground. 

Eccentric actions also help us to decelerate, a vital aspect of sport-specific rehab, as every sport involves deceleration in some way or another. 

  • Concentric: concentric contraction is when the muscle is contracting in its shortened position. Concentric muscle actions are one of the factors that play into our ability to overcome resistance (Schaefer et al. 2017).  This is typically the part of a lift that involves the GRIND.  In a squat, we are working concenterically when we are standing back up. In a bicep curl, the bicep is working concentrically during the active curl up. 

Just Fly Sports speaks on concentrics, “Most work done in the weight room is a measure of “concentric” outputs since a lift is only “good” if you ended up lifting the weight concentrically [standing it up, ‘finishing’ the rep]. This is only one phase of 3 (really 4) muscle actions, however, and if this is all we ever consider or train in the weight room, then we end up short-sighted to the full envelope of athletic performance possibility” (Smith).

  • Isometric: When you hold a position statically, with the muscle contracting but NOT changing it’s length, this is an isometric contraction. With an isometric contraction, the muscle is working, it’s just not shortening or lengthening. From the squats and bicep curls example, this would be the “pause” portion of a pause squat when you hold at the bottom. Planks, holly body holds, and wall sits are other examples of isometric contractions.  Your muscles are contracting, but the length remains the same. 

  • Oscillations: 

  • “Oscillatory isometrics occur in “semi-static” positions with pulsating movements over small joint ranges” (Natera). This entails quick “on/off” muscular actions executed across various ranges of motion. Oscillatory exercises  can be tailored to specific athletic disciplines such as the squat for Olympic weightlifters, the lunge for runners, or the 90/90 overhead position for overhead athletes. 

Here at Made 2 Move…

Interested in working with a PT who is just as passionate as you about all things muscles? Want to attack that pain or injury with a professional that will craft the most optimal rehab plan for YOU? Reach out to today to set up an appointment with a PT at any of our 4 locations!


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