If you strip resistance training back to its fundamentals, every rep you perform is built on three types of muscle action:
- Concentric contraction
- Eccentric contraction
- Isometric contraction
Most people perform all three in every workout without giving them much thought. But understanding how each one works — and how to use them deliberately — can significantly improve how you train, how you recover, and ultimately how you progress.
Because while a rep may look simple on the surface, what is happening beneath it is far more complex.
The Science of Muscle Contraction
At a physiological level, muscle contraction is driven by the interaction between two proteins: actin and myosin.
These proteins form cross-bridges within muscle fibres. When stimulated by the nervous system, myosin heads attach to actin and pull, shortening the muscle in what is known as the sliding filament theory (Huxley, 1957).
Energy in the form of ATP is required for this process, and calcium ions regulate the interaction.
What changes between contraction types is not the mechanism itself — but the outcome of that mechanism.
Concentric Contractions (The Lifting Phase)
A concentric contraction occurs when a muscle shortens as it produces force.
This is typically the “lifting” portion of a movement.
For example:
- Curling a dumbbell upward in a bicep curl
- Pressing the bar away from your chest in a bench press
- Standing up from the bottom of a squat
In this phase, the force produced by the muscle exceeds the external load, allowing movement to occur.
From a physiological standpoint:
- Cross-bridges form and actively pull the muscle fibres together
- Muscle length decreases
- Energy demand is relatively high
Concentric contractions are often associated with overcoming resistance — they are the most visible part of a lift.
Eccentric Contractions (The Lowering Phase)
An eccentric contraction occurs when a muscle lengthens while still under tension.
This is the “lowering” or “controlled descent” portion of a movement.
Examples include:
- Lowering a dumbbell during a bicep curl
- Bringing the bar down to your chest in a bench press
- Descending into a squat
In this case, the external load exceeds the force produced by the muscle — but the muscle is still actively resisting that load.
What makes eccentric contractions particularly interesting is how they behave physiologically:
- Fewer motor units are required compared to concentric contractions
- Greater force can be produced
- Mechanical tension is often higher
Eccentric contractions are also strongly linked to muscle damage — specifically the kind that contributes to delayed onset muscle soreness (DOMS) (Proske & Morgan, 2001).
Isometric Contractions (The Static Phase)
An isometric contraction occurs when a muscle produces force without changing length.
There is no visible movement, but the muscle is still active.
Examples include:
- Holding a plank
- Pausing at the bottom of a squat
- Holding a dumbbell halfway through a curl
In this case:
- Force is produced, but movement does not occur
- Muscle length remains constant
- Tension is maintained over time
Isometric contractions are particularly useful for improving stability and control, as well as strengthening specific joint angles.
Key Differences Between Contraction Types
While all three contraction types rely on the same underlying mechanism, they differ in how force is produced and applied.
A simple way to compare them:
- Concentric → muscle shortens, overcomes resistance
- Eccentric → muscle lengthens, resists resistance
- Isometric → muscle length stays the same, holds tension
Each plays a distinct role in both movement and adaptation.
Why This Matters for Training
Understanding these contraction types is not just theoretical — it has direct practical application.
Every repetition you perform includes all three phases:
- Lifting the weight (concentric)
- Lowering the weight (eccentric)
- Stabilising or pausing (isometric)
The way you control each phase affects:
- Muscle growth (hypertrophy)
- Strength development
- Injury risk
- Overall training quality
In other words, how you perform a rep matters just as much as the rep itself.
Using Concentric Contractions in Training
Concentric movements are typically where force is expressed most visibly. They are crucial for developing strength and power.
In training, the concentric phase should generally be:
- Controlled, but not excessively slow
- Performed with intent — especially in strength and power training
For example, in compound lifts like squats or presses, driving the weight upward with intent can improve force production and neuromuscular efficiency.
Using Eccentric Contractions for Muscle Growth
Eccentric training is often where a large portion of the muscle-building stimulus occurs.
Because eccentric contractions can handle greater loads and produce higher mechanical tension, they are strongly associated with hypertrophy (Schoenfeld, 2010).
Practical ways to emphasise the eccentric phase include:
- Slowing down the lowering portion of a lift (e.g. 3–4 seconds)
- Using heavier loads with controlled descents
- Incorporating eccentric-focused exercises
This increases time under tension and places greater stress on the muscle — both key drivers of growth.
Using Isometric Contractions for Control and Stability
Isometric contractions are often overlooked, but they offer unique benefits.
They are particularly effective for:
- Improving joint stability
- Strengthening weak points in a movement
- Enhancing mind-muscle connection
For example:
- Pausing at the bottom of a squat improves control and strength in that position
- Holding a plank builds core stability
- Isometric holds can reinforce proper positioning during lifts
They are also useful in rehabilitation settings due to their lower joint stress.
Integrating All Three Into Your Training
The most effective training programmes do not isolate these contraction types — they integrate them.
A well-performed rep naturally includes all three phases. However, you can manipulate them to achieve different outcomes.
For example:
- A slower eccentric increases hypertrophy stimulus
- A powerful concentric improves strength and explosiveness
- A pause (isometric) improves control and stability
You might structure a lift like this:
- 1 second up (concentric)
- 3 seconds down (eccentric)
- 1 second pause (isometric)
This level of control increases training quality without necessarily increasing load.
Exercise Examples
Most exercises can be adjusted to emphasise different contraction types.
For example:
Squat
- Concentric: driving up from the bottom
- Eccentric: controlled descent
- Isometric: pause at the bottom
Bench Press
- Concentric: pressing the bar upward
- Eccentric: lowering to the chest
- Isometric: paused bench press
Pull-Ups
- Concentric: pulling yourself up
- Eccentric: lowering under control
- Isometric: holding at the top
The movement stays the same — the focus changes.
Common Mistakes
A few common issues often limit the effectiveness of contraction-based training:
- Rushing the eccentric phase and losing control
- Neglecting pauses or stability work
- Using momentum instead of muscular tension
- Treating all reps the same, regardless of goal
Small adjustments in how you perform each phase can make a significant difference.
Concentric, Eccentric, and Isometric Contractions: Keep this in Mind
Concentric, eccentric, and isometric contractions are not separate tools — they are part of every movement you perform.
Understanding them allows you to move from simply “lifting weights” to training with intent.
You begin to control the rep, rather than just complete it.
And that is often where progress is made — not through doing more, but through doing it better.
References
- Huxley, A.F. (1957). Muscle structure and theories of contraction. Progress in Biophysics.
- Proske, U., & Morgan, D.L. (2001). Muscle damage from eccentric exercise. Journal of Physiology.
- Schoenfeld, B.J. (2010). The mechanisms of muscle hypertrophy. Journal of Strength and Conditioning Research.
- Enoka, R.M., & Duchateau, J. (2017). Rate coding and motor unit behaviour. Journal of Physiology.