34%, 20%, 12%: What Does a Strength Asymmetry Mean in Real Life?

A client-centered exploration of what a repeated side-to-side difference can mean in real life.

The number matters most when it explains what the body keeps doing under load

Thirty-four percent.

Sometimes the difference is 20%. Sometimes 18%, 12% or 8%.

Those numbers can appear when I compare the same muscle group on the left and right sides with a Kinvent dynamometer. The person being tested may have no pain at all. They can push hard, work, train and play their sport. Yet one side produces clearly less force than the other.

On its own, the number can seem abstract. The useful question is not only, ‘Is 20% a lot?’ It is: ‘Where is that 20% already appearing in this person's life?’

What the percentage actually measures

In the comparison used here, the percentage describes the difference in measured force between two sides during the same test. If one side produces 50 lb and the other produces 40 lb, the lower side produced 20% less force than the stronger side. That is what the number says.

It does not mean the whole person is 20% weaker, and it does not tell us the entire cause by itself. It tells us something precise and useful: for that muscle group, in that position, one side could not make the same force available as the other.

The important part is not to make the person practise the test until the score improves. What matters is whether the difference returns when the test is repeated and whether related comparisons reveal the same underlying direction.

A single muscle does not define the whole body. But when a meaningful difference repeats, it gives us a concrete way to see an organization that may otherwise remain hidden.

A small number can become very real

Imagine that one arm can produce 40 lb while the other reaches 38 lb. The difference is only 5% when the stronger side is used as the reference. Two pounds sounds insignificant - until the demand approaches those two pounds.

Load	40-lb side	38-lb side	What becomes visible
30 lb	75% of capacity	About 79%	Both sides can still look equally comfortable
38 lb	95%	100%	One side still has reserve; the other reaches its limit
40 lb	100%	Beyond its current maximum	One side completes the effort; the other must slow, shorten or recruit help

The asymmetry did not suddenly appear at 40 lb. The higher demand simply made it visible. The same principle applies when a task becomes faster, less stable or more repetitive.

The difference often appears before pain

At the gym, both arms may move a lighter dumbbell without an obvious problem. Near the end of the set, one arm slows down, shortens the movement or needs the shoulder and trunk to help. The person may interpret this as normal effort, even though the two sides are no longer solving the task in the same way.

At work, someone may always carry the tool, sheet of material or heavy object on the same side. They may say that one side simply feels more natural. In construction, one arm may comfortably control a load while the other can lift it only by changing the grip, rotating the trunk or bringing the object closer.

In daily life, the pattern may appear when climbing stairs, rising from the floor, carrying groceries, lifting a child, pushing a door or stabilizing on one leg. Nothing necessarily hurts. One option is simply more available, so the body keeps choosing it.

That is why a strength asymmetry can matter even when the person still feels strong. The body is completing the task, but it may be doing so with fewer choices.

Why repetition, speed and instability expose more

A single controlled effort is the easiest version of a task. Real life adds repetition, speed, changing angles, balance, surprise and incomplete recovery.

When the task stays easy, the difference may remain invisible. As the demand rises, the side with less available force reaches its ceiling sooner. The other side still has reserve. That difference in reserve can affect precision, timing and confidence before the person feels anything they would call pain.

Research in sport has linked inter-limb asymmetry with some tasks that depend heavily on unilateral force, including sprinting and changing direction (Fox et al., 2023). For the person reading this, the practical meaning is simpler: the more quickly and unpredictably the body must organize force, the harder it becomes to hide a side that is less available.

The hockey example: when one direction feels easier

Think about free skating. Many people turn naturally in one direction and feel awkward, hesitant or less secure when circling the other way.

That preference is not strength alone. It also involves balance, edge control, vision, timing, hip and ankle coordination, and a learned motor pattern. But the ice raises the demand. The surface is unstable, the body is moving and each turn asks one side to accept, organize and redirect force.

If that side provides less force or less control, the body is likely to keep choosing the direction that feels more predictable. The person does not have to think, ‘I will avoid the other side.’ The choice can happen automatically.

The same thing can occur when accelerating, stopping, crossing over, changing direction or recovering from an unexpected movement. A measurable difference becomes a movement preference; the preference is repeated; and repetition makes it feel normal.

Fatigue does not have to create the pattern - it can reveal it

There is an important difference between being tired everywhere and repeatedly losing the same side first.

A person can be globally fatigued after physical work, training or several demanding weeks and still remain relatively balanced. Both sides may produce less, but the body continues to distribute the demand coherently. By contrast, when the same knee keeps dropping, the same shoulder keeps rising or the same leg repeatedly stops contributing, fatigue is exposing a strategy that was already less stable.

Fatigue can change or magnify inter-limb asymmetry (Heil et al., 2020). In practical terms, it reduces the body's reserve. What was easy to compensate for during the first few repetitions becomes harder to hide later.

How the difference can spread through the body

When one side has less accessible force, the body still tries to complete the task. It redistributes the work.

The weaker side reaches its limit sooner. Another muscle contributes more. The trunk rotates, the shoulder lifts, the pelvis shifts or the grip tightens. A fascial chain carries more tension so the movement can continue. The more trusted side becomes the default, and the same solution is rehearsed again and again.

This does not mean that every tension or injury comes from an asymmetry. A traumatic injury can itself create a clear difference. But when an injury was not caused by a specific trauma, it is also reasonable to ask whether a pre-existing disorganization helped create the conditions in which that area became overloaded.

Pain or injury may therefore reveal an older pattern rather than explain its entire origin. The percentage gives us a place to start seeing how the body has been distributing demand.

Do we need 0% asymmetry?

Not as a rigid target. A person may reach 0% on one effort, but a living system has normal variability. A small, stable difference of a few percentage points is very different from results that repeatedly show 20% or 30%, or that swing unpredictably between large values within the same comparison.

The goal is not mathematical perfection. It is for both sides to remain sufficiently available and for the result to stay coherent as the demand changes.

What an immediate change can reveal

In my own observations, a comparison can begin near 30% and later measure around 8%. Other tests can move toward 5%, 2% or even below 1% within the same session.

The measured output may improve immediately, but that is not the same as instantly creating new muscular strength. No new tissue or muscle mass was built in those few minutes. What may have changed is access: strength that was already present—but dampened, compromised, poorly recruited or redistributed—became more available because the body organized the task differently.

This distinction is one of the most valuable things the measurement can reveal. The original result may not have represented the muscle's full existing capacity; it may have shown how much of that capacity the system could access at that moment. When the output changes without practising the test or spending months building strength, it suggests that part of the limitation involved access, recruitment, coordination or protection—not only an absence of strength that still needed to be developed.

Why stretching and strengthening may not be the whole answer

Stretching and strengthening can be useful. But if the body keeps avoiding one side or borrowing force from somewhere else, exercise can also make the person more efficient inside the same compensation.

If the shoulder rises every time the arm pushes, the arm may become stronger while the shoulder strategy becomes more established. If one leg consistently contributes less, the other leg can become even better at taking over. The person improves at completing the movement without necessarily changing how the body organizes it.

The more useful sequence is often to restore access first, then use movement and strengthening to consolidate that new capacity. The goal is not simply more force. It is more force that the body can distribute, adapt and use freely.

The percentage becomes useful when it returns to the person

The most relevant questions are not complicated:

What happens when the movement becomes faster? What changes after several repetitions? Which side does the body trust on an unstable surface? What appears when the person is tired? Does the same region repeatedly take over? Can the result change when the body reorganizes, without simply pushing harder?

A strength asymmetry matters because it makes an invisible pattern visible. It connects a number to the side that always tires first, the turn that never feels natural, the arm that changes its path under load and the strategy the person has been using without realizing it.

The objective is not to chase a perfect score. It is to help the body recover options - so strength is not only present, but available when life actually asks for it.

“Strength is not only what a muscle can produce. It is what the body can make available when the situation changes.”

Does one side always tire, slow down or compensate before the other? A precise measurement can help reveal what your body is actually making available. www.andyaudet.com

Andy Audet – Un Corps Équilibré

Specialist in Body Recalibration and Human Performance

Saint-Bruno-De-Montarville, Québec