What Really Makes a Hand Dominant?

For decades, it was believed that the dominant hand was naturally more skillful because one side of the brain controlled movements better. A new study challenges this idea by showing that the superiority of the dominant hand seems to arise primarily from accumulated practice throughout life, and not from an innate advantage. To reach this conclusion, researchers developed experiments that compared everyday movements, tool use, and even writing with the elbows.

For a long time, scientists believed that right-handed or left-handed people possessed a natural advantage on one side of the brain. This hypothesis suggested that the cerebral hemisphere responsible for the dominant side would control movements more efficiently, making one hand naturally more skilled at tasks such as writing, drawing, throwing, or using tools.

A new study proposes a different explanation. According to the researchers, the preference for using one hand may indeed have a biological origin, but the superior skill developed by that hand seems to be a consequence of years of daily practice, and not an innate capacity of the brain.

The researchers highlight an important difference that often goes unnoticed. One thing is hand preference, that is, the tendency to spontaneously choose one hand to perform most activities. This preference appears very early in human development, even during gestation, and is probably related to genetics and the development of the nervous system.

Another completely different matter is the skill of the dominant hand. The central question of the study was precisely this: is the dominant hand inherently more competent at birth, or does it become more competent because it is used thousands of times throughout life? The answer to this question has important implications for understanding motor learning, rehabilitation, and even child development.

To investigate this question, the team recruited volunteers and conducted a series of experiments that measured movements with extreme precision. Instead of using sensors attached to the body, the researchers employed a modern, markerless, three-dimensional capture system based on cameras capable of digitally reconstructing each participant's movement.

The volunteers performed various tasks while the computer recorded the position of their arms, hands, and the tools used. Then, mathematical programs analyzed the complete shape of the trajectories followed during the movements, allowing them to compare not only speed or final precision, but also the path followed by the limb throughout the execution of the task.

In the first experiment, participants simply extended their arm to reach objects positioned in front of them. In a second condition, a weight was attached to the wrist to make the movement more difficult, increasing the arm's inertia. If the dominant hand truly possessed a superior overall ability to control movement, it should have a clear advantage in these two situations.

However, the results showed exactly the opposite: in both normal movements and those performed with the heavier arm, there was practically no difference between the performance of the dominant and non-dominant limb. This indicates that controlling one's own arm does not seem to depend on an intrinsic superiority of one side of the brain.

The situation changed completely when researchers introduced a tool. Instead of moving just their arm, participants needed to control a cane-like rod resting on their forearm. In this case, the objective was no longer simply to bring the hand to a point, but to precisely control the trajectory of the tool tip. It was precisely in this task that a striking difference emerged.

The dominant arm was able to guide the end of the rod with much more precision, while the non-dominant arm had more irregular trajectories and greater difficulty in controlling the movement of the tip of the instrument.

To further test this hypothesis, the researchers created a completely new situation for all participants: writing using their elbow. Since virtually no one had prior experience performing this task, it offered an ideal opportunity to separate acquired skill from a possible innate advantage.

The result was surprising. The advantage of the dominant hand simply disappeared. Initially, both elbows performed similarly, and after a relatively short training period, both improved at virtually the same rate.

In some cases, the performance achieved by the trained elbows even surpassed that of the non-dominant hand in equivalent tasks. This demonstrates that, when no prior experience exists, both sides of the body have a similar capacity to learn new movements.

These results lead the authors to propose a new interpretation of hand dominance. Instead of believing that one side of the brain controls any type of movement better, they suggest that the observed advantage in the dominant hand arises because it accumulates far more hours of practice in specific tasks throughout life.

The ability would not be a general characteristic of the dominant limb, but a highly specialized motor knowledge, built through repeated training of complex movements, especially those involving controlling tools and objects.

This conclusion may influence areas such as rehabilitation after strokes, sports training, motor learning, and child development, showing that many differences between the two sides of the body may be reduced with proper practice, and are not necessarily determined from birth.

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Arm dominance is an emergent effect of practice executing complex trajectory shapes required by tools and objects

Ahmet Arac, Nicolas Y. H. Jeong Lee, and John W. Krakauer

PNAS, 123 (27) e2601569123, June 30, 2026

DOI:10.1073/pnas.2601569123

Abstract: 

Limb dominance is a human behavioral characteristic with many cultural, practical, scientific, and clinical implications. Yet why the dominant limb performs better across a range of motor skill-requiring tasks remains unanswered. Is it because of an intrinsic hemispheric advantage or instead is it the result of life-long practice with the dominant side? We tested these alternatives using two tasks either cross sectionally or after training. The first was 3D reaching with either an inertial challenge or the need to use a stick-like tool. The second required participants to write with their dominant and nondominant elbows. We applied a geometric analysis to quantify movement-trajectory shape. We show that 1) tool-use unmasks markedly inferior control in the nondominant arm, and this is because tools impose the need to generate unfamiliarly shaped movement trajectories; and 2) there is no general dominant limb motor control advantage, only task-specific experience or practice riding on top of an initial preference. These results reframe dominance as predominantly about learned control of tool kinematics rather than baseline asymmetry in control of limb dynamics.