Gesturing while we speak feels almost effortless. A new experiment suggests that the apparent ease hides a measurable coordination cost: when adults combined speech with hand gestures while standing upright, their bodies swayed more than when they made the same kinds of gestures without speaking.
The study, published in Scientific Reports on 28 September 2026, examined how speech, hand movement and balance compete for the brain’s motor and cognitive resources. Forty-one right-handed adults performed gestures under several controlled conditions while researchers simultaneously tracked postural sway and cortical oxygenation. The results indicate that the cost of communicating with the hands depends not only on whether speech is added, but also on which hand is used and the spatial perspective from which the gesture is produced.
Communication is also a balance task
Human communication is usually studied as a problem of language, meaning and social interaction. Yet conversation is also physical. Speakers breathe, vocalise, move their arms and hands, orient their heads and continuously make tiny postural corrections that keep the body upright.
Previous research has shown that speaking and postural control can interfere with one another. Co-speech gestures add another layer because the nervous system must coordinate a meaningful hand movement with language while maintaining balance. The researchers therefore asked whether gestures made during speech would increase postural instability relative to gestures performed without speech, and whether the effect would change with hand dominance or spatial reference frame.
The distinction between spatial reference frames matters. An egocentric gesture represents space relative to the speaker’s own body, while an allocentric gesture represents locations relative to objects or an external frame. Those perspectives can place different demands on spatial transformation and action planning.
How the researchers tested speech, gesture and posture together
The experiment involved 41 right-handed adults with a mean age of 25.9 years and a standard deviation of 6.8 years. Participants stood while completing gesture tasks that systematically varied three features: whether the gesture accompanied speech or was performed without speech, whether it was made with the right or left hand, and whether it used an egocentric or allocentric spatial perspective.
Posture was monitored using a wearable inertial measurement unit, or IMU. Rather than treating balance as simply maintained or lost, this allowed the researchers to quantify the small movements that occur as a person continuously stabilises the body.
At the same time, functional near-infrared spectroscopy, known as fNIRS, measured changes in cortical oxygenation over bilateral precentral and postcentral regions. fNIRS does not provide a direct reading of individual neurons. It tracks haemodynamic changes associated with neural activity, making it useful for studying brain function during tasks that involve more natural movement than is usually possible in a conventional scanner.
This combination was central to the study. A behavioural measure could show whether balance changed, while the neuroimaging measure could help identify whether the different communication conditions recruited overlapping cortical resources.
Adding speech increased postural sway
The clearest behavioural pattern was that postural sway increased when participants produced co-speech gestures compared with gestures performed without speech. In other words, adding a verbal task to the hand movement measurably changed the control of upright posture.
This does not mean that ordinary gesturing makes healthy adults dangerously unstable. The study measured subtle variations in sway under controlled experimental conditions. Its importance lies instead in showing that speech and gesture are not cost-free additions to balance control. Even in young adults, the nervous system appears to redistribute resources when several coordinated actions happen at once.
The effect also depended on the hand. Right-hand gestures produced more postural sway than left-hand gestures. Because all 41 participants were right-handed, this result is especially interesting. The dominant hand may support more strongly lateralised or more tightly coupled motor-language processes, although the design cannot establish a single mechanism for the difference.
Spatial perspective mattered as well. Egocentric gestures increased sway more than allocentric gestures. A gesture organised around the speaker’s own body therefore imposed a larger postural cost than one organised around an external reference frame.
The brain data point to overlapping motor-cognitive resources
The fNIRS measurements provided a complementary pattern. Co-speech gestures elicited greater activation in the left premotor and supplementary motor cortex than gestures without speech. These areas contribute to the planning, organisation and coordination of movement, making the result consistent with the idea that speaking and gesturing increase demands on shared motor-cognitive systems.
Egocentric gestures were also associated with greater activation in frontal cortex and Broca’s area than allocentric gestures. Broca’s area is widely associated with language but also participates in broader action and sequencing processes. The finding therefore fits a view in which communication emerges from interacting language, action and spatial-control systems rather than from a language system operating in isolation.
Taken together, the behavioural and cortical results tell a coherent story. The conditions producing stronger interference with posture also required additional recruitment of regions involved in motor planning and cognitive control. The strongest interference was seen for co-speech, right-hand and egocentric gestures.
Why a small increase in sway is scientifically useful
Postural sway can act as a sensitive window into dual-task interference. Maintaining upright posture is an active process, even when a person appears to be standing still. If another task draws on overlapping resources, the balance system may reveal the competition through small changes in movement.
The new findings extend this logic into everyday communication. A speaker is not merely choosing words while the rest of the body waits. Speech, gesture and posture unfold together, and the coordination of one system can affect another. That may help explain why communication changes when people are walking, carrying objects, navigating crowded spaces or completing other motor tasks at the same time.
The findings may also be relevant to future work on ageing, neurological conditions and rehabilitation. Populations with reduced balance capacity or fewer cognitive resources might experience different or larger dual-task costs. However, the present experiment did not test those populations, so clinical conclusions would be premature.
The dominant hand result raises new questions
All participants were right-handed, and right-hand gestures caused greater postural interference than left-hand gestures. One possible interpretation is that dominant-hand gesturing interacts more strongly with the left-lateralised systems involved in speech and motor planning. The increased left premotor and supplementary motor activation during co-speech conditions is compatible with that possibility.
But compatibility is not proof. A study including left-handed participants would be needed to test whether the pattern reverses with handedness. If left-handed speakers showed stronger interference from left-hand gestures, that would support a dominance-based account. If right-hand costs persisted regardless of handedness, other explanations would become more plausible.
What the study does not show
The experiment should not be interpreted as evidence that gesturing is harmful or that people should suppress hand movements while speaking. Co-speech gesture is a normal component of communication and can carry information that complements spoken language. The study focused on subtle balance effects under controlled conditions, not falls or clinically meaningful instability.
The sample was also narrow. The 41 participants were right-handed and relatively young, with a mean age below 26. The findings therefore cannot automatically be generalised to children, older adults, left-handed people or individuals with neurological, vestibular or movement disorders.
Another limitation is that experimentally instructed gestures cannot reproduce the full complexity of spontaneous conversation. Natural gestures differ in size, timing, emotional content, meaning and social purpose. Real-world communication also includes head movement, gaze, facial expression and interaction with another person.
Finally, fNIRS measures blood-oxygenation changes associated with cortical activity rather than neural firing itself, and its spatial coverage is more limited than some other neuroimaging techniques. The observed activation patterns support a shared-resource interpretation but do not establish a complete neural mechanism.
A more embodied picture of conversation
The broader contribution of the study is conceptual. Speaking, gesturing and standing are often treated as separate behaviours because researchers can isolate them experimentally. In everyday life they are components of a single coordinated action.
By measuring the body and brain at the same time, the researchers show that this coordination has detectable costs. Speech increased sway during gesture, dominant-hand gestures interfered more than non-dominant-hand gestures, and body-centred gestures produced more interference than externally referenced gestures. Meanwhile, cortical oxygenation changed in regions involved in motor planning, language and frontal control.
The effect is subtle, but that is precisely what makes it informative. Ordinary conversation can look effortless while relying on continuous negotiation between systems responsible for language, movement and stability. The next step is to learn how those trade-offs change across age, handedness, clinical populations and more natural social settings.
Source Information
Study: Co-speech gestures destabilize posture via shared motor-cognitive resources
Authors: Sasha Lifton Lewis, Weina Lu and Ingo Helmich
Journal: Scientific Reports
Published: 28 September 2026
DOI: 10.1038/s41598-026-73652-y
Study type: Controlled behavioural and fNIRS experiment involving 41 right-handed adults
