Weak Grip in Old Age May Start in the Brain, Not Just the Muscle

For decades, clinicians have measured the strength of an aging hand with a simple squeeze of a dynamometer, treating the number that appears as a straightforward readout of muscle. A new study suggests that this number tells a far more complicated story, one in which the brain and spinal cord play a leading role. Researchers at Ohio University, working with colleagues at Trinity College Dublin, report in the journal GeroScience that a substantial portion of age-related grip weakness may arise not from the muscles themselves but from a decline in the nervous system’s ability to coordinate the four fingers into a single, powerful contraction. The finding could reshape how scientists understand sarcopenia, the muscle-wasting syndrome whose primary clinical marker is low handgrip strength.

The team, led by Gregory M. Shaw and Brian C. Clark of the Ohio Musculoskeletal and Neurological Institute, focused on a phenomenon called the multi-finger force deficit, or MFFD. When people grip with all four fingers at once, each finger produces less force than it does when pulling alone, so the combined four-finger force falls short of the sum of the individual finger forces. Because the intrinsic force-generating capacity of a finger’s muscles should not depend on whether its neighbors are working at the same time, this shortfall is interpreted as a signature of central nervous system constraints, a limit on how well the brain can assemble and scale simultaneous commands to multiple digits. In younger adults the deficit is modest; in older adults, the new data show, it grows markedly.

What makes the study methodologically important is the device the researchers built to measure it. Previous investigations of the multi-finger force deficit typically used awkward postures, such as a pronated forearm pressed flat against a table, that bear little resemblance to the way grip strength is actually tested in a clinic. The Ohio group instead constructed a custom multi-sensor dynamometer that mimics the biomechanics of the standard Jamar hydraulic dynamometer, the instrument used in virtually all clinical grip assessments. Four S-type load cells, each coupled to a finger loop, recorded force from the index, middle, ring, and little fingers independently, while a 3D-printed wrist holder and Velcro-secured forearm support kept limb positioning identical to clinical guidelines: elbow flexed at 90 degrees, shoulder slightly abducted, wrist neutral. Grip values from the custom device correlated strongly with the Jamar standard, with Pearson’s r of 0.87 for the dominant hand and 0.90 for the non-dominant hand, confirming that the biomimetic setup was measuring the same thing clinicians measure.

Participants included 12 younger adults with an average age of about 24 years and 10 markedly older adults averaging just over 80 years, a group deliberately enriched with people in the middle-old and oldest-old ranges, many of whom showed clinically meaningful weakness. The results were striking. Older adults exhibited handgrip strength 48.8 percent lower than the young participants. Their multi-finger force deficit averaged 25.8 percent, compared with 16.5 percent in the young group, a statistically significant difference. In other words, when older adults tried to use their whole hand, they lost a substantially larger fraction of their available force to the problem of coordination alone.

The most provocative result emerged when the researchers stratified the older participants by the grip strength thresholds used by the European Working Group on Sarcopenia in Older People, the criteria that define probable sarcopenia in clinical practice. Older adults whose grip fell below the threshold, less than 27 kilograms for men and 16 kilograms for women, showed an average multi-finger force deficit of 33.4 percent, nearly double the 18.0 percent seen in their stronger peers. Because the deficit is a ratio, comparing simultaneous four-finger force to the sum of individually generated finger forces, this gap cannot be explained simply by having weaker muscles. The clinically vulnerable older adults could still generate considerable force with each finger in isolation; what they lost disproportionately was the ability to express those forces together.

The authors propose a compelling mechanistic account for this pattern, which they frame as a parallelization penalty. When the four fingers pull one at a time, the nervous system can concentrate its resources on a single digit command. When all four must pull simultaneously, the corresponding motor commands must be generated in parallel while preserving their relative weighting and stabilizing the wrist and hand. Individual fingers are not controlled through anatomically isolated cortical channels; their representations overlap extensively in the motor cortex, and selective finger output emerges from the pattern of activity across distributed cortical and corticospinal populations. Age-related cortical dedifferentiation, reduced segregation of sensorimotor networks, and altered inhibitory neurochemistry could blur this control system, allowing adequate performance when fingers act alone but creating competition when commands must be expressed concurrently. Reduced motoneuron excitability and diminished persistent inward currents, which amplify descending drive in spinal motor neurons, may further shrink the reserve available for high-force output in weak older adults.

The study added a second, independent line of evidence using cognitive dual-task testing, grounded in the idea that motor and cognitive operations draw on overlapping neural resources. Participants performed maximal grips while simultaneously reading aloud a passage from War and Peace, or while completing a visuospatial go/no-go task that required rapid decisions about numbers flashing on a screen. The effects were task- and age-dependent in an intriguing way. Older adults lost roughly 10 percent of their composite grip strength during the reading task compared with gripping alone, a significant decline, while younger adults lost only about 6 percent and showed no statistically significant drop in that condition. Younger adults, by contrast, were significantly affected by the go/no-go task, whereas the older adults maintained their grip force during it. The finding demonstrates that maximal grip strength is not a fixed property of muscle but a context-sensitive performance that fluctuates with cognitive load, and that the direction of interference depends on the nature of the secondary task.

Correlational analyses reinforced the link between the multi-finger force deficit and broader aging outcomes. Across all participants, a larger deficit in the non-dominant hand was associated with slower performance on the Four-Square Step Test of dynamic balance, slower fast-paced gait speed, poorer Purdue Pegboard dexterity, and longer completion times on the Trail Making Test difference score, a measure of executive function and cognitive flexibility. Notably, the deficit in the dominant hand showed no such associations. The authors interpret these patterns through the common-cause hypothesis, which holds that age-related declines in motor and cognitive function arise from shared neurobiological substrates, including white matter deterioration and changes in dopaminergic signaling, while cautioning that the cross-sectional, unadjusted correlations are hypothesis-generating rather than proof of mechanism.

The researchers are careful about what the multi-finger force deficit is and is not. It is not a direct measure of cortical connectivity, corticospinal excitability, or motoneuron gain, and the study’s small sample, fixed testing order, and exploratory subgroup analysis leave the sarcopenia comparison in need of replication. Grip strength below the EWGSOP2 threshold indicates probable rather than confirmed sarcopenia, and the behavioral design cannot isolate the precise neural cause. Still, the authors argue that the measure could eventually serve as a behavioral stress test of multi-digit neuromotor reserve, one that could be incorporated into routine grip assessment simply by adding single-digit trials to a conventional dynamometer test. Before that can happen, future work must establish test-retest reliability, normative values, diagnostic thresholds, and whether the deficit adds predictive value beyond grip strength alone, ideally in longitudinal cohorts that combine it with direct neurophysiological measurement.

If validated, the implications extend well beyond the laboratory. Handgrip strength predicts falls, hospitalization, and all-cause mortality, and in some cohorts it outperforms systolic blood pressure as a mortality predictor, yet it has long been treated as a gross index of muscle force. This study suggests that part of what the dynamometer is really probing is brain health, the capacity of an aging nervous system to orchestrate dozens of muscles, as many as 39 spanning the forearm and hand, into a coordinated burst of power. Weakness in an 80-year-old hand, the work implies, is partly a story about cortical organization, neural reserve, and the mounting cost of doing several things at once. For a rapidly aging population, that reframing could open entirely new avenues for detecting vulnerability early, and perhaps for training the nervous system, not just the muscle, to hold on to its strength.

Subject of Research: Neural mechanisms underlying age-related handgrip weakness assessed by multi-finger force deficit and cognitive dual-task testing

Article Title: Neural contributions to age-related handgrip weakness revealed by multi-finger force deficit and dual-task testing

Article References: Shaw, G. M., Clark, L. A., Grooms, D. R., Carson, R. G., & Clark, B. C. (2026). Neural contributions to age-related handgrip weakness revealed by multi-finger force deficit and dual-task testing. GeroScience. https://doi.org/10.1007/s11357-026-02517-z

Image Credits: AI Generated

DOI: 10.1007/s11357-026-02517-z

Keywords: sarcopenia, handgrip strength, multi-finger force deficit, aging, motor cortex, neural coordination, dual-task, GeroScience, dynamometry, corticospinal, executive function, older adults