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Reaction speed linked to aging and mortality risks
Scientists have discovered that how quickly a person responds to stimuli may reveal critical insights into brain function, heart health, and even the likelihood of early death. While reaction times naturally slow with age, maintaining average speeds could signal robust cognitive and physical well-being into later years.
Why reaction times matter
Simon Cox, a professor of brain and cognitive aging at the University of Edinburgh, explains that while some individuals are inherently faster, a noticeable decline in reaction speed often reflects cumulative age-related deterioration. "It serves as a marker for the combined functioning of multiple biological systems," he says.
Research has established correlations between slowing reaction times and heightened risks of age-related illnesses, including coronary heart disease, stroke, and respiratory conditions. One study even found a significant link between reaction speed and mortality from all major causes.
Beyond mortality, reaction times are tied to fall susceptibility, loss of independence, and dementia onset. However, Cox cautions that a single measurement offers limited insight due to individual variability influenced by genetics, fitness, lifestyle, and personality.
How to test your reaction time at home
The "ruler drop test" is a simple method to assess reaction speed. Here's how it works:
- Sit with your arm resting on a table, wrist hanging off the edge, thumb and forefinger poised upward.
- Have a partner hold a ruler vertically above your hand, aligning the zero mark with your thumb.
- Without warning, your partner drops the ruler; your task is to catch it as quickly as possible.
- The distance the ruler falls before being caught indicates your reaction time.
Performance benchmarks are as follows: excellent (under 7.5 cm), above average (7.5-15.9 cm), average (15.9-20.4 cm), below average (over 20.4 cm), and poor (over 28 cm).
The science behind slowing reactions
Reaction time relies on a network of sensory systems: perceiving stimuli, processing information, and executing physical responses. Alaa Ahmed, a biomedical professor at the University of Colorado Boulder, notes that physical responsiveness often declines first in midlife. "Fast-twitch muscle fibers weaken, and mitochondrial efficiency drops, making swift movements more taxing for older adults," she says.
Matthew Pain, a biomechanics professor at Loughborough University, adds that while the nervous system in healthy elderly individuals remains relatively intact-capable of rapid signal transmission-the body's ability to act on those signals diminishes. "The raw hardware is still strong, but execution slows," he explains.
Early warning signs and preventive measures
Sharp declines in reaction time may signal sensory or cognitive deterioration. A 2025 study found that reduced visual sensitivity to patterns could precede dementia by over a decade. "Aging affects nerve fiber efficiency in the brain's white matter, slowing information processing and muscle response," Cox says.
To mitigate decline, experts recommend dual-task training-combining movement with cognitive challenges. Examples include walking while turning your head, balancing on one leg while reciting the alphabet, or tossing a ball while naming objects. Even interactive fitness classes can enhance stimulus perception and coordinated responses.
Cox highlights the benefits of lifelong activities like sports, musical instruments, or intellectual pursuits. "Fast-response drills in sports or social engagement can bolster reaction times and slow cognitive aging," he notes.
Digital alternatives to the ruler test
Online tools like the Human Benchmark Reaction Time Test offer another way to measure speed. Users click a red box as soon as it turns green. Consistent monitoring can help track changes over time, providing early warnings of potential health issues.
