Quick home health tests: Check your reaction times

Your reaction times can reveal a surprising amount about what's going on inside your body, from your brain health to your risk of an early death.

Of the course of our lifetimes, our reaction times will slowly wane. It's one of the reasons why athletic performance tends to drop off from our 30s onwards.

Scientists are finding that being able to maintain an average reaction speed can be a key indicator that our brain is still in good working order, even into our latter decades. But that isn't all they can reveal. From your heart health to your overall risk of an early death, your reaction times can provide a window into the inner workings of the body. 

"Some people just tend to be faster than others, even before ageing effects really kick in," says Simon Cox, professor of brain and cognitive ageing at the University of Edinburgh in Scotland. "But a decline in reaction times probably indicates an accumulation of age-related degradation. It's a marker which tells us a lot about the combined functioning of quite a lot of biological systems."

But how can you assess your reaction time in the comfort of your home?

One easy assessment is a well-known experiment known as the "ruler drop test". You'll need the assistance of a family member or friend for this one, as well as a ruler:

• Sit in a chair, resting your arm on a table so that your wrist is hanging off the edge, with your thumb and forefingers facing up.

• Ask your partner to hold a ruler vertically, over your hand, with the "zero", where the numbers start, aligned with your thumb.

• Without warning, your partner should drop the ruler, while you try to catch it as quickly as possible.

• The distance the ruler falls before being caught is an assessment of your reaction time.

Broadly speaking, an excellent performance equates to catching the ruler at a distance less than 7.5cm, above average counts as 7.5-15.9cm, average is 15.9-20.4cm, while below average is anything over 20.4cm and poor is more than 28cm.

Population studies have noticed a correlation between the speed of decline in reaction times and risk of multiple age-related illnesses. In addition to a person's overall risk of death – one study found that there was a significant link between a person's reaction times and the likelihood of death from all major causes – there is also a strong relationship between this metric and the risk of death from specific conditions. This includes coronary heart disease, stroke and respiratory disease.

A person's reaction times are also associated with their susceptibility to falls, losing the ability to live independently and the onset of dementia.

However, according to Cox, a single reaction time measurement doesn't reveal all that much, as reaction speeds vary considerably from one person to another due to factors ranging from gender to genetics, physical fitness, lifestyle habits and even personality type. Cox notes that what is likely to be more important is how your reaction speed varies if you compare your performance on the same test over time – for example, at yearly intervals over the course of a decade - and whether it starts to noticeably decline.

As Cox points out, our ability to react relies on a network of interconnected sensory systems: how well we see, hear or even smell a given stimulus, how quickly our brain can process the information it's receiving from our eyes or ears and issue a signal in response, and finally how quickly our nerve fibres, muscles and tendons can enact what the brain is telling them to do. "All these pieces of the jigsaw can be affected by ageing, and not necessarily to the same extent in all people," says Cox.

There are two components to a reaction to the ruler drop test – the brain's ability to make a quick assessment that it has been dropped, and the speed with which the body can act on the brain's instructions to catch it. 

Researchers have found that the first component of this network which tends to break down, beginning in midlife, is our physical ability to act on the brain's signals. So, our brains might notice that the ruler has been let go within milliseconds – but it still takes a while for the body to catch up. 

At the University of Colorado Boulder, biomedical professor Alaa Ahmed has found that as we get older, our reaction times may depend more heavily on our overall bodily health than our brain. She says this may be because things like fast-twitch muscle fibres which enable our physical ability to respond quickly, have waned, or because our mitochondria – the components within our cells which generate energy – are working less well, meaning that we're less efficient at moving swiftly.

"Making a faster movement is more costly to older adults, so they rely primarily on reacting faster," says Ahmed.

At the same time, if we stay relatively well, our brain and central nervous system can still function strongly into our latter years. According to Matthew Pain, a professor of biomechanics at Loughborough University in the UK, scientists have assessed this by measuring the "startle reflex" in the ankles of healthy elderly adults in response to a loud sound. The results showed their brain's ability to respond to the sound and send a "move" signal to the ankle tends to remain relatively intact.

"The raw nervous system hardware in healthy elderly [people] is not that [much] worse," says Pain. "Purely based on the startle reflex, they could still react quickly enough to be disqualified at the Olympics for a false start. They wouldn't, however, be able to get out of the blocks very quickly." 

As well as the ruler test, reaction times can be assessed through simple computer games such as the Human Benchmark Reaction Time Test which involves waiting for a red box to turn green and then clicking on it as quickly as possible. Sharp deteriorations in performance over time can reflect a combination of sensory systems breaking down, as well as a slowing of the brain's decision-making. One study last year found that loss of visual sensitivity in seeing and responding to patterns can be one of the earliest signs of dementia, beginning more than a decade before symptoms begin.

"With age, the nerve fibres in the brain's white matter can start to communicate signals less efficiently, resulting in slower information processing," says Cox. "Once the decision has been made to react, the nerves that connect your brain to your muscles also need to be in good condition to transmit that message quickly, and these age too."

But there are things that we can all do to either slow or prevent this decline from happening. Pain recommends so-called dual task training, which involves simultaneous movement and cognitive training activities to tune both the brain and body. Examples include walking while turning your head from side to side, balancing on one leg while reciting the alphabet, or tossing a ball while verbally associating words.

Even things like such as participating in fitness classes via a TV screen or tablet can help with your reaction times. "This improves the ability to perceive [a stimulus] and respond with meaningful coordinated motions," says Pain.

Cox says that many of the activities which are often linked with healthy ageing, such as continuing to play a sport into later life, learning a musical instrument in retirement or simply keeping engaged with intellectual pursuits such as board games can have knock-on benefits for our reaction times.

"Sports performance drills which require fast responses could boost reaction times by enhancing both brain and body," says Cox. "And there's some evidence that generally keeping more socio-intellectually engaged is related to slower cognitive ageing across aspects of complex thinking."

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