Do you feel sluggish as you get older? That’s because it really takes more effort to exercise, research shows

Most older people will notice that they are no longer as quick on their feet as they used to be.

Now experts think they may have discovered why we tend to move more slowly as we age.

A team from the University of Colorado Boulder asked two groups of participants to perform a simple task that involved reaching for a target on a screen.

One group contained people between the ages of 18 and 35, the other group contained people between the ages of 66 and 87.

The researchers measured their reaction time during the task and how much energy was required, also called metabolic costs.

They found that it took the older participants more energy to complete the movement than their younger peers.

The study, published in the journal JNeurosci, is one of the first to experimentally explain the conflicting reasons why people over 65 may move a little slower than they used to.

It says: ‘Here, we first quantified the cost of achieving via metabolic energy expenditure in human participants and found that older adults expended more energy than young people at a given speed.

“So, objectively, transportation is more expensive for older adults.”

When participants were told they would receive a reward for their efforts, both groups reached the goal sooner – about 5 percent faster than when the trial was performed without a reward.

But they achieved the goal in different ways.

While younger participants moved their arms faster, the older group seemed to increase their speed by responding more quickly and starting to move their arm earlier.

When the team added a weight to the younger subjects’ arms, these differences disappeared – meaning the younger group stopped moving their arms faster and instead started improving their reaction time.

Robert Courter, co-lead author of the study, said: ‘The brain appears to be able to detect very small changes in the amount of energy the body uses and adjusts our movements accordingly.

“Even if you moved with just a few extra pounds, responding faster became the energetically cheaper option to get the reward, so the young adults imitated the older ones and did just that.”

The team said their findings could give doctors new tools for diagnosing a range of diseases.

Author Alaa Ahmed said: ‘Why we move the way we do, from eye movements to reaching, walking and talking, is a window into aging and Parkinson’s.

‘We are trying to understand the neural basis of this.’