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A 60-year-old’s muscles aren’t old at all

In studies, Danish researchers have shown that healthy 60–70-year-olds have a much better ability to repair muscle damage and build up muscle than scientists have previously assumed. 

Your hair turns grey and wrinkles start to appear. That’s what it’s like to grow old. Full stop.

The good news is, however, that the ravages of time are not completely merciless. New research, conducted at the University of Copenhagen and the Institute of Sports Medicine at Bispebjerg Hospital, reveals that they are not merciless at all.

These are the words of Anders Karlsen, the Lundbeck Foundation researcher who is heading the research project that was recently published in the scientific journal FASEB:

‘Contrary to previous assumptions, our project shows that human muscles can’t be considered old at the age of 60 or 70.
The studies we’ve conducted show the exact opposite; healthy 60–70-year-olds get full value for money if they start exercising – even when compared to the benefits seen in 20–30-year-olds.’

‘And the results “truly surprised” the researchers,’ says Anders Karlsen, who holds a PhD in human physiology and works at the Institute of Sports Medicine.

Human trials
But what have the researchers from the University of Copenhagen and Bispebjerg Hospital actually discovered – and how did they conduct the tests that led to the finding?

Paradoxically, it all began with the loss of muscle mass we experience as we grow older. It is a fact that we lose muscle mass as we age, particularly the so-called fast fibres we use, for instance, when we sprint.

However, the question is what the ageing process and loss of muscle mass mean for the 60–70-year-old’s potential for regenerating muscle – whether they need rehabilitation after a muscle injury or ‘merely’ want to improve their strength.

There has been a persistent assumption that 60–70-year-olds are less able to repair and build up muscle because the number of muscle stem cells declines with age.

Muscle stem cells are essential for the body to repair damage to muscle fibres. Anders Karlsen and his colleagues therefore decided to take a closer look at what a 60–70-year-old’s muscle stem cells are actually able to do when they are really needed.
To do this, they conducted a study with a clear focus on the performance of muscle stem cells in a group of 60–70-year-olds undergoing rehabilitation treatment to recover from a muscle injury.

Trials of this kind are extremely complicated, and there are several reasons for this.

In the first place, you need to ensure that the trial subjects are attempting to recover from exactly the same type of injury, in exactly the same muscle – otherwise, the results cannot be compared.

This requirement can only be sufficiently met if you actively induce the injury in the trial participants, after which they each attempt to heal the injury by exercise.

Electrical stimulation
Anders Karlsen explains that because it is so difficult to conduct trials of this kind on human beings, over the years, physiologists have largely sought their answers through animal trials:

‘For instance, we’ve used mice to demonstrate correlations between ageing and the ability to repair muscle damage – and we induced muscle injuries in the animals using a variety of toxins. Obviously, this isn’t a viable option in human trials, so we used electrical stimulation instead.’

The researchers gathered two groups of trial participants, all of whom were considered healthy from a medical point of view: Cohort A, consisting of seven young men between the ages of 20 and 30, and Cohort B, with 19 elderly men between 60 and 73.

Anders Karlsen explains that all participants received electrical stimulation – in one leg – 200 times, with the voltage increasing gradually up to 120 milliamperes:

‘The stimulation was given to the vastus lateralis. This is one of the muscles we use to stretch our knee, and it’s the muscle from which we usually take samples for physiological studies associated with weight training. The stimulations were in no way dangerous, but they weren’t comfortable for the participants either. They induced maximum muscle contraction and caused atrophy of some muscle fibres, which then needed to be regenerated through exercise. The electrical stimulation also initially caused pronounced soreness in the muscle.’

Both Cohort A and Cohort B exercised regularly with heavy weights, supervised by Anders Karlsen and his colleagues. Irrespective of their age, participants exercised both legs intensively, and a range of blood samples and muscle biopsies were taken.

Weight training lasted 13 weeks, and when all of the data were analysed, the researchers were able to conclude that the two groups had performed equally well, both with regard to regenerating the damaged fibres in the muscle and in terms of increasing muscle mass.

But how can that be explained?
‘The explanation is down to the level of function of the muscle stem cells,’ says Anders Karlsen. ‘And the interesting thing is that although the number of muscle stem cells indisputably declines with age, there doesn’t seem to be a proportional decline in the ability of these cells to get moving when it really counts. Certainly until we’re over 70 – our oldest participant was 73. Obviously, this study won’t tell us whether the muscle stem cells retain their capacity for emergency response into older age,’ says Anders Karlsen.

There is a logical explanation for limiting the trial participants to men: The two groups are easier to compare when the only substantial difference between them is age.

Does this mean that we can expect to find the same excellent capacity for emergency response in the muscle stem cells of healthy 60–70-year-old women?

‘In principle, yes,’ says Anders Karlsen, ‘but I can’t be more specific before we’ve conducted a similar study with female trial subjects.’

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