Running with a pram or stroller might make parents less susceptible to ankle pain and injuries to their calf muscles, foot arches and Achilles tendons. A survey of parents suggests there is a 37 per cent drop in injury risk with pram use. This may be partly due to changes in vertical forces – how much force our legs absorb with each step – when pushing a child.

“You get a little bit of a walker effect where you’re leaning and putting some weight on the stroller,” says at Pennsylvania State University, who ran with a pram after the births of her two children. “That led me to wonder, you know, is this actually protective?”

Previous research suggests that people running with a pram tend to have . They also lean forward more, with . Last year, Altman Singles and her colleagues found there is a when running with a pram, but whether this affects injury risk was unclear.

To learn more, Altman Singles and her team analysed self-reported running and injury data from 196 parents who used any kind of pram on at least some of their runs while their children were younger than 3 years old. These individuals were compared against another 53 mothers or fathers who ran when their children were the same age, but without prams. All the participants had some running experience before becoming parents.

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The two groups of parents covered similar total distances and were relatively well matched in terms of factors like age, height and weight. But there were many more women than men in both groups, particularly the pram one.

Overall, 30 per cent of the non-pram runners reported having had running-related injuries, compared with 19 per cent of the pram runners. These included a higher incidence of ankle pain, calf muscle injury, plantar fasciitis (heel pain that occurs when the thick band of tissue on the bottom of the foot becomes irritated or inflamed) and Achilles tendinitis (injury of the Achilles tendon).

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“Generally, stroller running involves rapid steps with short stride lengths,” says at Seattle Pacific University. “Although this can increase metabolic cost, it can also decrease the force production at each foot strike, which might explain some of these injury reductions.”

Wall-Scheffler says we should see this paper as a “great start” to understanding an important topic. However, future work should include a more balanced mix of men and women, she says. For instance, oestrogen and progesterone , which could affect a woman’s injury risk.

Future studies should also collect injury-related data more regularly over time and could even investigate the effects of different pram-pushing styles, such as using one or two hands, says Wall-Scheffler.

While exercise is important for a long and healthy life, ultramarathons may accelerate the ageing of cells in our blood. Athletes who ran 170 kilometres over mountainous terrain accumulated more age-related damage to their red blood cells than those who completed a shorter distance.

Long-distance running has been linked to health issues before, such as temporary suppression of the immune system and anaemia. But we only now have an understanding of what it does to red blood cells – which transport oxygen around the body – particularly when done outside on mountainous terrain.

at the University of Colorado Anschutz and and his colleagues analysed blood samples from 11 adults aged 36, on average, within a few hours before and after they ran a trail 40-kilometre race. They did the same for a separate group of 12 people of around the same age who competed in a 170-kilometre ultramarathon over similar terrain.

The researchers found that competing in either race seemed to cause the runners’ red blood cells to accumulate more damage from molecules known as reactive oxygen species, which are produced at higher levels when these cells need to deliver more oxygen around the body.

But such damage, which naturally accumulates as red blood cells age, was substantially higher in the ultramarathon runners. “Anecdotally, the blood after an ultramarathon looks like the blood of somebody who’s just been hit by a car,” says D’Alessandro. “The red blood cells accumulate damage and become more aged.”

Running the ultramarathon, but not the shorter race, also seemed to cause their red blood cells to shift more rapidly from a disc shape to a more spherical one, which is typically seen when they age. The disc shape allows them to bend and squeeze through tiny blood vessels in the spleen, where old red blood cells are destroyed. “This spherical shape means they get stuck in the spleen and eaten up by immune cells,” says team member , also at University of Colorado Anschutz.

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This damage is probably due to exercise increasing inflammation and particularly strenuous activity pushing red blood cells more forcefully around the body, he says.

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What’s more, only the ultramarathon runners experienced a roughly 10 per cent drop in their red blood cell numbers after the race, but this isn’t necessarily a problem for their health. This change is too small to cause anaemia and the body can probably rapidly recover from it, says Nemkov.

The researchers are now studying the red blood cells of ultramarathon runners a day after they have completed a race, in order to better understand how long these effects last. They also want future work to examine whether these changes affect runners’ performance. “This could just be what the damage signals look like to make the body more resilient to endurance running, or it could have a negative impact,” says Nemkov.

Researchers have identified neurons in mice that help build endurance after running. They suspect that similar cells exist in people, which could be targeted with drugs or other therapies to amplify the effects of exercise.

We have known for decades that the brain changes with physical activity. Yet scientists widely believed these effects are distinct from those occurring elsewhere in the body, like muscles growing stronger, says at the University of Pennsylvania. The latest findings suggest otherwise – the brain changes “are what coordinates all that other stuff”, he says.

To better understand how exercise influences the brain, Betley and his colleagues monitored neuronal activity in mice before, during and after treadmill exercise. They zeroed in on cells in the ventromedial hypothalamus, as previous research has shown that hinders fitness improvements in rodents. The same is probably true in people, because the region’s structure and function tends to be consistent across mammals, says Betley.

The team found that after the mice had run, activity increased in a group of neurons with a receptor called SF1, which . What’s more, the proportion of these cells activated by exercise grew with each additional day of running. By day eight, running activated about 53 per cent of the neurons compared with less than 32 per cent on day one. “So, just like your muscles build when you’re exercising them, your brain activity builds,” says Betley.

Next, the researchers used optogenetics – a technique that activates or inhibits neuronal activity with light – to turn off these neurons in a separate group of mice. The animals trained on a treadmill five days a week for three weeks. After each session, the neurons were inhibited for one hour. At the end of each week, the mice completed an endurance test, running to the point of exhaustion.

Over the course of the experiment, the mice increased the distance they ran on these tests by about 400 metres, on average, but this was roughly half the improvement seen in another group of mice whose neurons were left intact.

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It isn’t clear what the role of these neurons is, but it may relate to fuel utilisation, says team member , also at the University of Pennsylvania. During endurance activities, the body fuels itself with fat, as carbohydrate stores deplete more quickly. But inhibiting these neurons in the mice led them to “start using carbs a lot earlier on in the run”, says Kindel. “Then, they are kind of out of fuel.” The team found that inhibiting these neurons prevents the release of a protein called PGC-1 alpha in muscles, which helps cells use fuel more efficiently. These neurons also release a substance that increases blood sugar and replenishes energy stores, aiding muscle recovery.

Optogenetics requires invasive brain surgery, so isn’t feasible in people. But it may be possible to develop other interventions that could act on these neurons, says Betley. “I really do think that if we could find a way – a salt, a supplement – to activate these neurons, you can increase endurance,” says Betley.

When the researchers repeated the experiment, boosting rather than inhibiting activity in these neurons, they found just that: the mice developed Herculean endurance, running more than double the distance of control mice.

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A similar intervention could particularly benefit people who have difficulty exercising, such as older adults or those who have had a stroke, says Betley.

But there are many hurdles in the way. For one, we don’t know for sure if these findings translate to people. There is also the question of potential side effects, says at the University of Florida. These neurons seem to regulate energy uptake in muscles, so stimulating them too much could cause a dangerous drop in blood sugar, he says.

Even if we can safely activate these neurons in people, it won’t be a silver bullet for good health, says Betley. “All sorts of great things happen when you exercise – you’re less depressed, less anxious. There are cognitive improvements, cardiovascular improvements, muscle improvements,” he says. “I don’t think that activating [these] neurons is necessarily going to be the bottleneck through which all of those good things happen.”