I hated physical education at school. Cross-country was the worst: cold, boring and lung-burning. “Run, don’t walk!” the teacher would shout as we jogged reluctantly through the mud, only to walk as soon as we were out of sight.
Over the following four decades, my PE teacher’s angry barks have been echoed in the constant media reports telling me that I should run, whether informing me that jogging could increase my lifespan by years or that training for a marathon would make my heart younger.
The benefits of exercise are huge. If it were a drug, it would be a miracle cure. It keeps our hearts strong and blood vessels supple, lessens chronic inflammation and reduces the harmful effects of stress.
But do we need to run to get the benefits or can we get a sufficient dose just from walking in the limited time we have for exercise? And what about those who warn about the toll on joints from pounding the pavement? It is common knowledge that running causes arthritis and ruins the knees and hips – but does the evidence back this up? I wanted to find out if my PE teacher’s mantra was right.
The idea that running is the best exercise for us – indeed, that it is part of what makes us human – has many champions. Among them is Daniel Lieberman at Harvard University, who maintains that we evolved to run long distances. He thinks that our now largely untapped talent for persistence hunting – chasing animals over long distances – in hot conditions gives us an edge over other animals and shaped our evolutionary history.
And we aren’t just good at running because we are good at walking – in fact, technically they are quite different (see “Mechanics of locomotion”). A range of adaptations such as sweat glands and hairless skin to aid cooling, the right balance of muscle types and a special ligament to keep our head stable when running all mean that, over long distances, we can outrun almost any other animal. “Thanks to our evolutionary history, all of us have the anatomy and physiology needed to walk and run – assuming we are not disabled,” says Lieberman. “In today’s world, we have medicalised, commodified and commercialised exercise, but physical activity, at its heart, is something we evolved to do.”
It is somewhat ironic then that many of us today are almost entirely sedentary. The current US and UK government guidelines for physical activity recommend that adults do at least 2.5 hours of moderate exercise or 75 minutes of vigorous exercise every week. In the US, only half the population meet these guidelines, and the situation is only slightly better in the UK. But what counts as moderate and vigorous exercise?
Back in the late 1980s, Bill Haskell at Stanford University in California asked the same question and came up with a benchmark to compare exercise against – sitting quietly. When seated, we expend about 1 kilocalorie per hour for each kilogram of body mass. Haskell and his colleagues called this a metabolic equivalent, or 1 MET. For an 80-kilogram person, this resting metabolic rate represents around 1920 kcals per day.
Taking it easy
All physical activities can be expressed in METs, and there is now a Compendium of Physical Activities that contains an eclectic mix of them described using this system. This elegant solution to the definition of exercise has three categories: light exercise up to 3 METs, moderate exercise between 3 and 6 METs and vigorous exercise for anything over 6 METs (see “Measuring the burn”).
Strolling, at about 2 METs, is light exercise, while walking briskly is in the middle of moderate at 5 METs. The transition to running at around 7 kilometres per hour is where exercise enters the vigorous category. A really brisk walk and a slow run are roughly the same, in terms of effort and calories burned. But is this true of their health benefits too?
At first glance, it might seem that running has the upper hand here. A study from January, for example, was enough to make anyone sign up for a marathon. This looked at 138 first-time marathon runners and found that training for and completing the 26-mile race, even at a slow pace, is equivalent to a 4-year reduction in age of the cardiovascular system, or even more for those who are older and less fit.
Mechanics of locomotion
When people walk, at least one foot is always touching the ground. It is an efficient technique in which, mechanically, the body acts like an inverted pendulum during each foot’s contact. Each of us has an optimum stride frequency related to the length of our legs – the longer they are, the lower the frequency.
Running is less efficient and the motion is more like the compression of a spring than a pendulum’s swing. The movement is characterised by a flight phase when both feet are airborne, followed by one foot making contact with the ground for a mere quarter of a second or so. During this impact, the body experiences forces that are more than double those encountered when standing.
Running also gets a glowing bill of health in several large-scale studies that follow people for many years: they show that this exercise has a dose-related effect. More running is better, though with diminishing returns, but the good news for couch potatoes is that the largest gains come by going from nothing to something. “The biggest health benefits are observed with just a little running per week, less than 60 minutes, an amount that would fit in most people’s schedules,” says Angelique Brellenthin, an exercise researcher at Iowa State University.
Further benefits are clear from long-term US studies. In the National Walkers’ and National Runners’ health studies, Paul Williams and Paul Thompson of the Lawrence Berkeley National Laboratory measured the health of about 16,000 walkers and 33,000 runners over six years. Compared with walkers, runners had a 38 per cent lower risk of high blood pressure and a 71 per cent lower risk of type 2 diabetes.
When the researchers controlled for energy expenditure and weight difference between the groups, however, the benefits from walking and running were comparable. Williams later analysed data for breast and brain cancer, and the reductions in risk of death from running or walking were, again, similar if energy expenditure was the same.
Even a small amount of exercise brings significant health gains. This was the case in a massive study from 2011 that followed more than 400,000 people in Taiwan over an average of eight years, noting their exercise habits and the number of deaths from different causes. This showed that just 15 minutes a day of moderate exercise such as fast walking was enough to reduce risk of death by 10 per cent compared with sedentary participants. This effect could also be gained by around 5 minutes of vigorous exercise such as running, giving a time-versus-benefit ratio between running and walking of three to one (see “Survival of the fittest”).
Is exercise worth it?
Runners and other active people tend to live longer. But if these bonus years are equivalent to all the time spent working up a sweat throughout life, then is it all a waste of time? It is a pertinent question for those who find exercise a penance.
Duck-chul Lee of Iowa State University and his colleagues dug into the data to find out. They calculate that between the ages of 44 and 80, someone who runs 2 hours per week will spend a total of 0.43 years running. This would still provide an average “bonus” of 2.8 additional years of life on top of the time spent running. In other words, 1 hour of running typically adds an extra 7 hours to lifespan. “It is controversial whether progressively more running provides further mortality benefits, but running certainly provides cost-effective longevity benefits,” they concluded.
So far, so clear. If you have time on your hands, the gains of walking are comparable to those of a jog so long as you are moving at a moderate pace. But for the time poor, running is the best way to get a dose of exercise. “The fact that running confers similar benefits as walking but in half the time is one major reason that running is attractive for health,” says Brellenthin. “There may be additional benefits of running, particularly for cardiovascular health, related to the higher intensity of running. However, intensity is relative to individual fitness levels, and a brisk walk will provide numerous health benefits for people like beginners and older adults.”
This is great news for joggers and hikers, but not if our body gets worn out or injured in the process. Could this risk outweigh the benefits?
There is no doubt that running is a high-impact activity. When the foot hits the ground, a force equivalent to two or three times your body weight pushes up through the body. Bones, joints, muscles and ligaments must absorb this force. The question is whether this wears your joints out, as many of us believe.
“The largest gains come by going from nothing to something”
As I get older, this is something I worry about. I’m not alone. “Most people understand that exercise is good for you, that it is good for the cardiovascular system, but at what expense, if you’ve worn your knees out in the process?” says Alister Hart, a surgeon at the Royal National Orthopaedic Hospital in London. This question was on his mind back in 2012, when he was hobbling around after completing his first marathon, so he decided to study the impact of marathon running on knees.
Together with his colleague Laura Maria Horga and others, he recruited 82 runners taking part in the London marathon, all of whom were over 40 and had never run this distance before. Using MRI, the runners’ knees were scanned in detail six months before the race and again a few weeks after. The scans revealed that the knee’s main weight-bearing compartments – the parts most likely to develop arthritis in the long term – had become stronger as a result of the marathon training. “It was a very big surprise,” says Hart.
The kneecap part of the joint, however, did show damage, but follow-up scans revealed that this had reversed six months later, when the participants had reverted to less intense running regimes. Hart’s take-home message is “distance running can have long-term benefits for your knees”. The team also did a study on hips, which found that 560 kilometres of a marathon training programme, ending in the race, didn’t cause pre-arthritic changes in the hip joint. “Our findings suggest that the high impact forces during marathon running were well tolerated by the hip joint,” says Horga.
Wear and tear
Another treasure trove of data on wear and tear comes from the National Walkers’ and National Runners’ health studies. As part of this, Williams looked at osteoarthritis, which is caused by the breakdown of bones or cartilage in joints. He found that doing more running or walking actually reduced the risk of osteoarthritis and the need for hip replacements. It didn’t seem to matter if the participants walked briskly or ran slowly.
The idea that running wears the body out is a myth, says Lieberman. “In fact, quite the reverse. Running helps activate all kinds of repair and maintenance mechanisms,” he says.
But it is possible to overdo it. A 2017 meta-analysis including more than 125,000 people found that 3.5 per cent of recreational runners had osteoarthritis in the hip or knee compared with 10 per cent of sedentary non-runners. Yet 13 per cent of elite runners who had taken part in international competitions had such osteoarthritis. For recreational runners at least, it seems there is a sweet spot at which running protects against osteoarthritis.
That is good news for most joggers, but what about the risk of strains and sprains? “Running, like everything, however, has trade-offs including greater risk of injury,” says Lieberman.
When it comes to injuries such as sprains, walking beats running hands down. A study of the exercise habits of more than 14,000 Spanish graduates, for instance, found walking resulted in 40 per cent fewer injuries than running for equal energy expended. The injury rate of running was less than that of football, sailing and martial arts, and similar to that of skiing and tennis.
The risk of injuries from running depends on factors such as how long you have been doing it, as well as your age and sex. A 2015 meta-analysis of 13 studies of running-related injuries found that novice runners were most likely to get injured, sustaining around 18 injuries per 1000 hours of exercise. At an average pace of nearly 10 kilometres per hour, this is equivalent to about one injury every 540 kilometres, more than double the rate of more experienced runners. Unsurprisingly, one of the most important risks is the existence of a previous injury. “I think learning how to run sensibly and properly can help mitigate those risks,” says Lieberman (see “Avoiding the downsides”).
But what about those terrifying stories of people who cross a marathon finish line only to drop dead? Some studies show that the health benefits of running tail off, or even reverse, when running more than 4.5 hours a week. Crucially though, the risks from any amount of running are always lower than from doing no running at all and, on average, runners live three years longer than non-runners. “People who engage in high amounts of running still have health benefits compared to non-runners, but there is probably a point of diminishing returns,” says Brellenthin.
There is good news for runners on the obesity front too: runners tend to weigh less than walkers. This could be because thinner people are more likely to run, but a study by Williams suggests running helps shed excess weight. It showed that reductions in body mass index were significantly greater from running compared with walking when these activities were matched for energy expenditure. This could be due to a greater increase in metabolic rate after more intense exercise.
So where does this leave us in the walk/run debate? Was my PE teacher right that running is a better way to exercise than walking?
The research clearly shows that both are good for you. They improve cardiorespiratory fitness and reduce blood pressure, body mass index and the risk of a host of diseases. For the biggest bang for your buck though, running has the edge, mostly because you can get more exercise done in a given time. But if you expend the same amount of energy when you walk, the benefits are quite similar. In other words, if you prefer walking, go for a long one, ideally with a few hills. And remember that any amount of exercise is better than none.
This philosophy might explain the success of an exercise phenomenon that is sweeping the globe: parkrun. These free, timed 5-kilometre community events take place every Saturday morning in more than 20 countries. They are wildly popular, with 6 million people signed up. Key to parkrun’s success is that you can cover the distance however you want: by running, walking, pushing a child in a buggy or loping with a dog. Participants rate the impact on their fitness and happiness so highly (I know, because I carried out the research to find out) that family doctors in the UK now prescribe parkrun to their patients.
My PE teacher would be astonished to discover that I enjoy running now and rarely miss a parkrun. If I did meet him, though, I would gently point out that we don’t necessarily have to run. After all, the most important exercise is the one you actually do.