Now here’s a contagion that might not be so bad to encounter. A new analysis of the running habits of about 1.1 million people reveals that exercise is indeed contagious — though its communicability depends on who’s spreading it.
3 Signs You Need a New Pair of Running Shoes
The relationship you have with your running shoes isn’t meant to last forever. Here’s how to know when to buy a new pair to prevent injury and prolong an enjoyable running experience.
A comfortable and supportive pair of shoes are a runner’s best friend, but even the best aren’t built to last forever. Avid runners know working out in worn-out sneakers can cause unwanted running injuries like shin splints or runner’s knee. But how do you know it’s time to trash your sneaks and invest in a new set? Here, two running experts share the signs that cue a much-needed trip to your local shoe store.
You’re racking up miles
“As a rule it’s best to update your running shoes every 300 to 400 miles,” says Nikhil Jain, senior footwear product line manager at Brooks Running. Since wear and tear on the shoe itself isn’t always obvious, this method ensures you get new shoes before your worn ones cause pain or an injury.
You can easily track your runs with apps such as Strava, MapMyRun, or Wahoo, or with a fitness tracker. You could also opt for an old-school approach and hand write your runs in a journal. If you’re looking to eyeball your mileage based on time, take advice from a pro: New York City-based running coach John Henwood says he replaces his own shoes every two months.
You feel aches and pains
“As soon as one of my runners feels a shin splint, the first thing I do is ask them how long they’ve had their shoes for,” says Henwood. Knee pain and shin splints, which cause pain in the lower part of the leg, could both signal you need new shoes, especially if you haven’t changed up your running routine at all.
Not ready to part with your precious sneakers? Jain suggests keeping them around for leisurely walks or running errands. “While they may no longer be in good condition to run in, it’s likely that you won’t need as much cushion and support in your other activities,” he says.
Your shoes look shabby
According to Henwood, there are three areas on the shoe itself that signal it’s time for a replacement: the sole, the tread, and the exterior fabric.
“The cushioning in your shoe will be the first thing to break down because midsoles are designed to absorb shock and protect the body,” says Jain. “The tricky part is that this wear isn’t easily visible.” If the soles are shot, the shoe may appear lopsided from putting more pressure on one part of your foot than the others.
The tread of the shoe will be the next area to wear out, so if the bottom of the shoe appears flat and smooth, chances are your soles have lost their support and cushioning. Any holes that appear in the shoe’s exterior fabric provide a third red light that they’ve deteriorated.
To prevent your shoes from wearing out before you hit 300 to 400 miles, Henwood suggests using them exclusively for your runs. “If you’ve got running shoes, don’t walk around in them,” he says. “Have your running shoes for running and other shoes for walking because how you use them changes how they last.”
Jain also suggests rotating between two pairs of running shoes to prolong each pair’s life. “In addition, having more than one running shoe in your rotation helps you work a slightly different set of muscles in your feet, helping you strengthen them,” he says.
How Exercise Changes Fat and Muscle Cells
Exercise promotes health, reducing most people’s risks of developing diabetes and growing obese. But just how, at a cellular level, exercise performs this beneficial magic — what physiological steps are involved and in what order — remains mysterious to a surprising degree.
Several striking new studies, however, provide some clarity by showing that exercise seems able to drastically alter how genes operate.
Genes are, of course, not static. They turn on or off, depending on what biochemical signals they receive from elsewhere in the body. When they are turned on, genes express various proteins that, in turn, prompt a range of physiological actions in the body.
One powerful means of affecting gene activity involves a process called methylation, in which methyl groups, a cluster of carbon and hydrogen atoms, attach to the outside of a gene and make it easier or harder for that gene to receive and respond to messages from the body. In this way, the behavior of the gene is changed, but not the fundamental structure of the gene itself. Remarkably, these methylation patterns can be passed on to offspring – a phenomenon known as epigenetics.
What is particularly fascinating about the methylation process is that it seems to be driven largely by how you live your life. Many recent studies have found that diet, for instance, notably affects the methylation of genes, and scientists working in this area suspect that differing genetic methylation patterns resulting from differing diets may partly determine whether someone develops diabetes and other metabolic diseases.
But the role of physical activity in gene methylation has been poorly understood, even though exercise, like diet, greatly changes the body. So several groups of scientists recently set out to determine what working out does to the exterior of our genes.
The answer, their recently published results show, is plenty.
Of the new studies, perhaps the most tantalizing, conducted principally by researchers affiliated with the Lund University Diabetes Centre in Sweden and published last month in PLoS One, began by recruiting several dozen sedentary but generally healthy adult Swedish men and sucking out some of their fat cells. Using recently developed molecular techniques, the researchers mapped the existing methylation patterns on the DNA within those cells. They also measured the men’s body composition, aerobic capacity, waist circumference, blood pressure, cholesterol levels and similar markers of health and fitness.
Then they asked the men to start working out. Under the guidance of a trainer, the volunteers began attending hourlong spinning or aerobics classes approximately twice a week for six months. By the end of that time, the men had shed fat and inches around their waists, increased their endurance and improved their blood pressure and cholesterol profiles.
Less obviously, but perhaps even more consequentially, they also had altered the methylation pattern of many of the genes in their fat cells. In fact, more than 17,900 individual locations on 7,663 separate genes in the fat cells now displayed changed methylation patterns. In most cases, the genes had become more methylated, but some had fewer methyl groups attached. Both situations affect how those genes express proteins.
The genes showing the greatest change in methylation also tended to be those that had been previously identified as playing some role in fat storage and the risk for developing diabetes or obesity.
“Our data suggest that exercise may affect the risk for Type 2 diabetes and obesity by changing DNA methylation of those genes,” says Charlotte Ling, an associate professor at Lund University and senior author of the study.
Meanwhile, other studies have found that exercise has an equally profound effect on DNA methylation within human muscle cells, even after a single workout.
To reach that conclusion, scientists from the Karolinska Institute in Stockholm and other institutions took muscle biopsies from a group of sedentary men and women and mapped their muscle cells’ methylation patterns. They then had the volunteers ride stationary bicycles until they had burned about 400 calories. Some rode strenuously, others more easily.
Afterward, a second muscle biopsy showed that DNA methylation patterns in the muscle cells were already changing after that lone workout, with some genes gaining methyl groups and some losing them. Several of the genes most altered, as in the fat cell study, are known to produce proteins that affect the body’s metabolism, including the risk for diabetes and obesity.
Interestingly, the muscle cell methylation changes were far more pronounced among the volunteers who had ridden vigorously than in those who had pedaled more gently, even though their total energy output was the same.
The overarching implication of the study’s findings, says Juleen Zierath, a professor of integrative physiology at the Karolinska Institute and senior author of the study, is that DNA methylation changes are probably “one of the earliest adaptations to exercise” and drive the bodily changes that follow.
Of course, the intricacies of that bogglingly complex process have yet to be fully teased out. Scientists do not know, for instance, whether exercise-induced methylation changes linger if someone becomes sedentary, or if resistance training has similar effects on the behavior of genes. Nor is it known whether these changes might be passed on from one generation to the next. But already it is clear, Dr. Ling says, that these new findings “are additional proof of the robust effect exercise can have on the human body, even at the level of our DNA.”