Image copyright SPA Image caption Treadmills are the top selling piece of gym equipment in the US 
 
 It will surprise no-one familiar with the relentless whir of a treadmill to learn they were once used to a punish inmates in 19th century British workhouses. 
 
 Now, of course, no self-respecting gym is without one. They are comfortably the best-selling piece of gym equipment in the US. 
 
 They appeal to everyone from amateurs to Olympians, if nothing else, because it may seem a far more comfortable option than pounding the streets in the depth of winter. 
 
 But how safe are they? 
 
 The question has been raised by the sudden death of Silicon Valley entrepreneur, Dave Goldberg, who was found lying next to a machine at a Mexican resort. 
 
 The SurveyMonkey chief executive had slipped, banged his head and later died of his injuries. 
 
 Image copyright Getty Images Image caption Treadmills were used as a form of punishment in Britain during the 19th century 
 
 About 24,000 people were admitted to US hospitals last year with treadmill-related injuries, the Consumer Product Safety Commission (CPSC) estimates, with slips and strains the most common causes. 
 
 But deaths are rare, with 30 reported deaths over a 12-year period to 2012, according to the CPSC, and not all of these are caused by hazards specific to treadmills. Some people suffer heart attacks from the exercise, for example. 
 
 Indeed, you are more likely to be killed by lightning than by exercising on a treadmill. According to the National Oceanic and Atmospheric Administration, 261 people died in the US after being struck by lightning between 2006 and 2013. 
 
 Children, however, are at particular risk. 
 
 The daughter of US boxer Mike Tyson died after becoming entangled in the cable of a treadmill, and there are numerous cases of children suffering severe friction burns after trapping fingers and hands in the revolving belt. 
 
 Australia has even launched a public campaign on the dangers of treadmills to young children. 
 
 Image copyright SPA Image caption Regardless of risks, experts say exercise is better than inactivity 
 
 Few gym companies in the UK approached for information responded, but LA fitness said that the number of people injured on treadmills was "low - just 2% of all our accidents". 
 
 The company recommends being properly inducted on machines, knowing the safety features, having water at hand and not looking at your feet when you are running as among the best ways to stay safe. 
 
 And any inherent risks in with exercise need to be contrasted with the risks of inactivity. 
 
 Advice on exercising can appear confusing - one recent report suggested that intensive training may be as bad as not jogging at all. 
 
 But World Health Organization advice remains that adults should do at least 75 minutes of vigorous exercise a week. 

 People on treadmills in gym (Photo: Getty Images) 
 
 Serious injuries involving exercise equipment, treadmills in particular, are among the most common that emergency rooms see, according to data collected by the U.S. Consumer Product Safety Commission. 
 
 Hospital emergency departments across the USA treated some 24,400 treadmill related injuries last year, said CPSC spokeswoman Kim Dulic. 
 
 The agency counted 30 reported deaths associated with treadmills from 2003 to 2012. 
 
 Almost 460,000 people were sent to the hospital in 2012 for injuries related to exercise equipment, according to the agency's data. The vast majority—nearly 428,000 were treated and released for their injuries—but about 32,000 were hospitalized or were dead on arrival. 
 
 Treadmill injuries included broken bones, abrasions, rectal bleeding and people developing chest pain while working out on the machines, according to a review of the CPSC data base system. 
 
 The death of SurveyMonkey CEO David Goldberg, who authorities says suffered severe head trauma after slipping from a treadmill, comes nearly six years after the 4-year-old daughter of former heavyweight boxing champ Mike Tyson died in a treadmill accident at her home in Phoenix Ariz. 
 
 She had been strangled by a cord connected to the machine. 
 
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 Details on Dave Goldberg’s death are still murky. The entrepreneur and husband of Facebook’s chief operating officer, Sheryl Sandberg, was found bleeding out in a Mexican hotel gym on Friday. He died shortly afterward at a nearby hospital, but the strange circumstances are only slowly emerging. 
 
 Despite the darkness surrounding the incident, it is nonetheless shining a spotlight on the contraption at the center of the tech executive’s death: your run-of-the-mill treadmill. 
 
 Goldberg slipped and fell while using one of the machines during a stay near Puerto Vallarta. He hit his head and died from brain trauma and blood loss, local authorities told CNN. (The Four Seasons Hotel has denied earlier reports from authorities that he was staying at a Four Seasons.) 
 
 Dave Goldberg, one half of the Silicon Valley power couple with Sheryl Sandberg, is being mourned as a respected tech executive and progressive male feminist. Dave DiMartino, executive editor of Yahoo Music, shares memories of his former boss and friend. (Jorge Ribas/The Washington Post) 
 
 But his freakish accident actually isn’t that rare. Every year, tens of thousands of Americans are injured on treadmills. Thousands are taken to the emergency room. A handful die. 
 
 Data suggest that the problem is getting worse. As high-tech, high-powered treadmills proliferate, so, too, do the digital distractions that make the machines even more dangerous. 
 
 “We have to weigh the costs and the benefits of these types of activities and just be aware of what some of the risks are,” says Janessa M. Graves, a professor at the College of Nursing at Washington State University who led a 2013 study of exercise machine injuries. 
 
 [Related: How to safely use a treadmill: It’s not as easy as you think] 
 
 Treadmills are almost as old as Western civilization. The Romans used them to grind grain. They were later adapted to horses, then prisoners. It wasn’t until after World War II that cardiologists started recommending their use. When the first cheap home treadmill was invented in 1968, the trend was off and running. 
 
 Today, treadmills are the nation’s most popular type of exercise equipment. More than 50 million Americans now use them, CBS reported. The exercise industry grew by 3.5 percent in 2014 to a total of $84.3 billion, and “treadmills continue to be the largest selling exercise equipment category by a large margin,” according to the Sports & Fitness Industry Association. 
 
 But exercise equipment — and treadmills in particular — can also be dangerous. 
 
 “Almost 460,000 people were sent to the hospital in 2012 for injuries related to exercise equipment,” according to USA Today. “The vast majority — nearly 428,000 were treated and released for their injuries — but about 32,000 were hospitalized or were dead on arrival.” 
 
 Treadmills account for the majority of such exercise equipment injuries, Graves told The Washington Post in a phone interview. In a study of 1,782 injury reports from 2007 to 2011, she found that “treadmill machines comprise 66% of injuries but constitute approximately only one-fourth the market share of such equipment.” 
 
 “Mechanical belt-driven equipment may present disproportionate injury risk in mechanical home exercise equipment,” she wrote in her study. “While we do not have data on the use of these machines, our study suggests the need to consider the hazards associated with in-home mechanical exercise equipment in the context of exercise recommendations.” 
 
 Graves says she was shocked not only by the proportion of injuries caused by treadmills but also by the victims. “We were surprised by the number of pediatric injuries that we saw,” she says. “There was a pretty high incidence among kids, especially 0 to 4 years old, also 5 to 9 years old.” In many cases, kids turned on their parents’ treadmills, only to burn their hands on the fast-moving tracks or, worse, get their fingers caught in the powerful machines. 
 
 According to data from the National Electronic Injury Surveillance System (NEISS), roughly 19,000 people went to emergency rooms in 2009 because of treadmill injuries, including nearly 6,000 children. 
 
 
 
 Sheryl Sandberg, chief operating officer of Facebook, and her husband, David Goldberg, chief executive of SurveyMonkey, attend the Allen & Company Sun Valley Conference on July 9, 2014, in Sun Valley, Idaho. (Scott Olson/Getty Images) 
 
 Incidents like Goldberg’s death are outliers, Graves argues. Instead, most treadmill injuries among adults are simply sprains or strains to the lower extremities. “I don’t think our data suggests that those incidents that make the news are common,” she says. Those incidents are the ones that tend to stir debate, however. In 2009, Mike Tyson’s 4-year-old daughter, Exodus, died after getting her neck caught in a treadmill cord, setting off a national discussion over the safety of the devices. 
 
 What is concerning is the increase in exercise equipment injuries, Graves says. According to NEISS data, these injuries nearly tripled from 1991 to 2012. The same is true of treadmill injuries, she adds. 
 
 The rise in exercise-equipment-related injuries could be due to two factors: the spread in fitness equipment as devices have gotten cheaper and more powerful, and the proliferation of smartphones and other mobile electronic devices that may distract us as we try to run. The iPhone was introduced in 2007, for example, and exercise equipment injuries increased 45 percent over the next three years. 
 
 Commercial treadmills at health clubs also feature an increasing number of buttons to be pushed and monitors to be checked, not to mention built-in television controls for built-in screens. 
 
 Unfamiliarity with increasingly complex treadmills can be a factor in injuries, says Jared Staver, a Chicago personal injury attorney who says he has handled more than 100 cases involving gym injuries. 
 
 “Clearly if there’s not someone there to instruct a user, especially a novice user, in how to use a machine, then I think the technology and the knowledge of how to set the speeds and so forth could certainly play a role in an accident,” he said, stressing that he has no knowledge of Goldberg’s death beyond what he has heard from news accounts. 
 
 “There is an inherent risk to working out. We all know that. If you overdo it, you may hurt yourself and obviously you may even die,” Staver says. “It’s kind of ‘user beware.’ If you’re going to go on a foreign machine that you’ve never used before, you have a duty to yourself to make sure you are instructed on that machine’s particular use and you use it accordingly. If you don’t do that but instead go ahead full steam, you may suffer the consequences.” 
 
 Graves points out, however, you can get hurt using something as innocuous as a yoga ball or an elastic band — as Sen. Harry Reid (D-Nev.) did on New Year’s Day. 
 
 She says more research needs to be done to see if treadmills are really any more dangerous than other types of exercise equipment, and if cellphones are really a distraction to treadmill runners. 
 
 “I don’t think it’s outside the realm of possibility that if you’re running on a treadmill and you get this text from a reporter at The Washington Post, then you’ll stop and get thrown off the back,” she says. “So I don’t think it’s outside the realm of possibility that an injury can occur while being distracted by a mobile or electronic device.” 
 
 Goldberg’s family has not said how his fatal injury occurred or whether he was using a cellphone at the time.
– The sudden death of SurveyMonkey CEO David Goldberg after he apparently fell off a treadmill was a tragedy for those who loved him—and a reminder to everyone else that fitness machines can be dangerous if not used properly. In fact, according to data from the US Consumer Product Safety Commission, some of the most common serious injuries that ER staff witness each year are the result of people using exercise equipment, including treadmills, per USA Today. In 2012, nearly 460,000 people went to the hospital for exercise equipment-related injuries, and though most were treated and released, 32,000 of those people were either hospitalized or were dead on arrival. The numbers for the treadmill in particular have been high for a while: According to a 2011 CBS News report, some 19,000 people went to the ER in 2009 for treadmill injuries, including 6,000 or so kids. One of those kids who received media attention was Mike Tyson's 4-year-old daughter, Exodus, who died in 2009 after getting tangled in a treadmill cord. Quartz notes the bruises, broken bones, and worse that can result from treadmill accidents, and it cites a 2012 study that calls pediatric injuries from these machines an "emerging problem" that presents a "significant danger" to children. It's worrisome enough in Australia that there's now a campaign targeted to warning how risky treadmills are for young kids, the BBC notes. But although it's understandable to see how kids can use the machines incorrectly, how do we explain so many adult injuries? Michael Miller speculates in the Washington Post the rise in exercise equipment injuries could be partly attributed to more powerful equipment, as well as more distracting devices like smartphones. (Hopefully treadmill desks are safe.)