Weight Watchers shares dropped the most since their market debut more than 13 years ago, after the dieting company’s earnings forecast fell well short of analysts’ expectations. 
 
 The company has faced declining subscriptions and revenue as consumers migrate to digital methods for counting calories and keeping in shape. Weight Watchers International Inc. on Thursday reported that quarterly revenue had declined for the eighth straight period. 
 
 The stock fell 35 percent to $11.33 on Friday in New York, the biggest drop since the company’s initial public offering in November 2001. The shares had posted a 78 percent decline over the past three years through Thursday. 
 
 Weight Watchers said Thursday that it would seek to cut $100 million in costs and that Lesya Lysyj, its president of North America operations, would leave the company. 
 
 The company forecast earnings of 40 cents to 70 cents a share for this year, missing the $1.43 average of seven analysts’ estimates compiled by Bloomberg. The costs associated with a plan to “resize” aren’t reflected in the guidance, the company said. 
 
 Weight Watchers has attempted to remake its image this year with a new ad campaign and redesigned magazine introduced in January. 
 
 “They’re struggling to keep pace,” said RJ Hottovy, an analyst at Morningstar Inc. in Chicago. “Its changes in marketing, product and technology haven’t connected with consumers.” 
 
 ‘Disappointed’ 
 
 Chief Executive Officer Jim Chambers said the company’s turnaround would take longer than expected. 
 
 “I am disappointed that we are not yet where we hoped to be and our turnaround will take longer than anticipated,” Chambers said Thursday on a conference call. 
 
 Founded in 1961, Weight Watchers has built a system of dieting programs, food products and support centers for people seeking to slim down. 
 
 Meanwhile, with consumers paying more attention to how many calories they are burning from exercise or everyday activities, fitness gadgets have surged in popularity, with 51.2 million American adults using applications to track their health, according to Nielsen. That is making it harder for Weight Watchers to justify subscriptions starting at $20 a month, since activity trackers can be paired with free mobile apps that make it easy to analyze caloric input and output. 
 
 ‘Get Modern’ 
 
 “Weight Watchers really has to change what they’re offering -- they have to get modern,” said Meredith Adler, an analyst at Barclays. “People are just more digital now than they ever were.” 
 
 New York-based Weight Watchers has embraced activity trackers. Subscribers can use FitBit, Jawbone and the company’s own ActiveLink gadget to track diets and exercise. On the call, Chambers acknowledged that the company still had work to do to remake its image and offerings. 
 
 “I think you will see the Weight Watchers brand showing up differently going forward,” he said. 
 
 Weight Watchers’ membership declined 15 percent in the past quarter, to 2.51 million active subscribers. While profit, excluding some charges, matched analysts’ average estimate for 7 cents a share, revenue fell short of projections. Revenue declined 10 percent to $327.8 million in the fourth quarter, compared to an average analyst estimate of $334.3 million, according to analysts surveyed by Bloomberg. Last month, Weight Watchers was among the most-shorted stocks on the New York Stock Exchange. 
 
 Threat Downplayed 
 
 As CEO two years ago, David Kirchhoff said he didn’t see wearable devices -- along with social media and other technologies -- as a threat. Instead, they presented a chance for the company to enhance its methods, counseling and business model, he said on an earnings conference call in February 2013. 
 
 Three months later, on another call, Kirchhoff’s tone began to change: “In this cash-strapped environment, the sudden proliferation in popularity of free alternative offerings has created a surge of trial in these apps. The resulting impact is contributing to a challenging recruitment environment, similar to what we saw back in 2000 with the low-carb diet fad.” 
 
 In November, the battle appeared all but lost. 
 
 “Frankly, we were slow to innovate and add value to our products,” Weight Watchers Chief Financial Officer Nicholas Hotchkin said at an investor conference on Nov. 11. “We were particularly susceptible to the proliferation of free apps and activity monitors.” 
 
 Corporate Deals 
 
 The company’s best bet is to focus on providing weight-loss programs for corporations and health plans, which have been seeking ways to keep employees healthy and insurance costs low, according to Hottovy. This week, Weight Watchers announced a new partnership with health-care company Humana Inc. to offer diet programs at discounted rates on certain health insurance plans. 
 
 “The largest growth opportunity for this company is partnering with corporations and health plans,” Hottovy said. “That’s where they’ll really have a more comprehensive offering. That’s something Weight Watchers can provide that calorie counting apps maybe can’t.” ||||| Photo 
 
 Wired Well Personal technology for health and fitness. 
 
 Every January for the past decade, Jessica Irish of Saline, Mich., has made the same New Year’s Resolution: to “cut out late night snacking and lose 30 pounds.” Like millions of Americans, Ms. Irish, 31, usually makes it about two weeks. 
 
 But this year is different. 
 
 “I’ve already lost 18 pounds,” she said, “and maintained my diet more consistently than ever. Even more amazing — I rarely even think about snacking at night anymore.” 
 
 Ms. Irish credits a new wearable device called Pavlok for doing what years of diets, weight-loss programs, expensive gyms and her own willpower could not. Whenever she takes a bite of the foods she wants to avoid, like chocolate or Cheez-Its, she uses the Pavlok to give herself a lightning-quick electric shock. 
 
 “Every time I took a bite, I zapped myself,” she said. “I did it five times on the first night, two times on the second night, and by the third day I didn’t have any cravings anymore.” 
 
 As the name suggests, the $199 Pavlok, worn on the wrist, uses the classic theory of Pavlovian conditioning to create a negative association with a specific action. Next time you smoke, bite your nails or eat junk food, one tap of the device or a smartphone app will deliver a shock. The zap lasts only a fraction of a second, though the severity of the shock is up to you. It can be set between 50 volts, which feels like a strong vibration, and 450 volts, which feels like getting stung by a bee with a stinger the size of an ice pick. (By comparison, a police Taser typically releases about 50,000 volts.) 
 
 Other gadgets and apps dabble in behavioral change by way of aversion therapy, such as the $49 MotivAider that is worn like a pager, or the $99 RE-vibe wristband. Both can be set to vibrate at specific intervals as a reminder of a habit to break or a goal to reach. The $80 Lumo Lift posture coach is a wearable disk that vibrates when you slouch. The $150 Spire clip-on sensor tracks physical activity and state of mind by detecting users’ breathing patterns. If it detects you’re stressed or anxious, it vibrates or sends a notification to your smartphone to take a deep breath. 
 
 But the Pavlok takes things a step further, delivering a much stronger message. 
 
 To test the device, I wore it for a week, zapping myself every time I ate dessert. My goal was to curb my craving for sweets after dinner. First I zapped myself before and after I ate a square of dark chocolate, and did it again later in the week after eating ice cream, a red velvet cupcake and a chocolate chip cookie. 
 
 Set on low, it feels like a strong tickle. Set on high, it hurts. A lot. 
 
 It should be noted that the creator of Pavlok, Maneesh Sethi, once hired a woman to sit next to him and slap him on the face every time she saw him using Facebook, so he could increase his productivity. I called Mr. Sethi and told him that if we ever met, I’d try not to punch him in the face for creating such an awful torture device. “Yeah, I get that a lot,” Mr. Sethi said with a chuckle. “People either love it or hate it.” 
 
 “It’s not designed to be painful,” he added. “It’s instantaneous, a surprise sensation, a shock that knocks you out of automatic mode.” 
 
 But does this kind of self-imposed aversion therapy actually work? 
 
 “The most clever thing about this gadget is the name,” said Dr. Peter Whybrow, a Los Angeles author, psychiatrist and neuroscientist. “It’s an expensive spin on the idea of wearing an elastic band that you snap on your wrist to stop a certain behavior.” 
 
 Dr. Marc Potenza, a professor of psychiatry at Yale, says researchers have questioned the ethical nature of shock intervention when more comfortable options like cognitive behavioral therapies, pharmaceutical interventions and 12-step programs are available. 
 
 The practice of aversion therapy has been around for 80 years. Schick Shadel Hospital, based in Seattle, reports that it has successfully treated more than 65,000 people for alcohol or drug addiction using counter-conditioning methods like emetic drugs, which make people feel nauseated if they drink alcohol, or supervised shock therapy. The hospital’s medical director, Dr. Kalyan Dandala, said that he was interested in using Pavlok to help people continue recovery once they finish the 10-day inpatient treatment, but added that the device should be professionally supervised. 
 
 “It’s better suited as a prescribed tool for behavior modification,” Dr. Dandala said. “The company needs to refine it, put more education in the tool, and have more oversight.” 
 
 Michelle Freedland, a psychiatric nurse practitioner in Manhattan, has worked with five patients who use the device for nail biting, addictions, compulsive behaviors and more. 
 
 “When one of my patients told me he was using it last year to help him get out of bed in the morning, I was skeptical at first,” she said. “I mean, the notion of being shocked — you can have a little reservation. But when you understand how to use it properly and people are more engaged in their own treatment, they tend to follow through with it more.” 
 
 Mr. Sethi, the founder, said the company had just begun to collect data on the long-term success of the device, and was planning a clinical trial later this spring. The Pavlok has been available since November, and he said about 10,000 people had used it. 
 
 Despite the potential for pain and the lack of science backing a long-term effect, user feedback on Facebook groups and message boards has been enthusiastic about the device, especially as a last resort for problems like overeating and binge drinking. 
 
 Bud Hennekes, 24, a blogger in St. Louis, said he had used Pavlok to kick a nearly two-pack-a-day cigarette habit. “When I tried to quit before, I still had the craving to smoke,” he said. “When I used Pavlok, the cravings completely went away. I don’t know if it’s science or a placebo effect or what, and I don’t really care because it worked.” 
 
 Related: ||||| Weight Loss On Your Wrist? Fitness Trackers May Not Help 
 
 Enlarge this image toggle caption Paul Marotta/Getty Images for Fitbit Paul Marotta/Getty Images for Fitbit 
 
 Fitness trackers remain wildly popular, but do they make us fit? Maybe not, according to a study that asked overweight or obese young adults to use the tiny tracking tools to lose weight. 
 
 The 470 people in the study were put on a low-calorie diet and asked to exercise more. They all started losing weight. Six months in, half the group members started self-reporting their diet and exercise. The other half were given fitness trackers to monitor their activity. 
 
 After two years, both groups were equally active. But the people with the fitness trackers lost less weight. 
 
 Wait. What? We asked John Jakicic, a researcher of health and physical activity at the University of Pittsburgh and the lead author on the study, why this could be. 
 
 "These technologies are focused on physical activity, like taking steps and getting your heart rate up," says Jakicic. "People would say, 'Oh, I exercised a lot today, now I can eat more.' And they might eat more than they otherwise would have." 
 
 It's also possible, he says, that meeting daily fitness goals and step counts might motivate one person, but missing those same goals could discourage another. 
 
 The device in the study, which was published Tuesday in JAMA, the journal of the American Medical Association, wasn't a wrist-tracker like the Fitbits, Jawbones, Apple watches and Nike bands many use now. This device was worn around the upper arm. Instead of using heart rate to estimate activity like some devices do, it measured the heat generated by exercise. 
 
 Still, he says, the results from this study are relevant to the devices of today. 
 
 Overall the participants without fitness trackers lost 13 pounds, while the tech-enhanced group lost 7.7 pounds. They ranged in age from 18 to 35 years and had BMIs from 25 to 39. The study hopes to see whether helping young adults lose weight early on can head off more weight gain in middle age. 
 
 We reached out to Fitbit to see what it thought of the study. 
 
 "We are confident in the positive results users have seen from the Fitbit platform, including our wearable devices," the company said in a statement, adding that researchers use Fitbits and similar devices in clinical studies. 
 
 While those studies use wearable technology to investigate everything from heart disease to breast cancer, very few have looked at how good these trackers actually are at helping people achieve fitness goals. 
 
 "There aren't many — if any — long-term studies of wearable tech," says Dr. Mitesh Patel, an assistant professor of medicine at the University of Pennsylvania. Patel also studies fitness trackers but was not involved in this study. This study, Patel says, is the longest yet, "and that's why this research is important. We need more studies like this to show what wearable tech can and can't do." 
 
 A handful of short-term studies have looked at fitness trackers, with mixed results. One study, also conducted by Jakicic, found that fitness trackers could replace counseling in a weight-loss program. But another found that users get bored and abandon their wristbands after just a few months. 
 
 Ultimately, Patel says, these devices are most effective when the people using them are already dedicated to tracking their fitness. People who are less motivated might not get the same results. 
 
 "Overall, it doesn't look like assigning someone wearable technology will make that big of a difference," says Jakicic. 
 
 So should you bin your Fitbit? Not yet. Jakicic thinks that combining this technology with behavioral research can help scientists figure out which groups of people benefit from fitness trackers and even design interfaces that will be more motivational. 
 
 "These devices have some really cool tech, but how do you use them in a way that helps people?" asks Jakicic. "That's a science in and of itself."
– The booming fitness-tracker trend is making it easier for people to track their activity and therefore lose weight, which is essentially what Weight Watchers has been trying to do since 1961. The company has encouraged subscribers to use devices like Fitbit and Jawbone—and even has its own ActiveLink device. But while use of such devices soar (VentureBeat in November pointed to research that estimated 19 million trackers were in use in 2014, with that number slated to triple by 2018), Weight Watchers' membership keeps falling. It sank 15% in Q4 to a hair over 2.5 million subscribers, who pay a minimum of $20 for the service; Bloomberg points out that once a user invests in a tracker, the associated tracking apps are free. In early 2013, Weight Watchers didn't seem concerned by wearable devices. It acknowledged a challenge "similar to what we saw back in 2000 with the low-carb diet fad" a few months later. Now it's taking a hit: Revenue slid 10% to $327.8 million in the fourth quarter, and as of yesterday its share price had declined 78% over three years. It expects profit of 40 cents to 70 cents per share in 2015, while analysts had estimated profit of $1.43 per share, the Wall Street Journal reports. The company has announced a deal with Humana to bring discounted diet programs to certain health insurance plans, which an analyst suggests is the company's best option, but it will also undergo cost-cutting measures, including layoffs, to save $100 million. North American President Lesya Lysyj has already been let go.