In 1960, President-Elect John F. Kennedy wrote an article for Sports Illustrated called “The Soft American,” lamenting the declining role of physical activity in everyday life. “Today human activity, the labor of the human body, is rapidly being engineered out of working life,” he wrote. “By the 1970s, according to many economists, the man who works with his hands will be almost extinct.” That prediction didn’t quite pan out—but it’s certainly true that, for most of us, physical activity is now a choice rather than the necessity it was for our ancestors. Kennedy was concerned that Americans wouldn’t have the “vigor and determination” necessary to match the Soviet Union; today, we’ve realized that physical fitness is essential to the health of our bodies and minds. But the basic challenge remains the same: if you’ve just begun working out recently, or you’re about to head to the gym for the first time, you need to know what to expect. How hard to push, how long it will take to see results, how to make the most of your workout time, how to minimize the risks associated with starting an exercise program—these are the issues you should consider before getting started.

How long does it take to get in shape?
First, the good news. Your body actually starts getting stronger and healthier just hours after you start working out. But if you’re wondering how long it will take to rock a six-pack—well, you’ll have to be a bit more patient. A few years ago, exercise scientist Megan Anderson and her colleagues at the University of Wisconsin-La Crosse put 25 sedentary volunteers through an intense six-week exercise program modeled on the bold claims made by companies such as Bowflex and Body-for-Life. Despite sticking to the program religiously, zero percent of the subjects developed instant washboard abs. In fact, a panel of six judges could detect no differences whatsoever in their physical attractiveness before and after the program.

That doesn’t mean nothing was happening. After just a few strength training sessions, your brain learns to recruit more muscle fibers and make them contract all at once to produce a greater force. This “neural activation” kicks in after only a few workouts, allowing you to get stronger almost immediately, well before your muscles get noticeably bigger. Further strength gains come as the individual muscle fibers within your muscles get bigger, which starts in as little as two weeks if you’re training intensely. But it takes longer for these changes to be noticeable: even with sophisticated lab equipment, researchers can’t usually detect changes in fat and muscle composition until after about nine weeks of training. Similarly, a University of Tokyo study published in 2010 saw the biggest increases in strength after two months and the biggest boost in muscle size after three months. To achieve these rapid gains, the subjects were doing four very hard workouts a week. For the average person at the gym, it will take six months or more to see significant sculpting of the body even though strength has been increasing from day one.

Weight loss is more difficult to predict, because it depends on your starting point, your health history, your genetics, and your diet as well as your workout routine. But like strength training, aerobic exercise produces major health and performance benefits long before you see them in the mirror. Aerobic exercise increases the number of mitochondria, which are essentially the “cellular power plants” in your muscles that use oxygen to produce energy: the more mitochondria you have, the farther and faster you can run, and the more fat your muscles will burn. Studies have found that about six weeks of training will boost mitochondria levels by 50 to 100 percent.

Health benefits, on the other hand, kick in after a single bout of aerobic exercise. For about 48 hours after a workout, your muscles will be consuming more glucose than usual, helping to bring down blood-sugar levels. After a few workouts, your insulin sensitivity will begin to improve, offering further control of blood sugar.

The bottom line: “Getting in shape” is a journey that extends over months and even years, but the process—and the benefits— start as soon as you begin exercising. So if you’re having trouble staying motivated without immediate physical changes, track your strength and endurance gains along the way.

Am I exercising enough?
This is a hugely controversial question, but not in the way you might expect. Almost all experts agree about what the science says—but they’re bitterly divided about what message they should convey to the public. Decades of research have made two things crystal clear:
1. Every bit of exercise helps, even in scraps as short as 10 minutes.
2. More is almost always better.

The challenge is conveying the second message without discouraging the people who are still struggling with the first. And there are a lot of people struggling: in 2008, the Centers for Disease Control and Prevention found that a quarter of Americans hadn’t done any physical activity at all in the previous month. And less than half met the modest government mandated Healthy People 2010 goal of 30 minutes of moderate exercise five times a week. In Canada, only a third of people are meeting a similar goal of 30 minutes at a moderate effort, four times a week.

From a public health perspective, the top priority is getting those inactive people to start moving, even a little bit. Going from zero to slightly active offers the biggest possible health boost, according to a recent National Institutes of Health study that followed 250,000 men and women between the ages of 50 and 71. Those who were just slightly active but didn’t manage to meet the exercise guidelines were 30 percent less likely to die than those who were totally inactive. Stepping it up to moderate exercise reduced risk by only eight more percent, and adding in some vigorous exercise subtracted an additional 12 percent. When you combine that data, you find that getting half an hour of moderate to vigorous exercise five times a week cuts your risk of dying from all causes in half. So far, so good. The controversy starts when you ask what happens if you do more exercise than the government guidelines recommend. According to researchers like Paul Williams of the Lawrence Berkeley National Laboratory, you keep piling up more and more benefits. Williams has been following a cohort of 120,000 runners since 1991, tracking how much they run and what happens to their health. With this enormous sample size, his National Runners’ Health Study has been able to uncover a pronounced “dose–response” relationship between aerobic exercise and health: the more you do, and the harder you do it, the more benefits you get.

What kind of benefits, you ask? Well, in a series of studies stretching back over a decade, Williams has found that the risk of everything from big killers like diabetes, stroke, and heart attack to less common conditions like glaucoma, cataracts, and macular degeneration can be reduced by as much as 70 percent by going beyond the standard exercise guidelines. In every case, the benefits relate to both how much running the subjects do and how fast they do it. For example, every additional mile in your average daily run lowers your glaucoma risk by 8 percent. And speeding up your 10K time by one meter per second (the difference between, say, finishing times of 53 minutes and 40 minutes) lowers heart attack risk by about 50 percent.

It is true that overdoing your workout regimen can weaken your immune system (see p. 23), especially if you’re not eating and sleeping well. And elite athletes training for hours a day at extremely high intensities sometime suffer from “overtraining” syndrome. But the message of Williams’s research is that the risks of doing too much—and these results apply to all forms of aerobic exercise, not just running—pale in comparison to the benefits of doing a bit more.

Which should I do first: cardio or weights?
Let’s start with one incontrovertible fact: you can’t fulfill your ultimate potential as both a weightlifter and a marathoner at the same time. Too many hours sweating on the elliptical will hinder your ability to put on muscle, and pumping too much iron will slow your endurance gains. But most of us don’t want Olympic medals in both events. We just want some combination of reasonable cardiovascular fitness and non-vanishing muscles—a desire shared by many elite athletes. Top basketball players, for instance, need strength and explosiveness but also have to last for a full 40 to 60 minutes on the court.

The solution, according to Derek Hansen, the head coach for strength and conditioning at Simon Fraser University in Vancouver, British Columbia, and a speed consultant to numerous Olympic athletes, is to mix it up. For basketball players, he says, “we typically have our athletes lift weights, jump, and sprint one day, then do their aerobic work the next day.” When Hansen’s court-sport athletes are combining weight training with cardio in a single session, the weights come first, since building power is their first priority.

This approach—starting with whichever activity is most important to you—is widely used by elite athletes. Until recently, scientists thought it was simply a matter of logistics: if you’re tired from the treadmill, you can’t lift as much weight, so over time you put on less muscle. But new techniques now allow researchers to directly measure which specific proteins are produced in muscles after different types of exercises. It turns out that the sequence of cellular events that leads to bigger muscles is determined in part by the same “master switch”—an enzyme called amp kinase— that controls adaptations for better endurance. But you can’t have it both ways: the switch is set either to “bigger muscles” or to “better endurance,” and the body can’t instantly change from one setting to the other. How you start your workout determines which way the switch will be set for the session.

So if your goal is beach muscles, your weights routine should come first. If you’re preparing for an upcoming 5K race, do your full cardio workout before tacking on weights at the end. And if you’re looking for the best of both worlds, Hansen suggests mixing it up, both within a single session and from day to day: “The variability will be good, as it challenges your body and metabolism.”

Can I get fit in seven minutes a week?
Breathless claims about exercise regimens that produce near instant results with minimal effort are generally the domain of late-night infomercials. So it might seem surprising that one of the hot topics at the American College of Sports Medicine’s annual meeting over the last few years has been research into “high-intensity interval training” (hit), whose proponents suggest that many of the benefits of traditional endurance training can be achieved with a few short bouts of intense exercise totaling as little as seven minutes a week.

Exercise physiologist Martin Gibala and his colleagues at McMaster University in Hamilton, Ontario, have performed a remarkable series of studies in which their subjects cycle as hard as they can for 30 seconds, then rest for four minutes, and repeat four to six times. They do this short workout three times a week. “The gains are quite substantial,” Gibala says. Compared to control subjects who cycle continuously for up to an hour a day, five times a week, the hit subjects show similar gains in exercise capacity, muscle metabolism, and cardiovascular fitness. In fact, the group’s latest study shows that hit improves the structure and function of key arteries that deliver blood to the muscles and heart—just like typical cardio training. Similar studies by University of Guelph researcher Jason Talanian have found that high-intensity interval training also increases the body’s ability to burn fat, an effect that persists even during lower-intensity activities following the interval training.

The results are no surprise to elite cyclists, runners, and swimmers, who have relied on interval training for decades to achieve peak performance. To break the four-minute mile in 1954, Roger Bannister famously relied on interval sessions of ten 60-second sprints separated by two minutes of rest, because his duties as a medical student on clinical rotation limited his training time to half an hour a day at lunch. Such time constraints are the main reason Gibala advocates hit, since studies consistently find that lack of time is the top reason that people don’t manage to get the 30 minutes of daily exercise recommended by public health guidelines. “We’re not saying that it’s a panacea that has all the benefits of endurance training,” he says. “But it’s a way that people can get away with less.”

More recent studies have started to piece together exactly how hit sessions work. A study at the University of Western Ontario compared volunteers who ran four to six 30-second sprints with four minutes’ rest (just like Gibala’s hit workout for cycling) with another group running steadily for 30 to 60 minutes at a time. After six weeks of training three times a week, both groups made identical gains in endurance and lost similar amounts of fat. In the “long runs” group, the endurance gains came from increases in the amount of blood pumped by the heart; in the hit group, almost all the gains came from the muscles themselves, which improved their ability to extract oxygen from circulating blood. Since it’s important to have a healthy heart and healthy muscles, this suggests you shouldn’t rely exclusively on hit workouts. As with cardio and weights, a mixture is best.

High-intensity exercise is generally thought to carry some risks, so sedentary or older people should check with a doctor before trying hit. Interestingly, though, University of British Columbia researcher Darren Warburton has studied hit training in cancer and heart disease patients and found that these higher-risk populations can also benefit safely from hit. There is one catch—the disclaimer at the end of the infomercial, if you will. To cram the benefits of an hour-long workout into a few short minutes, you also have to compress the effort you would have spent. “That’s the trade-off,” Gibala says. “Going all out is uncomfortable. It hurts.” But at least with this approach, it’s over quickly.