What Marijuana Might Do to Your Brain

The stoner character may be more than stereotype: Smoking pot may actually make you lazy. Occasional marijuana use can affect your motivation, according to a recent study from Harvard Medical School.

Out of 40 college students, the half who smoked pot once or twice a week for a few months showed more changes in the brain areas regulating emotion, mental illness, and motivation than the drug-free undergrads. “Your motivation levels determine whether or not you get out of bed in the morning,” says study coauthor Anne Blood, Ph.D. "And we're seeing some pretty convincing changes in these regions.”

The Easiest Way to Keep Off Weight

Good news for your waistline: A shot of sunshine in the morning may lower your body mass index (BMI), according to a new study from Northwestern University's Feinberg School of Medicine.

Regardless of an individual's physical activity level, diet, sleep, or age, people who had most of their daily exposure to natural light between 8 a.m. and noon had significantly lower BMIs than those who got most of their exposure later in the day.

The reason: Natural light provides a boost to your circadian rhythms—or your body's internal clock—which is known to regulate your metabolism, hunger, and energy levels, says co-lead author, Giovanni Santostasi, Ph.D. In fact, previous studies have found that constant exposure to bright light later in the afternoon or at night can throw off your circadian clock and increase your risk of obesity.

The Worst Work Hours for Your Health

Bad news if you burn the midnight oil: People who regularly work night shifts are twice as likely to have diabetes, finds new research from the University of Pittsburgh.

And the risk remains even after they've retired and returned to a normal sleeping schedule.

How come? Previous research shows that messing with your biological clock and limiting sleep can lead to decreased resting metabolic rates and increased blood glucose concentrations, which set the stage for diabetes and other diseases, says study author Timothy Monk, Ph.D.

Are You Overhydrated?

You've heard it since you were a kid, from your parents to your gym teacher: Drink two liters (or eight glasses) of water every day. Lately, though, researchers have been questioning the tried-and-true water rule, and in fact, believe even health-minded individuals could be drinking too much H2O.

“There’s no scientific method behind those numbers,” says exercise physiologist Stacy Sims, Ph.D., a hydration researcher at Stanford University. “And the recommendation doesn’t take into account gender, environment, altitude, fitness level—factors that could affect fluid intake needs.”

In fact, there’s a lot of marketing behind popular hydration recommendations, Sims says—with potentially dangerous consequences. “Drinking too much fluid can lead to hyponatremia, which is when sodium in blood becomes too diluted,” Sims says.

How to Boost Desire in a Long-Term Relationship

When you've been with the same partner for a long time, there will inevitably be times when you want to climb them like a tree and times that you just don't. It's totally normal.

That said, mismatched libidos can sometimes become a bigger problem and lead to stress in a relationship—not to mention a lack of satisfaction. So researchers aimed to find out what strategies women were using to manage sexual desire differences in their bond and if any of them were particularly useful.

The Difference Between Slow and Fast Weight Training

Just like the beats of reggae versus merengue, your weight-training rhythms—a.k.a. the tempos at which you perform your reps—don't affect your body the same way. Look around the weight room and you'll see folks doing everything from long drawn-out movements to Energizer bunny-style repetitions. So who's got the right idea? As with many fitness questions, it's not so hard and fast. We talked to two trainers with different takes to get the lowdown on slow and quick strength-training speeds:

Should You Slow It Down?
The trainer: Ellington Darden, Ph.D., weightlifting guru and author of The Body Fat Breakthrough
The argument: It's great for building strength, and safer for beginners.

Should You Mix Walking Into Your Runs?

Do you know how to run-walk? You see, there's more to a run-walk training plan than just running until you have to walk: It's actually a technique that uses a mix of running and walking intervals to reduce impact on your body, build up your base level of fitness, boost speed, and help you recover more efficiently.

Sounds like magic, right? It's pretty simple: By walking every few minutes, you're adding valuable recovery time to your run. That means that instead of exhausting your body with long runs, you have time to slow down, catch your breath—and approach the next interval with more speed and energy.

Run-walk is an awesome strategy for beginner runners: Not only do you get to physically slow down and regroup during the walking intervals, but by breaking the run down into small increments, longer runs can seem more manageable, says Jenny Hadfield, running coach and author of Running for Mortals.

The Running Test You Should Be Able to Pass

Back in grade school, you ran one mile for the President's Challenge Physical Fitness Test to show how aerobically fit you were. As an adult, you’re lucky if sprinting on the basketball court or chasing your kids across the lawn doesn’t leave you sucking wind. But holding your own during a short run is important as you get older. Regular aerobic exercise reduces your risk of heart disease and helps keep your body fat low.

Test yourself with a 1.5-mile run on a flat road or track. “It’s a good predictor for your work capacity, ability to recover quickly, and do more work in general,” says Steve Di Tomaso, C.S.C.S., endurance athlete and strength coach for Envision Fitness in Maple Ridge, British Columbia, Canada. Compare your time to the average guy in your age group. If you fall short or want to be better than average, add Di Tomaso’s running and strength workouts to your routine to increase your gains.