Workout Timing 

Someone once said that no matter what facts you want to prove, you can always find a scientific study that proves—or disproves—them. That’s especially true of this week’s topic: the best time to do certain kinds of training.

Some studies say working out before bedtime is a bad idea; others say that it’s the best time for resistance work. Some studies say aerobics in the morning burns the most fat; others say it makes no difference. When it comes to conflicting studies, there’s only one way to learn which offer the most accurate information: Check the actual science with an expert in the field.

James Walker, Ph.D., is definitely a hands-on expert. He’s the sport science director at The Orthopedic Specialty Hospital (TOSH) in Murray, known for its training programs for elite athletes and the advanced physical therapy that restores injured athletes to their previous elite levels.

Walker, who has worked with many Olympians, says the human body’s hormonal cycles determine the best time to do specific kinds of training. Those cycles indicate that the most advantageous time to do aerobics is in the morning, before breakfast. At the same time, athletes and others will get the biggest benefit from resistance work when it’s done in the evening, close to bedtime.

Walker explains the science: “In the morning, you’ve basically fasted all night, so your sugar levels would be down. So, if you run or do other aerobics before breaking that fast, the preferred fuel [used for energy] would be fat. You would be more likely to burn fat if you do your aerobics before breakfast in the morning, especially if you drink some kind of caffeine before you start. That’s because caffeine releases free fatty acids into the bloodstream, where they are used for energy. That’s why [many] athletes drink caffeine before an event.”

The caffeine can be from coffee, tea or a sports drink. Walker says the form doesn’t matter, as long as it’s not carbonated (more about carbonation and bloodstream CO2 in a future column). But there’s another advantage to doing an aerobic workout before breakfast: Eating releases insulin, which dramatically slows down the mobilization of fat. Worse, if you eat before working out, you then have to burn off the calories from that food before your body gets around to burning your stored fat—and the process is further slowed by the insulin release.

With or without breakfast, Walker says that another benefit of doing aerobics in the morning is that it raises your metabolism, especially if you get intense. He says, “If you do low-intensity exercise, your metabolism will only stay up for so long. But if you drive up your heart rate, your metabolism will stay elevated longer. As intensity goes up, muscles get warmer and it takes longer to recover from the exercise. The repair and clearing of waste products that have been formed, and the recovery from oxygen deficit, all keep the metabolism elevated.”

Of course, that higher metabolic rate keeps on burning calories much faster, and it will stay elevated for many hours after you’ve stopped exercising.

Meanwhile, there are verifiably good scientific reasons to do weightlifting in the evening, especially if you want to tone your body or build bulk. (Note: It takes testosterone to build bulky muscles, so men get big, but women don’t.) As you push or pull your muscles against resistance, you use up the cellular energy in your muscles, leaving them exhausted—and hungry. “The first couple of hours after you go to sleep is when the most growth hormone is released. That builds your strength at night,” Walker says.

The main advantage is this: If your body is producing its largest amount of growth hormone just at the time when your muscle cells are most hungry and ready to absorb it, none of this valuable hormone goes to waste. Your needy muscles use it all. You get stronger a lot faster by scheduling your workouts for the optimum time your hormones can help you reach your goals.