When is the best time of day to do your aerobic exercise? The answer is any time! The most important thing is that you just do it. Continuous cardiovascular cycling sustained for at least 30 minutes, will burn body fat no matter when you do it as long as you stay within your correct “fat burning zone” However, if you want to get the maximum benefits possible from every minute you invest in your workouts, then you should consider getting up early and doing cardio before you eat your first meal - even if you're not a "morning person." Early morning cycling on an empty stomach has major advantages over exercising later in the day..
Early in the morning before you eat, your levels of muscle and liver glycogen (stored carbohydrate) are low. If you eat dinner at 7 p.m and you eat breakfast at 7 a.m., that's 12 hours without food. During this 12-hour overnight fast, your levels of glycogen slowly decline to provide glucose for various bodily functions that go on even while you sleep. As a result, you wake up in the morning with depleted glycogen and lower blood sugar - the optimum environment for burning fat instead of carbohydrate. How much more fat you'll burn is uncertain, but some studies have suggested that up to 300% more fat is burned when cardio is done in a fasted, glycogen-depleted state. So how exactly does this work? It's quite simple, really. Carbohydrate (glycogen) is your body's primary and preferred energy source. When your primary fuel source is in short supply, this forces your body to tap into its secondary or reserve energy source; body fat. If you ride your bike immediately after eating a meal, you'll still burn fat, but you'll burn less of it because you'll be burning off the carbohydrates you ate first. You always burn a combination of fat and carbohydrate for fuel, but depending on when you ride, you can burn a greater proportion of fat relative to carbohydrate.
Early morning riding creates a "afterburn" effect. When you ride your bicycle in the morning, you not only burn fat during the session, but you also continue to burn fat at an accelerated rate after the ride. This is because your morning cycling ride can keep your metabolism elevated for hours after the session is over. If you do your riding cardio at night, you will still burn fat during the session, so you definitely benefit from it. However, night-time riding fails to take advantage of the "afterburn" effect because your metabolism drops as soon as you go to sleep. Note: This is really good reason not to eat a carbohydrate meal in the evening. While you sleep, your metabolic rate is slower than any other time of the day. Burning fat isn't the only reason you should ride your bicycle in the morning. So, you say you're not a morning person? Remember, the effort is worth the results. Make a commitment to yourself to do it for just 21 days. Once those 21 days have gone by, you'll already be leaner and you'll be on your way to making morning workouts a habit that's as natural as brushing your teeth or taking a shower. Once you start getting used to feeling that buzz, you'll become "positively addicted" to it. The more you do it, the more you'll want to do it. Before you know it that early mornings ride will have you leaned-up in no time and you'll feel fantastic all day long!
Content for this article was adapted from information sourced from http://www.buildingbodies.ca/Cardio/early-morning-cardio.shtml, http://www.weightlossforall.com/burning%20fat%20time.htm, http://www.healthrecipes.com/fat.htm and http://www.womenfitness.net/cardiotiming.htm