However, if you feel as if you're sleeping away your entire weekend, here are a few things to keep in mind:
Make sure you're eating properly, especially after your runs. After running, especially a long run, you want to replenish energy as quickly as possible. Muscles are most receptive to rebuilding glycogen (stored glucose) stores within the first 30 minutes after exercise. If you eat soon after your workout, you can minimize muscle stiffness and soreness, and help reduce your fatigue.
After your runs, you'll want to consume primarily carbs, but don't ignore protein. A good rule of thumb for post-run food is a ratio of 1 gram of protein to 3 grams of carbs. Nutrition bars, such as Clif bars or Power bars, are healthy options. Other examples would be a bagel with peanut butter or a smoothie made with fruit and yogurt. Many runners like to drink chocolate milk after a long run, which also has the right carbs to protein ratio.
Get enough sleep during the week. Aim for 7-8 quality hours of sleep a night -- the right amount for most adults. Getting very little sleep during the week and trying to "catch up" on the weekends is not a good idea because it alters your sleep schedule. Your body is forced to adjust to these changes and, as a result, your quality of sleep is poor. Try to establish a more consistent daily sleep schedule.
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Make sure you're not overtraining. Running too many miles and not giving yourself any rest days will definitely leave you feel exhausted most of the time. Don't let your weekly mileage increase by more than 10%. Also, try to give yourself periodic "rest weeks" by dropping your mileage by 50% every fourth week. After a hard run, take a rest day. In addition, you should work some cross-training activities to your schedule. Doing activities other than running prevents boredom, works different muscles, and can give your running muscles and joints a break.