Exhausted runner trying to catch his breath.

In order to perform your best as a runner, you need to eat the right kinds of carbohydrates at the right times. That’s because carbohydrates are the major precursor of muscle glycogen, one of the major sources of “fuel” for running. However, this does not tell the whole glycogen story. Glycogen’s role in our bodies is much more than just a good source of fuel. It actually plays an important part in a whole array of other essential body functions. Here are six little-known, but important, reasons to pay closer attention to your carbohydrate intake levels – however far or fast you run:

1. Glycogen reduces muscle damage and soreness.

Muscle damage and soreness can be the most significant physiological effects of longer and higher-intensity runs. That noticeable, and sometimes severe, stiffness or soreness you feel after a longer-than-usual run or after an unaccustomed downhill run is a sign of physical muscle damage. This is caused by what are called eccentric movements, where muscles lengthen while contracting. It happens every time your foot hits the floor during a run, and especially when you are going downhill and using your legs to control or slow your momentum. Eccentric exercise causes tiny tears in muscle fibers, resulting in something known as delayed onset muscle soreness, or DOMS. This is the pain and discomfort you typically feel 24 to 72 hours after exercise and that lasts for several days. You can reduce the impact of DOMS by eating a combination of high-quality carbohydrates combined with protein both during and after exercise.

[See: 5 Unintended Consequences of Eating Too Much Protein.]

2. Carbohydrates support the immune system.

When you perform higher-intensity exercise, your blood produces more of the hormone cortisol. In effect, your immune system is suppressed and your body releases fewer antibodies, or specialized proteins released by the immune system that identify and neutralize foreign objects such as bacteria and viruses. However, when you eat carbohydrates during and after exercise, the body releases insulin, which counteracts the negative impact of cortisol on the immune system. In other words, you become more resistant to infection.

3. Ideal glycogen levels improve muscle building and recovery.

Whether or not you use resistance training as part of your workout, consuming a combination of carbohydrate and protein after you exercise will enhance your muscle growth and recovery, as well as maximize your glycogen levels. It will also boost insulin levels, which in turn increases blood flow to your muscles. This process flushes out waste products faster, resulting in increased protein synthesis, which means your muscles rebuild and recover faster. By the way, eating a 3:1 or 4:1 ratio of carbohydrates to protein is far more effective than taking either nutrient alone, since this combination gives you a “twofer”: It will maximize your glycogen stores at the same time as speeding your muscle recovery.

4. Glycogen powers muscle contractions.

Recent evidence has shown that glycogen, in addition to being an energy reserve, has an important role to play in maintaining optimal levels of muscle contraction. As your levels of muscle glycogen fall, so too does your capacity to produce force. You feel fatigued, even though your glycogen stores are still sufficient to provide fuel for energy. So, you may struggle to power up the hill, but still be able to maintain a steady pace for a while once you are back on level ground. Ensuring optimal glycogen stores will keep your muscle force higher, longer.

[See: 12 Psychological Tricks to Get You Through a Workout or Race.]

5. The right glycogen levels reduce your risk of injury.

Running for extended periods with low glycogen levels not only leads to early fatigue, but also may increase the risk of muscle injury. As your muscles start to run out of glycogen, they use their own protein for energy since they have to get fuel from somewhere. In essence, the muscle “eats itself to feed itself.” If this process continues, the risk of muscle injury increases. To make things worse, a damaged or injured muscle will not hold the same levels of glycogen as a healthy muscle – even with a high-carbohydrate diet. This can lead to bilateral differences in muscle contraction and fatigue (say, if you wind up favoring your right leg over your left), which further increases your potential risk of injury.

[See: 8 Lesser-Known Ways to Ruin Your Joints.]

6. Good sleep leads to good glycogen usage.

Trainers and athletes alike understand the importance of sleep, but its connection to glycogen is less well-known. Lack of sleep increases levels of hormones like cortisol, which breaks down muscle tissue. Lack of sleep also reduces levels of hormones like testosterone, which rebuilds muscle tissue and increases glycogen uptake. So, in brief, lack of sleep means lack of glycogen. Everything starts to feel that much harder, fatigue sets in earlier and running performance decreases. Other consequences of lack of sleep include slowed injury repair and tissue recovery, which can delay a return to training or competition. So get those early nights in before the longer runs! Already feeling good about your runs and recovery? Congratulations – you can also feel good that these other benefits are kicking in under the hood.