When running long distances for hours at a time, glycogen stores in the liver and muscles run low. In response, the body relies on the three types of Branched Chain Amino Acids (leucine, isoleucine, and valine) for fuel. Since the body can't produce BCAAs on its own, you need to get them from what you take in during a long run. BCAAs help promote muscle repair as well as growth, and reduce muscle soreness after exercise, however, while BCAAs may make you feel less tired after a workout, they generally don’t improve athletic performance. The BCAA leucine does enhance fat burning and balance blood sugar levels.
Athletes today consume more and diverse ergogenic aids to improve the density of skeletal muscle and exercise performance. As prolonged exercise depletes carbohydrate and mobilizes fat as an energy source, fat acts as an important energy substrate for muscle function. In order to improve exercise performance, carbohydrates and amino acids which are the source of protein, especially BCAAs, are critical. Amino acids help enhance metabolism which promotes cell proliferation and improve exercise performance as well as functional recovery during exercise. Also, they help perform better by contributing as the energy source and reducing the accumulation of serotonin, the central fatigue substance that accumulates during prolonged exercise.
Blood creatine kinase and blood lactate dehydrogenase concentrations are the indicators that reflect the degree of muscle damage and physical fitness from long-term physical activity. Creatine kinase is the main enzyme that controls the ATP-PC system and lactate dehydrogenase is the main enzyme that maintains the balance of sugar catabolism and anabolism. Both of these concentrations decrease after exercise for a long period of time after following a common diet. Taking BCAAs improves maximal oxygen uptake and lowers the concentrations of both.
Free fat acid, which is released from the adipose tissue to produce energy, is a major source of energy during exercise that requires long-term endurance. The amount of free fat acid during exercise or after exercise is totally affected by glycerol. Muscle capillaries are extended at the beginning of exercise to promote the use of free fat acid and this metabolic phenomenon concludes at the end of the exercise.
Glucose has a basic role in carbohydrate metabolism of skeletal muscle and is generated from muscle glycogen and blood. In particular, glucose produced from the liver during exercise with intensity of about 60 percent of maximal oxygen uptake starts to decrease around 90 minutes after the exercise begins, at which point glycogen stored in the liver is mobilized. However, when BCAAs are ingested, the BCAAs move to the muscle and are oxidized to supply additional energy. As a result, the amount of glycogen that is decomposed in the liver and released as glucose into the blood is reduced and accordingly. It has often been reported that the intake of BCAAs helps to prevent physical performance from deteriorating as quickly, which is usually caused by muscle glycogen depletion in the later stages of endurance exercises.
More research regarding the dosage of BCAAs needs to be performed under varying forms of exercise, as well as with changes in fatigue substances, muscle damage substances, and energy metabolism substances. Thus, how much and when to take BCAAs is still pretty much an individual experiment of one. I am currently experimenting with Scivation's Xtend Go to enhance performance during one hundred mile efforts and Hammer Nutrition's Endurance BCAA+ during 20-mile training runs.