Muscular fatigue and soreness are inevitable after intense workouts -- thus the emphasized importance on recovery days by coaches.
Cutting-edge scientific research also has shown that use of certain nutritional strategies during training can minimize muscle damage and aid quick muscle recovery, ultimately helping to rejuvenate your muscles for peak performance at your next workout.
Here's the latest scoop ...
While it would be nice if we all had an unlimited supply of glycogen to rely on during prolonged training bouts, the truth is that well-nourished athletes only have the capacity to store 1,500 - 2,000 calories of glycogen, which is enough to support approximately 2 - 3 hours of training.
Therefore the goal is to spare muscle glycogen and protein while soaking up the ever-so-abundant supply of energy available from fat (~100,000 calories). Training does enhance our body's ability to utilize fat as a fuel; yet nutrition becomes of paramount importance during runs extending beyond 25 kilometers or workouts lasting greater than 2 hours.
Unfortunately, because the maximum carbohydrate absorption rate during prolonged training falls about 50% short of the depletion rate from our muscles and liver, the body begins to use amino acids (which are supplied via breakdown of muscle protein) as an energy source in the later stages of a workout.
In fact, during extended exercise, up to 15% of the working muscles' total energy needs may come from protein. This can lead to significant net muscle protein loss during workouts, increasing the athlete's susceptibility to muscle damage, potential injury, and slowed recovery.
In order to replenish muscle glycogen stores and prevent muscle protein breakdown, it is essential to start refueling your engine with carbohydrates beyond 60 minutes of high-intensity training and 90 minutes of aerobic-based training.
While there is some evidence showing the benefits of protein use during endurance training, carbohydrate, not protein, remains the primary energy source for muscle and brain during exercise. In fact, many scientists discourage the use of protein during exercise since protein can slow gastric emptying if not consumed correctly, and it can negatively affect taste acceptance and consequent fluid consumption, thereby leading to dehydration.
Furthermore, there is conflicting evidence with regards to the actual benefits of protein. While Saunders et al discovered that cycling time to exhaustion and evidence of post-workout muscle damage were significantly lower when athletes consumed a carbohydrate-protein beverage in a 4:1 ratio (M.J. Saunders et al. "Effects of carbohydrate protein beverage on cycling endurance and muscle damage." Med Sci Sports Exerc. 36(7): 1233-1238, 2004.), a very similar study presented by the same research group at the 2004 American College of Sports Medicine Meeting showed no additional performance benefit of a carbohydrate-protein mixture. (B.C. Romano et al. "Effect of 4:1 ratio of carbohydrate/protein beverage on endurance performance, muscle damage and recovery." Med Sci Sports Exerc. 36(5): S126, 2004.)