If you can run 10 miles, why can't you run 20? Why do you "hit the wall" even if you are still aerobic? Your muscles, along with the amount of food and oxygen supply you have, all interact to give you an extra push of muscle endurance. All are equally important for the long-distance runner or bicyclist regardless of age, amount of muscle tissue, gender and vital capacity.
Fuel for the muscles is in the form of muscle glycogen; better known as muscle sugar. Within the muscle, lying ready for use, is the glycogen stored from the day before. What you have eaten 12 hours before exercise is the supply of muscle sugar you have available for use at a given time. Fuel delivered to your muscles via the blood stream while you are exercising is quite small, so most of your required energy will come from those 12 hours before exercise.
When your muscles relax or lengthen, the blood supply to those muscles increases, and when you contract or shorten the muscles, the blood supply is restricted. This pumping action is what boosts the blood supply to the muscles and thus adds to the oxygen store. Oxygen is the other important ingredient for muscle endurance. When your muscle sugar burns while you run, you give off a chemical called pyruvate. If you are aerobic, or taking in enough oxygen to not be breathless, this pyruvate will convert to carbon dioxide and water and leave via the lungs when you exhale. However, if you are having trouble breathing in a regular pattern, and feel the need for more oxygen, you become anaerobic, creating what is called oxygen debt. Now, the pyruvate is being converted into lactic acid and builds up in muscle tissue, also ending up in the bloodstream. Lactic acid impedes the contacting of muscles and will eventually bring a stop to your long-distance run.
Working on muscle endurance is important in any sport you choose. Prolonged use of a specific muscle group for a specific sport is usually a factor of winning in that sport. That is where the term "sport specific training" comes from. If you need greater arm strength for baseball, or greater leg strength for skiing, you work on enhancing those muscle groups to retain more muscle sugar and on endurance training to take in greater amounts of oxygen.
Overheating can also be a factor in the amount of time you can use a muscle, and the lack of fat reserves to break down into glycogen can be a contributing factor to muscle weakness.
Simply put, eat a good, nourishing, well-balanced diet, high in carbohydrates and low in fat. Expand your aerobic training rate so more oxygen enters your bloodstream. Drink plenty of water to cool those muscles while you work out and slow down if you become anaerobic so you can rid your muscles of lactic acid.
• Jerry Vance is the owner of Sweat Shop/Wet Sweat. She offers classes through the Carson City Recreation and Aquatics Center and is a fitness instructor for the Carson City Senior Citizens Center.