fast-twitch muscle fibers – Muscle fibers that contract and fatigue rapidly to power intense short-term exercise such as sprinting. They’re classified into two categories, A and B; fast-twitch A fibers have more of the characteristics of slow-twitch fibers than do fast-twitch B. Although your fast-twitch muscle fibers can’t be converted to slow-twitch fibers, with general endurance training your fast-twitch A fibers gain more of the characteristics of slow-twitch fibers. These adaptations are beneficial because your fast-twitch fibers then become better at producing energy aerobically.
glycogen – The storage form of carbohydrate in your muscles and the main source of energy during running. Endurance training reduces your body’s need to burn glycogen at a given pace and teaches your body to store more glycogen.
hemoglobin – A red blood cell protein that carries oxygen in the blood. The higher your hemoglobin content, the more oxygen that can be carried (per unit of blood) to your muscles to produce energy aerobically.
lactate threshold – The exercise intensity above which your rate of lactate production is substantially greater than your rate of lactate clearance. At effort levels above your lactate threshold, the lactate concentration rises in your muscles and blood. The hydrogen ions associated with lactate production inactivate the enzymes for energy production and may interfere with the uptake of calcium, thereby reducing the muscles’ ability to contract. You can’t, therefore, maintain a pace faster than your lactate-threshold pace for more than a few miles. For well-trained runners, lactate threshold usually occurs at 15K to half marathon race pace.
maximal heart rate – The highest heart rate you can attain during all-out running. Your maximal heart rate is determined genetically. In other words, it doesn’t increase with training. Successful marathoners don’t have particularly high maximal heart rates, so it isn’t a factor in determining success.
maximal oxygen uptake – Commonly referred to as
O2max; the maximal amount of oxygen your heart can pump to your muscles and your muscles can then use to produce energy. The combination of your training and your genetics determines how high a
O2max you have.
mitochondria – The only part of your muscle fibers in which energy can be produced aerobically. Think of them as the aerobic energy factories in your muscle fibers. The right types of training increase the size of your mitochondria (i.e., make bigger factories) and the number of mitochondria (i.e., make more factories) in your muscle fibers.
running economy – How fast you can run using a given amount of oxygen. If you can run faster than another athlete while using the same amount of oxygen, then you have better running economy. Running economy can also be looked at as how much oxygen is required to run at a given speed. If you use less oxygen while running at the same speed as another runner, then you’re more economical.
slow-twitch muscle fibers – Muscle fibers that contract and tire slowly and that power sustained submaximal exercise such as endurance running. Slow-twitch muscle fibers naturally resist fatigue, and they have a high aerobic capacity, high capillary density, and other characteristics that make them ideal for marathon running. The proportion of slow-twitch fibers in your muscles is determined genetically and is believed not to change with training.
O2max – See maximal oxygen uptake.
References and Recommended Reading
Alter, M. 1998. Sport stretch (2nd ed.). Champaign, IL: Human Kinetics.
Armstrong, L.E., A.C. Pumerantz, M.W. Roti, D.A. Judelson, G. Watson, J.C. Dias, B. Sokmen, D.J. Casa, C.M. Maresh, H. Lieberman, and M. Kellogg. 2005. Fluid, electrolyte and renal indices of hydration during 11 days of controlled caffeine consumption. International Journal of Sports Nutrition and Exercise Metabolism 15:252-265.
Beck, K. 2005. Run strong. Champaign, IL: Human Kinetics.
Bompa, T.O. 2005. Periodization training for sports (2nd ed.). Champaign, IL: Human Kinetics.
Brittenham, G., and D. Brittenham. 1997. Stronger abs and back. Champaign, IL: Human Kinetics.
Burke, L.M. 2007. Nutrition strategies for the marathon: Fuel for training and racing. Sports Medicine 37(4/5):344-347.
Cavanagh, P.R., and K.R. Williams. 1982. Effect of stride length variation on oxygen uptake during distance running. Medicine and Science in Sports and Exercise 14(1):30-35.
Chapman, R., and B.D. Levine. 2007. Altitude training for the marathon. Sports Medicine 37(4/5):392-395. Cheuvront, S.N., S.J. Montain, and M.N. Sawka. 2007. Fluid replacement and performance during the marathon. Sports Medicine 37(4/5):353-357.
Clark, N. 2008. Nancy Clark’s sports nutrition guidebook (4th ed.) Champaign, IL: Human Kinetics.
Cochrane, D.J. 2004. Alternating hot and cold water immersion for athlete recovery: A review. Physical Therapy in Sport 5:26-32.
Coyle, E.F. 2007. Physiological regulation of marathon performance. Sports Medicine 37(4/5):306-311.
Daniels, J. 2005. Daniels’ running formula (2nd ed.). Champaign, IL: Human Kinetics.
Eberle, S.G. 2007. Endurance sports nutrition (2nd ed.). Champaign, IL: Human Kinetics.
Eyestone, E.D., G. Fellingham, J. George, and A.G. Fisher. 1993. Effect of water running and cycling on maximum oxygen consumption and 2-mile run performance. American Journal of Sports Medicine 21(1):41-44.
Farrell, P.A., J.H. Wilmore, E.F. Coyle, J.E. Billing, and D.L. Costill, 1979. Plasma lactate accumulation and distance running performance. Medicine and science in sports and exercise 11:338-344.
Flynn, M.G., K.K. Carroll, H.L. Hall, B.A. Bushman, P.G. Brolinson, and C.A. Weideman. 1998. Cross training: Indices of training stress and performance. Medicine and Science in Sports and Exercise 30(2):294-300.
Foster, C. 1998. Monitoring training in athletes with reference to overtraining syndrome. Medicine and Science in Sports and Exercise 30(7):1164-1168.
Foster, C., L.L. Hector, R. Welsh, M. Schrager, M.A. Green, and A.C. Snyder. 1995. Effects of specific versus cross-training on running performance. European Journal of Applied Physiology and Occupational Physiology 70(4):367-372.
Foster, C., and A. Lucia. 2007. Running economy: The forgotten factor in elite performance. Sports Medicine 37(4/5):316-319.
Gellish, R.L., B.R. Goslin, R.E. Olson, A. McDonald, G.D. Russi, and V.K. Moudgil. 2007. Longitudinal modeling of the relationship between age and maximal heart rate. Medicine and Science in Sports and Exercise 39(5):822-829.
Goldenberg, L., and P. Twist. 2007. Strength ball training (2nd ed.). Champaign, IL: Human Kinetics.
Hawley, J.A., and F.J. Spargo. 2007. Metabolic adaptations to marathon training and racing. Sports Medicine 37(4/5):328-331.
Hickson, R.C., B.A. Dvorak, E.M. Gorostiaga, T.T. Kurowski, and C. Foster. 1988. Potential for strength and endurance training to amplify endurance performance. Journal of Applied Physiology 65(5):2285-2290.
Janssen, P. 2001. Lactate threshold training. Champaign, IL: Human Kinetics.