Determining the limiting factors in endurance training is essential for athletes looking to continue improving their endurance performance. In endurance training, most limitations are caused by fatigue. An understanding of what causes this fatigue on a physiological level can help athletes manipulate conditions in order to induce physiological adaptations that will improve endurance performance.
Endurance capabilities are measured through several markers. Following are some of the most important relative to physiological adaptation.
VO2 Max
Elite endurance athletes have very high VO2 max readings; however, evidence suggests that a person's VO2 max is largely genetically predetermined, reports Sports Fitness Advisor. However, an untrained person can improve his or her VO2 max by up to 20% with the right training. The goal of any endurance athlete should be to reach his or her upper-most limit in order to achieve the best possible performance.
Lactate Threshold
While VO2 max determines one's limit in aerobic performance, the lactate threshold is responsible for the time an athlete may remain training at this limit. Appropriate training that helps lactate accumulation and raise an athlete’s lactate threshold, improving overall endurance performance.
Exercise Economy
Alone, VO2 max and lactate threshold are not enough to determine an athlete's performance. The time or workload taken to reach the upper limit of either measure is essential — this is known as exercise economy. A higher exercise economy means less energy expenditure is required, no matter the exercise.
Substrate Utilization
A body's energy system can use either fat or carbohydrate stores in order to produce energy. During higher levels of intensity, carbohydrates are typically used more; however, with the right training, athletes can utilize fat as fuel even at higher intensities and therefore endure longer bouts of exercise.
To understand how these markers are affected by long-term endurance training, it is necessary to look at the physiological adaptations that occur. These can be divided into centrally and peripherally mediated adaptations.
Central (Cardiovascular) Physiological Adaptations
- Decreased heart rate
- Increased heart stroke volume
- Increased blood plasma
- Reduced blood viscosity
- Increased cardiac output
- Increased mitochondrial volume in muscle fibers being used
- Increase in number and size of myoglobin and oxidative enzymes
Peripheral Physiological Adaptations
- Capillarization; there is an increase in the surface area supplied by the venous and arterial capillaries. This allows for increased heat dissipation during intense exercise.
- Improved glycogen and fat storing capabilities in muscles; this allows for an increase heat dissipation during intense exercise, lengthening the time an athlete can work out.
- Development of slow twitch (type 1) fibers; these increase efficiency and resistance to fatigue.
- Catabolism; heightens an athlete’s capacity to use fat and glycogen stores as energy.
- Oxygen transportation and distribution efficiency increases.
- Oxidative enzymes; succinate dehydrogenase (SDH) and others enable mitochondria to break down nutrients to create ATP. These are present up to 2.5 times more than normal in well trained endurance athletes while myoglobin is present 75% to 80% more.
Athletes who want to improve endurance performance should know where they stand relative to the markers often used to identify physiological adaptations. Doing so will help them ascertain which physiological adaptations will best aid them in achieving their endurance performance goals.
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