Written by Anna Tong, AES, CSCS
When it comes to aerobic endurance sports, it is vital to understand the factors that influence and play a significant role in performance. This allows you to optimize and develop a sound training program while minimizing unnecessary training that may lead to overexertion, injury, or overtraining. The 3 main physiological factors that appear to affect aerobic endurance performance are the maximal aerobic power (VO2max), lactate threshold, and exercise economy (10).
Maximal Aerobic Power
Maximal aerobic power, also known as the ‘VO2max’, is the maximum amount of oxygen that your body can consume, distribute, and utilized (by the working muscles) during maximal exercise. The VO2max can be assessed by performing a maximal graded exercise test. In a maximal graded exercise test, the exercise load (speed) will gradually increase every 1 – 2 minutes until it reaches the maximum level you can tolerate or until your oxygen consumption has reached its peak or hit a plateau. Depending on your sport (running, cycling, rowing, etc.), it can be conducted on a treadmill, stationary bike, or rowing machine.
The VO2max test is commonly used to measure cardiovascular fitness (8, 27), and it is also a predictor of performance. Studies have shown a high correlation between VO2max and aerobic endurance performance (13, 16). Just like the size of a ‘car engine’, the higher the VO2max, the bigger the aerobic capacity. One way for our body to produce energy from fuel (carbohydrate, fat, and protein) is through oxygen. Therefore, the more oxygen your body is able to use during intensive exercise, the more energy you can produce to sustain the activity. Although other factors such as lactate threshold and exercise economy are superior predictors (29, 30) and important determinants of performance in distance running (31), higher VO2max values increased the potential for a successful performance. A high VO2max value reflects an increase in cardiac output which includes an increase in blood volume, capillary density, mitochondrial density, and stroke volume (28).
VO2max is also an excellent predictor of early death and health disease risks such as heart attack, diabetes, cancers, and stroke (11, 25). While genetics plays a huge factor in our max potential (12, 18), most of us can improve our current VO2max through training.
Lactate Threshold
The lactate threshold refers to the exercise intensity at which blood lactate begins a sudden increase above the resting levels (26) and it is normally expressed as a percentage of your VO2max. If VO2max is our aerobic endurance potential, then our lactate threshold plays a significant role in how much of that potential we are tapping. For example, lactate threshold typically occurs at 70-80% of VO2max in trained athletes but in untrained individuals, it occurs much sooner at 50-60% of VO2max (3, 6). What this means is that trained athletes are able to move faster and sustain longer compared to untrained individuals.
The increment in blood lactate, or lactic acid, signifies a change in energy metabolism from predominantly aerobic metabolism (occurs in the presence of oxygen) to predominantly anaerobic metabolism (occurs without oxygen) (14), especially when there is a change in exercise intensity from low to high. Theoretically, anyone could exercise at any intensity up to their VO2max. However, as the exercise intensity continues to increase closer to that at VO2max, there is also a sharp increase in the rate of lactic acid production. When the body produced lactate faster than it can clear, lactate accumulation increases as well and this caused the second spike in blood lactate. This is also known as the onset of blood lactate accumulation (OBLA) (9, 20, 22).
Have you ever experienced the ‘burning’/’sour’ sensation in your muscles during intensive exercise and subsequently, it would not be long before you feel the need to slow down or stop the exercise? This is due to the hydrogen ion resulted from the breakdown of lactic acid. An increase in hydrogen ion concentrations increases the acidity in the blood and muscle which eventually leads to muscular fatigue. Although lactate is not the primary physiological cause of fatigue during high-intensity exercise, it is accepted as a biomarker of fatigue because of its direct relationship to plasma metabolites that causes fatigue (2). Therefore, the lactate threshold test assesses your anaerobic ability by measuring your blood lactate at different stages/intensity of the test. This provides the exercise physiologist/ scientist an insight into how your body responds to the increase in exercise workload, allowing you or your coach to plan and program your training accordingly.
In sports performance, being able to sustain and maintain a high level of power output is one of the most important factors. The point at which the body’s maximal lactate clearance equals maximal lactate production is known as the maximal lactate steady state (MLSS) (1). Therefore, compared to the VO2max, the MLSS is considered to be a better indicator of aerobic endurance performance (1, 7).
Exercise Economy
Exercise economy refers to the energy cost of the activity required to perform at a submaximal effort level. The energy cost is determined by measuring the oxygen consumption (VO2) and the respiratory exchange ratio (RER). At the same exercise intensity, an individual with a good exercise economy consumed less oxygen compared to another individual with a poor exercise economy.
Due to the strong association with endurance performance, exercise economy is generally measured and assessed for individuals who are involved in distance running (4, 17), cycling (5, 15, 21), and swimming (24). Generally, endurance sports are predominately aerobic in nature. Therefore, measuring the RER along with VO2 when assessing the running economy is to ensure a steady-state (aerobic metabolism).
It appears that there are a number of physiological and biomechanical factors that can influence exercise economy. Better runners have slightly shorter stride length, greater stride frequency, increased mitochondria, and oxidative enzymes (19). For cyclists, exercise economy appears to be affected by body mass size, cycling velocity, and body positioning (aerodynamic) (5, 15, 21). During swimming, stroke mechanics appear to have the biggest impact on exercise economy (24), and compared to non-elite swimmers, elite swimmers are much more economical (23) and use less oxygen at any given swimming speed.
Apart from having the potential to perform, the ability to tap into the potential, and how efficient the energy is being utilized are critical for superior endurance performance. Understanding the factors and their role in endurance performance allows you and coaches to develop and incorporate effective training programs.
References
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