Content
- Anaerobic power
- VO2max
- Anaerobic Threshold and the Onset of Blood Lactate Accumulation
A highly powerful athlete, such as a weight lifter or hammer thrower, would have a very high peak power, demonstrating a high anaerobic power. However, they wouldn’t be able to sustain the effort, and would have a large decline in their power output over time. This reflects their ability to use the ATP-PC energy system
Anaerobic power reflects the ability of the adenosine triphosphate and phosphocreatine (ATP-PC) to produce energy. This is one of the factors that are analysed when carrying out the Wingate 30 second test. The maximal power output occurs within the first 5-10 seconds of the test. The ability to create a high power output is determined by the size and cross sectional area of the muscle, profile of the muscle fibres (High proportion of Type IIb is desirable for power), length of the limb (longer limbs produce more force) and also training status and levels of athlete fitness. This can be split into two areas:
After the ATP-PC system is depleted, usually within the first 10-12 seconds), the predominant energy system for the remainder of the test is anaerobic glycolysis. When working anaerobically, the accumulation of metabolic waste causes muscle fatigue. Metabolic waste includes the production of lactate and hydrogen ions, which contribute to lowering the pH of muscle cells, causing fatigue.
The ability to sustain power output despite fatigue is considered our anaerobic capacity, which is quantified when we look at the average or mean power across the test. The ability to sustain a high power output is determined by the ability to utilise, tolerate and remove accumulated metabolic waste products such as blood lactate.
The initial peak power to the end low power output reflects the depletion of the ATP-PC system and accumulation of metabolic waste during anaerobic glycolysis, and is reflected in the fatigue index, which is an indicator of anaerobic fatigue. This can be a useful measure to determine performance, as if you had 2 equally powerful athletes but one had a lower fatigue index, then, physiologically speaking, that athlete will probably be the better athlete than the other because they can sustain a higher power for longer.
A highly powerful athlete, such as a weight lifter or hammer thrower, would have a very high peak power, demonstrating a high anaerobic power. However, they wouldn’t be able to sustain the effort, and would have a large decline in their power output. This would mean they would have a lower mean power, and a high fatigue index/power drop.
An athlete that requires speed and power, such as 400 m sprinters, would have a lower peak power relative to the weight lifter, but a higher peak power relative to a long distance runner. However, the sprinter would be able to sustain the effort for longer than both, and therefore would have a higher mean power, and therefore a greater anaerobic capacity. They would also be less likely to have a large decline in their power output and therefore a lower fatigue index.
If an athlete were to focus on training to improve their anaerobic power, they would need to focus on muscular strength and resistance training. If an athlete wanted to improve their anaerobic capacity, they would need to complete training above their anaerobic threshold in order to increase their ability to utilise, tolerate and clear the accumulation of metabolic waste.
The VO2 max test is a method of measuring an individual’s cardiovascular fitness or aerobic capacity. VO2max stands for maximal oxygen consumption, and this reflects the maximum ability of the body to transport and utilise oxygen during exercise. It is the product of maximal cardiac output (the ability to transport oxygen) and the arterio-venous oxygen difference (the utilisation of O2).
When testing for VO2 mac, the main focus of this test is to analyse oxygen consumption. In order to do this, a breath by breath analysis system is used, which measures both the volume of air inhaled and exhaled and also the oxygen and carbon dioxide content of that air. Heart rate is also measured during the test
Aerobic exercise is exercise in which your oxygen consumption is greater than your carbon dioxide production. At increasing exercise levels, the production of carbon dioxide increases, and will exceed oxygen consumption. This will be the point at which the predominant energy system becomes anaerobic. The exact point at which this occurs is known as the Anaerobic Threshold.
The relationship between oxygen consumption and carbon dioxide production is reflected in a variable called the respiratory exchange ratio or RER value. The RER value is a good indicator of which energy system is being used. A value below 1 = aerobic metabolism; 1 = anaerobic threshold, greater than 1 = anaerobic metabolism.
When you are exercising utilising energy via anaerobic metabolism, there will be a point at which you can no longer sustain exercise and therefore fatigue, and that is your VO2 max. This fatigue is caused by metabolic waste products such as hydrogen ions and blood lactate.
From testing, we know that there is a linear relationship between heart rate, VO2 and exercise intensity. However, there will be a point where the VO2 does not increase, despite an increase in power output. VO2 may then plateau if the athlete continues to exercise, this is known as VO2max.
When testing for VO2 max the start of the test should be equivalent to a warm up intensity for the athlete, with the intensity getting progressively harder, until the participant reaches voluntary fatigue. The end of the test is therefore mainly driven by the participant, however there are certain physiological criteria that are used to confirm the attainment of VO2max. These are:
VO2 max is typically expressed as ml. kg. min, which is a measure relative to body mass. Males between 18 -25 average VO2 max score is between 42 -46 ml.kg.min, with a good score between 52-60 ml.kg.min. Females between 18-25 average VO2max score between 38 and 41 ml.kg.min, with a good score being 47-56 ml.kg.min. Elite endurance athletes, such as cross country skiers, can achieve values of up to 92 ml.kg.min.
For an individual looking to develop their aerobic capacity and VO2 max score, completing exercise high intensity intervals with a work to rest ratio of 1:1 is recommended as the most effective method.
The lactate threshold test determines the levels of lactate within the blood at increasing exercise intensities. Each stage should be 4 minutes in duration, with no more than 5 – 9 stages in total. This should continue until the participant achieves a near maximal intensity of around 80-90% of max heart rate.
The levels of blood lactate when resting can be anywhere between 0.8 and 1.5 mmol/L. During the lactate threshold test, blood lactate is taken at the end of each stage and the measured values are plotted against each workload to create a lactate performance curve. From this lactate performance curve, it is possible to identify different points:
The first indicator, is the lactate or Anaerobic threshold threshold, and this is the workload at which there is the first increase in lactate above resting values (usually 1 mmol.L above the measured resting value). The work rate required at anaerobic/ lactate threshold is considered a medium to high intensity but a steady effort that can be prolonged for up to 20-30 minutes.
The Onset of Blood Lactate Accumulation (OBLA) also known as the lactate turn point, is the point at which there is a distinct sudden and sustained increase in blood lactate. The work rate required at lactate turn point (OBLA) is considered as a hard or high intensity training effort.
These points are identified from the curve in the graph, the information is used as a measure of performance, as well as to prescribe exercise training for athletes.
Below the lactate turn point (OBLA), lactate is being produced at low rates by the working muscles as the predominant energy system is aerobic. The lactate that is produced is used as fuel within aerobic metabolism and is therefore it is cleared from the working muscles and therefore does not accumulate and cause fatigue.
Above the lactate turn point (OBLA), lactate is being produced at a rate greater than it can be cleared or utilised, and therefore accumulates in the working muscles, alongside other metabolic waste products such as hydrogen ions, that will eventually cause fatigue. Therefore, the lactate turn point (OBLA) indicates the exercise intensity at which an athlete cannot sustain exercise for long durations. With specific exercise training, it is possible to move the lactate turn point (OBLA), so it occurs at a higher exercise intensity, which means an athlete can work harder for longer before coming fatigued.
Once an athlete has completed the lactate threshold test, training zones based on the pace and heart rate achieved at both the anaerobic/lactate threshold and the lactate turn point (OBLA) can be prescribed. This can be in the form of steady state exercise (just under anaerobic/lactate threshold) or high intensity interval training above the anaerobic threshold.
For an athlete, training the anaerobic or lactate threshold is far more effective at improving performance than training to improve aerobic capacity. In terms of actual performance, lactate threshold is a more reliable and important predictor of performance than VO2 max. To put it simply, if you had two runners with the same VO2max, but runner A had a higher pace at lactate threshold than the pace at lactate threshold of runner B, runner A will run faster, reach the finish first, and win, because runner A is can sustain a higher pace for a longer duration before becoming fatigued.
With training, the body is able to improve its use of lactate as an energy source, its clearance mechanisms, and also it’s buffering capacity to negate the fatiguing effects of metabolic waste product accumulation. Therefore, carrying out lactate threshold testing pre and post training block is a good method of demonstrating performance improvements in athletes.