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Physiology Exercise

Lab practical 2 sheet – assessment questions  (14 marks)

Which energy system is dominant during the first sprint? How does energy system contribution change over the complete set of sprints? (6 marks).

For very short, high intensity exercise (in the range of 1-10 seconds), the ATP-PC is the predominant energy system that supplies most of the energy. It is a very powerful energy pathway but has a limited energy supply. The ATP-PC pathway peaks immediately after starting high intensity exercise such as sprinting but after 20 seconds of sprinting e.g. 200 m event the energy contribution is minimal.

Once the phosphocreatine stores have been used up, glucose then become the predominant or main energy supplier of ATP. The breakdown of glucose in anaerobic conditions is known as anaerobic glycolysis (AG) and ultimately results in the production of lactate and hydrogen ions.  As well as two ATP molecules for each molecule of glucose used.

The anaerobic glycolysis energy system contributes to ATP production within the first seconds and then reaches a plateau between 5-20 seconds during maximal exercise. If the exercise remains maximal, anaerobic glycolysis becomes the main energy source for about 15-100 seconds. The total energy store of the anaerobic glycolysis system is between 3 and 4 times that of the PC system; but the power output is significantly less from the AG system.

However, after about 20 seconds of maximal exercise, the energy contribution from the anaerobic glycolysis system starts to decline due to many contributing factors such as acid accumulation.

How does increased aerobic fitness (i.e. higher VO2 max) benefit repeated sprint ability? (4 marks).

A higher VO2 max benefits repeated sprinting ability by the following physiological adaptations:

  • An improved ability of the body to buffer the hydrogen ions and prevent acidosis and a rise in pH levels. This increases exercise tolerance to the acidosis and may decrease symptoms of fatigue
  • Has a role in improved recovery rates in between the bouts of sprinting and post exercise recovery
  • Improved cardiovascular function in terms of blood volume, left ventricle size and stroke volume; resulting in increased cardiac output. This is important for removal of muscle waste and metabolites and ultimate delivery of oxygen.
  • Peripheral adaptations include capillary density of muscle fibres, along with increased size and number of mitochondria (the power house of the working muscle).
  • There is a higher number of fast twitch type IIa fibres which have been converted from fast twitch type IIb fibres. The net outcome is a higher resistance to fatigue and a reduced burden on the AG system. Therefore, the athlete can exercise at that maximal intensity for longer.

Discuss/explain the likely mechanisms of fatigue during this type of repeated rowing activity? (4 marks).

The ability to perform repeated sprints is vital in rowing  with sprint distances varying along with recovery intervals between exercise bouts. PCr levels can rapidly recover after exercise as shown previously, and return to 50 per cent of resting values in 1-2 minutes and to 90 per cent of resting values after 3-4 minutes .

However, it can sometimes take up to 15 minutes for full re-synthesis in fast twitch type II fibres, which are depleted by the greatest extent during high- intensity exercise.
It is possible that glycogen depletion in fast twitch type II fibres may contribute to a reduced overall force production during a sprint. If an individual performs repeated sprints when muscle glycogen is depleted, fatigue often occurs earlier.

Recovery of muscle glycogen, unlike PCr or even pH can take over 24 hours to fully complete. Although the ability to deplete levels of PCr increases the more anaerobically trained an individual is.  There is evidence that those with a well-developed aerobic system can re-synthesisePCr more rapidly than less trained individuals.

Lactic Acid

It was, until recently, commonly thought that lactic acid was a major cause of fatigue during high intensity and middle distance exercise. It has since been widely accepted that this is not the case as it is the acid (H+) produced during anaerobic glycolysis that is more likely to cause the fatigue.In fact, lactate has been shown only to have beneficial effects as it actually decreases the level of hydrogen ions in the muscle and can also be converted to make glucose for the purpose of energy production.

When acid is produced during AG, both in the muscle and the blood, buffering can take place to prevent the build-up of acid by using buffers in the body such as bicarbonate. Acid accumulation can cause fatigue as a result of mechanisms such as inhibition of enzymes involved in anaerobic glycolysis (PFK), interference with calcium binding and familiar pain or ‘burn’ felt when performing extended bouts of high intensity exercise.


Lab practical 3 sheet – assessment questions  ( 20 marks)

1. Plot blood lactate against power and identify the lactate threshold and power at onset of

blood lactate accumulation (OBLA), explain how you identified lactate threshold? (6 marks)

In anaerobic conditions lactic acid (LA) and subsequently hydrogen ions  are produced. Lactic acid is constantly being produced even at low intensities but, due to the presence of oxygen, it is easily converted to ATP. It is lactic acid that is used to re-synthesise pyruvate, which is then broken down aerobically, mainly in slow twitch type I fibres, again to produce ATP.

When insufficient oxygen is available to break down pyruvate, or energy demands are too high for the aerobic system, the lactate is produced. Lactate enters the surrounding muscle cells, tissue and blood.  The muscle cells (mainly type I) and tissues receiving the lactate either recycle the lactate) to pyruvate to produce ATP for immediate use, or use it in the creation of glucose via the liver. The glucose formed can be taken up into the muscle and stored as glycogen in the cell until energy is required.

As exercise intensity increases, there are several terms that are used (in most cases interchangeably) to define the intensity at which there is a dramatic increase in blood lactate concentration such as lactate threshold (LT), onset of blood lactate accumulation (OBLA), and anaerobic threshold (AT).

Using these different definitions involves the complex interpretation of curves which can result in a variety of intensities being used to define, for instance, the lactate threshold (LT) (depending on the investigator). This is often described as the point at which the production of lactic acid overtakes the removal, and lactic acid starts to build up. For simplicity, many researchers use the concept of onset of blood lactate accumulation (OBLA) for training and investigation purposes. OBLA has been described as the intensity at which the blood lactate concentration reaches 4.0 mmol.  LT on the other hand is often expressed as speed, workload, heart rate, or percentage of V02 max.

2. Why does training status affect the lactate response to incremental exercise? (4 marks)

If LT or OBLA is reached by individuals at low exercise intensities, it can often indicate a potentially low fitness level of that individual, although there are other possible explanations. If this is the case, may mean that the ‘oxidative energy systems’ in the muscles of the individual are not working as well as if the individual had a higher level of fitness. There are many possible explanations that could account for an individual having a low lactate threshold or onset of blood lactate accumulation. It is often the case that the individual would have a combination of several factors that would affect the outcome  or measurement of LT or OBLA. Factors that could contribute to an individual having a low LT or OBLA are:

• Insufficient oxygen delivered to muscle cells
• Insufficient concentrations of enzymes necessary to oxidise pyruvate at high rates
• Insufficient mitochondria in the muscle cells
• Muscles, heart and other tissues are not good at extracting lactate from the blood.

It can be seen that factors contributing to a low LT or OBLA are trainable and that individuals who undergo a regular training programme  of correct intensity, are able to increase the point at which LT and OBLA occur; so increase their individual levels of fitness. This would be represented on a blood lactate graph by a right shift in the response curve (the curve would start to rise at a greater power output).


3. Plot oxygen uptake (VO2) against power to examine the VO2- work rate relationship?

(4 marks)

4. Add a trend line to the VO2-work rate relationship and calculate/report the R2

value for this line of best? What does the R2 value mean (2 marks).

The graph demonstrates that there is a  plateau of oxygen consumption with increasing power output. Oxygen consumption increases linearly until about 300watts and then it levels off. This point on the graph (R2 )is termed the VO2 max and informs us the maximum amount of oxygen that our bodies are able to delivery and utilise when exercising.

5. Why is it of interest to test the lactate threshold in endurance athletes? (4 marks)

Running speed or cycling power output at lactate threshold (LT) can be a very good predictor of endurance performance. For example, long-distance events such as the marathon (over 26 miles) are often performed by athletes at an intensity that is close to the LT of that athlete. In many sports such as cycling, maximum lactate steady state (MLSS) is used, which can be described as the highest exercise intensity at which lactate production matches lactate removal and would normally be between 245 and 275 watts. In other words, before lactate levels begin to increase significantly. Highly trained endurance cyclists can often exercise at an intensity of nearly 90% of V02 max at LT and be able to sustain this level for long durations (60 minutes for example). While changes in V02 max are related predominantly to central factors, the lactate response of an individual is primarily dependent on several peripheral factors within the exercising muscles. Factors include those such as the percentage of slow twitch type I fibres, levels of key aerobic enzymes, and mitochondrial size and number.


Lab practical 5 sheet – assessment questions  ( 20 marks)

1. Define steady state exercise? (2 marks)

Steady state exercise is an activity that maintains a balance between the energy required by the working muscles and the rate of oxygen delivery needed for ATP production ( aerobically). Supply of oxygen meets the demand of the activity and ATP production.

2. What percentage of VO2max would you expect a cyclist completing a 4000m time trial to reach, explain the reasons for your answer? (6 marks)

Research has indicated that many elite 4000 m cyclists will be performing at 120-130% of their VO2max.  This is a training adaptation as it takes about 120 seconds to reach our VO2 max, this is a metabolic adaptation rather than a dramatic increase in cardiac effectiveness and lung capacity due to anaerobic threshold training e.g. HIIT, hill climbs ad/or interval

In brief, increases in blood volume, left ventricle size and hence stroke volume result in an increased cardiac output which leads to increased oxygen delivery to the muscle and increased thermoregulatory ability (these are known as central adaptations). Peripheral adaptations (as opposed to central adaptations) include increased capillary density of muscle fibres, and increased number and size of mitochondria and aerobic enzymes. Slow twitch type I fibres, which are recruited during steady exercise, increase in size as a result of this type of training.

Fast twitch type IIbfibres can also be converted to more fatigue resistance fast twitch type IIafibres. The net result of this is increased power of the aerobic system and a reduced reliance on anaerobic glycolysis, thus reducing reliance on the limited muscle glycogen stores. This will reduce the premature reliance upon a proportion of the oxygen deficit. Also improved lactic acid utilization and buffering within  the muscle.


3. How could we theoretically calculate the percentage of aerobic and anaerobic contribution during a 4000 m cycling time trial? (6 marks) .

Set up a 4000 m time trial on an electromagnetically braked cycle ergometer in the lab and measure oxygen consumption and blood lactate ( pre/during/post).  Warm up at own pace and then 4000m as quick as possible.The overall aerobic response  can be calculated as the area under the VO2 power curve.

Calculation of the total anaerobic energy  contribution for 4000m trial; maybe could use the (MAOD) technique. This involves inducing an efficiency relationship in order to calculate the O2 demand at intensities associated with a maximal 4000-m time-trial. The total anaerobic energy contribution  (MAOD) (ml O2·kg-1) can be  calculated as the sum of the differences between the O2  demand and the measured V&O2.


4.What percentage of energy would you expect to be supplied by the anaerobic system during 4 000 m cycling time trial performance? (4 marks)


5.Why might it be important to understand the interaction between energy systems during exercise? (2 marks).

  • To assess if the training methods being used are appropriate
  • To test Fitness levels
  • To highlight anaerobic training adaptations
  • To improve time, power and speed



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