The Anaerobic Lactate (Glycolytic) System
The anaerobic energy pathway, or anaerobic glycolysis, creates ATP from ingested carbohydrates with lactic acid being a by-product. Anaerobic glycolysis provides energy via the breakdown of glucose without the need for oxygen. It produces energy for short, high-intensity bursts of activity lasting no more than several minutes until ‘onset blood lactate accumulation’ or OBLA. OBLA refers to the point at which lactate begins to accumulate in the blood, usually measured at 4 mmol/litre of blood. Lactic acid build-up increases until the lactate threshold is reached, at this stage muscle pain, burning and fatigue make it difficult to maintain intensity.
The Aerobic System
Aerobic metabolism fuels most of the energy needed for long duration activity such as distance running. It uses oxygen to convert nutrients (carbohydrates, fats, and protein) to ATP. This system is slower than the anaerobic systems because it relies on the circulatory system to transport oxygen to the working muscles before it creates ATP. Aerobic metabolism is used primarily during endurance exercise, which is generally less intense and can continue for long periods of time.
Energy System Recruitment
During exercise an athlete will progress through these metabolic pathways. As exercise begins, ATP is produced via anaerobic (ATP-CP) metabolism. With an increase in breathing and heart rate, there is more oxygen available and aerobic metabolism begins and continues until the lactate threshold is reached. If this level is passed, the body will not be able to deliver oxygen quickly enough to generate ATP and thus anaerobic metabolism starts once more. Since this system is short-lived and lactic acid levels rise, the intensity can not be sustained and the athlete will need to decrease intensity to remove lactic acid build-up Dick F. (2002).
The following table provides an approximation of the percentage contribution of the energy pathways in certain sports, Fox et al. (1993)
Fig 1. Energy System Recruitment. Source: Fox E. L. et al. (1993)
As the above table illustrates, different energy systems are employed at differing times and rates dependant upon the duration and intensity of the exercise. For example it can be seen that ‘Sprints’ (specifically 100m) almost exclusively (90%) utilize the ATP-CP energy pathway whilst ‘Distance running’ primarily used aerobic metabolism. Sprinting requires a short, but extremely intense bout of activity which requires immediate energy delivery, thus utilizing the only system capable of immediate energy delivery: ATP-CP. Distance running, although employing the ATP-CP and the slightly ‘longer lived’ aerobic glycolysis system relies primarily on the aerobic metabolism in order to fulfill energy demand. With very little need for ‘explosive power’ the body can employ the usage of intramuscular glycogen stores.
The graph below illustrates how the three energy systems interact during exercise. Correct training will extent the time to exhaustion thus improving fitness.
Fig 2. Energy Systems. Source: Brian Mac, Sports Coach
With appropriate training, these energy systems adapt and become more efficient, allowing greater exercise duration at higher intensity, thus resulting in musculoskeletal and cardiovascular adaptations.
Adaptations to Exercise
When undertaking any physical task, the human body responds through a series of changes in function that involve most of its physiological systems. Movement requires activation and control of the musculoskeletal system with the cardiorespiratory system providing the ability to sustain this movement over extended periods, Astrand P, Rodahl K (1986). When the body engages in exercise training over extended periods each of the physiological systems undergo specific adaptations that increase the body’s efficiency and capacity. The magnitude of these changes depends largely on the intensity and duration of the training sessions, the force or load used in training, and the individuals’ initial level of fitness.
One of the reasons for undertaking fitness activities for most individuals is the enhancement of cardiovascular function and aerobic capacity. During the transition from rest to exercise cardiac output increases rapidly. ’Thereafter cardiac output rises gradually until it reaches a plateau when blood flow meets the exercise requirements’ (McArdle W, Katch F & Katch V 2001). In its most basic form this initial increase in demand triggers changes in the cardiovascular system including an increase in heart rate and stroke volume in order to supply oxygen demand. As training continues and becomes long term, cardiovascular adaptations become more permanent with the heart becoming stronger and more efficient, this increases the efficiency of both the pulmonary and systemic circulation systems delivering more oxygen and removing more waste products.
With increased and sustained training it can be seen that pulmonary adaptations also occur. During exercise the body requires more oxygen and therefore the breathing cycle adapts by employing complimentary muscles. These muscles allow for more efficient respiration.
The following muscles and their functions all play a part in this cycle:
- Internal and External Intercostals - Expansion and contraction of the rib cage
- Sterno Clado Mastoid - Elevates rib cage.
- Scalenes - Elevates rib cage.
- Pectoralis minor - Elevates rib cage.
- Quadratus lumborum - Pull lower ribs inward during expiration
- Abdominals - Compress the abdomen
- Obliques - Compress the abdomen
The result of these extra muscle functions is:
- An overall increase in Minute Ventilation (VE) ( VE = TV x F )
- An increased Tidal Volume (TV).
- An increased Inspiratory Reserve Volume (IRV).
- An increased Expiratory Reserve Volume (ERV).
- An increase of Forced Vital Capacity (FVC), TV + IRV + ERV.
- A decrease in Residual Lung Volume (RLV).
The combination of increased cardiac output and pulmonary function result in the muscles receiving more oxygen, thus increasing aerobic capacity. Similar adaptations can also be seen during anaerobic training although to a much lesser degree.
Anaerobic training, although of marginal benefit to the cardiopulmonary system, is primarily concerned with short explosive burst of power, and training concentrates primarily on relevant muscle groups. Although aerobic and anaerobic training produces muscular adaptations, those adaptations differ. A distance runner or triathlete for example will develop mainly sarcoplasmic protein, while a weight lifter will develop mainly contractile protein, Edgerton, V.R (1978). When muscles are forced to contract they will increase in size and strength, in terms of anaerobic training therefore, muscles must be overloaded to a state of hypertrophy. This increase in size and strength as a result puts little demand on the cardiopulmonary system and therefore has limited benefits to aerobic capacity.
Clearly, both aerobic and anaerobic training allows for health improvements as a result of physiological adaptations, but when training exceeds the body’s recovery capacity an emotional, behavioral and physical condition called overtraining can occur Mac B, (2008). The individual will often cease making progress. The most common symptoms are often disturbed sleep patterns and a loss of progressive improvement in training. In the most undesirable instance an individual can even begin to lose strength and fitness. Neuromuscular fatigue affects the central nervous system and makes the individual more prone to injury and illness; this is a direct result of overtraining and can be avoided by initiating the correct training program which is tailored to the individual athletes needs.
The importance of fatigue and the knowledge to maximize the efficiency of energy systems is essential. As previously stated, when there is insufficient ATP availability muscular contraction will weaken and performance will deteriorate, this combined with hydrogen ion (lactic acid) accumulation, where excess hydrogen increases the acidity of muscle tissue, are some of the main components of fatigue. Glycogen depletion and the decreased availability of calcium ions also contribute to a decrease in performance, as does a decrease in availability of the neuro-transmitter acetylcholine. In all therefore there are several important aspects to consider when discussing fatigue, moreover it is important to understand the importance of the recovery process.
Recovery immediately after exercise initially involves the recovery of oxygen dept known as ‘excess post-exercise oxygen consumption’ (EPOC). This can be defined as ‘the amount of oxygen consumed during recovery above that which normally would have been consumed at rest in the same period of time ’, Wesson K et al, (2000). This recovery process has 2 distinct components:
Alactacid Debt: The first and fastest component of the oxygen dept that is replenished, it allows the restoration phospocreatine used during the employment of the ATP-PC energy system. This faster recovery rate normally takes between 2 – 3 minutes, in which time 2 – 3 litres of oxygen is consumed providing the catalyst for resynthesis.
Lactacid Debt: This slower replenishment is utilized to remove excess lactic acid from the muscles, where lactic acid is oxidized to produce carbon dioxide and water. This process takes approximately one hour but can be accelerated by using ‘cooling down’ as an exercise recovery.
Along with EPOC the body also needs to replenish its stores of glycogen. This process can take over 24 hours and often as long as 48 hours depending on the type and intensity of exercise. It is generally accepted that a high carbohydrate meal within 1 hour of exercise cessation will greatly enhance recovery times.
Long term recovery brings repair and, as a result, physiological adaptation to training, this is especially important when undertaking anaerobic training where microtrauma is the catalyst for muscular adaptations Edgerton VR, (1978). Tearing of muscle fibers, muscle sheaths and connective tissue along with stress to the tendons and bones creates an environment in which the body can be left in a weakened state. This can, at times, result in cessation of training thus removing the training stimulus; this is a direct result of the emotional and behavioral damage caused by overtraining. The removal of the training stimulus will result in the loss of the efficiency, strength and capacity that has been gained through training-induced adaptations. Detraining, as it is known, creates an environment where the body, after months or possibly weeks, will revert back to its prior state and all benefits are subsequently lost.
Experimental Report
In order to observe the physical adaptations to exercise more closely the following methodology was utilized in order to establish the individual’s initial fitness level.
Methodology:
Bleep Test
Equipment:
Tape measure
Flat smooth surface of over 20m
Marking cones or lines
The Multi Stage Fitness Test C.D. or Tape
Tape recorder or C.D. player
Recording sheets
Method:
- Measure out the 20m section and mark accordingly
- Athlete places foot on the line at the end of each shuttle run
- The athlete must run as long as possible until he/she can no longer keep up with the bleep tone.
- Record the number of shuttles completed at that level by the athlete
- Cool down
Sergeant Jump
Equipment:
Tape measure
Jump board (at measured distance from the floor)
Recording sheets
Method:
- Measure distance to bottom of jump board from ground
- Athlete to crouch and jump straight upwards, touching the jump board at the highest point.
- The height is taken and recorded
- The test is repeated three times
- The highest score is used
Sit and Reach
Equipment:
1 Evenque Sit and Reach Bench
Flat even surface
Recording sheets
Method:
- Place sit and reach bench against wall
- Remove footwear and sit with feet flat on side of bench
- Using a gentle forward motion slide the hands along the top of the bench
- Record the highest number reached
- Repeat three times
- The highest score is used
- Along with the measurements mentioned above blood pressure was measured three times and the mean worked out, and the resting heart rate was taken, again three times with the mean worked out.
- Statistical measurements were taken HR – BP – Weight – Bleep Test – Sit and Reach - Static Jump.
Subsequently the individual was then required to undertake a fitness regime for three weeks; this regime was based upon the Fartlek training principle (Appendix 1). Following this period the subject was once again tested using the same methods as previously employed. By analyzing the two sets of results it should be possible to gauge the adaptations to exercise that have taken place.
Pre and post exercise statistics
The following measurements were taken before the implementation of training.
- Weight 88.5 kg
- Height 178 cm
- Resting HR 72 BPM
- BP 132/92 mm/Hg
-
% H2O 43.7
Results 1
The results of the tests were as follows:
Bleep test: - Level 7.2. Predicted VO2 max = 37.1.
Sergeant Jump (at + 1m)
Sit and Reach Test:
Blood pressure:
Heart rate:
Results 2
After the period of three weeks training testing was once again repeated and the following data was collected:
Bleep test: - Level 9.2. Predicted VO2 max = 43.9.
Sergeant Jump:
Sit and Reach Test:
Blood pressure:
Heart rate:
Discussion
As shown by the above results, the training schedule appeared to have brought about physiological adaptations, the most significant indicator of this being VO2 max increasing to 43.9 from 37.1, as indicated with a bleep test result of 9.2, a marked rise from 7.2. VO2max as a test gives a good indicator of fitness levels and progression. ML O'Toole, PS Douglas, (1995).
The ability of the individual to gain a higher result in the bleep test also indicated an increase in lactate threshold, as time and intensity was increased over the 3 week training period, this is echoed by the bleep testing. Thus adaptations to the energy pathways will have taken place along with cardiopulmonary improvements involving muscular adaptations. In particular cardiovascular efficiency was seen to improve with a diastolic blood pressure of 103 dropping to 91.
Overall muscular improvements due to the development of contractile protein can also be seen via the increase in ability during the sergeant jump. Overall, muscular improvements invariably took place; this is due to the specific and nature of the Fartlek training principle, which is designed as a progressive system using both duration and intensity as training methods.
A marginal improvement in the sit and reach test with the initial reading of 26cm increased to 26.66 was also observed, and although primarily only one of the components of fitness did indicate adaptations due to exercise.
In essence therefore a marked improvement was seen after only 3 weeks of training. This is not only verified by the pre and post exercise testing, but clearly indicated by the ability of the individual to begin at a low intensity run of 20 minutes and increase to a run of 50 minutes with a Fartlek interval of 50s at 20 minutes and 50s at 30 minutes.
Conclusion
Although blood pressure saw a decrease after the allotted time span it could be suggested that testing methods were not accurate enough to determine whether this was a result of actual fitness adaptations. Potentially an exterior influence such as hydration levels, desensitization to the pre exercise response or even the state of mind of the individual could have played a part in this change. In order to rectify this anomaly it would be necessary to test a larger number of individuals.
As with the blood pressure tests, the sergeant jump test could have been subject to variability due to hydration levels, footwear worn by the athlete and again state of mind, again it would be necessary to utilize a larger number of test subjects.
On the subject of Fartlek training and its use as a testing and training method: Fartlek develops aerobic and anaerobic capacities which also assist in other aspects of fitness (Holmer, G. 1977.) It was felt that the Fartlek method would work well with the bleep test as they both rely on similar characteristics of movement and energy expenditure. The distance portion of Fartlek utilizes the aerobic and anaerobic lactate energy pathways, as does the mid section of the bleep test. Whereas the sprinting section of Fartlek employs the usage of the ATP-CP system and anaerobic lactate system. It was seen to be an efficient way of obtaining accurate test results.
Appendix 1
Three week Fartlek training plan.
References and Bibliography
Astrand P, Rodahl K. Textbook of work physiology. 3rd edition. New York: McGraw-Hill Book Company, 1986.
Brookfield, J. Self Perception in a Moving World. Butterworth and Heinman, New York. 2004
Dick F (2002) Sports Training Principles 3rd ed. A & C Black
Edgerton, V.R. Mammalian muscle fiber types and their adaptability. Amer. Zool. Vol 9: 113-125, 1978
Fulcher K & Fox P (1998) Fit for Sport Metro Books
McArdle, WD. Katch, FI, Katch, VL. Essentials of Exercise Physiology, 3RD Edition. 2006. Lipcott Williams and Wilkins, Baltimore.
ML O'Toole, PS Douglas - Sports Med, 1995. http://www.ncbi.nlm.nih.gov/ pubmed/7604198
National Audit Office. 2001. http://www.nao.org.uk/pn/00-01/0001220.htm
National Health Service. http://www.publications.parliament.uk/pa/cm200607/ cmhansrd/cm070123/text/70123w0029.htm
Powers & Howley (2005) Exercise Physiology, Human Kinetics USA
Quesenberry, C.P. 1998. Pubmed accessed 14/06/2008 .http://www.ncbi.nlm.nih.gov/ pubmed/9508224
Shankar, K. Exercise Prescription. 1999. Hanley and Belfus, Inc. Philadelphia. ISBN 1-56053-258-0
Smith DJ. "A framework for understanding the training process leading to elite performance". Sports Medicine (Auckland, N.Z.) 33 (15): 1103–26.
Watson A & Hennessy L C M (1995) Physical Fitness & Athletic Performance 2nd ed.
Wilmore & Costil (2004) Exercise Physiology, Human Kinetics, Canada
World Health Organization, online Q & A. Nov 2006. http://www.who.int/features/ qa/49/en/index.html
Fig 1. Energy System Recruitment. Source: Fox E. L. et al The Physiological Basis for Exercise and Sport, 1993. Brown (William C). Co, U.S.
Fig 2. Energy Systems. Source: Brian Mac, Sports Coach. http://www.brianmac.co.uk/lactic.htm. Accessed 15/12/2008.
http://www.brianmac.co.uk/idealw.htm
http://www.coolnurse.com/calories_burned.htm
