Although coaches, instructors, fitness trainers, and physiologists often differ on the terminology of the different aerobic training methods, generally one can divide the training into the following sections. Training zone determination can be performed by measuring lactic acid levels, heart rate in relation to power production, and/or changes in EMG amplitude and muscle fatigue at various points through a progressive stage test. From this information, critical fatigue thresholds can be determined and much more detailed training prescription that focuses on what the athlete needs to work on the most is the result.
This type of aerobic exercise is performed as an entry-level type of conditioning to lead to higher intensity exercise. Another purpose for this long duration, lower intensity cardiovascular exercise is to gradually train the muscles to use the oxygen delivered in the blood for energy and, performance wise, to help create the necessary changes to metabolise lactic acid. Since this type of training mainly recruits slow twitch (type I) muscle fibers, there tends to be little direct effect on anaerobic energy production. The slow twitch muscle fibers’ energy systems are primarily aerobic as dictated largely by the concentration of the aerobic enzymes contained within the fiber. These aerobic and anaerobic enzymes (the latter being in higher concentrations in type IIa and Iib fibers) are ultimately linked to the myosin heavy chain proteins of that particular fiber. Subjecting these muscle fibers to this type of training is believed to help boost these enzymes as well as the number of mitochondria within these fibres which helps in producing more energy (ATP) from oxidation of fat and carbohydrate metabolism. As one becomes more trained, the less carbohydrates they use for energy and the greater fat metabolism of free fatty acids contributes to the process. The energy is then used to help power muscle contraction and aid in the breakdown of lactic acid molecules. Past research and practical appliaction suggest that the stimulus is primarily duration and not intensity based. Other physiological changes would be increases in myoglobin content and increased capillarization. To help deal with the increased demand for oxygen to the muscles there is an increase in stroke volume both at rest and during exercise, partially contributing to the changes in heart rate (although the autonomic nervous system has a role in this as well). Interestingly, actual muscle blood flow is often reduced due to the increased efficiency of the muscles at using the oxygen in the blood
Therefore in order to develop a good aerobic base an individual would need to run at a lower intensity for as long as possible. A good aerobic base would be defined as creating a good concentration of enzymes to help in the oxidation of fatty acids and lactic acid in combination with good capillarization to reduce any rate limiting steps in the energy production cycle that occurs at higher intensities. In addition, a good aerobic base would also help deal with the excess production of lactic acid and to keep it from climbing to critical levels from gylcolysis. Determination of this training zone is based on staying under the aerobic threshold. The aerobic threshold is determined by a slight deflection in ventilation rate when moving from one stage to the next in a progressive aerobic power test. Other methods include surpassing a given level of 2.0 mmol/L of lactic acid blood concentration (this is the method that the Peak Centre uses most often), or changes in the amount of CO2 expired as well as examining the respiratory exchange ratio. A combination of all those factors would be taken into account to find the aerobic threshold. For a more targeted approach towards indiviudal muscle response, recruitment patterns and conduction velocity can change with increasing workload and changing lactate levels in the muscle fibers, monitoring the EMG amplitude combined with frequency spectral changes will also allow you to help find individual thresholds that are muscle specific.
To mark the training zones in order to make it applicable to all types of training, heart rates are generally used. Since heart rates are fairly individualised (fitness level, size of heart, hydration level, stress level, etc.), the heart rate is recorded or extrapolated at the time the deflection occurred or when the individual surpassed the 2.0 mmol/L mark. There is also a margin of error worked into the heart rate zone to allow for measurement error and environmental factors. Generally, as the individual spends more time training in the proper zone, the heart rate for that particular zone will change (increase).
An example of a long slow distance exercise or Zone 1 would be an easy jog or bike for 30 – 60 minutes. Although considered an entry-level type of conditioning, it is a training method that is used 60% – 80% of the time independent of fitness levels. Even Olympic calibre athletes still spend much time in the off-season building a good “aerobic base” to excel at higher intensities. However, it is important to remember that this type of exercise does little to directly boost VO2 max.
To perform this type of exercise: This type of training is an easy paced type of exercise where your heart rate should be about 120 – 140 beats per minute (bpm) that can go on for as long as 60 minutes. If your heart rate is above 160, you are probably going a bit to fast. Slow down and check your heart rate again in about 5 minutes. You should be going at a pace where you are breathing heavier but you can speak in fluid sentences. In other words you do not have to take occasional big breaths in order to get enough air.
This training method also continues to help to improve the delivery and metabolism of the oxygen in the blood as outlined in Zone 1/LSD type training, but also introduces higher levels of lactic acid to the blood. During Zone II training, your body is still relying on aerobic metabolism for the majority of the energy production, however anaerobic metabolism also begins to significanlty contribute as well in varying degrees. This is because the rate and amount of energy you are expending can no longer be provided by only aerobic metabolism, anerobic energy production needs to kick into help provide the extra energy. As anaerobic metabolism increases, lactic acid also increases proportionately when exercisisng below anaerobic threshold.
As you train at a Zone II pace, Type IIa fibers (or fast, oxidative glycolytic – FOG fibers) are recruited. As these muscle fibers have both aerobic and anerobic enzymes, the anaerobic system and lactate delivery and production cycle is now trained under the exercise stimulus as well. This training helps get the exercised muscles used to being exposed to moderate levels of lactic acid, trains the muscles to remove it from the blood, increase muscle capillarization, as well as help increase anaerobic enzymes within the muscle fiber responsible for its resepective energy production. More specifically, it begins to train the enzymes to help transfer the lactic acid molecules across the muscle fiber membrane wall. This leads to better recovery and an ability to do more work at a higher intensity as it speeds the clearing of lactic acid from the blood and makes anerobic metabolism that much more efficient.
In addition, the slow twitch fibers are also exposed to a higher lactate environment and therefore enables those fibers to help deal with higher lactic acid levels as well. Similar to LSD or Zone 1, this training technique is also a stepping stone to higher intensity work.
To perform this type of exercise: This type of exercise is a bit harder than LSD where your heart rate may bounce between 140 – 160. For example, exercise for 10 minutes at 140 bpm and then increase intensity to go about 10 minutes at 160 bpm. This cycle can continue for 35-40 minutes. A heart rate above 180 would indicate you are probably going to fast again, therefore slow down and re-check your heart rate. The light intervals should have you breathing at a fairly heavy rate where you could not speak in fluid sentences. This is usually at a pace where going a bit faster would feel considerably more uncomfortable.
The name for this type of training comes from what is referred to as anaerobic threshold. Anaerobic threshold is the point your body switches from using mainly oxygen to generate energy (aerobic) to burning the body’s sugar (gycogen) stores. It is desirable performance wise to be able to do a high rate of work (run at a fast pace for example) before your body reaches this point. When working above anaerobic threshold, most individuals last anywhere from 15 seconds (in extremely high rates of work such as sprinting) to 5 – 15minutes (such as fast running) before fatigue sets in and they eventually have to slow down. The cause of this fatigue is a result of rapidly climbing lactic acid that ultimately affects affects muscle contraction, ventilation rate, blood pH, and neural functoning
At anaerobic threshold, the muscle fibres and circulatory system are just able to cope with the amount of lactic acid produced by Type IIa fibers and possibly some Type IIB (fast twitch) fibers. In this situation the body is metabolising lactic acid within the muscle fibers, liver, and respiratory system and is able to keep the level under homeostatic control. However, a slight increase in pace would tip this balance in favour of the anaerobic system and would result in lactate levels climbing rapidly (logarithmically actually!) as production would exceed the amount the body could handle.
The short, high part of the intervals at this zone helps to gently exceed this balance and place the body in a state with excess lactic acid. The lower intervals help to train the system to get rid of the excess lactate in the body. By repeating these intervals, your anaerobic threshold should rise slightly as the body becomes more accustomed to dealing with lactic acid at higher levels. By following the threshold training method outlined in your exercise program, this helps your body deal with lactic acid better by stressing the appropriate enzymes and allows you to do a greater amount of higher intensity work before fatigue slows you down. In essence it helps to raise your anaerobic threshold which is somewhat determined by your lactate and ventilatory threshold depending on how you interpret anaerobic threshold. At the Peak Centre they believe anaerobic threshold occurs at 4.0 mmol/L of blood. In a large percentage of people this is generally true however it is not unusual to see a lactate threshold up around 5.0 mmol/L as well. A true anaerobic threshold is determined from several lactic acid measurements over a period of time and combined with ventilation readings to look at ventilatory threshold. This would obviously make for an impractical test, however looking at lactate threshold and ventilatory threshold combined would probably be accurate for a one time field test.
Physiological changes affected by training at anaerobic threshold or by training in zone III would include raising the anaerobic threshold, increases in anaerobic enzyme activity and efficiancy, and other changes similar to that for Zone II
To perform this type of exercise: This type of exercise is harder than MI or Zone II and where you will really start to breathe heavier and feel the lactic acid build up. For this exercise your heart rate should bounce between 160 – 180 where you go for about 5 minutes at 160 bpm and then increase intensity to go about 5 minutes at 180 bpm. Essentially, when you start to feel the muscles burn and starting to get tired you go back down to the easier intensity in order to recover. This cycle can continue on for up to 30-35 minutes. At the end of this type of cardio you should feel really tired and that you probably could not go on any more. Signs of fatigue you should be aware of are not being able to follow proper technique for longer than a couple of minutes and not being able to follow a certain pace without overshooting or undershooting your target heart rate.
Zone IV and V helps to improve your body’s ability to use oxygen at higher intensities thereby improving your maximum aerobic fitness level or VO2 max. At VO2 max, your aerobic system is working at 100% maximum of energy production along with a certain percentage of your anaerobic system, so much so that any increase in pace will result in your body less able to produce energy from oxygen resulting in a drop of oxygen metabolism. The goal of Zone IV training is to help boost VO2 max by increasing the amount of time you are spending at VO2 max. The lower portion of the intervals allow your body to recover and lower lactic acid levels to allow you to increase your pace back up to max to help boost your VO2. Physiological changes from maximum exercise results in an increase in stroke volume from cardiac hypertrophy and increase in contraction efficiency; increases in lactic acid production combined with better tolerance of higher lactic acid levels; and increases in pulmonary function and lung volumes resulting in better gas diffusion capabilities (ability to move large amounts of oxygen and carbon dioxide across a larger surface area. Although Zone V can also increase VO2 max, the main goal of this type of training is to decrease the amount of time it takes for your body to reach VO2 max. This will allow an athlete to reach his/her maximum aerobic power in minimal time thereby maximizing his her speed (an 800m runner is a good example of someone who would benefit from this type of training). Similar to Zone IV, other benefits include increasing the concentration of enzymes that help transport lactic acid from the muscle cell into the blood stream. One indication that may illustrate that the lactate is being removed from the exercising muscle would be a maximum lactate for a distance runner of about 8 – 10 mmol/L lactic acid in the blood.
To perform this type of exercise: This will be the hardest exercise that you will have to perform and you will really feel the lactic acid fatigue and burning as well as your breathing will be fast and deep. Similar to the last 2 exercise methods your heart rate should bounce between 120 and 180-185 bpm with about 2 – 5 minutes at the high level and about 2 – 5 minutes at the low level. Similar to threshold training, you should only exercise at the higher intensity until you really start to feel the fatigue and burning sensation, then slow down to the lower intensity. This should be repeated for a total of about 30 minutes or as long as you can last. With this type of exercise you will experience a rise in heart rate with each interval at the lower intensities. This is fine and is to be expected.
Checking your heart rate
As your perform aerobic exercise heart rate increases with a corresponding increase in intensity. Taking a heart rate (HR) measurement every so often will insure you stay at the proper intensity. This type of monitoring helps to set a proper exercise pace for those who choose to exercise outdoors. It is also important to remember to allow at least 3 minutes for HR to stabilize after the beginning of exercise or after a change in pace or intensity and to measure it either while doing the exercise or immediately upon stopping. For longer duration exercise heart rate drift is common and is in part due to dehydration.