This article is originally published in the NESTA Personal Fitness Trainer manual.
Benefits of Aerobic Training
Your clients probably know it as “cardio.” Aerobic exercise is any type of cardiovascular conditioning performed for a sustained period of time. It can include activities like walking, swimming, running, or cycling.
Aerobic exercise differs from anaerobic exercise such as weightlifting or sprinting which involves quick bursts of energy, performed at maximum effort for a short time.
It All Comes Down to O2. As the body adapts to aerobic training (with oxygen), the body seeks to work more efficiently with oxygen in three ways:
Increase VO2max and Submaximal Endurance
Remember that VO2max (aerobic capacity) represents the maximum amount of oxygen that can be delivered AND utilized by the body.
Most researchers use VO2max as the best indicator of cardiorespiratory endurance. According to the General Adaptation Syndrome (GAS), if the cardiovascular system is stressed through appropriate aerobic exercise the body will both adapt and become more efficient at delivering and utilizing oxygen. This improved oxygen utilization allows for more work to be performed with less effort. There are many factors that affect how much aerobic capacity can be improved, including genetics, gender, and age, to list just a few. A typical sedentary person who trains 3x/week, for 30 minutes a session at 75% of initial VO2max for 6 months can expect a 15- 20% increase in VO2max.
Utilization vs Presentation: What is the Limiting Factor for Improvement?
Aerobic capacity tends to increase proportionally with increases in training volume. With increased training, aerobic capacity will eventually reach an upper limit and VO2max will no longer increase even with harder and longer training sessions. Is it the delivery of oxygen (presentation theory) that is the limiting factor or the ability of muscles to process the oxygen (utilization theory)? Both the presentation and utilization of oxygen improve with exercise and there is evidence that supports both theories. However, a majority of studies indicate that it is the presentation of oxygen (delivery) that is the limiting factor in increased endurance performance.
Increases in Muscle Utilization of O2 (QO2)
Endurance training increases both the size and number of mitochondria in muscles. With more (and bigger) mitochondria, there are more enzymes to allow for oxidative metabolism. The maximal amount of oxygen that a muscle can use is known as the muscle’s maximal respiratory capacity or QO2.
Increases in Muscle Presentation of O2
With endurance training, the amount of blood leaving the heart is increased (cardiac output) and the efficiency of blood flow to the working muscles is improved. The delivery of oxygen is improved in many ways through endurance training such as:
- Increased Cardiac Output
- Increased left ventricle size, leading to increased stroke volume
- Maximum heart rate stays the same or decreases (because the heart is more efficient)
- Increased Blood Flow
- Increased capillaries in trained muscles
- Increased capillary openings
- Increased blood volume
- Better blood distribution
Even MORE Benefits of Aerobic Training
Increase in Lactate Threshold/ Anaerobic Threshold (whichever name you choose)
At low intensities, aerobic metabolism dominates. As intensity increases, anaerobic metabolism starts to contribute to the energy needs of the body and acid is produced. The highest level of sustained intensity of exercise for which measurement of oxygen uptake can account for the entire energy requirement is known as the Anaerobic Threshold (AT). To review, this is the point there is a substantial increase in blood lactate. Again, this is known as the Lactate Threshold (LT).
What’s the difference between AT and LT? Mainly, how the information is gathered. LT is objectively found by taking blood samples during various intensities of an incremental exercise test.
AT is determined through a ventilatory test where ventilation, VO2, and VCO2 are directly measured. It is a noninvasive estimate of lactate threshold. For all practical purposes, AT represents LT.
Why Does Anaerobic Threshold Matter?
Anaerobic threshold is a strong indicator of an athlete’s performance capability. While aerobic capacity can be increased with exercise, there is a limit to how much it can be improved. Athletes who maximize their genetic capacity for increasing VO2max can still increase aerobic performance. Remember that AT/LT is the point when lactate begins to accumulate in the blood. At this point, lactate clearance from the blood cannot keep up with lactate production. Accumulation of acid is a major contributor to fatigue. It might be helpful to think of AT as the point at which an athlete begins to “redline”. An athlete with a higher AT (as a % of VO2max) is able to maintain performance at a higher level than an athlete with the same VO2max but a lower AT.
Look at the figure showing two athletes with the same VO2max. One athlete has an AT of 75% of VO2max, the other has an AT of 88% of VO2max. Notice that the athlete that reaches AT at 88% can maintain a higher race pace before “redlining”.
Muscle Fiber Adaptations
Aerobic training emphasizes the usage of Type I or slow-twitch (ST) muscle fibers. These muscle
fibers will adapt to stress through muscle hypertrophy (growth in cross-sectional area). While these fibers have the capacity to grow (by as much as 25%), the fibers will not result in a hypertrophic response as much as Type II (IIa and IIb) or fast-twitch (FT) muscle fibers would, in response to anaerobic strength training. This may be why bodybuilders tend to look just a little different than marathon runners (yes, that’s just a little sarcasm).
Increased Oxidative Capacity (increased fat metabolism)
Improvements in the muscles’ aerobic energy system functioning through aerobic training create greater systemic efficiency in the use of fat as a significant (or dominant) energy source during exercise. The improved capacity of aerobically trained muscle fibers to use fat is caused by increased fat storage in the muscle fiber, an enhanced ability to mobilize free fatty acids (FFAs), and the improved capacity to oxidize fat.
What is RER and Why Should We Care?
RER (Respiratory Exchange Ratio) is the ratio of CO2 expired to O2 consumed. This ratio is an estimate of the type of energy substrate that the body is currently using predominantly (carbohydrates vs fat) for fuel. Without going into too much science (you can thank us later), the lower the RER number, the greater the percentage of fat being utilized for energy. RER testing shows that aerobic training decreases RER at submaximal effort levels (fat is ”burned” more efficiently).
Decreased Exercise HR and HR Recovery
One of the biggest myths that still persist in the fitness industry is that the goal of cardiovascular training is to train hard enough to raise the heart rate. In truth, at a constant intensity, exercise heart rate should decrease over time. The true goal of cardiovascular training is to make the cardiovascular system more efficient. With proper training, working (training) heart rate and maximum heart rate may both decrease.
A positive indicator of improved CV fitness is realized when heart rate recovery also decreases (improves) over time. Complete heart rate recovery is the time it takes the heart to return to its normal resting rate. During recovery, the body is transitioning involvement from the sympathetic nervous system back to the parasympathetic nervous system.
In general, a more fit person will recover quicker than an unfit person because the body is becoming more efficient at utilizing available oxygen and more efficient at the transport of nutrients and waste. This is cardiovascular efficiency.
Excess Post-exercise Oxygen Consumption (EPOC)
What is happening during the initial recovery period when oxygen demand (and heart rate) is still high? From rest to the start of an aerobic exercise session, it takes time for the oxygen transport system to meet the new energy demands. Because of this, anaerobic metabolism dominates at the beginning of a workout (ATP- CP, glycolysis).
During recovery, anaerobic energy substrates (ATP, CP, and Glucose) must be replenished and by-products (excess H+) removed. This is performed aerobically. Energy demands are not just increased during exercise, but immediately after as well. Following light exercise, EPOC may last several minutes. During intense exercise (such as playing in a football game) or prolonged exercise (such as Olympic or longer distance triathlons), EPOC may last up to 36+ hours. The more well-conditioned the athlete, the less time spent in EPOC following intense or prolonged exercise due to a greater capability for faster recovery.
Benefits of Cardiovascular Training – Summary
- Increased stroke volume (increase heart efficiency) due to increased size of the left ventricle
- Increased cardiac output, workload, and O2 consumption at maximum effort
- Increased heart rate variability
- Increased oxygen utilization
- Decreased blood pressure
- Decreased resting and exercise heart rate
- Increased number of mitochondria (cells utilize oxygen better)
- Increased plasma volume
- Improved respiratory efficiency
- Increased number of capillaries
- Increased myoglobin in muscle cells
- Increase insulin sensitivity
- Increased lactate threshold (due to increase rate of lactate removal)
- Increased ATP, CP and glycogen stores
- Increased release of fatty acids
- Increased ability to oxidize fat, glycogen-sparing, increased endurance at sub-maximal workload
Overreaching, Overtraining, and Detraining
While there is a great majority of individuals who do not exercise enough, there are also a large number of individuals who exercise too frequently or at levels above the appropriate intensity. While the physiological rationale for over-training was examined at the beginning of this chapter, overtraining does not necessarily result from overly intense exercise. Experiencing high levels of emotional or mental stress can also lead to similar symptoms.
For our purposes here, we will refer to overreaching as a state where a few days of rest or light exercise enables the body to recover and return to a normal (what is normal depends upon the individual) physiological state.
Overtraining is a state of fatigue or physio- logical malfunctioning where it may take weeks, months, or even years to return to a normal physiological state and be able to progress and improve significantly. If fatigue and high stress are recognized and dealt with early enough, the ramifications of malfunctioning bodily systems are much easier to overcome.
Detraining refers to diminishing physiological capacity as training becomes infrequent or ceases altogether. Detraining begins to occur and performance gains diminish significantly once a frequent exerciser has not exercised for 2-3 weeks. Detraining does not apply to an individual who exercises very infrequently or who has never exercised. If an individual experiences any number of these symptoms following a few days of complete rest or light exercise (active rest), overreaching or overtraining should be considered and a qualified health professional should be contacted. If symptoms are uncontrollable or continue to progress, a medical doctor or general practitioner must be consulted.
Over Training Signs:
- elevated resting heart-rate/blood pressure difficulty sleeping or restlessness
- fatigue, irritability
- decreased interest in exercising
- immune system breakdown (illness or allergies) failure to progress or improve
- excessive weight loss/soreness frequent muscle cramps or strains
- amenorrhea (lack of menstruation)
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This article is originally published in the NESTA Personal Fitness Trainer manual.
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