Aerobic exercise is one of the type of physical exercise which helps in promoting physical fitness and preventing health illness.Aerobic exercise is defined as any form of physical activity that produces an increased heart rate and respiratory volume to meet the oxygen requirements of the activated muscle.The American College of Sports Medicine (ACSM) defines aerobic exercise as any activity that uses large muscle groups, can be maintained continuously and is rhythmic in nature.
Aerobic exercises are typically moderate-intensity exercises performed to improve one’s cardiorespiratory fitness and in promoting energy expenditure and fat utilization.As the name suggest these kind of exercises depend primarily on aerobic energy- production i.e. muscle groups activated by this type of exercise rely on aerobic metabolism i.e. using oxygen to extract energy in the form of adenosine triphosphate (ATP) from amino acids, carbohydrates and fatty acids.
Examples of aerobic exercise include walking, cycling, swimming, jogging, dancing, hiking, long distance running,etc.
Effects of aerobic exercises
Aerobic exercises mainly shows an effect in health-related components of fitness especially cardiovascular endurance and body composition. There is various neuromuscular adaptation following aerobic exercises. Physiological effects of aerobic exercises are explained below:
- Heart rate: Resting HR decreases with aerobic training and is lower at any given workload. The maximum HR is unchanged.
- Cardiac output:Maximum CO increases, whereas resting CO is stable. Resting SV increases, with a corresponding decrease in the resting HR.
- Aerobic capacity: Maximal aerobic capacity or maximal oxygen uptake (VO2max) is a measure of the maximum amount of oxygen that an individual can use per unit of time during strenuous physical exertion at sea level.Maximum aerobic capacity increases with aerobic training. The resting Vo2 is stable, as is the Vo2 at a given workload. The changes are specific to the trained muscles.
- Stroke volume: SV increases at rest and is maintained at a lower HR, resulting in a lower RPP for a given level of exertion.
- Myocardial oxygen capacity: Maximum Mvo2 usually does not change, but at a given workload, Mvo2 decreases with training. This reduces episodes of angina.
- Peripheral vascular resistance (PVR): Aerobic training reduces arterial and arteriolar tone, thereby decreasing cardiac “afterload” and PVR. The reduction in PVR results in a lower RPP and a lower Mvo2 at a given workload and at rest.
- Higher endurance during intense physical activity because of blood volume increase.
- Lungs volume increase
- Cardiac muscle strength
- HDL level increase (the ratio of total cholesterol to HDL decrease reduces the risk of atherosclerosis)
- Emotional stress overcoming and enhancing mental and emotional well being
- Increase bone density.
Before prescribing or doing any aerobic exercises, it is very necessary to do pre-participation health screening to ensure exercise training can be safely initiated. It is also important to do exercise testing used for diagnostic (i.e., identify abnormal physiologic responses), prognostic (i.e., identify adverse events), and therapeutic (i.e., gauge the impact of a given intervention) purposes as well as for physical activity counseling and to design an exercise prescription.
Standard graded exercise tests (GXT) are used clinically to assess a patient’s ability to tolerate increasing intensities of aerobic exercise. Grade treadmill testing,cycle ergometer, arm ergometer are some examples, and Bruce treadmill test remains one of the most commonly used protocols in grade treadmill testing. Via these testing, it would help to identify the criterion measures for cardiovascular fitness and exercise capacity.
Maximal aerobic power or maximal oxygen uptake (VO2max): It is a measure of the maximum amount of oxygen that an individual can use per unit of time during strenuous physical exertion at sea level.Maximal aerobic power is typically expressed in absolute power as L/min or normalized for body weight as mL · kg−1 · min−1.It is convenient to express oxygen uptake in multiples of sitting/resting requirements. Peak metabolic equivalents (MET): One metabolic equivalent (MET) is a unit of sitting/resting oxygen uptake (≈3.5 mL of O2 per kilogram of body weight per minute [mL · kg−1 · min−1]). METs are a useful, convenient, and standarized way to describe the absolute intensity of a variety of physical activities. Light physical activity is defined as requiring 3 METs, moderate as 3–6 METs, and vigorous as 6 METs.  V̇o2 max is influenced by age, sex, exercise habits, heredity, and cardiovascular clinical status.
American College of Sports and Medicine (ACSM), 2014 has prescribed aerobic exercises based on FITT ( frequency, intensity, time, type) in different conditions and age groups.
Cardiovascular Disease/ Risk factors and Aerobic Exercise
Cardiovascular diseases (CVDs) are the number one cause of death globally, taking an estimated 17.9 million lives each year. Out of many cardiovascular diseases, heart attack and stroke being the most common cause of death. Lifestyle modification is the first line of treatment suggested by WHO and American heart association which includes diet and exercise. Supervised cardiac rehabilitation protocols are there to guide the treatment.
A randomized controlled trial done in 2019, has shown benefits of combined training (aerobic 30 minutes/session plus resistance 30 minutes/session) 3 days/week for 8 week rather than aerobic exercise and resistance exercise alone. Combined training provided significant reductions in peripheral (-4 mmHg) and central diastolic BP (-4 mmHg), increase in CRF (4.9 ml/kg/min), increase in upper (4 kg) and lower (11 kg) body strength, and increase in lean body mass (0.8 kg).
Diabetes and Aerobic Exercise
Supervised exercise interventions improve glycated hemoglobin (A1C), triglycerides (TG), and cholesterol (9) in people with type 2 diabetes. Both aerobic and resistance exercise are beneficial, and it is optimal to do both types of exercise. At least 150 minutes per week of aerobic exercise and at least 2 sessions per week of resistance exercise are recommended.
It is very important to maintain the dose of insulin and time of exercise and also carbohydrate intake during and after exercise to prevent post-exercise hypoglycemia. For detail please have a look at this guideline.
Chronic pain and Aerobic Exercises
Aerobic exercise programs have shown physiological, psychological, and articular benefits in patients with chronic diseases (e.g., arthritis, osteoarthritis, and fibromyalgia). Aerobic exercise stimulates the release of endorphins that relieve pain by inhibiting the pain pathways. It makes the patient more active, reducing the fear of moving (kinesiophobia) and increasing self-confidence.
A systematic review protocol published in 2019 has shown the effect of aerobic exercise and chronic non- specific low back pain. Aerobic exercise with a duration of 15 to 60 continuous minutes and intensity of 60 to 90% of the maximum heart rate had shown significant improvement.
Mental health and Aerobic Exercise:
In the systematic review and meta-analysis done in 2019 across 11 eligible trials (13 comparisons) involving 455 patients, aerobic exercise delivered for an average of 45 minutes, at moderate intensity, three times/week, for 9.2 weeks and showed a significantly large overall antidepressant effect.
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