Types of Exercise
A comprehensive exercise program includes aerobic, muscle strengthening, flexibility, and balance exercises (Johnston 2014; Chodzko-Zajko 2009).
Aerobic ExerciseAerobic exercise is rhythmic and prolonged physical activity that elevates the heart and breathing rates. Examples of aerobic activity include fast walking, running, bicycling, and swimming. Aerobic training increases cardiorespiratory fitness, improves cerebral blood flow, and reduces the risk of death due to heart disease and all causes (Johnston 2014; Wang 2015a; Burton 2004; Ainslie 2008).
"Aerobic exercise" refers to aerobic metabolism, in which oxygen is used to regenerate the energy-storing molecule ATP (adenosine triphosphate) in the mitochondria. Glucose in the blood, glycogen (stored carbohydrate) in muscle cells, and free fatty acids in blood and muscle cells provide fuel for ATP production (Baker 2010).
Muscle-Strengthening ExerciseMuscle-strengthening or resistance exercise involves forceful muscle contraction against external resistance (Johnston 2014). This type of exercise increases muscle strength, size, and endurance, and prevents sarcopenia, or age-related loss of muscle mass and strength. Strength training, when undertaken at an adequate pace, also improves cardiovascular endurance. Examples of muscle-strengthening exercise include weight training using free or machine weights, resistance bands, or body weight (Johnston 2014; Chodzko-Zajko 2009; ACSM 2013).
Flexibility ExerciseFlexibility or stretching exercises entail slow and steady stretching of muscle groups. Stretches should be held for 10 to 60 seconds without jerking or bouncing, and repeated two or three times, progressively increasing the stretch. While mild discomfort is expected, flexibility exercises should not be painful, as pain may indicate minor muscle tearing. Flexibility exercise combined with muscle-strengthening exercises improve range of motion and relax muscles. Stretching before exercise may increase mental preparedness, but there is conflicting evidence as to whether it prevents injury; stretching after exercise, when muscles are warm, may be more effective (Garber 2011; Johnston 2014; Witvrouw 2004; Mayo Clinic 2017).
Balance ExerciseBalance exercises, such as holding positions on one leg or using balance boards, may help those with problems with awareness of motion and relative position as well as prevent falls (Johnston 2014; Johnson 2017). The American Heart Association and American College of Sports Medicine recommend balance exercises for individuals who fall often or have mobility problems. The guidelines include recommendations for the following types of activities (Chodzko-Zajko 2009):
- Increasing the difficulty of postures and decreasing the base of support, such as progressing from two-legged postures to one-legged postures
- Movements that disturb the center of gravity, such as heel-to-toe walking and turning in place
- Postures that stress certain muscle groups, such as standing on toes or heels
- Reducing sensory input, such as standing with eyes closed
Muscle strengthening exercise also improves balance by strengthening muscles and tendons that support joints (Johnston 2014).
High-Intensity Interval TrainingHigh-intensity interval training, or HIIT, is becoming increasingly popular. This type of exercise training consists of short, repeated bursts of intense exercise followed by periods of recovery (Smith-Ryan 2015; ACSM 2014).
High-intensity interval workouts can be performed using several different protocols. The high-intensity exertion phase can last from five seconds to eight minutes, and is followed by recovery periods of no or low-intensity exercise that can last as long as the active phase. During exertion, the heart rate reaches 80-90% of maximum. Perhaps the most common protocol involves 30 seconds of maximal effort cycling followed by four minutes of recovery, with the cycle repeated four to six times per session, three times per week. Other less-demanding formats have also been devised (ACSM 2014; Shiraev 2012; Boutcher 2011).
In a 12-week study in previously sedentary men, a total exercise time of 30 minutes per week, of which only three minutes was intense exertion, was compared with 150 minutes per week of moderate-intensity continuous training. Despite a 5-fold-less time commitment, interval training was found to be equally effective as traditional endurance training at improving insulin sensitivity, cardiorespiratory fitness, and skeletal muscle mitochondrial content (Gillen 2016).
Several other studies have indicated HIIT is superior to continuous moderate-intensity training at improving cardiorespiratory fitness, vascular endothelial function, insulin sensitivity, and arterial stiffness. HIIT also improves blood pressure and cholesterol profiles; promotes fat loss while maintaining muscle; and may be of particular benefit to those with or at risk of type 2 diabetes (Ciolac 2012; ACSM 2014; Jelleyman 2015; Weston 2014).
In a review of studies in patients with lifestyle-induced chronic diseases, HIIT was nearly twice as effective as lower-intensity continuous exercise at improving cardiorespiratory fitness—a strong predictor of mortality (Weston 2014).
Despite perceptions that compliance with recommendations for more vigorous exercise is poor, a study in prediabetics found short-term adherence to HIIT was greater than traditional continuous workouts (Jung 2015). In another study, high-intensity interval running was perceived to be more enjoyable than continuous running (Bartlett 2011). In addition, since "lack of time" is the most common excuse for avoiding exercise, the shorter duration of HIIT can be a major workout incentive (Gibala 2012; Jung 2015; ACSM 2014).
HIIT should be adjusted to a person’s own fitness level. People with health conditions are advised to obtain medical clearance prior to starting a HIIT program (ACSM 2014).