What is the weekly total time recommended for cardiorespiratory training if moderate intensity exercise like brisk walking?

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Baseline Characteristics of Study Participants

	Group	Group
Below	Meets	Exceeds	Non-Responders	Responders
M	SD	M	SD	M	SD	M	SD	M	SD
Age (yrs)	48.1	9.3	51.2	6.5	50.8	9.3	49.5	9.2	51.0	8.2
Education (yrs)	16.5	4.4	14.8	3.2	16.8	3.9	16.4	4.5	16.0	3.4
Body mass index (kg/m2)	28.0	5.8	29.4	5.3	27.8	5.1	28.4	4.9	28.2	5.6
VO2Baseline (l/kg/min)	2.4	0.9	2.1	0.6	2.0	0.7	2.1	0.7	2.1	0.7
Sex
Men (n)	7		12		22		19		22
Women (n)	9		8		16		13		20

The department of health and human services of the United States has published guidelines for physical activity for Americans in 2018. It is the modified from one from the 2008 US Physical Activity Guidelines and the World Health Organization (WHO) Physical Activity Guidelines in 2010 [2]. The Ministry of Health and Welfare of Korea issued guidelines of physical activity for Koreans in 2013. The Korean and US guidelines are similar, and the revised guidelines have the same basic principles, although some guidelines have been revised and supplemented.

In all the physical activity guidelines, adults are encouraged to practice moderate aerobic physical activity for at least 150 minutes per week, or alternatively 75 minutes of high intensity exercise. High intensity exercise means vigorous intensity exercise. In this article, both words have been used as the same meaning. We can assume 1 minute of high intensity activity is equal to 2 minutes of moderate intensity activity. When combining high and moderate intensity activities, the guidelines of 150 minutes or more per week should be based on moderate intensity activity. For example, if you have 50 minutes of high intensity activity per week (100 minutes as moderate intensity) and 60 minutes of moderate intensity activity, it will be calculated as 160 minutes of moderate physical activity.

The latest US guidelines state that the moderate aerobic physical activity should be at least 150–300 minutes. This suggests that it is a minimum goal to increase to 300 minutes as much as possible, rather than just 150 minutes per week. It also stated that more than 300 minutes of moderate physical activity is linked to more health benefits.

Moderate physical intensity refers to the exercise intensity corresponding to 3 to 5.9 metabolic equivalents (METs), while high intensity refers to 6 METs and more. One MET is an oxygen uptake of 3.5 mL/kg/min when an adult is resting and corresponds to an energy consumption of 1 kcal/kg per hour. Moderate (3 to 5.9 METs) and high intensity (over 6 METs) physical activities are broad, but the high intensity is roughly double the intensity of moderate intensity.

During light-intensity activities most people are able to sing, during moderate-intensity they can talk but not sing, and during vigorous activities, even talking is difficult.

In the past, physical activity for more than 10 minutes at a time was recommended because evidence was based on the research that studied physical activities for longer than 10 minutes. But it is now known that exercising for as little as 10 minutes is effective, so exercise duration is no longer emphasized [3].

Since sparse exercise, defined as between 1–2 times per week, increases the risk of injury, it is recommended to exercise three or more days a week, for as many days as possible. Particularly, some papers showed that chronic disease patients should perform exercises for more than 3 days a week. Because increased insulin sensitivity by acute bout of exercise dissipate in 48–72 hours [4].

Many data sets define the intensity of exercise by the type of physical activity. The most extensive and accurate list is the compendium of physical activities from the University of South Carolina [5]. Intensities of daily activities, such as gardening, house chores, as well as sports activities, are clearly defined.

It is inappropriate to express intensity of exercise by the amount of sweat. Sweating ability varies from person to person and is affected by temperature and humidity. To be more precise, the intensity can be expressed as heart rate or maximum oxygen uptake, but this is too complicated to use in practice.

Muscle strengthening exercises or resistance exercises reduce the risk of injury, and help maintain weight. It is better to space muscle strengthening exercises to 2 to 3 times a week by each muscle groups rather than on consecutive days. This is because micro-tears in muscle fibers caused by muscle strengthening exercises need time to recover. Moreover, if exercise is performed frequently, the risk of injury may increase.

Muscle strengthening exercises include dumbbells, weight-lifting, push-ups, sit-ups, knee-flexion and extension, and moving objects. Most of the exercises using instruments at a gym are muscle strengthening exercises.

A typical method of determining the appropriate weight for an individual is as follows:

First, there is a way to express the load as a percentage of the maximum weight, or 1 repetition maximum (RM). Approximately 60%–70% of 1 RM (moderate to hard intensity) is for novice to intermediate exercisers to improve their strength. At 80% or higher of 1 RM (hard to very hard intensity) is when experienced strength trainers to improve strength. With 40%–50% of 1 RM (very light to light intensity), older persons and sedentary people initially beginning to exercise can start to improve strength.

The second is a method that estimates appropriate starting weight by what can be lifted. It is used largely because it is easy to measure. Generally, the weight recommended for resistance exercise is the one that can be lifted 8 to 15 times at a time.

Muscle strength is usually increased by the weighted exercise with eight repetitions, while muscular endurance is improved by the one 15 repetitions. Therefore, at the beginning, using a weight that can be lifted only 8 times at a time is recommended. If the designated weight can be lifted 15 times at a time, then it can be increased.

The easiest way is to breathe while doing muscle strengthening exercises is slowly without a pause while lifting a weight for 3 seconds, resting for 1 second, then lowering it for 3 seconds. This is repeated 8–15 times, which is called a set. It is appropriate to perform three sets of muscle strengthening exercise.

Guidelines recommend the elderly or 65 years of age or older should do same physical activities as adults. Especially for the elderly, prevention of falls is important, so balance, leg strength, and flexibility should be improved.

Physical activities for fall prevention should be performed more than 3 times a week, which can include the following: standing on one leg, moving the upper body while standing on one leg, standing or moving on a heel, standing with closed eyes, and standing on a soft, bumpy, or inclined floor. Physical activity should be modified according to the physical fitness and situation to prevent injury.

Children and adolescents should perform 60 minutes or more of physical activity daily which includes aerobic, muscle and bone strengthening activities.

Most of the 60 minutes or more per day should be either moderateor vigorous-intensity aerobic physical activity and should include vigorous-intensity physical activity for at least 3 days a week. They should also include muscle and bone-strengthening physical activity on at least 3 days a week. Jumping, hopping, skipping, and dancing are activities that are good examples of these.

Warming up and cooling down should be done pre- and post-exercise period. These are physical activities with an intensity of about 50% of the originally planned exercise and may include stretching [6]. For example, you can walk and stretch before and after jogging.

Although the evidence of warming up for prevention of injuries is weak, it is recommended to be carried out to prevent musculoskeletal injuries and heart attacks. Cooling down is also recommended to promote recovery from minute injuries and to prevent dizziness after exercise.

Physical activity should also be performed for chronic patients because regular physical activity is very important for general health maintenance and prevention of cerebrovascular disease. Primary care physicians should encourage the patients with chronic diseases to perform physical activity, educate them on how to exercise safely in accordance with their physical strength, and give them precautions for exercise [7].

Table 1 summarizes the recommendations of primary care physicians recommend physical activity for the patients based on the WHO, US, and Korea Physical Activity Guidelines.

Recommendations for physical activities for the patients in primary care

Recommendations
1.	Primary care physicians should frequently check on the amount of physical activity performed by the patients and encourage physical activities.
2.	Educate patients to perform the following physical activities:
	1)	Move as much as possible and avoid sedentary activities.
	2)	For substantial health benefits, adults should perform at least 150–300 min/wk of moderate-intensity, 75–150 min/wk of vigorous-intensity, or an equivalent combination of moderate- and vigorous-intensity aerobic activity. Preferably, aerobic activity should be spread throughout the week. Additional health benefits are gained by engaging in physical activity beyond the equivalent of 300 minutes (5 hours) of moderate-intensity physical activity per week.
	3)	Adults should also perform muscle-strengthening exercises of moderate or greater intensity that involve all major muscle groups on 2 or more days a week, as these activities provide additional health benefits.
	4)	Guidelines for the elderly (aged 65 years or older) are as follows:
		(1)	The key guidelines for adults also apply to the elderly patients depending on their condition.
		(2)	Balance training and fall prevention exercises should be performed more than 3 times a week
		(3)	Older adults should determine their level of effort for physical activity relative to their level of fitness.
	5)	Guidelines for children and adolescents
		Patients should perform 60 minutes or more of moderate-to-vigorous physical activity daily with the following distribution:
		(1)	Aerobic: Most of the daily activity should be either moderate-or vigorous-intensity aerobic physical activity and should also include vigorous-intensity physical activity on at least 3 d/wk.
		(2)	Muscle-strengthening: Children and adolescents should include muscle-strengthening physical activity as part of their 60 minutes or more of daily activity on at least 3 days a week.
		(3)	Bone-strengthening: Children and adolescents should include bone-strengthening physical activity on at least 3 days a week.
3.	Warming up and cooling down exercises are recommended in the pre- and post-exercise period, respectively.
4.	If patients have chronic diseases, they must engage in physical activity, as outlined above; however, the following considerations should be kept in mind:
	1)	Regular physical activity is crucial to maintaining health and preventing cardiovascular disease complications.
	2)	Patients must consult their physician and work out safely according to their fitness level.

Exercise is one of the main treatment methods for some musculoskeletal disorders [10]. Chronic pain leads to muscle atrophy and joint contracture, fatigue and even depression, which exercise can then alleviate.

Muscle strengthening exercises and flexibility and balance training are the cornerstones for the treatment of musculoskeletal diseases.

Muscle strengthening exercise is recommended to be performed 2–3 times a week. It is necessary to leave more than one day of rest in between to relax and strengthen muscles.

Stretching is required for whole body muscles. Larger muscles such as the calves, thighs, hamstrings, lumbosacral spine, and anterior shoulder muscles particularly should be stretched to be flexible. For those with back pain, it is essential to stretch the muscles behind the waist and femur. Range of motion exercises are helpful for the arthritic joints.

A sense of balance prevents injuries caused by falls. Although balance improves to some extent with muscle strengthening or stretching exercises, it is preferable to have active balance training.

Exercise therapy is effective in the treatment of some musculoskeletal problems such as shoulder instability and/or impingement syndrome, myofascial pain syndromes (upper trapezius, sternocleidomastoid muscle, levator scapulae, and other such muscles), adhesive capsulitis, tennis and golf elbows, osteoarthritis, patellofemoral pain syndrome, and chronic low back pain.

In order to treat musculoskeletal pain of the shoulder, exercises for shoulder stability and rotator cuff strengthening are important. Muscle strengthening and stretching of the wrist are needed for tennis and/or golf elbow. To prevent and treat knee osteoarthritis, walking, cycling and swimming are recommended. Aerobic exercise and muscle strengthening training around the joints are needed for the treatment of osteoarthritis. Weight reduction of 5% of total body weight improves osteoarthritis if the patient is overweight. Overall, exercise reduces musculoskeletal pain and improve function, quality of life as well as mental health.

Exercise is not recommended for acute lower back pain although it is effective for chronic lower back pain (LBP). Core stabilization exercises are recommended for chronic LBP. Aerobic exercise is also good for chronic LBP.

Exercise should be modified according to the individual’s response. For example, if the patient feels pain during the musculoskeletal exercise, it is recommended to hold the exercise. If the patient feels pain next day as well, the amount of exercise should be reduced 50%. From there, they can gradually increase the amount.