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Chapter 4 General Principles of Aerobic Exercise Prescription

Aerobic activities involve rhythmic, repeated, and continuous movements of the same large muscle groups for at least 5 min. Anaerobic or resistance activities use muscular strength to move a weight or work against a resistant load and are fully discussed in chapter 8. A program of regular exercise that includes cardiorespiratory, resistance, flexibility, and neuromotor training beyond activities of daily living to improve and maintain physical fitness and health is essential for most adults (Physical Activity Guidelines Advisory Committee 2008, Garber 2011)

All exercise programs need to be designed to address mode (type of activity), intensity (how difficult), frequency (how often), duration (how long), and appropriate progression. Rates of progression depend on an individual’s functional capacity, medical and health status, age, individual activity preferences and goals, and tolerance to the current level of activity (Colberg 2011). Empowering individuals to set their own specific goals is the ultimate aim of such programming.

Case in Point: Aerobic Exercise Rx for Uncomplicated T2D

KK is a 50-year-old woman who was recently diagnosed with type 2 diabetes (T2D) during a routine annual checkup with her primary care physician. She has already met with a dietitian to improve her dietary plan, but she wants to get started doing more exercise to manage her blood glucose levels without the need for medications. In the past decade or two, she has gone through phases of being more active—walking daily—and periods of more inactivity, and she was in one of the latter when diagnosed; she does do a lot of standing and walking, though, in her full-time job. Since being diagnosed a month ago, she has lost ~10 lb thanks to dietary improvements, but she has another ~40 lb that she still desires to lose. Her goal with her physical activity is to lose more weight, get more fit, and keep her diabetes in check (without medications).

Resting Measurements

Height: 64 inches

Weight: 170 lb (180 lb at diagnosis)

BMI: 29.2 (high end of “overweight” category)

Heart rate: 80 beats per minute (bpm)

Blood pressure: 135/75 mmHg

Fasting Labs (1 Month after Diagnosis)

Plasma glucose: 105 mg/dl (controlled with lifestyle intervention only)

A1C: 6.2%

Total cholesterol: 180 mg/dl

Triglycerides: 125 mg/dl

High-density lipoprotein cholesterol: 50 mg/dl

Low-density lipoprotein cholesterol: 105 mg/dl

Questions to Consider

1. What type of aerobic exercise should KK start doing?

2. What would be the best exercise Rx for her in terms of exercise frequency, intensity, and duration?

3. How should her exercise training progress over time?

4. Are any precautions needed for KK when she exercises?

(Continued)

GENERAL AEROBIC EXERCISE RECOMMENDATIONS

Aerobic (or cardiorespiratory) exercise is defined as continuous, dynamic exercise that uses large muscle groups and requires aerobic metabolic pathways to sustain the activity (Haskell 2007, Physical Activity Guidelines Advisory Committee 2008). Examples include walking, jogging, running, cycling, swimming, water aerobics, rollerblading, and cross-country skiing. Aerobic exercise has been the mode of physical activity traditionally prescribed for diabetes management and prevention. Most of its benefits in terms of management of blood glucose levels are related to acute and chronic improvements in insulin action. The acute effects of a recent bout of exercise account for most of these improvements, but admittedly are short-lived, whereas regular exercise training generally results in a more lasting effect through different mechanisms (Hawley 2008, Winnick 2008).

Aerobic Exercise Recommendations for Adults

The American College of Sports Medicine (ACSM) recommends that most adults engage in moderate-intensity aerobic training for at least 30 min/day on ≥5 days/week (a total of at least 150 min weekly), vigorous-intensity training for at least 20 min/day on ≥3 days/week (at least 60–75 min/week), or a combination of moderate- and vigorous-intensity exercise to achieve a similar amount of training (Haskell 2007, Nelson 2007, Garber 2011). The latest federal guidelines (2008) are similar, but allow for 150 min of moderate or 75 min of vigorous activity weekly (Physical Activity Guidelines Advisory Committee 2008). For additional and more extensive health benefits, adults should increase their aerobic physical activity to 300 min (5 h) a week of moderate-intensity, or 150 min a week of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate- and vigorous-intensity activity (Physical Activity Guidelines Advisory Committee 2008). Additional health benefits are gained by engaging in physical activity beyond this amount. The recommended physical activity guidelines and prescription for adults and older adults are available online through the ACSM (www.acsm.org) or U.S. federal guidelines (www.health.gov/paguidelines).

Aerobic Exercise Recommendations for Adults with Diabetes

For individuals with type 1 diabetes (T1D), exercise recommendations are closely aligned with those for apparently healthy people (Haskell 2007, D’Hooge 2011), whereas recommendations for T2D are more reflective of guidelines for obesity, hypertension, and sedentary lifestyles (Sigal 2007; Colberg 2010, 2011) given that ~80% of adults with diabetes are overweight or obese. Most individuals with T2D also have a low aerobic capacity (Boulé 2003), leading to the recommendation that they engage in 150 min of moderate (or higher-intensity) aerobic activity weekly (Colberg 2010, American Diabetes Association 2013). Such individuals should focus on appropriate exercise durations to achieve adequate levels of calorie expenditure (Levine 2005, 2008). Recommendations for women with uncomplicated gestational diabetes (GDM) include engaging in 30 min of moderate intensity activity like brisk walking on most days of the week (150 min weekly) (Committee on Obstetric Practice 2002).

INDIVIDUAL AEROBIC EXERCISE SESSIONS

Each aerobic exercise session generally has three distinct parts or phases:

• Warm-up

• Conditioning phase

• Cooldown

Warm-Up

Doing a warm-up includes 5–10 min of a physical activity done at a slower speed or lower intensity, such as cycling slowly before picking up the pace. Warming up before moderate- or vigorous-intensity aerobic activity allows a gradual increase in heart rate (HR) and breathing at the start of activity (Physical Activity Guidelines Advisory Committee 2008). It may help reduce muscle injury and facilitates a safe transition from rest to exercise by stretching postural muscles, increasing blood flow, elevating body temperature, and increasing oxygen availability and metabolic rate. Alternately, warming up for a muscle-strengthening activity involves doing exercises with lighter weights or resistance to start.

Conditioning Phase

This phase is the most important for achieving fitness and other goals as it includes the actual activities to enhance cardiorespiratory fitness, muscle strength and endurance, or flexibility (depending on the training protocol). Time spent doing the warm-up and cooldown counts toward meeting aerobic activity guidelines only if the activity is of at least moderate intensity (e.g., walking briskly as a warm-up before jogging) (Physical Activity Guidelines Advisory Committee 2008).

Cooldown

A cooldown includes at least 3–5 min of doing a lower-intensity activity to help the body gradually recover from the conditioning phase and safely transition back to a resting state. Perhaps most important, cooling down helps prevent blood from pooling in the arms and legs (and thereby lessens the chance of fainting at the end of exercise), as well as aids in the removal of metabolic by-products like lactic acid immediately after exercise. HR monitoring can be effective in monitoring recovery from an exercise bout. If an individual takes medications for hypertension that act as vasodilators, he or she may require a longer period of active cooldown to prevent hypotensive episodes postexercise (Balady 2007).

EXERCISE PRESCRIPTION FOR AEROBIC TRAINING

The exercise prescription is an actual plan for an individual to follow to reach his or her physical fitness or diabetes management goals. The five components of typical aerobic exercise prescription should at a minimum include the following:

• Mode

• Intensity

• Frequency

• Duration

• Progression

Mode

The types, or modes, of aerobic activity that are recommended for individuals with diabetes are highly dependent on their preferences and skill level. Although health-related benefits of improved physical fitness do not depend on the type of aerobic exercise done, the actual fitness gains are somewhat activity specific. Walking is the most common type of physical activity done by individuals with diabetes and often is the most convenient. Other low-impact or non–weight-bearing types of activity, such as cycling, swimming, and aquatic or chair exercises, may be more appropriate for those with complications or coexisting conditions like peripheral or autonomic neuropathy (Browning 2005, Duncan 2005, Colberg 2009). For individuals without lower body joint limitations, jogging and running are acceptable higher-intensity activities.

Although the mode of physical activity (e.g., walking, running, swimming, chair exercises, rowing, etc.) is important to consider, any type of increased movement appears to initially improve an individual’s fitness level. Sedentary adults or youth who begin to participate in any physical activity experience measurable results in their fitness levels. Individuals should choose activities that can safely and effectively improve cardiovascular endurance and maximize caloric expenditure (Haskell 2007, Nelson 2007, Colberg 2010). A wide range of physical activities can be included in the exercise prescription, and all possible activities that the individual is interested in doing should be considered, if they are safe to perform. As he or she becomes more successful and confident, options can be expanded and other types of physical activities can be added or substituted.

Intensity

Determining appropriate aerobic exercise intensity is important for anyone with diabetes. The prescribed intensity must match the individual’s current fitness capabilities. For example, if an activity is too easy, it may not raise fitness levels effectively, but if it is too hard initially, the individual may not be able to complete the workout, may become injured, or may be discouraged from exercising altogether. Physical activity guidelines for adults focus on both moderate-intensity activity and vigorous-intensity activity (Haskell 2007, Physical Activity Guidelines Advisory Committee 2008, Garber 2011). Examples of activities in each of these categories are given in Table 4.1 (Physical Activity Guidelines Advisory Committee 2008). As a rule of thumb, a person doing moderate-intensity aerobic activity can talk, but not sing, during the activity. A person doing vigorous-intensity activity cannot say more than a few words without pausing for a breath.

Table 4.1 Intensity of Various Aerobic Physical Activities (Based on Absolute Intensity)

Moderate

Vigorous

• Walking briskly: 3 mph or faster (but not race-walking) • Water aerobics and pool exercise • Bicycling: slower than 10 mph • Tennis (doubles) • Ballroom dancing • General gardening • Rollerblading • Hiking • Skateboarding • Canoeing • Softball and baseball • Housework (like sweeping)

• Race-walking, jogging, or running • Swimming laps • Tennis (singles) • Aerobic dancing • Bicycling: 10 mph or faster • Jumping rope • Heavy gardening (continuous digging or hoeing, with heart rate increases) • Hiking uphill or with a heavy backpack • Jumping rope • Martial arts (e.g., karate) • Kickboxing or boxing • Sports like basketball, soccer, and tennis • Active games that involve running and chasing

Individuals can do either moderate-intensity or vigorous-intensity aerobic activities, or a combination of both. It takes less time to get the same benefit from vigorous-intensity activities as from moderate-intensity activities. In general, 2 min of moderate-intensity activity is the equivalent of 1 min of vigorous-intensity activity (Physical Activity Guidelines Advisory Committee 2008). It is also possible to benefit from interspersing faster intervals into any low- or moderate-intensity workouts to make greater gains in fitness levels (Johnson 2006, 2008).

Engaging in moderate- to vigorous-intensity physical activity is generally recommended to achieve aerobic and metabolic improvements in people with diabetes (Sigal 2004, 2006; Colberg 2010). Lower-intensity activities will expend calories and help with weight maintenance, but they may or may not have much of an acute impact on blood glucose levels or enhance cardiovascular fitness as much (Duncan 2005, Hansen 2009). Appropriate measures of intensity include the “talk test,” perceived exertion, and target HR.

“Talk test.” When starting out with an exercise program, the easiest measure of intensity for anyone to use is the “talk test.” An individual should be able to carry on a conversation during aerobic activity without struggling to breathe. If he or she is breathing too heavily to talk, the intensity has exceeded the ventilatory threshold and is harder than a moderate workload. The only drawback to the use of this test is that it cannot discern when exercise intensity is too low, but upon starting an exercise program, it is safer for the individual to err on the low side than on the high side.

Perceived exertion. Use of perceived exertion is another easy way for individuals to estimate their exercise intensity. This is a subjective rating based on general fatigue and can be used along with target HR estimations or as a substitute to guide the intensity of activity. Several scales, including the Borg scales, can be used to assign numbers to intensity levels, or individuals can simply state how they feel. When subjective perceived exertion is used, a person should focus on full-body feelings of exertion and general fatigue. Generally, a moderate- to vigorous-intensity exercise corresponds to a subjective rating of “somewhat hard” (for moderate) to “hard” (for vigorous) (Garber 2011). Less fit people generally require a higher level of effort than fitter people require to do the same activity. Relative exertional intensity can be estimated using a scale of 0 to 10, where sitting is 0 and the highest level of effort possible is 10. Moderate-intensity activity is a 5 or 6 out of 10. Vigorous-intensity activity is a 7 or 8 (Physical Activity Guidelines Advisory Committee 2008).

Target HR. Exercise intensity can be prescribed and monitored using HR. The ACSM recommends the following HR measurement: exercise intensity of 40–89% of HR reserve (HRR). (This range roughly corresponds to 64–93% of maximum HR, or HRmax.) The recommended intensity range of 40% to 89% is broad because deconditioned individuals can gain improvements in cardiorespiratory fitness at lower intensities, whereas individuals with greater fitness typically require a higher minimal threshold to achieve similar gains (Garber 2011). Therefore, the prescribed intensity range should be based on an individual’s fitness level, duration of diabetes, presence and degree of complications, and personal goals. Using this method, moderate-intensity exercise is in the range of 40% to 59% HRR, whereas vigorous-intensity exercise is defined as 60–89% HRR (Garber 2011, Physical Activity Guidelines Advisory Committee 2008). A severely deconditioned person can start even lower than 40% HRR (e.g., light intensity is considered 30−39% and very light is <30%) and progress from there to more moderate levels over time.

Exercise intensity can be calculated most accurately if an individual’s maximal HR (MHR) has been determined with an exercise stress test. A true resting HR (RHR) is best measured upon awakening; measuring at other times of day, even at rest, may not yield the same results. The difference between the MHR and RHR is defined as the HRR.

The Karvonen formula, which relies on the calculation of HRR, commonly is used to calculate a single target HR or HR range in bpm (Garber 2011):

HRR = MHR – RHR

Percent HRR (% HRR) = HRR × Desired Intensity

(% as decimal)

Karvonen Formula: Target HR = [(MHR – RHR) × Desired Intensity] + RHR

If someone’s actual MHR has not been measured, target HR ranges can be approximated using the following equation to estimate maximal values:

MHR = 220 – Age

This equation should be used with caution because of the large standard deviation, which can cause the HR estimation to be off by 12–15 bpm (Garber 2011). This procedure may overestimate the maximal HR of some individuals with diabetes, particularly those with autonomic neuropathy (Colberg 2010, 2011). If cardiac autonomic neuropathy is present, exercise intensity is better prescribed using the HRR method with MHR directly measured, rather than estimated, for better accuracy (Colberg 2003).

An alternate equation that may be more accurate for estimating maximal HR in an older population utilizes 70% of age rather than full age (Garber 2011):

MHR = 208 – (0.7 × Age)

Table 4.2 Sample Calculation Using Karvonen Formula for Target Heart Rate Range of 40–89% of Heart Rate Reserve

In general, exercise performed at lower levels (<40% HRR) has a lesser glucose-lowering effect than exercise done at higher intensities—unless it is done long enough. Glucose disposal during high-intensity exercise is roughly proportional to the total work performed (time × intensity). On the other hand, vigorous exercise (≥60% HRR) may result in transient hyperglycemia and cause an excessive rise in systolic blood pressure (Colberg 2010).

Frequency

Physical activity sessions can be performed in a variety of combinations of frequency and duration. Most research concludes that physical activity should be performed 3–5 days/week to achieve significant health benefits. The latest guidelines for T2D suggest that individuals should undertake at least 150 min a week of moderate to vigorous aerobic exercise spread over at least 3 days, with no more than 2 consecutive days without aerobic activity, if their goals are to improve glycemic control, enhance fitness, and achieve target caloric expenditure (Colberg 2010, 2011; American Diabetes Association 2013). Exercise that is limited to 2 days/week results in less improvement in cardiovascular fitness.

Moreover, since the duration of glycemic improvement after an exercise session is usually >2 h but <72 h, regular physical activity is needed to lower blood glucose (Boulé 2001, O’Donovan 2005). For individuals taking insulin, being active on a daily basis may help to balance caloric needs with insulin dosages, as well as maintain higher levels of insulin sensitivity to allow for reduced insulin dosing. Obese individuals may need to be active more frequently (5–7 days/week) at lower intensities to optimize weight loss and maintenance (Ross 2000, 2004). In addition, to achieve sustained major weight loss, the optimal level of activity needed is typically greater than that needed to improve glycemic control.

Energy expenditure also can be used to guide exercise programming. The ACSM recommends a target range of 150 to 400 calories/day expended via physical activity (Garber 2011). This represents a minimum threshold of 1,000 calories a week, which is associated with reduction in all-cause mortality risk. For previously sedentary people, this minimal threshold can be an initial goal, but to achieve maximal weight loss, they should work up to expending 300–400 calories/day, or 2,000 calories/week. Energy expenditure in excess of 2,000 calories/week in physical activity has been associated with successful short- and long-term weight loss (Garber 2011).

Duration

The exercise duration is directly related to caloric expenditure requirements and inversely related to the intensity of exercise required to achieve the same results. In other words, to gain maximum caloric expenditure and glycemic benefits, lower-intensity exercise needs to be performed for longer periods of time compared with higher-intensity exercise.

The recommended weekly exercise duration for adults differs somewhat by guideline. Recent joint guidelines from the ACSM and American Heart Association (2007) recommend 150 min of moderate activity (30 min, 5 days/week) or 60 min of vigorous physical activity (20 min on 3 days) for all adults (Haskell 2007, Nelson 2007). U.S. federal guidelines (2008) recommend 150 min of moderate or 75 min of vigorous activity, or an equivalent combination, spread throughout each week (Physical Activity Guidelines Advisory Committee 2008).

The latter recommends an exercise volume of 500–1,000 metabolic equivalents (METs) min/week, where an MET is the ratio of the rate of energy expended during an activity to the rate of energy expended at rest. For example, 1 MET is the rate of energy expenditure at rest, whereas a 4-MET activity expends four times the energy used by the body at rest. MET minutes are the metabolic equivalent of physical activity times the number of minutes the activity is done. Thus, levels of 500–1,000 METs min/week are achievable with 150 min of weekly walking at 4 mph (6.4 km/h; intensity of 5 METs, or five times resting levels) or 75 min of jogging at 6 mph (9.6 km/h; 10 METs).

Although both of these guidelines apply to most adults with T1D, the majority of people with T2D lack sufficient aerobic capacity to jog for that duration or they have orthopedic or other limitations. The mean maximal aerobic capacity in such individuals is estimated to be only 22.4 ml/kg/min, or the equivalent of 6.4 METs (Boulé 2003), making 4.8 METs (~75% of maximal) the highest, sustainable intensity. Thus, most individuals with T2D have to undertake ≥150 min of moderate to vigorous aerobic exercise per week to achieve optimal cardiovascular risk reduction (Colberg 2010). The ADA’s Standards of Medical Care make a similar recommendation that individuals with diabetes perform at least 150 min of weekly moderate-intensity aerobic physical activity (American Diabetes Association 2013).

Although a minimum dose has not been determined, some cardiovascular and glycemic benefits may be gained from lower exercise volumes (Hansen 2009). Additional benefits likely result from engaging in durations beyond recommended amounts, however (Jakicic 2003, Houmard 2004). If someone has a higher aerobic capacity (>10 METs), such as many younger individuals with T1D, T2D, or GDM, he or she may choose to exercise at a higher absolute intensity for less time to achieve the same cardiovascular and glycemic benefits. Bouts of physical activity lasting 60 min or more may be required to achieve weight loss or to prevent weight regain (Physical Activity Guidelines Advisory Committee 2008).

Whether the actual length of each exercise session matters is an interesting question. Although 20 min has been the minimal recommendation for cardiovascular benefits, multiple shorter bouts of 10 min have been shown to result in measurable improvements (Eriksen 2007). Similar gains occur when physical activity is accumulated throughout the day as three bouts of 10 min compared with a single prolonged activity session of similar duration and intensity (i.e., a 30 min bout of continuous activity) (Haskell 2007). Thus, if desired, physical activity may be broken down into sessions of a minimum of 10 min spread throughout the day (Garber 2011). Severely deconditioned individuals may need to exercise in multiple sessions of short duration (5–10 min), begin at low levels with brief rest intervals, and progress slowly to higher-intensity exercise. Initially, sessions can be done for 10–15 min, increasing progressively over time to >30 min (Garber 2011). Closer to 60 min of daily exercise may be necessary to achieve significant weight loss in adults (Ross 2000, 2004).

Progression

Appropriate progression of aerobic training is required to help individuals effectively and safely achieve aerobic exercise goals. Initially, the focus should be on increasing frequency and duration of the exercise rather than intensity. Individuals should increase physical activity gradually over time whenever more activity is necessary to meet guidelines or health goals, and inactive individuals should “start low and go slow” by gradually increasing how often and how long activities are done (Physical Activity Guidelines Advisory Committee 2008). Progressing in this manner increases the likelihood of creating and sustaining an activity habit and lowers the risk of injury or demotivation (Garber 2011).

A full exercise prescription, to be truly effective, should include both how to start a fitness program and what to reasonably expect in terms of progress, as shown in Table 4.3. The individual must understand the type, quantity, and rate of progress to expect. Over a period of time averaging at least 4–6 months, each individual moves through three distinct stages of a fitness plan: initial, improvement, and maintenance.

Table 4.3 Progressive Stages of Exercise Training

Initial stage. In this stage, individuals begin to form physical activity habits that can be integrated into their lifestyles. Unfortunately, most people never make it out of this critical stage, either because they attempt activities that are too hard for them given their fitness level or because they develop unrealistic expectations for what they will be able to accomplish and when, which leads to discouragement and a cessation of training. To help ensure success, individuals should be helped to understand that significant changes (like loss of body weight) may not occur during this period. Also, they need to understand that building fitness habits takes 4 weeks or longer, especially when people start out with very poor fitness levels. Setting specific fitness goals can help with motivation during this stage. For individuals who are starting with a higher fitness level, this stage often can be skipped.

Improvement stage. During this second stage, the focus shifts from developing habits to improving fitness levels. The individual now has improved stamina and endurance, is able to spend longer amounts of time doing physical activity, and can begin adding to duration or intensity of workouts. Over the 3 months (or longer for deconditioned and older individuals) of this stage, health benefits begin to become measurable. If individuals see these changes as permanent without further training needed, however, their exercise habit may start to weaken, and they may start missing workouts. Individuals who already have higher levels of fitness will begin their program in this stage when undertaking new types of training or setting new fitness goals. The progression shown is for individuals with an ultimate goal of participating in vigorous aerobic exercise. For many individuals with T2D, however, doing moderate-intensity workouts may be an appropriate endpoint, although frequency and duration may progress.

Maintenance stage. Once someone has successfully met his or her initial fitness or blood glucose management goals, it is important to develop new goals and plans to enhance motivation and continued participation. A new goal may be something like “prevent weight regain” or “train for a competitive event.” To ensure continued safety and effectiveness of training in all individuals with diabetes, medications may need to be adjusted or other changes made to training if any existing health comorbidities progress or new ones arise.

SAFETY CONSIDERATIONS

Everyone who engages in physical activity should do so with safety in mind. To do physical activity safely and reduce risk of injuries and other adverse events, people should understand the risks yet should exercise confidently given that physical activity is safe for almost everyone. They should start with and do types of physical activity that are appropriate for their current fitness level and health goals, increase their physical activity gradually over time, start at the lower end of the intensity spectrum and progress slowly to prevent injuries, and use appropriate gear and sports equipment in safe environments.

Although specific safety considerations required for exercise participation by individuals with diabetes will be addressed in many chapters that follow, it is important to mention a few of these guidelines here (also see Table 4.4):

• Individuals should monitor their blood glucose both before and after activity to promote safety and understanding of its glycemic effects.

• All individuals with diabetes who are treated with insulin, sulfonylureas, or meglitinides should carry rapidly absorbed carbohydrates (e.g., glucose tablets or gels) with them while performing physical activity to treat hypoglycemia rapidly.

• They should be aware that certain medications can impair exercise tolerance; for example, β-adrenergic blockers lower the HR response to physical activity, as well as mask hypoglycemic symptoms and lessen the strength of counterregulatory (glucose-raising) hormonal responses.

• All individuals should wear clothing and shoes appropriate for the activity to reduce chance of injury.

• They should wear some form of diabetes and personal identification.

• Individuals need to use caution when exercising—particularly vigorously—in extremely hot, humid, smoggy, or cold environments.

• Because seasonal changes in blood glucose control have been related to environmental temperature, they should find safe and available places to be active indoors when the weather is colder.

• An individual should stop any activity if he or she experiences any symptoms like pain, lightheadedness, or shortness of breath.

Table 4.4 General Guidelines for Safe Exercise Participation with Diabetes

Perform self-monitoring of blood glucose (SMBG)	Check SMBG levels before and after each exercise session to ensure adequate pre-exercise control and to better understand and predict future glycemic responses. If blood glucose is >250–300 mg/dl with moderate or higher levels of urinary or blood ketones, exercise should be postponed; >250–300 mg/dl without ketones, okay to exercise, but use caution; <100 mg/dl, consider eating a snack consisting of easily absorbed carbohydrates (~20–30 g), based on insulin regimen and circulating insulin levels expected during the activity; 100–240 mg/dl, exercise is recommended.
Keep a daily log	Record the time of day the SMBG values are obtained and the dose of any medications taken. Also, approximate the time (min), intensity (heart rate), and distance (miles or meters) of exercise session. Such details aid the individual in understanding the glucose response to an exercise bout.
Plan ahead for exercise sessions	The need for adjustments to medications or food intake can be anticipated based on anticipated exercise (duration and intensity). If needed, carry extra carbohydrate (~10–15 grams for every 30 min) to prevent or treat hypoglycemia.
Ensure hydration	Hydrate before and rehydrate after each exercise session to prevent dehydration.
Modify caloric intake accordingly	Through frequent SMBG, caloric intake can be regulated more carefully on days with and without exercise participation.
Adjust insulin accordingly	If using insulin, reduce rapid- or short-acting insulin dosage to limit hypoglycemic episodes.
Exercise with a partner	Diabetic individuals should exercise with a partner until their glucose response is known and to promote exercise adherence.
Wear a diabetes identification (ID) tag	Diabetes ID with relevant medical information should always be worn. Hypoglycemia and other problems can arise that require immediate attention.
Wear good shoes	Always wear proper-fitting and comfortable footwear with socks to minimize foot irritations and limit orthopedic injury to the feet and lower legs.
Practice good hygiene	Always take extra care to inspect feet for any irritation spots to prevent possible infection. Tend to all sores immediately, and limit any irritations.

Case in Point: Wrap-Up

Because KK has most recently led a sedentary lifestyle, she should start with an initial exercise prescription that allows her to progress slowly toward higher levels of cardiovascular fitness over a period of weeks to months.

Exercise Program Goals

Mode of Activity: KK has stated that she enjoys walking and has done that activity from time to time, so the recommended activity to start will be brisk walking.

Intensity: Because KK already does quite a bit of lifestyle activity, she should be able to start with moderate (brisk) walking at a comfortable pace that feels “somewhat hard” to maintain. To improve her fitness levels faster, she should consider adding short intervals of faster walking interspersed into her normal walking pace. If she wants to monitor her intensity using a target HR, a minimal starting intensity of 40% HRR gives her a target of 117 bpm, or a moderate range (40–59%) of 117 to 135 bpm.

Frequency: KK’s goal should be a minimum of 3 nonconsecutive days of walking per week, with a goal of progressing to 5 or more days over the next several months. She should be advised to not go more than 2 consecutive days without doing some aerobic activity (to keep insulin action higher).

Duration: If KK initially cannot walk for 30 min continuously, she should be advised to aim to do 10–15 min at a time spread over the day. Her initial goal should be a minimum of 150 min spread throughout the week, or possibly a lesser total time if she walks more intensely.

Progression: KK’s long-term exercise goals should focus on progressively increasing her activity to reach the minimum recommended levels of 150 min of moderate or vigorous exercise spread throughout the week. Her target HR can remain either in the improvement phase (minimum target HR of 117 bpm, equal to 40% HRR) or progress as she is able, as fitness gains will result more quickly with a higher-intensity workout. Once she has reached the maintenance phase, she can substitute some alternative aerobic activities for variety, and she should consider adding in resistance training at least 2 days a week.

Daily Movement: To help with weight loss, KK should engage in as much daily movement as possible, including standing more and taking steps throughout the day. As a possible motivator, she should consider getting a pedometer and setting a daily step goal.

Possible Precautions: KK has minimal risk factors for cardiovascular disease (mainly diabetes), so she should not be required to have an exercise stress test before starting her walking progress. She has had a recent checkup with her doctor with good results (other than the diagnosis of T2D). She should consider, however, investing in a good pair of walking shoes and athletic socks to avoid the development of any orthopedic limitations related to her exercise program.

People with diabetes of any type will benefit from getting specific aerobic exercise prescriptions from their health-care or fitness professional. This prescription should include specifics about what types of activities they should be doing, how hard they should be working out, how often and how long, and when they need to progress and what to expect in terms of reasonable progression through the phases of a training program. Empowering individuals to set their own specific goals is the ultimate aim of such programming.

Professional Practice Pearls

• Aerobic (or cardiorespiratory) exercise is defined as continuous, dynamic exercise that uses large muscle groups and requires aerobic metabolic pathways to sustain the activity (such as brisk walking, cycling, and swimming).

• Commonly, the warm-up and cooldown involve doing an activity at a slower speed or lower intensity (such as engaging in 5–10 min of brisk walking before and after jogging).

• The aerobic exercise prescription should address mode (type of activity), intensity (how difficult), frequency (how often), duration (how long), and appropriate progression.

• Although doing any physical activity can be beneficial to health, moderate- to vigorous-intensity physical activity is generally recommended to achieve aerobic and metabolic improvements in people with diabetes.

• Lower-intensity activities will expend calories and help with weight maintenance, but may or may not have much of an acute impact on blood glucose levels or enhance cardiovascular fitness as much.

• Appropriate measures of intensity include the “talk test,” perceived exertion, and target HR (using the Karvonen formula for HR reserve).

• Physical activity should be performed 3–5 days/week to achieve significant health benefits, with no more than 2 consecutive days without aerobic activity to optimize insulin action; exercise done only 2 days/week results in lesser fitness improvements.

• Both moderate- and vigorous-intensity aerobic activity should be performed in episodes of at least 10 min, with a goal of 30 min or more of continuous activity.

• Progress by increasing physical activity gradually over time whenever more activity is necessary to meet guidelines or health goals; inactive individuals should “start low and go slow” by gradually increasing how often and how long activities are done.

• A full exercise prescription should include both how to start a fitness program and what to expect in terms of progress over a period of 4–6 months, including initial, improvement, and maintenance phases (although fit individuals may skip the initial phase).

• For individuals with T1D without complications, exercise recommendations are similar to those for individuals with no known health problems (i.e., a minimum of 150 min of moderate or 60–75 min of vigorous activity weekly).

• Recommendations for T2D closely align with guidelines for sedentary adults and older adults; most individuals with T2D should at the very least undertake 150 min or more of moderate to vigorous aerobic exercise per week for cardiovascular risk reduction.

• Women with uncomplicated GDM should engage in 30 min of moderate intensity activity like brisk walking on most days of the week (150 min weekly).

• Empowering individuals to set their own specific goals is the ultimate aim of providing them with a specific exercise prescription for aerobic training.

REFERENCES

American Diabetes Association: Standards of medical care in diabetes—2013. Diabetes Care 36 (Suppl. 1):S11–S66, 2013

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