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Regular exercise and increased physical activity level help to prevent coronary heart disease (CHD), yet fewer than 25% of adults adhere to this behavior.1 Exercise is important for patients with CHD to prevent reoccurrence, treat, and manage the disease. This health-promoting behavioral change has many benefits for patients with CHD including increased endurance, quality of life (QoL), symptom threshold, and ability to carry out daily activities and live independently. Although exercise is a powerful therapeutic intervention, many barriers exist for patients to adopt and maintain this health promoting behavior. The presence of functional limitations and disability represent a significant barrier to exercise participation. Often, those individuals who could benefit most from exercise are least able, which creates a vicious cycle (Figure (Figure1)1) of deconditioning, activity restriction, and chronic disease.2 In older populations, CHD is a known risk factor for precipitating disability onset.3 Patients with CHD who are recovering from coronary artery bypass (CAB) surgery are particularly vulnerable to concomitant functional limitations and disability.
Many factors can inhibit physical activity and exercise adherence and therefore make patients susceptible to sedentary behaviors. Patients with functional limitations and disability particularly have barriers to exercise participation due to their activity restrictions. Development or progression of functional limitations and disability often occurs after hospitalization or restricted activity, especially in older adults. Older persons, with a history of multiple disease processes, may already be functioning at fairly low levels of physical independence, which is then compounded by CHD and CAB surgery. Disability immediately following hospitalization often will regress to premorbid levels, but this does not always occur. Hospitalization itself may contribute to progression of disability in vulnerable populations.2 Patients recovering from CAB surgery may be particularly prone to activity restriction due to fear of physical activity and/or adverse disease related symptoms. Patients with CHD also commonly have pre-existing comorbidities, such as osteoarthritis and chronic low back pain, that may be exacerbated with exercise. Austrian et al4 found that older patients with chronic pain commonly reported fear of pain or injury as a barrier to exercise participation. In other patient populations, the presence of pain or disability is predictive of poor exercise compliance.5,6 A recent retrospective study found that 5-6 years following CAB surgery non-exercising women had lower function than more active groups, suggesting a link exists between function and physical activity level.7 In patients recovering from CAB surgery shortness of breath, fatigue, and pain were common and related to function.8 Recently, Zimmerman et al9 found that an education intervention reduced symptom influence with physical activity in patients during the first 6 weeks following CAB surgery.
Following CAB surgery, functional status may be impaired due to the secondary effects of the surgical procedure, in addition to the direct effects of coronary heart disease on cardiac performance. The myocardial muscle experiences some direct injury during CAB surgery.10,11 Blood lost during surgery and cardiopulmonary bypass machine use causes reduced blood volume, hematocrit, and albumin.12,13 Atrial fibrillation is also a common complication following CAB surgery.14,15 Rates of postoperative infections at the surgical incisions may be as high as 15%.16,17 The incidence of saphenous vein site wound complications, including hematoma, dehiscence, cellulitis, necrosis, abscess, and incomplete spontaneous epithelialization, is reportedly as high as 44%.18–21 Paletta and colleagues21 recently reported that 4.1% of patients with saphenous venectomy for CAB required additional surgery for wound complications, including amputation. Risk factors for saphenous vein graft complications include female Median Sternotomy gender, diabetes, peripheral vascular disease, intra-aortic balloon pump use, older age, and longer cardiopulmonary bypass time.19,21–23 Interestingly, a subjective preference for radial artery versus saphenous vein grafts by patients has been reported.24 Radial artery harvesting has few side effects, that resolve completely during recovery.24–26 Potential complications of radial artery graft donation numbness,24–27,29,30 include parasthesias,24–29 compartment syndrome,31 hand weakness,24,26 local arterial oxygen desaturation,30,31 infection,16,24 scar hypersensitivity,30 and hand ischemia.30 Sadaba and colleagues32 recently reported normal hand function, assessed by strength tests and questionnaire, in 20 patients 12 months following CAB surgery with radial artery harvesting. But it appears that hand function following radial artery harvesting may deteriorate with cold exposure and or muscular fatigue.26 The occurrence of cognitive and memory deficits may be as high as 90% following CAB surgery.12,33–37 This iatrogenic neurologic insult is thought to be due to systemic inflammation, cerebral hypoperfusion, atheromatous debris from cannulation, or microemboli (platelet aggregates, red blood cell fragments, air bubbles).12,33–35 Cognitive and memory deficits may impair patient ability to initiate, coordinate, modify, and/ or complete motor activities required for functional tasks. Adverse cerebral outcomes following CAB surgery result in higher rates of discharge to intermediate- or long-term care facilities than with no adverse cerebral outcome.38 Mild to moderate cognitive deficits have been shown to reduce level of function in geriatric patients admitted for inpatient rehabilitation.39 Furthermore, Cohen and colleagues40 have demonstrated a positive relationship between neurocognitive performance and the degree of QoL improvement following cardiac rehabilitation. All of these sequella of CAB surgery may contribute to significant functional limitations in patients during acute recovery.
Of particular interest to physical therapists, are the factors associated with increased risk for sternal incision complications and the activity restrictions imposed to minimize these complications. Sternal instability, dehiscence, and mediastinitis following median sternotomy have an incidence rate of 0.4 – 5%, but patients with these serious sternal complications have a mortality rate of 14 – 47%. In addition, these complications with chest surgical wound healing may be exacerbated secondary to tissue ischemia of the anterior chest wall with harvesting of internal mammary arteries.41–45 Known risk factors for sternal complications are listed in Table Table1.1. Interestingly, no research evidence has established post-operative activity level and arm movements as being associated with sternal complications. Typical activity restrictions immediately following median sternotomy (6-12 weeks) include no lifting/pushing/pulling > 10 lbs, no driving, and avoiding unilateral should abduction/flexion > 90 degree. Recently, El-Ansary and colleagues46 examined a variety of upper body activities in patients with chronic sternal instability. In this patient population, pushing up from a chair during sit to stand transfers created the greatest sternal separation and elevating both arms simultaneously overhead produced the least amount of sternal separation. They also found that patients with chronic sternal instability experienced the greatest amount of pain during transitions from supine to short sitting and sudden lose of balance and the least amount of pain when reaching above shoulder height.46–47
Previous research has begun to elucidate functional characteristics of patients with CHD following CAB surgery. In patients with CHD entering an outpatient cardiac rehabilitation program, we found function was more limited in patients surgically-treated than those medically-treated. In addition, we found that performance-based and self-report outcome measures do not provide synonymous information regarding functional status in patients with CHD suggesting that it is important to include both measurement types.48 We also evaluated activities of daily living (ADL) and QoL in 52 patients before, 2 weeks after, and 2 months after CAB surgery. We found that older, as compared to younger patients, had a greater number of previous surgeries and comorbidities and lower pre-CAB surgery ADL and QoL functional scores. Older persons with a history of multiple disease processes may already have some impairment in physical function. Elderly persons with depression, sedentary behaviors, and poor social support, are at risk for difficulty with full recovery of function after CAB surgery. We found QoL scores for physical functioning, role limitation due to physical health, and pain were decreased from pre-CAB surgery as compared to 2 weeks post-CAB surgery and they returned to baseline values at 2 months post-CAB surgery. Differences over time in their ability to perform daily tasks that involved vigorous and moderate activities, lifting or carrying groceries, walking more than a mile, and bathing or dressing were found. This depressed physical function immediately following CAB surgery may be related to surgeon determined post-CAB limitations, fear of activity, and/or low habitual activity levels. We also found that the number of participants reporting difficulty or pain with ADL was greater than those reporting need for assistance. The incidence of ADL deficits in personal care increased at 2 weeks as compared to preoperatively for all domains. We found that in all except 1 instance participants more frequently reported having difficulty or pain with ADL tasks than needing assistance with ADL tasks suggesting that degree of difficulty or pain is a more sensitive indicator of limitation in ADL performance than degree of dependency alone in patients recovering from CAB surgery. Results also showed that 2 months after CAB surgery many patients reported difficulty and / or pain with mobility, personal care, and hand activity ADL tasks.49–51
Next, we examined functional status in patients during subacute recovery (<6 mo) from CAB surgery across multiple domains in patients over 60 years.52,53 Outcomes measured in this study included QoL, symptoms, ADL, depression, stress, endurance, and cognition. All study participants identified experiencing multiple symptoms related to CAB surgery with the greatest impact with regards to cardiac symptoms. The greatest number of study participants had deficits in performing home chores needing assistance (36%), having difficulty (56%), and/or experiencing pain (44%). Study results suggest that within this timeframe of recovery patients still have deficits in function.52 We also described balance ability and evaluated the relationship between balance and endurance in patients following CAB surgery. Twenty-four percent of subjects scored less than threshold values on one or more of these balance assessments. We found significant correlations among balance, endurance, and ADL assessment scores as seen in Table Table2.2. Results of this preliminary study suggest that some patients recovering from CAB surgery have impairments in balance. This study revealed a direct relationship between balance performance and endurance capacity. It is possible that patients with impaired balance self-limit habitual activity level which leads to deconditioning, or that low endurance capacity predisposes them to balance deficits. Patients with identified balance problems may be at risk for falls and/or sedentary behaviors.53
Clinically important functional deficits are common in patients at the time of hospital discharge for CAB surgery. There were also significant correlations between pre-CAB surgery ADL ability and symptom impact, walking speed, and strength (r=0.32–0.59). We found significant correlations between balance and measures of endurance, walking speed, and strength (r = 0.44-0.66). Study results suggest that patients with greater strength have a greater ability to independently carry out their ADL. Findings also imply that persons more comfortable with their gait will display more independence with ADL. Results suggest that components of physical functioning are interrelated; therefore patients after CAB surgery will usually have a global presentation of dysfunction instead of isolated losses of strength, balance, or endurance.54
At 3 month follow-up in the same study participants, we examined physical activity, exercise self-efficacy, age, and cognitive function. Walking, cardiac rehabilitation, gardening/yard work, and fishing were the most commonly reported sports/leisure activities. Significant correlations were found between exercise self-efficacy and cognitive function (r=0.39), physical activity (r=0.37), and age (r= −0.60). There was little to no correlation between age and physical activity scores, but age was inversely related to both Self-efficacy for Making Time (r=-0.44) and for Resisting Relapse (r=-0.60). Results suggest that individuals who engage in more household activity may be better able to resist relapse from to a sedentary lifestyle because they have established task-management abilities. Results suggest that with aging, decreased physical function, more co-morbidities, and reduced access to facilities/equipment, opportunities for exercise participation may be restricted.55
We have also interviewed study participants using open-ended questions regarding exercise behaviors and health at each follow-up interval. Responses were audio-recorded, transcribed, and analyzed. Data were coded by identifying significant statements, grouping them into meaningful units, and generating rich, thick descriptions of patients' perceptions. A summary of the 6 month qualitative data is provided in Table Table3.3. Factors that helped people to exercise produced 10 themes, factors that prevented respondents from exercising resulted in 9 themes, and feelings about health and QoL formed 7 themes. Perceived activity limitations data revealed patients were still exercising caution in terms of returning to physical activities 6 months following surgery.56,57
In summary, physical therapy intervention, in a variety of settings, can reduce functional limitations and disability in patients recovering from CAB surgery thereby facilitating greater physical activity level and promoting exercise behavior.
Oxygen is an element, a gas, and a drug that, for people with lung disease, is an essential part of their lives. Oxygen and the nutrients in food combine to supply the cells of the body the energy needed to achieve all human activity: everything from bodily functions, such as breathing, to performing activities of daily living. For some pulmonary diseases, such as chronic obstructive pulmonary disease (COPD) and interstitial pulmonary fibrosis (IPF), supplemental oxygen is necessary to continue to perform the activities of everyday life.1
For those who need it, supplemental oxygen is beneficial. There may be improvement in sleep, cognition (mental alertness and stamina), and mood.2,3 Oxygen has also been found to prevent and improve heart failure (cor pulmonale) in people with severe pulmonary disease.4 In 2 major randomized clinical trials, The British Medical Research Council Clinical Trial and The Nocturnal Oxygen Therapy Trial (NOTT), investigators were able to improve survival outcomes by using long term oxygen therapy in the treatment of patients with COPD and chronic stable hypoxemia.3,5 Both of these studies found that using nocturnal oxygen therapy (NOT) and continuous oxygen therapy (COT) for at least 12-15 hours per day improved survival.
Oxygen is used in a variety of settings. Patients with pulmonary or cardiac disease who are hospitalized are often on supplemental oxygen during an acute phase of their illness. Oxygen may be delivered in Intensive Care Units via ventilators and on cardiac, pulmonary, general medicine, and surgical hospital units. Supplemental oxygen is used in skilled nursing facilities, in the home, and in the community. Consequently, physical therapists (PTs) will encounter patients requiring oxygen supplementation in a variety of work settings. As a result, it is imperative that physical therapists understand the proper use of oxygen and logistics regarding oxygen equipment.
The American Physical Therapy Association (APTA) recognizes the role physical therapists have in the administration and adjustment of oxygen while treating various patient populations.6 The APTA's Guide to Physical Therapist Practice (2nd ed) delineates the physical therapist's scope of practice in the management of patients who require oxygen to improve ventilation and respiration/gas exchange. The APTA is unaware of any regulations that prohibit the use of oxygen for patient management if it is prescribed and if parameters set by the physician are maintained.7 Physicians specify oxygen flow rates in their orders. Any deviation in the prescribed dosage requires an updated order from the physician. The Food and Drug Administration (FDA) of the United States Department of Health and Human Services states that “medical oxygen is defined as a prescription drug which requires a prescription in order to be dispensed except….for emergency use.”8
Within the APTA's Guide, supplemental oxygen is listed as a procedural intervention within the scope of physical therapist practice under Prescription, Application, and, as appropriate, Fabrication of Devices and Equipment (supportive device) to improve ventilation and respiration/gas exchange.6 The APTA has a position statement adopted by the House of Delegates which states:
“PT patient/client management integrates an under standing of a patient's/client's prescription and nonpre scription medication regimen with consideration of its impact upon health, impairments, functional limita tions, and disabilities. The administration and storage of medications used for physical therapy interventions is also a component of patient/client management and thus within the scope of PT practice. Physical therapy interventions that may require the concomitant use of medications include, but are not limited to, agents that facilitate airway clearance and/or ventilation and respiration.”9
Each individual State Board of Physical Therapy may have official statements or opinions regarding the administration of oxygen in addition to the professional organization's statement.
In 2006, 12.1 million United States adults aged 18 years and older were estimated to have COPD.10 However, the National Health and Nutrition Examination Surveys (NHAMES) estimates that approximately 24 million adults in the United States have evidence of impaired lung function, indicating that COPD is under diagnosed.11 COPD is the 4th most common cause of death in the United States and ranges from 5th to 14th worldwide. Of the 10 most common causes of death in the United States, COPD is the only disease with an increasing mortality rate. Mortality from COPD is increasing most rapidly in those areas of the world with the greatest tobacco use, and among women.12
The population in the United States is aging. Considering that the first of the “baby boomers” are reaching 60+ years of age and that the fastest growing population in the United States is over 85 years of age,13 physical therapists must be prepared to treat the older population, be knowledgeable about their multiple medical problems, and be competent in using a range of modalities, such as supplemental oxygen, to augment improvement in their functional ability. Supplemental oxygen may be required by people of varied ages and with varied types of pulmonary, cardiac and blood diseases such as COPD, IPF, congestive heart failure (CHF), cystic fibrosis (CF), and sickle cell anemia.
A thorough knowledge of oxygen equipment is imperative for the physical therapist. Pulse oximetry is a noninvasive method of photoelectrically determining the oxyhemoglobin saturation of arterial blood.14 A sensor is placed on a thin part of the patient's anatomy such as a fingertip or earlobe and a light containing both red and infrared wavelengths is passed through the skin to the small arteries. A microprocessor compares the signals received and calculates the degree of oxyhemoglobin saturation based on the intensity of transmitted light.14 Larger, stationery oximetry monitors are typically used in intensive care units. Small, hand-held, portable monitors are easily clipped to the distal end of a finger or attached to the earlobe by an earlobe clip.
A variety of oxygen delivery devices may be used to administer oxygen to the patient. The most common is the nasal cannula which can provide oxygen flows from 0.25 to 6 liters per minute (LPM). An oxymizer delivery device is a nasal cannula with a reservoir incorporated into the tubing mechanism.15 During exhalation, the reservoir fills with oxygen and is available to the patient upon the next inhalation, essentially providing equivalent saturations at lower flow rates. Manufacturers state that an oxygen savings of approximately 75% may be obtained by using the oxymizer and lower flow rates provide greater patient comfort.15
Additionally, oxygen masks are used to deliver even higher concentrations of supplemental oxygen. When pulmonary patients exercise, higher percentages (FiO2) of oxygen are needed to meet the demand of working muscles and to maintain oxygen saturation levels within prescribed limits (usually 88% to 90%).14 Two types of oxygen masks may be used during exercise with pulmonary patients. The venturi mask uses a mechanical opening which increases the rate at which the oxygen flows into the mask (commonly 24% to 50%). A partial rebreather mask has a reservoir bag attached and delivers between 70% to > 80% of oxygen. A non rebreather mask also incorporates a reservoir bag, but can deliver up to 100% oxygen. Flows between 7 and 10 LPM are required to keep the reservoir bag inflated at all times.16 Less conspicuous forms of oxygen delivery are available for low to moderate oxygen flow patients. Transtracheal oxygen delivery consists of a small catheter being surgically placed into the trachea through the second and third tracheal rings. Transtracheal is well accepted by patients and delivers oxygen more efficiently than a nasal cannula. Because oxygen is delivered directly into the trachea, approximately 50% less oxygen is needed.16 Other more aesthetically appealing methods of oxygen delivery exist such as small oxygen tubes being imbedded into eyeglass frames.17
Physical therapists must be well-informed about the varied pathologies that may lead to the need for supplemental oxygen. A broad spectrum of pulmonary, cardiac, and blood abnormalities warrant the use of supplemental oxygen. Accordingly, PTs should be able to choose the proper equipment for individual patients with various diagnoses by using cardiopulmonary evaluation techniques, monitoring equipment, and evidence based practice. Oxygen flow rates may require titration depending on the level of physical activity (rest versus exercise versus sleep). In addition, different diagnoses, due to their pathophysiology, require lower or higher oxygen flow rates depending on the patient's activity level.
The physician normally sets the flow rate for sleep and rest, but with exercise, the PT is instrumental in determining the proper oxygen flow rate needed. It is important to communicate with the physician regarding oxygen requirements during exercise. With this knowledge, the physician can make crucial decisions concerning the patient's medication effectiveness, dosage, stability of the disease, and surgical options.
A few basic concepts of oxygen delivery, functional ability, and biomechanics are necessary to guide the patient, physician, and oxygen vendor in meeting a patient's specific equipment needs. There are essentially 3 types of oxygen delivery systems. First, an oxygen concentrator has the ability to deliver oxygen up to a level of 5 LPM. It is a device that separates oxygen from room air. There are stationary models, under electrical power, that are suitable to use around the house and during sleep. Different lengths of oxygen tubing are available to accommodate movement from room to room. More recently, portable oxygen concentrators have become available that allow a patient to move in and out of the house and community under battery power. These units are much smaller, sit in a small 2 wheeled stroller, and are pulled along behind the patient similar to a rolling suitcase. These units are appropriate for patients on oxygen flows, at rest and with exercise, between 1 and 5 LPM. The oxygen production is only limited by the life of the portable battery charge when away from an electrical outlet.18
Second, compressed gas oxygen tanks are available in a range of sizes for portable use. These are also mobile on a 2 wheeled stroller or in a pack that can be supported over the shoulder. More recently, these tanks are being manufactured from aluminum rather than iron or other heavy metals, which is much lighter-weight and manageable for small frame individuals. These tanks are used with an oxygen flow regulator which attaches to the top of the cylinder. The regulator must be manually changed to a full tank once the tank is emptied. There are 2 types of regulators: continuous flow and pulsed dose oxygen conservers. The continuous flow delivers oxygen during the full respiratory cycle (inspiration and expiration). Variations of these regulators will allow flow rates between 0.25 and 25 LPM. At a flow rate of 2 LPM, one E cylinder tank will last approximately 4-5 hours.18 The oxygen conserver regula-tor delivers oxygen during inhalation only (demand system), or at pre-set intervals (pulsed system); thus, saving on the amount of oxygen used over time.19 These regulators are typically used with smaller compressed gas tanks and deliver oxygen for variable lengths of time dependent on the interval and volume of oxygen puffs and the size of the tank. An E cylinder tank with an oxygen conserver regulator can provide oxygen delivery > 15 hours at a flow rate of 2 LPM.18 Depending on the pathology and the individual oxygen requirements, the PT must decide which compressed gas oxygen tank and regulator will best meet the patient's needs. Ambulatory oxygen systems are defined as those weighing less than 10 lbs. Many patients find 8.5 lbs. a practical weight to carry, but smaller framed patients may be better served with a unit in the < 5 lb. range.20 Biomechanical and psychomotor factors to be considered are that some patients have difficulty with the manual task of changing regulators due to weakness of the hands, joint deformities, pain, or cognitive deficits. Other patients who have osteoporosis or back pain may have difficulty lifting compressed gas tanks in and out of a car due to their weight and awkward shape. Still other patients with gait abnormalities have difficulty maneuvering tanks in strollers over curbs, steps, and through doors.21
A third type of oxygen delivery is a liquid oxygen system. A large stationary tank is typically delivered to the patient's home. The patient is also provided with a portable tank that is refilled off of the stationary tank. Portable liquid tanks come in a variety of sizes and weights. The largest liquid system has the capability of a 15 LPM flow rate and can be carried either on the shoulder, in a backpack, or in a 2 wheeled stroller. One of the smallest units has a maximum of 4 LPM flow rate, pulsed or continuous, and may be carried by the small handle on the unit or worn around the waist in a waist pack.18
For Medicare Part B patients, supplemental oxygen is supplied by a Durable Medical Equipment (DME) carrier. The physician must complete and sign a Certificate of Medical Necessity (CMN) describing the patient's need for oxygen, arterial blood gases or oxygen saturation levels, prescribed flow rate, and medical diagnosis. If a specific type of portable system or flow rate is required for a patient to participate in a full range of physical activities, it must be noted on the CMN. Otherwise, because DME suppliers are reimbursed at a fixed rate, regardless of the oxygen system they provide the patient, suppliers realize a larger profit by providing less costly systems. A supplier cannot change a physician's prescription; therefore, it must be filled as written.22
In conclusion, it is not uncommon for PTs to treat a variety of patients who require supplemental oxygen, either on an in-patient or out-patient basis. It is within the physical therapy scope of practice to administer and adjust oxygen according to the physician's prescription. The physical therapist must have a thorough knowledge of oxygen equipment and how to use various devices to meet the physiological and biomechanical needs of the patient.
The prevalence of obesity has increased in the United over the past 20 years. Data from the Center for Disease Control (CDC) has indicated that in 1994 (the first year that data were available for all 50 states), 16 states had an adult obesity incidence of 15 – 19% and the remaining 36 states had an incidence of 10 – 14%. In contrast, by 2006, the most recent year for which data are available, the incidence of obesity had increased to two states with obesity incidence of 30%, 20 states with 25 – 29% obesity, 24 states with 20 – 24% obesity, and 15 – 19% obesity in the remaining 4 states. Public health initiatives aimed at promoting heath and weight loss for obese individuals recommend walking as the preferred form of exercise. The CDC promotes 30 minutes of moderate intensity physical activity (including brisk walking) on most days of the week.1 Although walking is a popular, convenient, and relatively safe form of exercise, factors associated with the increase in body mass may compromise the potential benefits of this form of exercise for the obese population.
Physical therapists are commonly involved in the evaluation of fitness level and the provision of exercise prescription for obese individuals. Common tests of fitness and modes of exercise often include walking. However, for obese individuals, walking is associated with greatly increased energy costs as well as potentially adverse physical responses due to stress and biomechanical changes in gait. Therefore, it is important for physical therapists to consider the impact of obesity on walking prior to recommending walking for fitness assessment or exercise prescription.
The objectives of this symposium were to:
The increase in body mass is associated with changes in many of the components of normal gait. Gait speed has been shown to be slower in some2 but not all3 studies that have examined gait in obese individuals. Reported gait speeds vary from 0.9 to 1.4 m/s in obese individuals as compared with 1.4 m/s in individuals with a BMI in the normal range3. A slower gait speed has implications for successful functioning in the community. Most traffic lights are timed so that an individual walking at a minimum of 1.22 m/s will be able to successfully cross the street. With gait speeds below 1.22 m/s, many obese individuals may not be able to safely cross a street with a traffic light.
There are several factors that likely contribute to the slower observed gait speed. Obese individuals demonstrate a decreased cadence relative to individuals with a normal BMI from an average of 1.8 to 1.4 steps/min.4 This represents a 22% slower cadence for obese individuals and has been attributed to the increased effort required to move the heavier leg. Another factor to consider is that with an increase in BMI, there is an accumulation of adipose tissue in the leg leading to an increase in thigh circumference. The increased thigh circumference necessitates circumduction of the leg with each stride. This results in the step width of obese individuals being 50% greater (0.15 vs. 0.10 m) than that of normal weight individuals.3,4 The increased step width provides an increased base of support and increased stability. However, the increased step width is also associated with a shorter stride length, decreasing the distance covered with each step. Stride length decreases on average from 1.50 to 1.16 m with obesity due to the increased lateral movement of leg while walking.4 In summary, obese individuals walk more slowly due to the increase in thigh circumference that necessitates substantial lateral motion of the leg that does not translate into forward movement.
The most common complaint associated with walking for obese individuals is knee pain. In this regard, there is a marked increased in the incidence of knee pain in obese individuals.5 Studies examining the biomechanics and ground reaction forces during walking have demonstrated that obese individuals experience a 40% increase in mechanical forces across the tibial articulating surfaces.3 Furthermore, the increased loads in the knee are concentrated in the medial compartment. These alterations in knee joint forces associated with obesity have led to the observation that obese individuals are 10 times more likely to have a knee replacement than normal weight individuals.6
Skin protection is another consideration for obese individuals who engage in walking. The increased thigh circumference causes more friction of the inner thighs during walking. This friction can cause skin breakdown which is painful and will decrease an individual's ability to continue ambulation.5
Walk tests are commonly used for the evaluation of functional capacity. Walk tests are timed, self-paced tests that provide quantitative measures of speed and distance. Walk tests have been shown to be very reliable, valid, and responsive to change in many healthy and patient populations across the lifespan. The walk tests that have been utilized as a measure of functional capacity in obese individuals include the 2km Walk Test, 800m Walk Test, 400m Walk Test, and the 6 Minute Walk Test (6MWT). The 2km Walk Test takes about 18 minutes for obese participants to complete and was observed to underestimate oxygen uptake by ~17%7 Furthermore, more than 50% of the participants experienced lower extremity discomfort during the test. The 800m Walk Test takes ~8 minutes for obese individuals to complete. Even though this test is shorter than the 2 km Walk Test, 2% of individuals were unable to complete the test.8 The 400m Walk Test also had a completion rate of less than 100% for obese individuals.9 The 6MWT has been the most commonly used test for obese individuals and empirical validation of the test as been performed.5 Comparative data are available for females between the ages of 18 and 65 years.5
Many health care professionals, including physical therapists, endorse the CDC's recommendation of accumulating 30 minutes of moderate activity on most days of the week (including brisk walking) for health and weight loss/management. However, this recommendation may not be appropriate for obese individuals. Obese individuals expend more energy during walking than do non-obese individuals.3 Heart rates (HR) at self-selected walking speeds average ~70% age predicted maximal HR for obese and compared to 58% for non-obese individuals.10 The effort associated with self-selected walking speeds is rated as an 11 on the RPE rating scale.10 Surprisingly, an increase in walking speed of just 10% has been observed to produce HRs of ~94% age-predicted maximal HR and an RPE of ~15 in obese individuals.11 Therefore, the recommendation to engage in brisk walking may be too demanding for many obese individuals.
Given the above concerns, are there safe recommendations for walking for obese individuals? Browning and Kram3,12 have suggested that slower walking for a longer duration may be a more desirable approach to achieving energy expenditure at a rate that can be tolerated by the obese individual. Moreover, these investigators have demonstrated that walking at a slower speed significantly reduces the loads on the knee and therefore may be less damaging to the knee joint than walking at self-selected or brisk speeds.3 Therefore, walking at a slower speed may reduce discomfort, reduce musculoskeletal stress, and will likely increase compliance to the activity recommendations. Despite the slower gait speed, it is essential to monitor HR during the activity to ensure that the individual is exercising at an intensity that is appropriate.