Chapter 42: Exercise Prescription for Patients with Osteoporosis

Epidemiology Osteoporosis is a skeletal disorder characterized by compromised bone strength that results in an increased susceptibility to fracture. 200 million women worldwide currently have osteoporosis. Osteoporotic fractures are low-trauma fractures that occur with forces generated by a fall from a standing height or lower and are most common at the spine, hip, and wrist. Hip fractures are considered to be the most devastating consequences of osteoporosis. Costs $17 billion per year in United States Osteoporosis among men and women Although women are more susceptible, men also can have osteoporosis and often go undiagnosed.

Basic Bone Physiology Bone is a biphasic material with crystals of hydroxyapatite (calcium phosphate) and an organic collagen matrix. Cortical bone Trabecular bone Modeling and remodeling: affect the quantity, quality, and structure of the bone; regulated by hormonal and mechanical environments Osteoblasts: bone-forming cells Osteoclasts: bone-reabsorbing cells

FIGURE 42-1. Bone is a dynamic tissue that is vascularized and innervated. Cortical bone is dense and stiff and makes up the shaft of long bones. Cortical bone also provides a shell of protection around trabecular bone, which is more porous and flexible and is found at the ends of long bones and in vertebrae.

FIGURE 42-2. Bone remodeling is the coupled actions of osteoclasts and osteoblasts whereby a portion of older bone is resorbed by osteoclasts and replaced with newly formed bone by osteoblasts. The new bone begins as osteoid (unmineralized matrix). Eventually, the osteoid incorporates mineral.

Osteoporosis Pathophysiology Skeletal fragility Bone quantity: amount of bone material present Rapid accumulation during adolescence Peak in second to third decade of life Negative bone balance: decline over time with aging where reabsorption is greater than formation rate Bone material quality: ability to withstand stressors Amount of bone in human skeleton decreases with menopause and advancing age. Increased mean tissue mineralization and changes in collagen properties increase fracture risk with age. Increased microdamage accumulation

FIGURE 42-3. Normal pattern of bone mineral accretion and loss throughout the lifespan in men and women.

Osteoporosis Pathophysiology Skeletal fragility Bone structure: distribution of bone material in bone space Structural differences in cortical bone geometry may explain some of the differences in fracture rates between men and women. During growth, long bones of boys have greater gains in periosteal (outer) diameter, resulting in greater overall bone size in boys that remains throughout life. Increased porous bone results in loss of bone strength and increased fracture risk. Falls Falls significantly increase the risk of fracture, especially when skeletal fragility exists. Most hip fractures occur after a sideways fall and landing on the hip. Hip fractures are a common occurrence because of falling.

FIGURE 42-4. Slice of trabecular bone in a normal (A) and an individual with osteoporosis (B) showing loss of trabecular connectivity and increased microdamage with ageing.

Diagnosis of Osteoporosis Measurement of bone mineral density (BMD) by dual- energy X-ray absorptiometry (DEXA) is the primary method of diagnosis. World Health Organization (WHO) criteria Osteopenia (low bone mass): site-specific bone density between 1.0 and 2.5 standard deviations below the mean for young white adult women Osteoporosis: bone density that is 2.5 standard deviations or more below the mean for young white adult women

Risk Factors for Osteoporotic Fracture BMD Age Risk of hip fractures increases three to six times from 50 to 80 yr of age, independent of BMD status. Family history of fracture Previous fracture Physical inactivity Medication use Hypogonadism Menopause Hyperthyroidism and bariatric surgery risk for secondary osteoporosis

Bariatric Surgery: A Risk Factor for Osteoporosis? With rapid and dramatic weight loss, there is an increasing concern that bariatric surgery may negatively affect the skeleton by accelerating bone loss and increasing bone fragility. Recent review showed that BMD loss may be as high as 15% at the hip 1 yr following gastric bypass procedures.

Clinical Management Pharmacologic therapy Several categories are FDA approved. Antiresorptive agents: act by suppressing bone resorption. Bisphosphonates, salmon calcitonin, hormone replacement therapy (HRT), selective estrogen receptor modulators (SERMs), and receptor activator of nuclear factor kappa-B ligand (RANKL) inhibitors Anabolic agents: promote bone formation Regulation of calcium homeostasis: parathyroid hormone (PTH)

Antiresorptive Agents and Increased Risk of Fracture With long-term use, antiresorptive medications may lose value in preventing fracture and, in some cases, may lead to fracture. Long-term bisphosphonate use remains controversial. Fractures appear to occur infrequently Lack of strong evidence FDA has issued warning regarding possible risk

Lifestyle Modifications Adequate calcium (1,000–1,500 mg · d–1) intake Adequate vitamin D (600-800 IU · d–1) intake Regular exercise Exercise is the only lifestyle modification that can simultaneously ameliorate low BMD, augment muscle mass, promote strength gain, and improve dynamic balance — all of which are independent risk factors for fracture. Smoking cessation Avoidance of excessive alcohol intake Visual correction to decrease fall risk

Exercise and Osteoporosis Physiologic response of bone to exercise Acute physiologic response Exercise causes compression, tension, or torsion of bone tissue and ultimately deformation, which is the basis for chronic adaptations. Chronic physiologic response Changes via modeling/remodeling take up to several months. Maintenance of bone tissue quality through targeted remodeling

Exercise and Osteoporosis Osteogenic activities Response is site specific. Loading/stress should be designed to affect the location in which osteoporosis is identified (e.g., spine, hip). Rest is important for proper bone adaptation or response.

Exercise and Osteoporosis Exercise during youth: building a strong skeleton Exercise in youth is deemed very important for adult bone health. Period of maximal velocity of height growth may be most important period of bone mineral accumulation. Studies suggest that the bone response to loading is optimized in prepuberty and early puberty. Exercise prescription for optimizing bone development in youth ACSM Position Stand on Physical Activity and Bone Health: 10– 20 min, 3 d · wk–1 of impact activities such as plyometrics, jumping, moderate-intensity resistance training, and participation in sports that involve running and jumping (soccer, basketball) Ten jumps, three times per day has also been shown to significantly increase bone mineral density in the proximal femur and intertrochanteric regions.

Exercise and Osteoporosis Exercise during adulthood: maintaining a strong skeleton Goal of exercise in adulthood is to gain bone strength and to offset bone loss observed during this time in life. Not as much research in men as women but appears men can also retard the BMD loss associated with aging. Exercise prescription to preserve bone health during adulthood ACSM Position Stand on Physical Activity and Bone Health: 30–60 min · d–1 of a combination of moderate-to-high intensity weight-bearing endurance activities (three to five times per week), resistance exercise (two to three times per week), and jumping activities

Exercise for the Elderly and Individuals with Osteoporosis Exercise testing for those with osteoporosis Not contraindicated Use of cycle ergometry may be indicated in patients with severe vertebral osteoporosis if walking is painful. Vertebral compression fractures compromise ventilatory capacity and may affect balance during treadmill walking. May have increased false-negative test rate because of inability to exercise to significant level of stress Maximal muscle strength testing may be contraindicated in those with severe osteoporosis because of risk for fracture.

Exercise Prescription for Individuals with Osteoporosis Should consult with patient’s physician first Pain may limit exercise program options Pain management may be an important part of the care ACSM position statement on physical activity and bone health: “Exercise programs for elderly men and women should include not only weight-bearing endurance and resistance activities aimed at preserving bone mass but also activities designed to improve balance and prevent falls.”

Exercise Prescription for Individuals with Osteoporosis Contraindicated exercise for individuals with osteroporosis Contraindicated because they can generate large forces on relatively weak bone Twisting movements (e.g., golf swing) Dynamic abdominal exercises (e.g., sit-ups) Excessive trunk flexion Exercises that involve abrupt or explosive loading High-impact loading

Exercise Prescription for Individuals with Osteoporosis Flexibility training for individuals with osteoporosis Increased flexibility can be of benefit (especially with posture). Many commonly prescribed exercises for increasing flexibility involve spinal flexion and should be avoided. Slow and controlled movements should be the rule. Avoid ballistic-type stretching.

Exercise Prescription for Individuals with Osteoporosis Aerobic training for individuals with osteoporosis Goals Increase aerobic fitness Decrease cardiovascular disease risk factors Help maintain bone strength Improve balance Perform 3-5 d · wk–1 at an intensity of 40%–59% of VO2 reserve or heart rate reserve (HRR) Initial goal of 20–30 min per session with slow increase to 30–60 min once tolerated. When possible, exercise mode should be weight bearing.

Exercise Prescription for Individuals with Osteoporosis Resistance training for individuals with osteoporosis Goals Improve bone health Improve balance to lower risk of falling Perform 2–3 d · wk–1, 8–12 repetitions at a moderate intensity (60%–80%) Those with osteoporosis should avoid any ballistic or jumping activities.