Osteoporosis and Osteopenia
There are approximately 206 bones in an adult human skeleton as well as related cartilage, ligaments and tendons. The skeleton’s primary function is to provide support, protection, leverage, blood cell production, energy metabolism, endocrine functions and also serve as a reservoir for calcium and phosphorus. Bone is a highly dynamic material and responds to stimuli including muscular contractions that result in movement around joints and movement. However, a lack of stimuli results in loss of bone mass and subsequently bone strength. There are several disorders that affect the skeletal system including osteoporosis, osteopenia and osteoarthritis that have a significant impact on an individual’s health and well-being. Due to the prevalence and incidence of these diseases and the proposed positive effects exercise has on them, exercise professionals should be aware of the pathophysiology, treatments and exercise interventions.
Osteoporosis has been defined by the World Health Organisation as a bone mineral density (BMD) at the hip or spine ≤ 2.5 standard deviations (SD) below the “young normal adult score” (denoted as a T-score ≤ 2.5 SD) and measured by dual-energy x-ray absorptiometry (DXA) (Neto et al., 2015). Bone density values in individuals can be expressed in relation to a reference population in standard deviation (SD); when SDs are used in relation to the young healthy population, this measurement is referred to as the T score. A Z score compares bone density to the normal at that age, and a score of -2 indicates bone density below normal for a person of that age.
BMD categories established by the World Health Organisation (WHO):
Normal: hip BMD greater than the lower limit of normal which is taken as 1 SD below the young adult reference mean (T score ≥-1).
Low bone mass (osteopenia): hip BMD between 1 and 2.5 SD below the young adult reference mean (T score less than -1 but above -2.5).
Osteoporosis: hip BMD 2.5 SD or more below the young adult reference mean (T score ≤-2.5).
Severe osteoporosis: hip BMD 2.5 SD or more below the young adult reference mean in the presence of one or more fragility fractures (T score ≤-2.5 plus fracture).
This has been further defined functionally by the National Institutes of Health that states osteoporosis as a decrease in bone strength resulting in an increased risk of fracture (Evans et al., 2011). As noted previously human bone tissue is highly dynamic with active and mature cells involved in bone deposition and resorption (Figure 1). Therefore, bone mass at any period is a function of the net effects of bone development and resorption biomechanisms. Osteoporosis is consequently a result of cumulative net bone resorption.
Figure 1. Bone Remodelling Cycle
In the UK over 3 million people are estimated to have osteoporosis and there are estimated to be over 500,000 fragility fractures that occur in the UK each year (Office of National Statistics, 2014). Fragility fractures are estimated to cost the UK around £4.4 billion each year (Office of National Statistics, 2014). Hip fractures in isolation account for 69,000 emergency admissions into hospitals, accounting for 1.3 million bed days at a cost of £1.5 billion each year (Lawrence et al., 2005; Department of Health, 2013). Wright et al., (2000) estimated that the prevalence of osteoporosis in the USA also varies among racial and ethnic groups, affecting approximately 7.7 million non-Hispanic white, 0.5 million non-Hispanic black, and 0.6 million Mexican American adults. Significant sex variances in osteoporosis have been reported, with females eight times more likely to have type 1 and two times more likely to have type 2 osteoporosis (Wright et al., 2000). Smith and colleagues (2009) further specified that the increased mortality and morbidity related with osteoporosis is almost 24% of individuals over 50 years of age with hip fractures who die within 12 months after the fracture.
Pathophysiology of Osteoporosis: An Overview
Osteoporosis can be categorised as either primary or secondary. Primary osteoporosis sometimes termed age-related osteoporosis, is the most prevalent and represents the cumulative loss of bone-related ageing in males and females (Surgeon General Report, 2004). The decline [in part] is a consequence of the declining activity of bone-forming cells (osteoblasts) after the age of 35-years (Smith, Wang and Bloomfield, 2013). This results in a minor but gradual loss of the bone mass year on year. Primary osteoporosis can be further subdivided as type 1 or type 2.
Type 1 osteoporosis (often termed as postmenopausal osteoporosis) normally occurs from 50-to-65 years of age and results in accelerated bone resorption and decreased bone development due to the loss of oestrogen binding to its receptors on the bone (Clark and Khosla, 2010). This phase of bone loss lasts from 4-to-10 years, results in a loss of 5- to-10% cortical bone and 20-to-30% trabecular bone (Clark and Khosla, 2010; Riggs, 2002). This bone loss is followed by type 2 osteoporosis (referred to as senile osteoporosis) which is a slower but a continued phase of loss after the age of 70, resulting in an additional loss of 20-to-25% of cortical and trabecular bone.
Type 2 osteoporosis is believed to be triggered by a combination of factors including decreased renal vitamin D production and subsequent calcium absorption, decreased nutrient intake, decreased physical activity, and decreased oestrogen and testosterone activity (Riggs, 2002; Surgeon General Report, 2004). In ageing males, testosterone levels decrease and so does the amount of circulating testosterone available to be converted by the aromatase enzyme to oestrogen (Riggs, 2002). Ageing males also experience an increase in sex hormone-binding globulin which binds both testosterone and oestrogen, consequently reducing bioavailability and negatively affecting bone mass and strength (Harman et al., 2001).
Type 3 or secondary osteoporosis is an outcome of another disease state (e.g., cystic fibrosis, anorexia nervosa, Crohn’s disease) or medication use (e.g., glucocorticoid-induced osteoporosis) (Surgeon General Report, 2004). However, it has been suggested that there are other risk factors including inactive lifestyle, smoking, alcohol abuse, excessive protein, sodium and caffeine intake (Kanis and McCloskey, 1998). Importantly, osteoporosis is a significant health concern due to the elevated risk of bone fractures, health disorders and also significantly increases morbidity and mortality rates (Surgeon General Report, 2004). Fortunately, advancement in the management of osteoporosis can positively treat the disorder if diagnosed and treated promptly.
Figure 2. Conceptual model of the pathogenesis of fractures related to osteoporosis.
Effects of Exercise in Clients with Osteoporosis
Recommendations by the National Osteoporosis Foundation indicates that individuals with Osteoporosis should regularly perform weight-bearing and muscle-strengthening exercise as a treatment and preventative measure (Cosman et al., 2014). It has also been suggested that cyclical weight-bearing movement patterns performed at a moderate to high intensity are beneficial (Moreira et al., 2014). Individuals with bones that are excessively fragile or have another condition that prevents them from performing high-intensity activity should engage in light intensity (Smith, Wang and Bloomfield, 2009). Load or weight-bearing activities have positive benefits as increasing muscular strength improves bone mass and strength via a transfer of mechanical stress to the bone via the tendons. Additional, benefits due to improvements in the client's muscular strength are improved balance and proprioception that the risk of falls (Moreira et al., 2014). Evidence by Roghani and colleagues (2013) suggests that aerobic exercise can provide a positive stimulus that improves markers of bone synthesis and breakdown.
Exercise Guidelines for Clients with Osteoporosis
Clients with osteoporosis should always undergo pre-exercise screening in which the exercise professional will be made aware of: (1) exercise limitations due to previous fractures; (2) muscle imbalances or weaknesses; (3) balance issues; (4) identification of other chronic disorders; and (5) currently prescribed medication. Additionally, information must be gathered regarding the severity and location of osteoporosis in which to help formulate effective and safe programming. Furthermore, exercise testing can be performed to establish the client's baseline values and establish exercise tolerance levels. However, medical clearance before testing should be given by a physician or health care professional.
Summarised in Table 1 are program design NSCA recommendations for clients with osteoporosis. Clients with osteoporosis are typically deconditioned, therefore initial use of light-intensity training is suggested (Smith, Wang and Bloomfield, 2009). For clients with mild to moderate osteoporosis (T-score < 3), aerobic exercise and weight-bearing exercises should be encouraged. Exercises that involve large muscles including walking or running should be performed at light-to-moderate intensity, 30-to-60 minutes per session, three to five days per week (Smith, Wang and Bloomfield, 2009). Clients with severe osteoporosis (i.e., changes to spine [kyphosis] or had multiple fractures) should follow the same recommendations for duration and frequency but perform low impact exercises at a light intensity. It is recommended that clients should perform resistance training aiming for two to three sets of 8-to-10 repetitions at a loading of 60-80% 1RM with a training frequency of two or three days per week (146). Clients that are suitably conditioned may also use free weights as this will increase proprioceptive and balance. A more conservative approach should be adopted for clients that have severe osteoporosis including limiting high impact or twisting activities that cause bone or joint pain.
Incorporated into the exercise plan should also be appropriate forms of flexibility training that seek to increase the client’s mobility and range of motion. In particularly are exercises that focus on the hip, knee, and pectoral girdle, with a recommendation of three stretches per muscle group, holding each stretch for up to 30 seconds, at a frequency of five to seven days per week (Smith, Wang and Bloomfield, 2009). The client must avoid excessive twisting, flexion, and extension of the spine especially for clients diagnosed as severely osteoporotic or with a history of fractures. Lastly, functional training that promotes improvements in balance and proprioception is suggested with a training frequency of 2-to-5 days per week.
Table 1. NSCA Exercise Program Recommendations for Clients with Osteoporosis
Osteopenia is a bone condition characterised by a decreased density of bone, which leads to bone weakening and an increased risk of breaking a bone (fracture). The World Health Organisation has defined osteopenia as a bone mineral density of 1.0-to-2.5 SD below that of a “young normal adult “(clinical value T-score of -1.0 to -2.5 SD) (Watts et al., 2008). These individuals are at greater risk of osteoporosis and other related health concerns (Figure 1).
Figure 3. Various stages on decreased bone density.
Pathophysiology of Osteopenia
Osteopenia largely has the same pathophysiology as that already described above for osteoporosis. However, the loss in bone mass and strength has not fully developed to the same degree (Figure 3). Additionally, there are various factors that are not limited to menopausal females that can contribute to osteopenia including hypothalamic amenorrhea, anorexia nervosa, inadequate calcium intake, or vitamin D deficiency (Kim et al., 2002).
It has been suggested that individuals who have been diagnosed with osteopenia ensure they intake appropriate levels of calcium and vitamin D. This is to exclude malabsorption disorders including Crohn’s and celiac disease or the effects of various medications such as neomycin and cholestyramine. Furthermore, assessing the individuals previous and current physical activity programs can provide essential information concerning any previous exposure to appropriate bone-forming stimuli throughout their life. If the individual is diagnosed with osteopenia it allows for the employment of applicable interventions that increase the prospect of slowing the rate or potentially reversing the effects of this disorder.
Effects of Exercise and Recommendations for Clients with Osteopenia
Several studies (Bolton et al., 2012; Mosti et al., 2014) have established the positive effects of various modes of exercise including aerobic and resistance training have on the treatment and management of osteoporosis. These modes of exercise place appropriate cyclical strain on the bone which may be an effective means of increasing BMD and strength. Osteopenia shares similar pathophysiology as osteoporosis, therefore the exercise recommendations for osteopenia are the same (see above exercise recommendations). The only exception is that the absolute risk of fracture is lower than that of osteoporosis, so high intensity or high impact exercise may be incorporated into a program. However, consultation with the client’s physician must be made to determine fracture risk as part of the assessment phase of implementing an exercise program.