Skeletal System Pt2 (1) PDF

SKELETAL SYSTEM EXP01Y2 SPECIAL APPLICATIONS TO HEALTH AND FITNESS The following sections discuss three practical implications of skeletal health: Osteoporosis The female athlete triad Skeletal injuries OSTEOPOROSIS Osteoporosis, meaning “porous bones,” is a condition ch...

SKELETAL SYSTEM EXP01Y2 SPECIAL APPLICATIONS TO HEALTH AND FITNESS The following sections discuss three practical implications of skeletal health: Osteoporosis The female athlete triad Skeletal injuries OSTEOPOROSIS Osteoporosis, meaning “porous bones,” is a condition characterized by compromised bone strength that increases the risk of fracture. Bone strength is determined by both bone density and bone quality (including external geometry and internal microstructure). Osteoporosis results from an imbalance between bone resorption and bone formation. Resorption occurs faster than formation, leading to a loss in BMD. Clinically, osteoporosis is defined by a BMD more than 2.5 SD (T-score > −2.5) below the young normal adult average. OSTEOPOROSIS The most common fracture sites related to osteoporosis are the hip, spine, and wrist. Spinal vertebral fractures occur when an osteoporotic bone is literally crushed by the weight of the body, resulting in a loss of height, curvature of the spine, and considerable pain. The cause of osteoporosis is not known, although several risk factors have been identified (See Table 16.7 in the textbook) OSTEOPOROSIS Genetic risk factors include race, sex, family history, and body size. Nutritional risk factors include low calcium intake, excessive alcohol consumption, and consistently high protein intake. Lifestyle factors associated with osteoporosis include a lack of physical activity and smoking. Physiological factors include inadequate levels of oestrogen delayed menarche, amenorrhea, or an early menopause. OSTEOPOROSIS Several research studies have indicated that the rapid loss of BMD following menopause is related to the decrease in oestrogen levels. The low activity levels of females, particularly older women, also contribute to the risk of developing osteoporosis. BMC is positively related to long-term physical activity. In addition to its positive effect on BMD, exercise may also help prevent fractures by increasing muscular strength and coordination, thereby decreasing the risk of falling. The risk of falling is affected by the individual’s coordination, sight, and muscular strength. THE FEMALE ATHLETE TRIAD The female athlete triad is a syndrome of interrelated conditions including disordered eating, menstrual dysfunction, and skeletal demineralization. The syndrome was once narrowly defined in terms of the extremes of each of these conditions, but it is now recognized that each ranges along a continuum from health to disease. Although eating and reproductive disorders can occur in male athletes, no comparable syndrome has been identified in males. Thank you testosterone! THE FEMALE ATHLETE TRIAD – DISORDERED EATING Disordered eating is considered the key to the development of the female athlete triad. A female athlete who thinks that a lower body weight will improve her athletic performance begins to diet. Initially, this strategy may prove successful (although in the long run, it often is not), and so her dieting becomes more extreme. Alternatively, possibly unknowingly, she does not increase her caloric intake to meet her exercise energy requirements. Regardless of the initial cause, she has reduced energy availability. THE FEMALE ATHLETE TRIAD – DISORDERED EATING Energy availability is defined as dietary intake minus exercise energy expenditure. This is the amount of dietary energy remaining for all other physiological functions. Humans need dietary energy for five functions: cellular maintenance, thermoregulation, movement, growth, and reproduction. If a large proportion of the available energy is used for movement (exercise training), there may be insufficient energy available for the other functions. Reproductive functions seem particularly vulnerable to the effects of insufficient energy. In exercising females, reproductive function and bone turnover are impaired when energy availability is decreased more than 33%. THE FEMALE ATHLETE TRIAD – DISORDERED EATING 1. Lowering body mass to improve performance. 2. Unknowingly or unable to meet increased energy demands. Disordered eating involves a continuum of abnormal eating behaviours from low energy availability to clinically diagnosed eating disorders. Clinically diagnosed eating disorders include anorexia nervosa, bulimia nervosa, and eating disorders not otherwise specified THE FEMALE ATHLETE TRIAD – MENSTRUAL DYSFUNCTION Menstrual dysfunction is one mechanism through which low energy availability is thought to impact bone health. The female reproductive system is controlled by the hypothalamus-pituitary- ovarian axis. A key role is the secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus  THE FEMALE ATHLETE TRIAD – MENSTRUAL DYSFUNCTION Low energy availability decreases GnRH release. Inadequate GnRH results in the suppression of luteinizing hormone and follicle- stimulating hormone, which causes, in turn, inadequate secretion of oestrogen (oestradiol) and progesterone. The resultant disruptions in menstrual function can include: Try pronouncing these 1. Luteal suppression (phase defects in which ovulation occurs but implantation cannot) words?! 2. Anovulation, 3. Oligomenorrhea (irregular and inconsistent menstrual cycles), 4. Amenorrhea Amenorrhea may be either primary (the failure to achieve menarche by age 15) or secondary (no menses for a minimum of 3 consecutive months in a female who has attained menarche) THE FEMALE ATHLETE TRIAD – MENSTRUAL DYSFUNCTION While the athlete often feels the absence of a regular menstrual cycle is a good thing, physiologically it is not. A major concern with amenorrhea is that the low levels of circulating oestrogen (hypoestrogenia) can negatively impact a bone. This is true for both primary amenorrhea (almost half of bone mass accrual occurs during adolescence and young adulthood) and secondary amenorrhea. An athlete who misses more than six consecutive menstrual periods has increased risk of failure to reach potential peak bone mass or premature bone loss. Athletes should have a BMD similar to or higher than (depending on the site and sport) sedentary individuals and nonmenstruating athletes, not lower, and regularly typically do. THE FEMALE ATHLETE TRIAD Non-weight bearing bone THE FEMALE ATHLETE TRIAD – SKELETAL DEMINERALIZATION Skeletal demineralization is also linked directly to low energy availability—possibly in a dose-response relationship. A study by Ilhe and Loucks (2004) showed that markers of bone formation were suppressed at moderate levels of energy restriction, whereas markers of bone resorption increased only when the energy restriction was severe enough to suppress oestrogen. The primary role of oestrogen in bone metabolism is to reduce the rate of bone resorption. Low energy availability likely initially affects metabolic substrates and hormones other than oestrogen (insulin, growth hormone, IGF-1, cortisol, leptin, and thyroid) that are important in bone metabolism, and then, with more severe energy restriction, it impacts oestrogen as well THE FEMALE ATHLETE TRIAD – SKELETAL DEMINERALIZATION Note that although exercise is a stressor and thus elicits neurohormonal responses in the body, exercise itself does not appear to cause the female athlete triad beyond the impact of its energy cost on energy availability. No particular body weight or body composition appears to be a critical threshold level beyond which a disruption of the hypothalamus-pituitary-ovarian axis occurs. Both eumenorrheic (regular menstrual cycling) and amenorrhoeic athletes span a common range of body weight and composition. THE FEMALE ATHLETE TRIAD – SKELETAL DEMINERALIZATION Finally, while oestrogen is important for both menstrual and bone health, oestrogen supplementation alone has not been shown to restore BMD to normal in amenorrheic athletes. The Clinically Relevant Focus on Research box (See text book) presents a case study demonstrating the roles of calcium, oestrogen, and energy availability in the treatment and recovery of low BMD resulting from amenorrhea. SKELETAL INJURIES Skeletal injuries can be categorized as resulting from microtrauma or macrotrauma. Macrotrauma injuries are sudden acute incidents, such as a broken leg or clavicle from impact or a fracture at the epiphyseal growth plate. Growth plate fractures have the greatest potential for harm. The probability of a growth plate injury is greatest in automobile accidents, falls, contact sports, and dynamic resistance training. Fractures of the growth plate can result in progressive bone shortening, deformity, or joint incongruity. Fortunately, acute traumatic growth plate injuries are less frequent than other injury types, and most such injuries appear not to result in growth disturbances. SKELETAL INJURIES Microtrauma injuries are overuse injuries from chronic repetitive overtraining. The anatomical site of microtrauma depends on the sport. Microtrauma injuries to bone generally involve an uncoupling or imbalance between bone resorption and bone deposition, called a stress reaction. Stress reactions refer to maladaptive areas of bone hyperactivity where resorption progressively exceeds deposition. SKELETAL INJURIES Early minor stress reactions may have no clinical manifestations. The individual feels no pain and has no swelling or tenderness. As the overuse continues and the imbalance becomes more extreme, several clinical symptoms may occur, including degeneration and loosening of portions of bone from the joint capsules the formation of bone spurs, inflammation of bone and cartilage, and/or stress fractures. A stress fracture is a hairline break in a bone that occurs without acute trauma is clinically symptomatic, and is detectable by X-rays or bone scans. It is often difficult to determine exactly when a bone’s stress reaction becomes a stress fracture. SKELETAL INJURIES A typical fine hairline fracture may be undetectable by X-rays or bone scans for 3–4 weeks after pain occurs. Although exercise training can and does have a beneficial impact on bone growth and health, too much exercise training, usually in the form of repetitive overuse or rapid increments of intensity or duration, can be detrimental. Fractures are more likely if the bone already has a low BMD. The concern about overuse injuries therefore focuses on female athletes exhibiting the female athlete triad and young growing athletes of both sexes. The concern for amenorrheic athletes is well founded. A higher prevalence of stress fractures has been documented in this population than in female athletes with normal menstrual cycles in a variety of sports SKELETAL INJURIES The highest incidence of stress fractures occurs between the ages of 10 and 15, at the time of peak growth. Some researchers have suggested that a normal imbalance between bone matrix formation and mineralization occurs during the growth spurt. Furthermore, during this growth spurt, muscle imbalances can occur around joints as the muscles, tendons, and ligaments are stretched and become progressively tighter when the bones elongate. A muscle that is fatigued from overuse, is weak or out of balance with its antagonist, and/or is inflexible is less able to absorb shock, allowing abnormally high stress to be transmitted to the bone. This situation increases the risk of stress fractures, other repetitive stress reactions, and impact injuries. SKELETAL INJURIES The primary risk factor for overuse injuries is training error, particularly abrupt increases in intensity, duration, and frequency. Workload should not increase more than 10% per week in young training athletes. Other risk factors include the aforementioned musculoskeletal imbalances of strength, flexibility, or size; errors in technique or skills; anatomical malalignments; footwear that fits improperly; and running on hard surfaces such as concrete and tarred roads. Adequate nutrition, reasonable training regimens, and maintenance of normal hormonal levels are keys to good bone health.  We will discuss this during our collaborate session. An online assignment will be mentioned BONE HEALTH: A CASE STUDY OF CYCLING WHY ARE CYCLISTS SO FRAGILE?