Factors that influence bone health
Growth, and subsequently maturation, can be seen in three subtly connected phases: infancy, childhood, and puberty . While all three are equally important, dance training generally begins during late childhood into puberty; thus, information regarding the latter two phases will form the core content of this chapter. Firstly, the chapter presents an evaluation of the distribution and determinants of injury in dancers. Next, a topical view of bone growth and maturation is discussed. Finally, the interface between bone health and nutrition will be addressed, concluding with a consideration of hormones and bone health.
Epidemiology/Scope of the Problem
Physical and artistic demands are often at odds in the dance profession. When analyzing trends and patterns seen in dancers, most studies observe the distribution and determinants of varying rates and types of injuries. Research reveals a surprising comparison of injury rates; 4.4 injuries per 1000 h in dancers  versus 4.1/1000 h in contact sports . Cheerleading is an example of an aesthetic sporting activity, which contains a great deal of dancing. An estimated 208,800 children from 5 to 18 years of age were treated in US hospital emergency departments for cheerleading-related injuries between 1990 and 2002 . Similarly, in a recent retrospective study spanning 17 years, researchers reported that more than 113,084 children with dance-related injuries were treated in US emergency departments . The data revealed that 55% of dance-related injuries occurred in “classical dance” genres (ballet, tap, jazz, and modern). Adolescent dancers (15–19 years) constituted 40% of the injuries, and research in adult dance populations is comparable [13, 14], extending the observation that dance is not without physical risk.
Physical activity enhances skeletal formation and bone mineral density (BMD) , yet in professional dancers and other artistic athletes an open question is whether dance activities retard skeletal growth and maturation [16–18]. Physical examination via anthropometry and physiological assessments via specialized scans are established methods of measuring skeletal development and maturation. Israeli researchers determined the body structure and adipose tissue distribution of 1482 female dancers aged 8–16 years compared with a control group of 226 non-dancer girls . Fourteen anthropometric measurements across 15 indices recorded significant difference related to the extent and distribution of adipose tissue. At age 8, both groups showed similar weight, while at age 13, non-dancers were significantly heavier than dancers (48.4 ± 9.8 and 40.6 ± 8.7 kg, respectively). At age 15, weight differences between the two groups decreased to only 2 kg. Moreover, adipose tissue distribution at menarche was 13 years among dancers and 12 years in non-dancers. The researchers concluded that any concerns about dance retarding growth and maturation were negligible, as the differences could be a consequence of “teacher selection”.
Anthropometry provides physicians and health care professionals with a macroscopic view of the body. However, physiological changes that occur in dancers are due in part to the intensity of their training combined with negative energy balance. Low BMD is a chronic condition often seen in both genders, which is modifiable via balanced nutritional intake. Dual energy X-ray absorptiometry (DXA) techniques offer an effective means of evaluating the influence of diet and the consequence of intense dance activity by measuring changes in lean tissue, bone mineral content, and fat across key body areas. DXA is generally considered a suitable method for examining and studying children because this technique contains low irradiation and negligible time needed to perform the scans .
Several observational studies have utilized DXA to ascertain bone health in adolescent dance populations. In one of the most comprehensive studies to date, Burckhardt and colleagues, during an internationally renowned ballet competition for pre-professional dancers, examined 127 female participants with average age of seventeen . Using DXA scans, they conducted assessments for body mass index (BMI), bone mineral content (BMC), and bone mineral apparent density (BMAD) at the lumbar spine and femoral neck. Additionally, pubertal stage (Tanner score), psychometric data gathered via the EAT-40 questionnaire, and a self-reported three-day dietary record were collected. The results revealed that BMI for age was on average normal in only 43% of the dancers, while 16% had a more or less severe degree of thinness (12.6% Grade 2 and 3.1% Grade 3 thinness via Tanner scores). For 117 participants, the average age for menarche was late, 13.9 years, with 10 participants found to have primary amenorrhoea, and one secondary amenorrhoea. In terms of diet, the results revealed that food intake, evaluated by the number of consumed food portions, was below the recommendations for a normally active population in all food groups except animal proteins, where the intake was more than twice the recommended amount. Most of the population was in the final stages of their pre-professional education. Thus, their daily activity would qualify as high intensity, intermittent training . In this group, with low BMI and intense dancing, BMC was low and associated with nutritional factors; dairy products having a positive and non-dairy proteins a negative influence, highlighting the adaptable influence of nutrition.
While DXA to date has been the gold standard by which bone health is assessed, it should be interpreted with some caution. The areal or surface density measured is the quantity of BMC per cm2, which means that bigger bones have greater surface bone density with a comparable real volumetric BMD (g/cm−3). Larger differences are seen in African Americans than in Caucasian American populations . This difference in measurement can be avoided by combining areal BMD with bone and body size-corrected BMC . A recent systematic review of bone health in dancers demonstrated that large discrepancies in methodology complicate ascertaining how large the low BMD problem is in female dancers . Thus, more consistency across studies is needed. Clinical studies have begun to explore the use of computed tomography together with high-resolution magnetic resonance imaging, which offers a three-dimensional depiction of the microarchitecture of both cortical and cancellous bone compartments .
Bone Growth and Maturation
During the first 18 months of life, a child will develop approximately 25% of peak bone mass, and by the age of 18, approximately 90% of total peak bone mass has been gained. The last 10% occurs in the final phases of maturation, leading to a fully ossified skeleton, which can happen at any time in the subsequent 10 years, depending on the gender and genetics of the individual . The addition of weight-bearing exercise during puberty confers maximum bone accretion, interconnecting with hormonal development as the child matures. Growth hormone (GH), insulin-like growth factor-1 (IGF-1), and sex hormones all have effects on bone accretion . Another hormone, leptin, via leptin receptors found in bone, has been suggested as a good biomarker to assess pubertal delay in a young ballet dance population . Adolescence is a period of rapid development towards building adult skeletal strength and thus becomes the key growth phase when discussing physical activity. In girls, the years before menarche provide advantageous osteogenic benefits resulting from weight-bearing physical activity, particularly with regard to bone modelling.
In childhood and throughout adolescence, bones are sculpted by a process called modelling, which allows for the growth of new bone at one site and the removal of old bone from another site within the same bone. Three key principles determine bone remodelling: cellular responses that are mutually dependent on strain, load, and frequency of stimulus—i.e., dynamic (not static) loading—which exerts the strongest bone adaptation response, and as bone cells tend to favour routine movement, variation of stimulus is important to elicit a consistent level of response . Hence, regular weight-bearing physical activity is a modifiable behavior that enhances bone health during growth, and possibly reduces risk of fracture in later life . Research into classical dancers who perform a myriad of repetitive dance steps of short duration has pointed to an osteogenic effect on weight-bearing sites of the skeleton , which might help dancers who started ballet early avoid bone problems later in life .
When discussing bone maturation in children, two additional concepts are important: plasticity and elasticity. Bones in children allow for a greater degree of deformation than do adult bones before they break. Plastic deformation characterizes bone that deforms but does not fracture . Thus, low modulus of elasticity in growing bones means the bone can be angled beyond its elastic limit without producing a fracture. The periosteum, a fibrous sheath that covers bones, is much thicker in children than in adults and acts as a restraint to displacement. The thick periosteal sleeve is important for paediatric skeletal remodelling. Because of it angular deformation of a child’s bone may cause a fracture of the cortices without displacement.
The epiphysis, the rounded end of a long bone, is a secondary ossification site in the growing skeleton, making it sensitive to trauma. Epiphysis development is of crucial concern in all young dancers but particularly in female dance students who wish to pursue a career in classical dance, where they will be called upon to transfer their body weight and balance on the tips of their toes in pointe shoes. This manoeuvre can lead to overuse injuries seen frequently in classical dancers . The fusion of the epiphyses generally occurs earlier in the foot than the leg. From age five through age 12 the average girl’s foot grows 0.9 cm (0.35 in.) per year, reaching an average foot length of 23.2 cm (9 in.) at age 12. Hence, the recommendation from physicians to dancers and their support team is to start pointe training around that age, with the caveat that all bodies develop at different rates . During the dynamic growth spurts bones generally lengthen more rapidly than the musculotendinous junctions. Restriction of the muscle tendon units equates to more traction stress on the growing tissue at the insertion point. When coupled with the demands of dance technique proficiency, repetition of many dance steps can cause inflammation and microavulsions at the bone–cartilage junction . Dancers are susceptible to working long hours rehearsing similar movement patterns across dance choreographies. Insufficient time to recover, nutrient deficient diets, and inadequate caloric intake when compared to energy expenditure can ultimately lead to avoidable overuse injuries .
During maturation in adolescence bone continue to grow in length and width, as well as to increase in cortical thickness. There is a substantial increase in bone mass and bone density during this period. These processes are interdependent and are influenced by internal factors both genetic and hormonal, and external factors such as nutrient intake and physical demands placed on the system. Gender differentiation, for example, has traditionally been seen as a non-modifiable factor, as males typically have a longer pre-pubertal growth period and in puberty their growth spurt occurs up to 18 months later than in girls, which translates to different skeletal proportions in the lower extremities . Children with intersex disorders, or those who opt for gender reassignment, may be an exception.
Regardless, a convincing factor crucial to successful bone maturation is nutrition. The remodelling of bone is a coordinated relationship between endocrine and nutritional physiology via cell signalling proteins, cytokines, as well as circulating hormones, parathyroid hormone (PTH), insulin-like growth factor 1 (IGF-1), and calcitonin, a naturally occurring hormone that helps to regulate calcium . Additionally, vitamin D is ultimately converted to its biologically active form 1,25-dihydroxyvitamin D (1,25-OH2-D), which stimulates calcium absorption in the intestine. Both calcium and vitamin D are continually emphasized for their role in growth and maturation in children and will be covered later in more detail. While physical activity does confer positive gains in skeletal health, dance as a specific form of exercise is not without its challenges, as discussed below.
Nutrition and Bone Development in Young Dancers
It should be clear that a balanced diet is important for growth, achieving good health, and providing for the basic energy needs in developing youth [37, 38]. Performance nutrition in the context of dancing enhances physical and artistic performance by decreasing fatigue and the risk of disease and injury . Balancing energy intake with energy expenditure is crucial for preventing an energy deficit or excess. Energy deficits may cause delayed puberty, menstrual dysfunction, decreased muscle mass, and increased susceptibility for fatigue or injury , while energy excess can result in needless weight gain . We classify the foods we eat into two broad categories: macronutrients and micronutrients. Macronutrients include carbohydrates founds predominately in foods such as vegetables, baked goods and fruit, fats from foods such as butter and olive oil, and protein from foods such as meat, eggs, and/or plant-based sources. Micronutrients are the vitamins and minerals in our food.
Dietary fats, carbohydrates, and proteins are the basic building blocks from our food that are converted into substances needed for energy, growth, and repair and maintenance of bodily structures. Fats are naturally found in animal and plant foods and provide an abundant source of fuel for energy, which we use mainly when the body is inactive. Carbohydrates, converted into simple and complex sugars, also contain a rich source of energy and are quickly broken down in the body to provide a rapid energy source to the muscles . Proteins, both animal- and plant-based, contain amino acids which form the building blocks of most cells and tissues in the body: hair, muscle, organs, nails, and even tears. A balance in protein ingestion is important to bone health, as imbalance can affect urinary calcium retention or excretion . A classification of macronutrients can be seen in Table 11.1.
Classification of macronutrients
Fats, triglycerides, three fatty acid chains, the alcohol glycerol
Disaccharides (sucrose, lactose)
Monosaccharides (glucose, fructose)
Use in the body
Easily available, preferred energy for physical activity
Energy 17 kJ/g (4 kcal/g)
Key form of storage
Provides insulation of body tissue and nerve fibres. Maintains cellular structure, hormones Energy 39 kJ/g (9 kcal/g)
Tissue growth and repair. Production of antibodies, enzymes, haemoglobin
Energy 17 kJ/g(4 kcal/g) more utilised in the absence of sufficient carbohydrates and/or fats
Fruits, vegetables, tubers and starchy edible roots, sugar based foods, refined foods
Plant based (avocado, nuts, vegetables oils) Animal based (dairy, butter, meats)
Plant based (peas, legumes, pulses) Animal based (meats, seafood, eggs, dairy)
An entire spectrum of micronutrients is important for maturation. Successful bone health requires adequate intake of these micronutrients and the metabolic bioavailability of calcium and vitamin D , which is detailed below.
During the first year of life, calcium intake predominately comes from human milk, or if that is not available an infant-based formula alternative. After year one, the major source of dietary calcium in the USA is derived from dairy-based products. Table 11.2 provides an overview of calcium sources from animal, vegetarian, and vegan sources . Calcium is a key to bone remineralization. The adult human body contains about 1000–1500 g of calcium, and depending on gender, race, and general body size up to 99% is found in bone as hydroxyapatite, a naturally occurring mineral form of calcium apatite. Studies in children and adolescents have shown that ingestion of calcium-enriched foods enhances the rate of bone mineral acquisition and peak bone mass [44, 45]. In a study that assessed calcium balance across 34 studies pooled by age group, Matkovic and Heaney  determined an optimal threshold intake of 1500 mg/d for children, adolescents, and young adults.
Calcium found in foods
Standard portion size
Calories in standard portion
Calcium in standard portion (mg)a
Low-fat milk (1%)
Skim milk (non-fat)
Reduced fat milk (2%)
Low-fat chocolate milk (1%)
Reduced fat chocolate milk (2%)
Whole chocolate milk
Orange juice, calcium fortifiedb
Soymilk (all flavours)b
Almond milk (all flavours)b
Yoghurt and soft cheeses including dairy alternatives
Plain yogurt, non-fat
Plain yogurt, low-fat
Vanilla yogurt, low-fat
Fruit yogurt, low-fat
Ricotta cheese, whole milk
Mozzarella cheese, part-skim
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