Centre of Gravity
As adults, our centre of gravity is around our waist level - meaning we have a relatively steady centre. In children the centre of gravity is much higher, around chest level. The result of this is that children tend to have less stability and more difficulty balancing; centre of balance can change rapidly in children as their bodies grow, so don't expect perfect balance to start showing until the late teens. Equally energy expenditure is higher, as they have to work harder to maintain balance. In activities such as cycling where they are not having to centre their weight energy expenditure will be the same as an adults, but in dance or similar activities they have to work much harder.
Training technique can be problematic, in any physical discipline, due to these changes as everything is constantly having to be learned and relearned as the body changes. Dance training has a host of benefits for children out with their technical performance - strength, fitness, neuromuscular control, increased BMD, confidence, discipline, self-respect and respect for others - don't push it too much if they're struggling with technique, it'll come when their bodies stop changing.
Girls' muscle mass percentage tends to stay pretty stable from childhood to adulthood, whereas boys' increases by 40-55%. Pre-puberty the development of muscle strength will be pretty equal between both genders, however during and after puberty (14-16 years in boys, 11-13 in girls) males will make considerably greater strength developments even when on an identical training programme to females. Girls' muscle strength develops in accordance with increase in weight and height, whereas boys' strength and muscle mass increases are due to increased levels of androgenic hormones.
Strength Training and Young People
Many parents worry that strength training is somehow bad for children; as with any form of exercise, it has a huge number of benefits provided it's appropriate for the young people you're working with. Strength training programmes will benefit both boys and girls, not only for their muscular development but by increasing bone mineral density. Weight bearing exercise stimulates bone growth; as peak bone density is achieved before the age of 20 in both genders, accrual of good levels of BMD in children and teenagers is crucial for prolonged skeletal health.
Be aware of the age that strength levels between the genders start to split and tailor classes accordingly. Injuries will occur if you push girls to match boys' strength levels during and post-puberty.
Children are more prone to fracture and bone injury than adults due to the skeleton not being fully developed. However due to the fact the fact their bones are still growing and superior blood supply, injury tends to be less serious and recovery quicker.
Epiphyseal fusion marks the maturity of the skeleton. Fusion can be affected by repetitive stress caused by physical training, which may manifest as heel pain in children up to the age of 12 years, knee pain up to around 16 years and back pain up until around 20 years.
Children have higher levels of flexibility that adults, with a gradual decrease in flexibility levels from the age of 5-15 years. The period around the growth spurt, around 11-14 years, is typically the worst stage for flexibility. Muscle struggles to keep up with the rate of bone growth and while sarcomeres have to catch up with bone muscle elasticity suffers. Do not push dancers' flexibility at this stage, work on other areas of skill development and if dancers are putting pressure on themselves explain why they are struggling with flexibility.
Boys and girls body fat levels will change due to physiological developments. At the age of 8 years, girls will have around 18% BF, with boys around 16%. This changes dramatically by the end of puberty, with average levels in women around 26-28% and men around 14-16%, mean will typically have around 10% less BF than women. These differences are due to the effects of oestrogen in women and testosterone in men. Body fat in women is closely related to oestorgen levels, if BF levels drop too low amenorrhea will result from the body identifying it does not have adequate BF levels to reproduce.
Young female dancers should be taught of the reasons for increases in body fat and be educated as to safe and responsible ways of controlling body composition without resorting to damaging behaviours and restricted dietary intakes as this can have catastrophic health implications.