Physical and Motor Development

1. Physical and Motor Development Implications for Training Michael Horvat

2. Physical and Motor Development • Children do not grow at a constant rate and there are individual differences in physical development at any given chronological age • Group of 14-year-olds can have height differences as great as 9 in. and 40 lbs. 11 yr old girl may be taller and more physically skilled than 11 yr old boy • Differences correspond to variations in timing and magnitude of growth during puberty (girls 8-13, boys 9-15)

5. Physical and Motor Development • Maturity assessment can be used to evaluate growth and development patterns in children and can be used to measure fitness including muscular strength and motor fitness for fitness testing and athletic competition. • Sensitivity to individual differences in abilities and past experiences important for training adaptations i.e. in early or late maturing children • Training age or length of time in training can influence adaptation to training and magnitude of gain

6. Physical and Motor Development • During peak height velocity (12 in girls and 14 in boys) children are at an increased risk for injury. • Relative weakening of bone, muscle imbalances between the flexor and extensor groups around a joint and relative tightening of muscle tendon units spanning rapidly growing bones are risk factors for overuse. Emphasize flexibility, correct imbalances, decrease volume and intensity of training

7. Learning Activity • Preadolescent children can improve strength with resistance training. Neurological factors as opposed to hypertropic factors are responsible for these gains

8. Physical and Motor Development • Muscle and bone growth • Prenatal by hyperplasia (number of cells) • hypertrophy (size) • I year little difference in fiber distribution • Undifferentiated prior to 30 weeks gestation • Type I 40% at birth, Type II 45% at birth • fiber size increases at 2 years; max rate at 10-16 years • Sarcomeres (length) • Muscle mass-minimal during childhood; increases in boys 17-20, 54% of weight; increases in girls 13-16, 45 % of weight

9. Physical and Motor Development • At birth 25% muscle mass; 40% in adulthood; peak mass 16-20 in girls and 18-25 in boys • Puberty a tenfold increase in testosterone production in boys and increase in muscle mass; Girls increase is estrogen causes increase in body fat, breast development widening of hips • Muscle increases in hypertrophy not hyperplasia • Mass is affected by exercise and diet or both • Fiber size and number decrease in aging from neural factors, vascular changes, collagen, motor end plates and isotonic twitch

10. Physical and Motor Development • Bone formation occurs in diaphysis (central shaft of long bone) and growth cartilage (located at epiphyseal or growth plate, joint surface and apophyseal insertions of muscle tendon units • When epiphyseal plane becomes ossified long bones stop growing. Bones typically fuse during early adolescence with girls 2-3 yrs before boys

11. Physical and Motor Development • Particular concern is vulnerability of growth cartilage to trauma and overuse-disrupt blood and nutrient supply and permanent disturbances • Trauma from falls or excessive repetitive stress may result in a ligament tear or epiphyseal plate fracture. Peak incidence occurs at peak height velocity

12. Learning Activity • Growth cartilage in children is located at the epiphyseal plate; the joint surface, and apophyseal insertions. Damage to the growth cartilage may impair growth and development of affected bone

13. Physical and Motor Development • Skeletal Growth: 2 month primary ossification centers • Postnatal- growth of epiphyseal plate Layers of epiphyseal plate zone of resting cells proliferative zone hypertropic zone calcified cartilage zone • Osteoblasts • Bony skeleton 14% of wt;97 % of ht. • Functions protection of vital organs support of body weight storage of minerals structural leverage for movement bone marrow storage

17. Physical and Motor Development Structure, stiffness, strength > function • Aging losses-women 30, men 50 • Bone mass in third decade; men half of women • Appositional growth( laying down new bone on outer surface of the bone and is absorbed from the inner surface. Continues throughout life. In childhood and adolescence formation greater than absorption

18. Physical and Motor Development • Osteoporosis • Osteopenia, ostemalacia • Other terms • epiphyseal plate-growth zone composed of hyaline cartilage • metaphysis-wider part of shaft of long bone • diaphysis-shaft of long bone formed by primary centers • epiphysis-ends of long bone formed by secondary centers

19. Physical and Motor Development Developmental Changes in Strength • Increases in muscle mass throughout preadolescence and adolescence increase strength. Growth curves are similar to muscle mass. • In boys peak gains in strength occur about 1.2 yrs after peak height velocity and 0.8 years after peak wt. velocity with weight being primary indicator. This pattern suggests that during periods of rapid growth, muscle increases in mass, then strength. • In girls, peak gains is strength also occur after peak height velocity although there is more variation in strength

20. Physical and Motor Development The relationship of strength to height and weight • Although strength is essentially equal in boys and girls during preadolescence, hormonal differences during puberty are responsible for the acceleration of strength development in boys and the continuation of approximately the same rate of strength development of girls during preadolescent years • On average peak strength is attained by 20 yrs in untrained women and 20-30 in untrained men • An important factor in the expression of muscular strength in children is the development of the nervous system

22. Physical and Motor Development • If myelination of nerve fibers is absent or incomplete, fast reactions and skilled movement cannot be successfully performed and high levels of strength and power not possible. • As the nervous system develops, children improve in skills that require balance, agility, strength and power. • Since myelination of many motor nerves areare incomplete until sexual maturation children should not be expected to respond to training in the same way or reach the same skill level until they reach neural maturity.

23. Physical and Motor Development • Early maturing child has an advantage in strength compared to a later maturing child with less muscle mass • Physical differences and body proportions also give some children advantages. • Although late matures tend to catch-up, many other factors such as motivation, coaching and ability will contribute to success

24. Physical and Motor DevelopmentImplications for Training Children • Changes in neuromuscular functioning are at least partially responsible for exercise induced adaptations in children. Changes in hypertrophy can significantly impact training-induced strength gains in adolescents and adults but unlikely for preadolescents due to inadequate levels of circulating testosterone (preadolescence 20-60 ng/100; adolescence 600ng/100 in males and females unchanged) • It appears that preadolescents have more potential for an increase in strength due to neural factors such as increases in motor unit activation, recruitment and firing. Also intrinsic muscle adaptations, improvements in motor skill performance and coordination of involved muscle groups, muscle synergy can aid strength performance in preadolescence

25. Learning Activity • A parent approaches you about beginning a strength training program for his 10-year-old son/daughter. What advice would you give him?

26. Physical and Motor Development Potential Benefits • Program interventions have potential to influence many health and fitness related measures • May help reduce injuries in sport and recreation activities • Regular participation may decrease fatness among obese children and adolescents • Regular participation has a favorable influence on growth at any stage of development and has been shown to enhance bone density in children and adolescents

27. Physical and Motor Development • May also increase a young athlete’s resistance to acute and overuse injuries • Aid in preparing young athletes for demands of sport competition and overcome sedentary life styles • In contrast to early sport specialization the development of fundamental fitness and motor skills aid in sport success • Elimination of injuries is unrealistic but aids young athletes in handling the duration and magnitude of forces in practice and competition

28. Physical and Motor Development Concerns • Biggest concern is potential injury to the epiphyseal plate • Also concerns for repetitive use of soft tissue injuries to lower back, shoulder, and arm

29. Physical and Motor Development Program Design • Resistance training • Plyometrics • Prehab exercise to base and core movements