Pediatric Exercise Physiology Applications for the Teacher and Coach Why is information important?  Teachers and coaches work with individuals between ages of 5 and 18 years of age  Children and adolescents compete in sports  Advise on potential benefits  Advise on potential hazards  Dispel inaccurate myths  We must understand the impact of exercise on the physiological aspects of growth and development. What we do know!  As children’s size increases, so do almost all of their functional capacities: Strength Motor abilities Cardiovascular and Respiratory function Aerobic and Anaerobic capacities Understanding how these capacities develop and how we can use this knowledge is the goal. How do we define the state of a child’s or adolescent’s maturity?  Chronological age  Skeletal age  Stage of sexual maturation Puberty  Sexual maturation Important to identify because normal growth patterns and responses to exercise training are substantially different in children than in adolescents. MarkersWomen- menarche Men- ten fold increase in testosterone Both- dramatic increase in ht. and wt. Does exercise training affect growth or body size?  Exercise or physical training has no effect on height, body build or biological maturation.  Exercise and PT has the following positive effects on children and adolescents: ↑ CR fitness, stronger muscles and bones ↓cardiovascular disease risks and obesity Body Composition  Although at puberty boys develop more lean body mass than girls, girls stay the same or slightly increase fat mass  Physically active children and adolescents have lower body fat % and more fat-free wt. than inactive peers.  Enforced inappropriate wt. or body comp. standards can lead to disorder eating and dangerous methods of wt. loss Implications  Weight class sports should be matched for age as well as body weight.  Because girls gain fat mass at puberty girls aerobic fitness declines (if looking at V0₂)  Energy needs for growth in children complicate the issue of wt. loss in growing children. Medical supervision may be needed.  Children greatly benefit from PA in prevention of obesity (prevention is the key!) Regarding Bone mass in Children and Adolescents  Young bone is more responsive to osteogenic stimuli.  Evidence indicates that physical activity during growth (particular running and jumping activities or multi-joint exercises) if preformed progressively can significantly increase bone mass.  Achieving peak bone mass as an adolescent will contribute to maintaining more bone mass during later decades of life where bone mass is diminished. Vulnerability to Injury  Overuse and traumatic injury can cause injury to the growth plate of bones.  Excessive throwing, or repetitive micro- trauma can cause premature closing of growth plate and retard normal bone growth. How much training is optimal? Aerobic Fitness Considerations  Smaller heart, total blood volume= smaller stoke volume and lower cardiac output  Heart rate response to a given sub max work is higher than and adults  Max H.R. of children is higher Implication for activities such as cycling at Max: performance is limited because of this reduced capacity deliver O₂ VO₂  Normally expressed relative to body weight V0₂ doesn’t reflect the significant gains in endurance performance that are noted with maturation and training. Body surface area is now considered a better means of reducing the effect of body size instead of body weight  Events such as distance running, children’s performance is far inferior to adults. (smaller hearts, ↓ stroke volume  Endurance training yields improvements that are 1/3 those of adults.  Children exert more energy compared to adults in wt. bearing activities for the same relative intensity of work compared to adults. Endurance performance and economy of movement  Children are less economical runners Higher metabolic rates Greater ventilatory equivalents Disadvantageous stride rates to stride lengths Implications regarding aerobic performance Children are working relatively harder for the same absolute intensity. children under 14 years not train or run more than a 10k Ages 12 and younger – 2 mile on flat is appropriate (Micheli, 1981) Most studies reviewed by Rowland indicate improvement of 7-26% in VO₂ Max Adult ACSM standards of training can be used for children. Training effect is the same. Use the Borg Scale of perceived exertion to monitor intensity. Anaerobic Performance  Anaerobic capacity is lower than adults as measured by power output (Wingate test). Lower muscle glycogen (energy source). Lower lactate concentrations at max work rates. (they tend to rely on fat oxidation for fuel) Children differ in hormones response and reflect higher stress response to exercise. Implications: Activities of high intensity lasting 15 sec. to 2 min. will be limited compared to adults. Training program should be age/size group specific. Training will improve anaerobic capacity. Strength in Children  Prepubescent strength gains occur in the absence of changes in muscle size.  Children are able to get stronger because of growth and:  Improvements in neural mechanisms  Learned motor skill coordination  Increased motor unit activation Strength in Adolescents  Strength gains at puberty are a result of growth, increasing body weight and muscle mass.  Boys experience greater strength because of the anabolic effects of higher levels of circulating testosterone.  Boys can gain greater mass and strength than women Potential Hazards with Resistance Training  Acute musculoskeletal injuries Epiphyseal fractures- injury to growth plate at the end of long bones Risks involve premature closure of growth plate  Chronic musculoskeletal injuries  Repeated micro-trauma due to overuse Include stress fractures, cartilage damage Implications of Strength Differences  Children can gain significant strength if proper training and safety precautions are taken: Limit wt. to not more than a 10 RM. 1 RM should be avoided. Proper technique should be taught with no load. All major muscle groups should be included especially core muscles. Exercises using own body weight are appropriate for children. The Young Nervous System  As children grow they develop better balance, coordination and agility as their nervous system matures  Myelination of muscle fibers is important for the conduction of nervous signals.  Fast reaction time, skilled movement and fine motor control cannot occur before nerve fibers are completely myelinated.  This continues well beyond puberty.  Development of strength is also dependent on myelination. Implications  Children are not capable of fine motor skill development.  Skills will take a long time to refine.  Gross motor movement (large muscle) should be the emphasis. (positioning and understanding strategy can be the focus). Heat Stress in Children  Children: have a lower capacity to lose body heat through sweating. Produce more body heat per mass unit than adults A child has a greater ratio of body surface area to mass. Children’s bodies rely on convection and radiation more than adults. This ratio is advantageous unless the environment temp. is higher than skin temp. Acclimation rates of children are slower than adults. Implications  Children should take frequent breaks while exercising in the hot temperatures and high humidity.  Activities lasting more than 15 minutes should be reduced  Shade should be provided  Frequent breaks for water and electrolytes is imperative. Thirst mechanism is not sensitive enough to replace fluid when needed.  Protection from sun is a must.  Allow more time for children a adolescents to acclimate to new climates. Cold Exposure in Children  Because of the larger ratio of surface area to mass, children lose more heat through conduction placing them at more risk for hypothermia  Implication: Due to greater risks children should dress in more clothing layers than the typical adult.  Children may not realize they are at risk for frostbite. Exercise Induced Asthma  A condition brought on by faster breathing when exercising that causes constriction of airways making breathing difficult.  13% of population have it, many athletes  Symptoms: coughing, tight chest, wheezing, fatigue, shortness of breath What to do about EIA  Identify symptoms: coughing, difficulty breathing fatigue, not being able to perform  Make sure they use the preventive inhaler 15 minutes before class (albuterol-broncodialator)  Try to avoid triggers: pollen, cold temp. pollution, cold and allergy.  Use intermittent warm up, wear a mask or scarf in cold.  Know what kids have this condition and work with parents. Rhabdomyolysis A life threatening condition that can lead to kidney failure and death  Resulting from too much and too intense exercise  Excessive muscle breakdown causing enzymes and myoblobin to be released in the blood stream  Kidneys try to filter out the muscle components but kidney failure could result.  Rare occurrence but documented cases exist in high school and college  Risk factors- drugs, severe exertion, heat stroke  Symptoms- dark urine, weakness, fatigue Conclusions  Children are not just smaller versions of adults.  Children and adolescents don’t follow the same rates of change (early and late biologic maturers).  They have many physical developmental differences that must be considered in planning activities and especially when training for sports.  Much about the exercising child is not yet know so err on the side of being conservative. Bibliography  Rowland, Thomas, W., Children's Exercise Physiology, (2005). Human Kinetics, Champaign IL.  Kenney, W., Wilmore, J, Costill, D., 2012, Physiology of Sport and Exercise, 5th ed., 2012, Human Kinetics, Champaign, IL.  Powers, S. and Howley, E. Exercise Physiology, 2009, McGraw –Hill, New York, NY.