Is Resistance Training Inappropriate and Unsafe for Children? Term Paper

Abstract

Many position stands and review research papers confirmed the benefits and risks of resistance training. Children being at a state of growth are more prone to injuries. Therefore, the aim of this essay is to review the specifics of children strength gain in response to resistance training. Besides, reviewing, in the lights of risks children are prone to, how to set up and the essentials of design of a successful resistance training program for children.

Introduction

Children as a term refer to males and females individuals who did not develop secondary sexual characters (pubic hair, penile testicular, breast, fat distribution and other puberty related changes). This is usually around 11 years for females and around 13 years in males, a period in human development called pre-adolescence (Behm et al, 2008).

Resistance training points to a special method of muscle conditioning, which includes progressive use of different resistive loads (gradually increasing the stress placed during exercise training). Resistance training uses different training styles to promote health, fitness and sports performance (Behm et al, 2008).

Thus, the concept of resistance training does not mean resistance to exercise, on the contrary, it means exercising the muscles against external resistance causing them to contract. This results in increased muscles length, mass, tone, strength and performance. Second, resistance training is different from weightlifting, weight training and strength training where the main objective is competition and bodybuilding, which puts enormous strain on the young muscles, tendons and cartilages (American College of Sports Medicine: Position stand, 2002).

Lastly, why this essay focuses on children? Fleck and Kraemer (2004, p. 11) marked few questions specific to children when considered for resistance training; first, are children physically and psychologically prepared to participate in a resistance-training program. Second, is how to tailor the program individually; third, being in an active development period, what are the appropriate styles and techniques. Should the child have a balanced physical exercise-training program associated with the resistance-training program? In addition, during this pre-adolescence period of development that needs tailoring specific resistance training following recognised guidelines to avoid injuries (Rockett et al, 2004).

Physiological Mechanisms of Resistance Training how they differ among children and adults (How does it work)

Understanding of the physiological mechanisms of muscle strength gain in response to resistance training and the differences of these mechanisms in adults and children is essential before designing a program suitable for children. Studies show that muscle strength gain occur within 8 weeks of training (similar to adults) because of two mechanisms first is improved neuromuscular system and second is the morphological muscular changes in response to training (Tsolakis et al, 2004). The relative contribution of these two mechanisms varies in children and adults (Behm et al, 2008).

Morphological changes in response to resistance training

Morphological changes include increased muscle size secondary to muscular structural changes like increased muscle fibres’ size, hyperplasia, changes in fibre type composition and connective tissue. In children, increased muscle size is less observed than in adults, although increased muscle strength is well observed (Malina, 2006). Behm et al (2008) reported studies that used anthropometric measures for muscle hypertrophy showed limited evidence, however, studies that used more sensitive measures like MRI showed better evidence of muscle hypertrophy in children. Increased muscle size in children is mainly the result of increased numbers (proliferation) and increased growth of myofibrils, which are the contractile muscle fibres (Folland and Williams, 2007).

Other possible morphological changes produced by resistance training are increased musculo-tendenous stiffness although less reported in children than in adults (Lambertz et al, 2003). Second is the increased angle of pennation (the angle made by insertion of skeletal muscle fibres into a tendon), which relates to the muscle functional characteristics and contractile force potential. It occurs because of increased packing of myofibrils, which means increased muscle strength (Reeves et al, 2004). Research suggests the existence of both changes in children; however, definite measurable evidence is still lacking (Behm et al, 2008).

Neuromuscular changes in response to resistance training

Because of the previously explained limited evidence of muscle hypertrophy in children, strength gains are presumably secondary to neuromuscular changes. However, these changes are difficult to define and looked upon as alterations in coordination and better recruitment of muscles involved in a specific action and inferences stand on indirect evidence (Folland and Williams, 2007). One possible explanation is neuromuscular changes result in increased torque effort to size relationship (Folland and Williams, 2007). An alternative mechanism is increased agonist muscles activation, which relates not only to decreased antagonist muscles activation, but also to improved inter-muscular coordination (Lambertz et al, 2003). Folland and Williams (2007) suggested that neuromuscular alterations occur earlier than morphological changes in children. They also suggested the consequences of coordination depend on the previous level of physical activity and training experience.

Malina (2006) summarized the current concepts of possible physiological mechanisms in children suggesting that resistance training in children results in increased muscle strength partly because of muscle hypertrophy. More specific for children evidence suggests that neuromuscular changes are earlier and play a significant role through increasing neuromuscular motor unit activation, improving inter-muscle coordination. Malina (2006) also suggested that resistance training produces better neuromuscular learning that is the muscle learns to act more efficiently in response to a stimulus.

Benefits (health outcomes) of resistance training in children

Obviously, the first benefit of resistance training in children is increased muscle strength. The Council on Sports Medicine and Fitness of the American Academy of Pediatrics (2008) inferred many studies showed that once week training for 8 weeks can increase muscle strength in children. It is true that training frequency, training intensity and duration affect the outcome; however, with all modes of resistance training, muscle strength increases.

In addition to preventing childhood obesity, resistance training improves insulin sensitivity and results in beneficial effects on the lipid profile (increases high-density proteins and decreases low-density proteins). In addition, there is evidence that resistance training (especially weight bearing) results in better minerals accumulation in bones. Resistance training, similar to other form of physical activity, results in psychological and social beneficial effects; it promotes socialisation skills, enables children to be involved in a team environment. Involvement in resistance training improves the quality of life of disabled children giving them the impression of normalising their life style (Broderick et al, 2006).

Faigenbaum (2007) summarised the beneficial effects of resistance training in children as follows: 1) it increases local muscle strength, power and endurance. 2) It increase bone mass, 3) Improves cardio-respiratory fitness, 4) improves blood lipid profile, 5) Improves body composition. In addition, 6) it improves motor performance skills, 7) it enhances sports performance and increases resistance to injury, 8) It improves mental health and well-being, besides stimulating a positive attitude towards physical activity.

Resistance training in paediatric clinical practice

Primary prevention of disease

A) Prevention of childhood obesity: The number of obese children is increasing all over the world in a near epidemic pattern. Research evidence suggests that resistance training can be a safe and effective method to fight this epidemic provided proper guidelines are followed (President’s Council on physical Fitness and Sports, 2007). In 2007, the Council on Sports Medicine and Fitness and Council on School Health (American Academy of Pediatrics) recognized that childhood obesity is a multi-factorial problem; however, making activity-promoting changes, including resistance training in the environment and discouraging children from sedentary activities are essential to a successful outcome.

B) Prevention of early vascular changes and cardiovascular risk factors:

Meyer et al (2007) showed that endothelial function, intima-media thickness in addition to elevated cardiovascular risk factors in obese children and adolescent are improved within six months of regular exercise. This improvement linked to changes in body mass index, waist-hip ratio, and better lipoprotein and triglycerides profiles; in addition, low-degree inflammation factors like C-reactive protein improve as well.

C) Prevention of type II diabetes: Type II diabetes is becoming a health problem in children and adolescents (Knower et al, 2001), however; many studies showed that moderate intensity resistance training can improve glycaemic control and lower fasting insulin level in obese type II diabetes (Dunstan et al, 2006).

Secondary rehabilitation in chronic illnesses

Morton et al (2005) applied weight free resistance training three times weekly for six weeks to a group of children with cerebral palsy. Results showed muscle strength is increased, while muscle tone decreased and maintained its decline on follow up. Standing, walking and jumping improved and continued improvement during follow up. They observed no adverse effects accompanied the encouraging training results.

Evans and Morgan (2007) suggested that skeletal muscles dysfunction contribute to and is a consequence of the COPD disability in children. The stated that pulmonary rehabilitation in these patients should be directed towards improving both the health status and physical functioning irrespective of reversing the impaired pulmonary function. They inferred that physical training including properly designed resistance training is a key component of any pulmonary rehabilitation program.

Risks (safety issues) of resistance training in children

Although enough evidence now exists, that backs implementation of resistance training during childhood, yet much of the controversy stems from misconceptions of parent, coaches and even some physicians. Another reason for this controversy is that current children’s resistance training guidelines depend mostly on best evidence practice rather than scientific evidence (Vehrs 2005). In addition, much of the concern about resistance training in children comes from the data of the National Electronic Injury Surveillance System (NEISS) of the US Consumer Product Safety Commission. The NEISS estimates sports injuries to take place in 20940 to 26120 individuals under 21 years every year with muscle strains accounting for 40 to 70% of injuries and the lower back region is the commonest region affected. About growth, the NEISS data suggest that appropriate resistance training does affect linear growth, cartilaginous growth plates or the integrity of the cardiovascular system (Committee on Sports Medicine and Fitness, 2001).

The Council on Sports Medicine and Fitness (2008) suggested caution should be considered for the following patients before taking a decision of resistance training: 1- Children and adolescents with hypertension, 2- Young athletes with seizure disorder. Besides, 3- Individuals receiving chemotherapy with anthracylclines since they are cardio-toxic drugs; this adds to the possibility of acute heart failure, 4- Those with moderate to severe pulmonary hypertension as strenuous exercise may aggravate their condition. Fifth, the council advised caution before taking a decision about children with Marfan’s syndrome because of the dilated aortic root component and 6- Although obese children may deceptively look strong because of their weight, however; they are usually unconditioned with poor strength and should be observed closely during training practice.

In 2007, the Australian Strength and Conditioning Association (ASCA) looked deeply into the sports injuries issue of resistance training in children. The children’s skeleton is characteristically immature with many cartilaginous growth plates that close at different ages; besides trauma causing injuries to ligaments tears in adults are likely to cause growth plate injuries or avulsion fractures in children. Further, Children are more prone to osteochondroses, having rapidly growing skeletal system. The disorder is characterized by interrupted bone blood supply and occurs in boys more than girls, it may occur intra-articular, extra-articular or spinal and its aetiology is still largely unknown. However, stress, ischaemia, and a genetic factor may be partly or as a whole responsible for the disease. Another type of injury specific for children is traction apophysitis (a painful condition of the calcaneal apophysis), which is a type of extra-articular (non-articular) osteochondroses. Excessive loading of the calcaneal tendon-growth plate interface is blamed for the condition, which may also affect the tibial tuberosity (ASCA, 2007).

Children are also more prone to heat-related disorders than adults when exercising in a hot environment because they have a higher surface area to body mass ratio and they are slower to acclimatize to hotness and have a higher tendency of dehydration. In addition, lower exercise efficiency expected in children than adults produces more heat for a certain work load. It should be noticed that obese children are at higher risk for heat-related disorders; besides, certain medications like antihistamines and anticholinergics increase the risk. Diabetic, cardiac, and children with cystic fibrosis are more prone to heat-related disorders (ASCA, 2007).

Techniques of resistance training in children

In addition to the previously medical conditions, other non-medical conditions influence the technique, model or type of resistance training in children. One physiological fact to remember that is in resistance training energy production does not depend on oxygen; in other words, energy is produced anaerobically. The consequences are energy is produced rapidly with the production of high levels of lactic acid; therefore, resistance training cannot be maintained for periods as long as other types of physical exercise (Miller, 2008).

Some factors that affect the technique of resistance training in children

The Council on Sports Medicine and Fitness and Council on School Health (2006), recommends that up to six years of age infants and children need a safe encouraging and minimally structured play environment. At this age, children should be given the chance to enjoy outdoor activity.

However, at age 6 to 7 years, a child can be introduced to basic exercises with minimal or no weight to develop the training session concept. At 8 to 10 years the number of exercises, loading and lifting gradually increase in frequency and weight, yet at the same time exercises should be kept simple with close observation of tolerance to stress. At age 11 to 13 years, all basic techniques should be taught with progressive loading of each exercise and introducing more advanced exercises; yet with little resistance (ASCA, 2007).

Keller (2008) reviewed the literature examining the effects of gender and physical activity on the development of fitness. Keller (2008) suggested that pre-pubertal gender difference is difficult to explain unlike pubertal and post-pubertal differences, which are caused by intrinsic neuro-endocrine differences. Gender differences in motivation, practice, activity level and parental support seem to have a significant role, however; the interaction of genetic and environmental factors in determining development of fitness is still unclear. Research points to evidence of differences between genders in preferences and degree of participation attributed mainly to sociocultural environmental factors (Keller, 2008).

Before designing or selecting a resistance training program, it is important to foresee the relationship between the volume, intensity and frequency of training and strength improvement or gain that is the dose-response relationship (Rhea et al, 2003). Rhea et al (2003) performed a meta-analysis study to examine the dose response relationship for strength development. Their results showed that training with mean intensity of 60% of one repetition maximum produces maximum gains in untrained children of 3 days per week frequency. In trained children, 80% mean intensity of one repetition maximum results in maximum gains of 2 days frequency per week. Mean training intensity is the repetition range for a certain weight; the authors inferred their results support the concept of progression in resistance program design (Rhea et al, 2003).

Croix (2007) pointed to non-individual factors that determine choosing a particular type or model of resistance like equipment availability and familiarity. Croix (2007) pointed to the importance of considering what muscle group (s) to include, desirable muscle action, joint angle and movement pattern to achieve. To choose a proper technique, there are factors related to the technique that need consideration like technique familiarity, learning curve and safety (Croix, 2007).

Types of resistance training

Based on the above discussion, resistance training programs can be classified into minimal threshold, optimal threshold programs and proposed effective dose programs (Baechle and Earle, 2008 pp. 324-335 and 569-577). A minimal threshold program considers the minimal amount of training over 6 weeks time that results in weekly volumes calculated as frequency x duration x intensity x mean volume / duration in weeks expected to produce significant strength effect. It is suitable for children who just want to get involved in resistance training and has a low incidence of injury. Optimal threshold resistance training programs target a weekly volume that optimally improves strength over 6 weeks period. It is suitable for children enjoying minimal threshold training, and can be a second stage training after 2 to 4 weeks of minimal threshold training. There are two common models for proposed effective training, first is proposed effective training (prescription) one that is 1 day a week, 7 repetitions maximum (RM) for 3 sets (body parts). It is suitable for children finding difficulties reaching a resistance training facility. Second is effective training two for 3 non-consecutive days a week, 7 RM for 1 set. It is suitable for initial training and enables children to engage in another form of physical activity (Baechle and Earle, 2008).

Guidelines of resistance training in children

In 2008, the Council of Sports Medicine and Fitness-American Academy of Pediatrics revised the previously issued policy statement on children resistance training and concluded the following recommendations. 1) A complete medical examination including history of previous injuries or low back pain is mandatory to identify possible risk factors. During examination, a discussion is advised to identify the aim of resistance training, motives and expectations. At the same time, the candidate should be informed that resistance training is a part of an overall fitness lifestyle. 2) Resistance training should not start before the age of 7 to allow for the maturity of posture control skills. 3) Care should be taken that most resistance training equipments and methods are designed for adults. 4) Explosive rapid weight lifting during training is not recommended for children. 5) Safety precautions of resistance training techniques and equipments should be strictly followed. 6) Instructors and personal trainers for children should be certified with specific paediatric resistance training qualifications (the Council on Sports Medicine and Fitness, 2008).

Essentials to Design a resistance training program in children

Designing a resistance training program is a dynamic process that starts by determining the individual’s needs for training and the achievable training goals that is program individualisation, If includes the exercise prescription process, assessment of training progress and development of target achievement based on the individual’s needs. To be able to do this, a professional must determine the values of certain variables, which are what muscle actions to use, the resistance to use, the training volume (both number of sets and repetitions), repetition velocity among other variables. More important, the clinician should be able to change any of these variables to meet the individual’s specific need (Kraemer and Ratamess, 2004). Once a child is judged healthy to participate in a resistance-training program, the next step is to perform a needs analysis to set the resistance training goals through answering questions centred on the goals of resistance training. Some key questions are what are the injury or health concerns that should limit the exercise or its intensity, second, what type of equipment to use whether free weights, machines, medicine balls; the answer to this question should consider availability and child’s preferences. Third, what is the objective training frequency and are there time limitations to influence the workout duration. Fourth, what muscle groups need training and if more than one, what prioritisation schedule the particular child needs. Fifth, what types of muscle actions are targeted, concentric, eccentric or isometric the child needs, finally is the overall objective of training for a sport or an activity (Kraemer and Ratamess, 2004).

After a successful resistance training program, it is important to plan for a maintenance program, which is a resistance training program to keep the achieved level of fitness and muscular strength. In this case, configuring the feature-benefit of the program is of prime importance and may necessitate reducing the training volume, frequency and intensity (Kraemer and Ratamess, 2004).

Thus, the key to a successful program design is proper planning for safety and prevention of injury and individualising resistance training, which may necessitate manipulating the program elements to suite a particular child.

Conclusions

Current evidence shows that resistance training in children is beneficial if conducted on individualized basis, in a safe environment and according to age appropriateness. It is beneficial to health, prevents childhood obesity and cardiovascular risks besides it benefits to self-esteem and other socio-psychological concerns. Resistance training programs are safe and tolerated provided program design considers proper progression in addition to attention to fun and enjoyment.

References

1. American College of Sports Medicine, 2002. Progression Models in Resistance Training for Healthy Adults: Position Stand. Medicine & Science in Sports and Exercise, 34 (2), 364-380.
2. Australian Strength and Conditioning Association (ASCA), 2007. Resistance Training for Children and Youth: A position Stand from the Australian Strength and Conditioning Association. Part one. Beenleigh, Queensland: Australian Strength and Conditioning Association.
3. Baechle TR and Earle RW, 2008. Essentials of Strength Training and Conditioning. 3rd edition. Champaign, IL: Human Kinetics Publishers.
4. Behm DG, Faigenbaum AD, Falk B and Klentrou P, 2008. Canadian Society for Exercise Physiology position paper: resistance training in children and adolescents. Appl. Physiol. Nutr. Metab, (33), 547-561.
5. Broderick CR, Winter GJ and Allan RM, 2006. Sport for special groups. MJA, (184), 297-302.
6. Committee on Sports Medicine and Fitness-American Academy of Pediatrics, 2001. Strength Training by Children and Adolescents. Pediatrics, (107), 1470-1472.
7. Council on Sports Medicine and Fitness, 2008. Strength Training by Children and Adolescents. Pediatrics, (121), 835-840.
8. Council on Sports Medicine and Fitness and Council on School Health, 2006. Active Healthy Living: Prevention of Childhood Obesity through Increased Physical activity. Pediatrics, (117), 1834-1842.
9. Croix M De Ste, 2007. Advances in paediatric strength assessment: changing our perspective on strength development. Journal of Sports Science and Medicine, (6), 292-304.
10. Dunstan DW, Vulikh E, Owen N, Jolley D, et al, 2006. Community center-based resistance training for the maintenance of glycemic control in adults with type 2 diabetes. Diabetes Care, (29), 2586-2591.
11. Evans R and Morgan M, 2007.Pulmonary rehabilitation: what is it and why does it work? J R Coll. Physicians Ednb, (37), 339-342
12. Faigenbaum AD, 2007. State of Art Reviews: Resistance Training for Children and Adolescents: Are There Health Outcomes. American Journal of Lifestyle Medicine, 1 (3), 190-200.
13. Fleck, SJ and Kraemer WJ, 2004. Designing Resistance Training Programs. 3^rd edition. Champaign, IL: Human Kinetics Publishers.
14. Folland JP and Williams AG, 2007. The adaptations to strength training: morphological and neurological contributions to increased strength. Sports Med, (37), 145-168.
15. Keller BA, 2008. Development of Fitness in Children: The influence of Gender and Physical activity. American Journal of Lifestyle medicine, 2 (1), 58-74.
16. Knower CW, Barrett-Connor E, Fowler SE, Hamman RF et al, 2001. Reduction in the incidence of type 2 diabetes with lifestyle intervention. N Eng J Med, (346), 393-403.
17. Kraemer WJ and Ratamess NA, 2004. Fundamentals of resistance Training: Progression and Exercise Prescription. Med. Sci. Sports Exerc. 36 (4), 674-688
18. Lambertz D, Mora I, Grosset JF and Perot C, 2003. Evaluation of musculotendinous stiffness in prepubertal children and adults, taking into account muscle activity. J. Appl. Physiol, (95), 64-72.
19. Malina RM, 2006. Weight training in youth-growth, maturation and safety: An evidence-based review. Clin. J. Sport Med., (16), 478-487.
20. Meyer AA, Kundt G, Lenschow U, Schuff-Werner P et al, 2006. Improvement of Early Vascular Changes and Cardiovascular Risk Factors in Obese Children after a six-month Exercise Program. J. Am. Coll. Cardiol., (48), 1865-1870.
21. Miller T, 2008. Central and Peripheral Adaptations to Training. Nsca’s Performance Training Journal. 7 (1), 19-21.
22. Morton JF, Brownlee M and McFadyen AK, 2005. The effects of progressive resistance training for children with cerebral palsy. Clinical Rehabilitation, (19), 283-289.
23. Reeves ND, Narici MV and Mangaris CN, 2004. Effect of strength training on human patella tendon mechanical properties of older individuals. J. Appl. Physiol, (96), 885-892.
24. Resistance Training for Obese Children and Adolescents, 2007 (Research Digest, Series 8, No.3) Washington, D.C.: President’s Council on Physical Fitness and Sports.
25. Rhea MR, Alvar BA, Burkett LN and Ball SD, 2003. A Meta-Analysis to Determine the Dose Response for Strength Development. Med. Sci. Sports Exerc., (35 (3)), 456-464.
26. Rockett JC, Lynch CD and Buck G, 2004. Biomarkers for Assessing Reproductive Development and Health: Part 1-Pubertal Development. Environmental Health Perspectives, 112 (1), 105-112.
27. Vehrs PR, 2005. Strength Training in Children and Teens: Dispelling Misconceptions-Part one. ACSM’S Health & Fitness Journal, (9 (4)), 8-12.