Children and resistance training

Resistance exercise and different populations

Resistance exercise is a safe and effective method of conditioning for people with a wide range of needs, goals, and abilities. Much of what we know about resistance training comes from studies of the acute and chronic responses of adult men. However, research on children, women, and older adults has grown significantly.

Strength and conditioning professionals need to understand age- and sex-related differences in body composition, muscular performance, and trainability when designing and evaluating resistance training programs. Major professional organizations support youth participation in resistance training when it’s performed with appropriate instruction, gradual progression, and qualified supervision.

In this chapter, resistance exercise is defined as a specialized method of conditioning in which an individual works against a wide range of resistive loads to enhance health, fitness, and performance. This differs from the sport of weightlifting, in which individuals attempt to lift maximal weight in competition, specifically in the clean and jerk and snatch exercises.

Key terms:

• Childhood refers to the period before the development of secondary sex characteristics.
• Adolescence refers to the time between childhood and adulthood.
• Youth or young athlete applies to both children and adolescents.
• Older adult generally refers to individuals over 65 years of age.

Muscular strength in this chapter is expressed in both absolute terms (total force in pounds or kilograms) and relative terms (strength ratio to body mass, fat-free mass, or muscle cross-sectional area).

Children

Growth, development, and maturation

Growth, development, and maturation describe changes that occur in the body throughout life.

• Growth refers to an increase in overall body size or a specific body part.
• Development describes the natural progression from prenatal life to adulthood.
• Maturation refers to the process of becoming fully functional.

Puberty is a period of major change, including the development of secondary sex characteristics and the transition into young adulthood. During puberty, large changes occur in body composition and physical performance, and these changes can vary widely between individuals.

Although it isn’t a formal stage of maturation, peak height velocity (PHV) represents a higher-risk period for injury. During this window, it’s especially important to reinforce proper technique and progress training loads conservatively.

Chronological age versus biological age

Rates of growth and development vary widely, so chronological age (age in months or years) is an imperfect measure of maturity. Children don’t grow at a constant rate, which can create large differences in physical development among children of the same age.

For example:

• A group of 14-year-olds may have a height difference of up to 9 inches (23 cm) and a weight difference of up to 40 pounds (18 kg).
• An 11-year-old may be taller and more physically skilled than a 14-year-old due to differences in the timing, tempo, and magnitude of puberty.

A more informative measure is biological age, which considers skeletal age, somatic (physique) maturity, and sexual maturation. Two children with the same chronological age may differ by several years in biological age.

Stages of maturation:

Sexual maturation is often measured using Tanner’s five-stage scale, which evaluates secondary sex characteristics such as breast development in girls and genital and pubic hair growth in boys.

• Stage I represents a prepubescent state with no visible signs of maturation.
• Stages II-IV reflect progressive development of secondary sex characteristics.
• Stage V indicates full sexual maturity.

Skeletal age assessment uses X-rays to evaluate bone ossification. Peak height velocity (PHV), the fastest rate of growth during puberty, is another key indicator of maturity. Strength and conditioning professionals should account for individual differences in maturation and adjust training programs accordingly.

Muscle and bone growth

Children gain muscle mass steadily throughout development:

• At birth, muscle accounts for 25% of body weight.
• By adulthood, this increases to approximately 40%.

During puberty, hormonal changes (such as increased testosterone in boys and estrogen in girls) contribute to further development:

• Boys experience a large increase in muscle mass and shoulder widening.
• Girls experience increased body fat accumulation, hip widening, and smaller increases in muscle mass.

Bone formation occurs primarily in:

• Diaphysis (primary ossification center) - central shaft of a long bone.
• Growth cartilage (secondary ossification center) - located at the epiphyseal (growth) plate, joint surfaces, and muscle-tendon insertions.

Growth cartilage is vulnerable to trauma and overuse injuries, especially during peak height velocity. Proper technique, progressive loading, and qualified coaching can help reduce this risk.

Developmental changes in muscular strength

As muscle mass increases, muscular strength also increases. In both boys and girls, strength gains generally follow growth patterns similar to body mass:

• Boys experience peak strength gains about 1.2 years after peak height velocity.
• Girls experience peak strength gains slightly later, with greater individual variability.

Adolescents can achieve nearly 50% greater strength gains than children, particularly after peak height velocity.

Youth resistance training

Research supports resistance training as a safe and effective method for children when programs are appropriately designed and supervised. Major sports medicine organizations endorse youth participation in resistance exercise.

Key considerations for youth training:

1. Children are not miniature adults - They are physiologically less mature and often new to training.
2. Training should match maturity level - Overloading young athletes can be counterproductive.
3. Programs should progress gradually - It’s better to underestimate abilities than to exceed them.

Most youth injuries result from poor technique or excessive loading, not from properly supervised resistance training. This is why coaching quality, correct movement patterns, and gradual overload are central to youth program design.

Responsiveness to resistance training in children

Early studies suggested that children had limited potential for resistance training adaptations, but those findings were influenced by short study durations and low training volumes. More recent evidence shows that:

• Neural adaptations (improved motor unit activation and coordination) are the primary drivers of strength gains in children.
• Gains in muscular strength and performance are possible before puberty, even without large increases in muscle mass.

Strength and conditioning professionals should consider biological age alongside chronological age and structure programs around individual developmental needs.

Resistance training adaptations in youth

Research shows that boys and girls can increase muscular strength beyond what would be expected from growth and maturation alone, as long as training intensity and volume are adequate. Studies also indicate that children as young as 5 years old can benefit from resistance training, and multiple training methods can be effective.

Strength gains in youth:

• Maximum strength gains of 10% to 90% have been reported in studies.
• Untrained preadolescents typically gain 30% to 40% strength after short-term (8 to 20 weeks) resistance training programs.
• After the initial adaptation phase, the rate of strength gain slows, which is why progressive training is needed over time.

The variability in strength gain can be influenced by:

• Biological age
• Program design and exercise selection
• Quality of instruction
• Previous levels of physical activity

The effects of detraining

Children may experience periods of detraining for reasons such as:

• Seasonal training schedules
• Lack of motivation
• Injury or illness
• Travel or other external factors

Detraining occurs when resistance training is reduced or stopped. The effects include:

• A decline in strength gains, although children may retain some training-induced adaptations.
• Differences in how quickly strength is lost, with some children showing rapid declines and others maintaining strength longer.

Research suggests that more frequent training (2+ sessions per week) leads to better strength retention than once-per-week training.

Neuromuscular and hormonal influences on strength gains

Neural contributions:

• Strength gains in children occur primarily through neuromuscular adaptations rather than muscle hypertrophy. These include:

• Improved motor unit activation
• Better coordination of muscle groups
• Enhanced neural recruitment patterns

While hypertrophy is unlikely in preadolescents, adolescents may have more difficulty increasing muscle mass due to low circulating levels of testosterone, growth hormone, and insulin-like growth factor.

Hormonal changes in strength development:

• Prepubescent boys and girls: Testosterone levels range between 20-60 ng/100 ml.
• During adolescence: Testosterone levels in males increase significantly (up to 600 ng/100 ml), while females’ levels remain relatively unchanged.

Because of these hormonal differences, preadolescents rely more on neuromuscular improvements for strength gains, while adolescents may begin to experience some hypertrophy due to hormonal influences.

Potential benefits of youth resistance training

Youth resistance training programs can provide health and performance benefits, including:

• Improved muscular strength, power, and endurance
• Enhanced anatomical and psychosocial parameters
• Reduced risk of injury in sport and recreational activities
• Increased motor skill development and sport performance

Obesity prevention and metabolic health

Global data indicate a rise in childhood obesity, with about 16.9% of American youth (ages 2-19) classified as obese. Resistance training can help by:

• Reducing fat mass and improving insulin sensitivity
• Enhancing cardiovascular function
• Supporting bone density and long-term skeletal health

Although resistance training does not affect genotypic maximum growth potential, it can support lean mass and overall health during development.

Potential risks and concerns

Properly designed youth resistance training programs are relatively safe compared with many other sports and activities. However, concerns include:

• Risk of overuse injuries
• Improper technique or supervision
• Potential for excessive loading on immature joints

To minimize risks:

• Training should prioritize technique, with higher loads introduced only when appropriate.
• Warm-up, cool-down, and recovery strategies should be included.
• Progression should be gradual rather than focused on lifting heavy too soon.

Research suggests that youth athletes who participate in preseason conditioning programs experience fewer injuries than those who do not.

Program design considerations for children

An effective youth resistance training program should:

1. Be well-rounded, addressing strength, endurance, agility, and motor skills.
2. Be age-appropriate, ensuring emotional and physical readiness for participation.
3. Incorporate individualized progression, allowing children to develop at their own pace.

Key components of a safe youth resistance training program:

• Medical screening: Ensuring participants are healthy and free from conditions that could limit safe participation.
• Qualified instruction: Trainers should use clear, age-appropriate language and emphasize proper technique.
• Emphasis on skill development: Encouraging children to focus on movement quality rather than lifting maximal weights.
• Gradual increase in intensity and volume: Programs should progress in a way that challenges children without excessive fatigue or unnecessary injury risk.

How can we reduce the risk of overuse injuries in youth?

• Prior to participation, children should be evaluated by a sports medicine physician to identify any potential medical concerns.
• Parents should be educated on the benefits and risks of competitive sports.
• Children should be encouraged to follow long-term training programs rather than intense short-term bursts of activity.
• Training programs should be multifaceted, including resistance training, plyometrics, agility, and dynamic stabilization.
• Youth coaches should implement proper recovery strategies to reduce overtraining risk.
• Children should maintain healthy lifestyles with balanced nutrition, hydration, and sleep.

Strength assessment in youth

Assessing strength in youth is important for designing effective training programs. However, 1-repetition maximum (1RM) testing is not always practical in research or sport settings due to:

• Time constraints
• Large class sizes
• Lack of coaching expertise

Alternative strength assessment methods:

• Submaximal repetition equations (e.g., estimating 1RM from multiple reps)
• Field-based jump protocols (e.g., vertical jump, long jump)
• Handgrip strength tests

Field-based measures can be useful for tracking performance, but technical proficiency should remain the priority in youth training.

Importance of technique in resistance training

Proper exercise technique is essential for both injury prevention and performance. Poor form can place abnormal stress on the musculoskeletal system and increase injury risk.

Teaching proper technique:

• Start with unloaded implements (PVC pipes, wooden dowels, or light barbells).
• Provide immediate and clear feedback to correct mistakes.
• Emphasize consistent form before increasing weight.

Strength and conditioning professionals should monitor technique regularly to ensure proper movement execution and to avoid cumulative fatigue from repetitive poor mechanics.

Youth resistance training guidelines

A summary of best practices for youth resistance training:

• Education first: Each child should understand the benefits and risks of resistance training.
• Qualified supervision: Training should be designed and overseen by competent strength and conditioning professionals.
• Safe environment: Equipment should be age-appropriate and free of hazards.
• Dynamic warm-ups: Should be performed before resistance training.
• Progressive overload: Increase resistance gradually (e.g., 5% to 10%).
• Monitoring tolerance: Adjust intensity based on the child’s ability to tolerate exercise stress.
• Controlled repetition schemes: Use 6 to 15 reps per set for single-joint and multi-joint exercises.
• Advanced lifts: Exercises like the snatch and clean and jerk can be introduced with proper technical proficiency.
• Training frequency: Two or three sessions per week are recommended for most youth.
• Spotting techniques: Adults should assist with heavier lifts when needed.
• Periodization: Programs should systematically vary intensity to avoid burnout and overtraining.