Athlete or not, embarking on a resistance training program is not something that should just happen with a snap of the fingers. The integration of resistance training, in order to optimize youth physical development, requires thought. In this article, I review the research on how and when to integrate resistance training into the lives of children, as well as debunk the myth that resistance training destroys growth plates and stunts growth.
Physical Activity and Obesity
Recent physical activity guidelines for youth predominantly focus on aerobic activities, with recommendations of at least 60 minutes of moderate-to-vigorous-intensity physical activity each day . In fact, the World Health Organization (WHO) explicitly states that “most of the daily physical activity should be aerobic” for youth aged 5-17 years old . Although aerobic activity shouldn’t be discounted, its popularity overshadows the critical importance of resistance training in today’s youth. If adequate levels of muscular fitness and movement skills aren’t developed, the benefits of developed aerobic qualities are limited . Although this article will primarily focus on performance, the increasing trend of obesity in U.S. youth warrants mentioning . While 13.9% of U.S. youths were obese in 1999-2000, 18.5% were obese in 2015-16 . In a meta-analysis comparing concurrent aerobic-plus-resistance exercise versus aerobic exercise alone to improve health outcomes in pediatric obesity, García-Hermoso et al. (2018) found that concurrent aerobic-plus-resistance exercise improved body composition, metabolic profiles, and inflammatory state, compared with aerobic exercise alone . This data speaks towards the importance of including resistance training in youth, not only for athletic performance benefits, but also for improving general health.
Why Resistance Training is a Good Idea for Youth
Muscular fitness is developed through resistance training and should be promoted at all stages of long-term athletic development in order to support motor skill acquisition, enhance motor performance, improve health and well-being, and to reduce the risk of sustaining sports-related injuries [2, 5-7]. In youth, participation in resistance training is associated with increased muscle strength, power and motor skill performance [8-10], reduced adiposity and unhealthy weight gain [11-13], increased skeletal health [14-18], and reduced sports-related injury risk [19-28], independent of aerobic fitness level .
The foundation of athletic development for young athletes relies on muscular fitness, which can easily be developed via an appropriately designed resistance training program that focuses on enhancing qualities of neuromuscular ﬁtness and function (i.e., agility, balance, coordination, reaction time and speed), [30-32].
What About Injury Risk?
Traditionally, and for unscientific reasons, resistance training in youth has been, wrongfully, frowned upon. The concern regarding resistance training in youth revolves around the potential for epiphyseal plate (i.e. growth plate) injury, which grew from studies and case reports published in the 1970s and 1980s . Although injuries did occur in these studies and reports, it was found that most of these injuries were related to improper form and lifting program design . Many studies suggest that, when effective supervision and guidance are provided, there is no increased incidence of physeal injury when children lift weights [10, 34-36]. It may appear to be obvious that some risk of injury exists with resistance training, as it would with any other physical activity, but this risk in not elevated by lifting when put in context of the sports in which youth are participating ; not even close. In a comparison of injury rates from many different youth sports and physical activities, including resistance training, Hamill (1994) found resistance training and weightlifting to be very safe activities, and concluded that “there seems to be no rational case for continued widespread anxiety about weight training or weightlifting in children,” . In Hamill’s investigation, youth rugby had an injury risk ~230x greater than resistance training . It’s likely that resistance training in youth ultimately reduces injury risk, given the increased strength, skeletal health, and motor coordination that resistance training provides. This sentiment is echoed by multiple professional organizations; these organizations support the notion that participation in appropriate resistance training improves overall health in youth, denying the traditionalist mantra that resistance training adversely affects the development of children and adolescents [8, 11, 29, 39]. In fact, within the 10 key summary points from the National Strength and Conditioning (NSCA) position statement on long-term athletic development, Lloyd et al. (2016) suggest that all youth should be encouraged to enhance physical fitness through a focus on muscular strength development :
When to Start
Resistance training benefits have been observed for children as young as 5 years of age through school-based intervention programs [40-44]. Although resistance training can be effective at this age, that does not mean it is appropriate for all children, at this stage of life . In an International Consensus Position Statement on Resistance Training in Youth, Lloyd et al. (2014) advise that a child should only participate in a structured resistance training program when he or she (1) exhibits sufficient levels of balance and postural control, and (2) is emotionally mature enough to receive and follow directions, which typically occurs around 6-7 years old [19, 45-47].
Although there’s not a specific age when a child “should” begin resistance training, it’s important to introduce resistance training during childhood (preadolescence), as opposed to during adolescence, for a few reasons. In their meta-analysis, Behringer et al. (2011) found that resistance training improved motor skill performance, such as running, jumping, and throwing, in both children and adolescents, but the improvements were greater in children . These findings were replicated in a more recent systematic review by Peitz et al. (2018), as well . There are other reports that suggest children demonstrate greater training-induced gains in strength [7, 50-52] and motor skill performance [50, 52-54], compared with adolescents. Additionally, children are primed for the acquisition of fundamental motor skills and foundational strength because they exhibit higher levels of neural plasticity prior to puberty [29, 55], which renders them more “pliable” to mental and physical growth [32, 55]. It makes sense that the strength gains in pre-pubertal children are attributed mostly to neural adaptations [37, 56], whereas additional morphological adaptations (i.e. muscle hypertrophy), due to the increase of sex hormones with the onset of puberty, are likely the primary contributors to the increased effects of resistance training in adolescents .
There may be specific windows of opportunity during preadolescence where there is naturally occurring accelerated adaptation for a range of biomotor qualities [6, 57]. Failure to incorporate resistance training within these windows may limit current, and future, development of such abilities, including intramuscular and intermuscular coordination, and motor control [6, 57].
Measuring individual maturation rates through peak height velocity (PHV) and peak weight velocity (PWV) may be a better strategy to identify when and how to implement resistance training, as opposed to using chronological age [12, 57]. PHV refers to the maximum velocity of growth in stature and PWV is characterized by rapid increases in weight via muscle mass, primarily due to increasing sex hormone concentrations . Where the athlete is on the PHV and PWV continuums, as well as maturational status, sex, and initial training level, should determine the primary focuses for that athlete. The training adaptation is dictated by the athlete’s stage of growth, which may be better characterized by growth rate, as opposed to chronological age. For example, Lloyd & Oliver (2012) suggest that during earlier stages of growth (i.e. prepubescence), foundational movement skills, speed, and agility should be emphasized in training because and the adaptive responses to the appropriate training methods will be neural in nature . Once the child reaches adolescence, advanced physical components (sport-specific skills, power, and hypertrophy) become more important focuses owing to the increased androgenic internal environment associated with this stage of development . As opposed to using specific ages to dictate resistance training commencement and advancements, it would be wise to identify the athlete’s levels of emotion and physical maturity, and stages of growth, to guide programming demands.
The benefits that resistance training provides revolves around the proper execution of the training programs. Myers et al. (2017) suggest there are three critical aspects to the proper design and implementation of resistance training programs :
- Education regarding proper lifting form
- Adequate supervision of trainees
- Effectively scaled lifting and progression of exercises
Supervision of resistance training is crucial for optimal youth development . In addition to ensuring safety during resistance training, research suggests that supervision can result in greater strength gains, power and speed improvements, and movement quality in youth [58-60], ultimately increasing the efficacy of youth training programs .
Intensity matters, even in youth. In their meta-analysis, Behringer et al. (2011) found a dose-response relationship between average resistance training intensity (%1RM) and gains in motor performance skills, such as running, jumping, and throwing, in children and adolescents . However, it’s extremely important to keep intensity low (i.e. use body weight or very light weights) for all exercises until proper technique is learned [29, 48]. Once proper technique is exhibited frequently, increasing intensity is recommended to optimize training adaptations.
Various types of resistance training can be effective for inducing desired adaptations . A variety of implements and bodyweight exercises should be used to develop muscle strength, particularly in pre-PHV athletes, Howard (2018) suggests . Each type of resistance training, including machine-based, free weight, and functional training, has specific benefits and limitations . When comparing training types against one another, no clear picture evolves, and they seem to follow the principle of training specificity . Therefore, the prescribed resistance training should be governed by the individual needs of the child or young athlete. If in doubt, it’s important to acknowledge that machine-based resistance training may promote a safer environment for young athletes, particularly when supervision cannot be ensured, whereas supervised resistance training using free weights allows full range of motion that better mimics sports-specific movements .
A recent meta-analysis by Lesinski et al. (2016) found that a training period of >23 weeks, 5 sets/exercise, 6–8 repetitions/set, a training intensity of 80–89% of 1 repetition maximum (RM), and 3–4 min rest between sets were most effective to improve muscle strength . Therefore, resistance training programs in youth should aim to incorporate exercises using fewer repetitions and higher intensities to improve physical performance measures of youth athletes but, once again, only when proficiency in movement has been attained.
When designing a program for youth athletes, it’s incredibly important to keep in mind a few key notions from the Youth Physical Development (YPD) model proposed by Lloyd & Oliver (2012):
- The need for individualization of the model should not be underestimated when dealing with athletes of different sex, maturity status, and training history.
- The development of muscular strength should be a priority at all stages of development for both males and females
- During prepubescence, strength, foundational movement skills (FMS), speed, and agility should be the main physical qualities targeted because the primary training adaptations are neural during the beginning stages of development.
- Once the child reaches adolescence, additional physical qualities, such as sport-specific skills, power, and hypertrophy, become more important owing to the increased androgenic internal environment associated with this stage of development.
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