There is now a compelling body of scientific evidence that resistance training by children and adolescents can have positive effects  on health and fitness and enhance sports performance.
Adapting the official statement of the UK Strength and Conditioning Association on youth resistance training, an international team of experts from the fields of pediatric exercise science, pediatric medicine, physical education, strength and conditioning and sports medicine has now published a consensus statement with comprehensive guidelines on youth resistance training (Lloyd RS, et al. 2014). The statement has been endorsed by 10 leading professional organizations within the fields of sports medicine, exercise science, and pediatrics.
The statement makes the following six key points:
Commenting on the statement, Jennifer Weiss, MD, an orthopedic surgeon with the Southern California Permanente Medical Group at the Los Angeles Medical Center, said she was "impressed by the sensitivity of the authors to varying levels of experience and body awareness among children and adolescents. The concise numbered points in the summary are practical and easy to follow. The more that we learn about strength, especially of the core, the less busy we think we will keep the surgeons (present company included), and this is a wonderful thing. The acknowledgement of the psychosocial component to training at a young age is also important, as forming these healthy habits early in life give these developing athletes a great foundation."
While he viewed the statement as "very comprehensive," and could understand "why it was endorsed by so many organizations," physical therapist and certified strength and conditioning trainer Keith Cronin expressed concern that the number of qualified resistance training professionals might outstrip the demand. "Whenever something comes out on the topic of something athletes and coaches want to do more of, care is needed. The general public tends to take a small piece of information and it becomes a 'runaway train.' The concerns I have are that the number of qualified trainers to work with young athletes is in my opinion limited."
Cronin also said it was critical to emphasize a key message point of the statement: that, "in order to reduce the chances of non-functional overreaching or overtraining, and to allow natural growth processes to occur, resistance training should not simply be viewed as an additional training session within the overall youth training programme, but as an alternative commitment in place of sport-specific training sessions and/or competitive [games]." It is important that parents understand, Cronin said, that training "not add to the current volume of sports but to be a substitute." (see training frequency section below)
~ Five key variables:
~ Fundamentals of technical competency should be a priority at all times.
~ Child-size equipment (light barbells, small dumbbells or fixed machine weights) should be used to allow children and adolescents to properly and safely execute a movement with correct technique.
~ Range of exercises for beginners: For youth with minimal training and poor technical competency (e.g. low training age), a range of exercises should be employed designed to promote the development of muscle strength and enhance overall fundamental motor skill competency. Once a child can demonstrate appropriate technical competency, they can be introduced to more advanced exercises that challenge the child in terms of coordination and require greater levels and rates of force production.
~ Incorporate free weights after develop proper technique: Once bodyweight exercise technique (e.g. bodyweight squatting, lunging, pressing and pulling movements) is sufficiently developed, exercises with free weights should be incorporated into the training program.
~ Advance to dynamic exercises: For technically competent youth, dynamic qualities can be enhanced with multijoint (e.g. squatting), velocity-specific training in the form of free-weight resistance training (e.g. weightlifting and plyometrics )
~ Two key training variables (routinely adjusted within a training session or overall phase of training, depending on the primary training goal of the individual):
~ Volume and intensity inversely related: the greater the load (intensity), the lower the number of repetitions that can be completed (volume).
~ Volume and intensity considered synergistically: when prescribing resistance training, both volume and intensity must be considered in order to maximize physiological adaptation and minimize risk of injury.
~ Appropriate training intensity is a percentage of one repetition-maximum (1 RM)
~ Use of 1RM measurement (actual or predicted) to determine training intensities typically unnecessary for untrained or sedentary youth with a low-training age and poor technical competency first begin to participate in formal resistance training.
~ Start novices out with low volume (1-2 sets) and low-moderate training intensities (≤60%1 RM) for a range of exercises and movement patterns.
~ External load can be increased over time after the athlete has used an appropriate repetition range to develop technical competency and acquire a base level of adaptation.
~ When first beginning multijoint resistance training exercises (e.g. squatting) children should perform fewer repetitions (1-3) and be provided real-time feeback after each repetition to ensure safe and correct movement technique (especially true for weightlifting exercises).
~ Progress once a child is competent in basis exercise technique, for example, to 2-4 sets of 6-12 repetitions with a low-moderate training intensity (≤ 80% 1 RM)
~ Further progress to periodic phases of lower repetition ranges (≤6) and higher external loads (≥ 85% 1 RM) in training as training age and athletic competency increases (again with the proviso that technical competency remains).
Important note: not all exercises need to be performed for the same number of sets and repetitions within a training session. A qualified professional, however, must observe and monitor for the effects of accumulated fatigue during the training session to minimize the risk of fatigue-induced breakdown in technique, which may predispose youth to training-related injury (a recent study found that nearly 8 in 10 (77.2%) of acute resistance training-related injuries in youth and adults are accidental, and that most are avoidable with appropriate supervision, sensible training progression based on technical competency and a safe training environment).
~ Frequency and amount of feedback will vary. Depending on the learning environment, qualified professionals will need to provide feedback to ensure that technical competency is maintained throughout each set of the training program, the frequency and mode of which will depend to a large degree on the number of individuals training, type of exercise being performed and the stage of learning and personality traits of the youth involved (for example, when coaching a novice, constructive feedback may be most helpful if it is provided after each repetition).
~ Children recover more quickly: Research indicates that children can recover more quickly from fatigue-inducing resistance training and, because their muscle tissue is more pliable, are less likely to suffer muscle damage following this form of exercise.
~ 1 minute rest periods enough for most children, although the rest period may need to be increased to 2-3 minutes as the intensity of training increases, especially if the exercises require a higher level of skill, force or power production (e.g. weightlifting or plyometric exercises). Again, with the caveat that within-session resistance training performance should, however, always be monitored to ensure that correct technique is maintained throughout the training session.
~ Warning: commercial metabolic high-intensity resistance training programs characterized by insufficient recovery between sets and exercise may result in the performance of potentially injurious exercise movements.
~ Adequate time for rest and recovery between sessions needed. Remember: youth are still growing and developing, resistance training programs should provide .
~ 2-3 sessions per week on non-consecutive days is most appropriate to develop muscular strength levels in children and adolescents.
~ Close monitoring of youth participating in resistance training with high training frequency.
~ Training frequency may increase as children go through adolescence and approach adulthood, especially for youth in competitive sport.
~ Sampling and exposure to a variety of physical activity experiences is recommended to help promote long-term physical development,
~ Parents, coaches and ﬁtness professionals should be aware of the potential difﬁculties when youth participate in numerous activities resulting in the accumulation of high exercise volumes.
~ For youth participating in competitive sports, in-season resistance training is needed to maintain gains in muscular ﬁtness and reduce injury-risk. However, to reduce the chances of non-functional overreaching or overtraining, and to allow natural growth processes to occur, resistance training should not simply be viewed as an additional training session within the overall youth training programme, but as an alternative commitment in place of sport-speciﬁc training sessions and/or competitive ﬁxtures.
~ Depending on the competitive demands of the sport, anywhere between one and three resistance training sessions should be completed in-season to enable the development (or at least the maintenance) of previously acquired strength gains, and to allow adequate time for rest and recovery.
~ Increased lesson time in physical education, taught by well-trained specialists may hold a realistic and evidenced-based opportunity to increase muscle strength and motor skill competency, which would facilitate an overall improvement in general physical ﬁtness. Research demonstrates that exposure to resistance training with qualiﬁed supervision during exercise lessons or physical education classes does not have an adverse effect on after-school performance in adolescent athletes.
~ While moderate movement velocities may typically be recommended for youth when learning new movements or exercises, there is also a need to promote the intention to move quickly to develop motor unit recruitment patterns and ﬁring frequencies within the neuromuscular system.
~ A child with limited training experience may need to perform resistance exercises with a moderate speed to maximise control and ensure correct technical development (eg, limb alignment, maintenance of correct posture); however, a participant with a training history of several months should be exposed to much greater movement velocities.
~ Repetition velocities may also ﬂuctuate within a session; for example, the movement preparation phase (including low load technical warm-up exercises) may consist of slower, controlled movements, however, the main strength and power exercises (inclusive of weightlifting and plyometric exercises) will involve rapid movement speeds. For resistance training exercises, the mass of the resistance will govern the velocity at which the movement is performed. Although heavy strength development exercises such as squatting, deadlifting, pressing and pulling will typically involve slower movement velocities, there should always be an intention to move as explosively as possible to promote appropriate neuromuscular adaptations and to maximise the transfer of training effect, providing the individual can demonstrate appropriate technique. The development of high velocity movement may be especially important during the growing years when neural plasticity and motor coordination are most sensitive to change.
Loyd RS, Faigenbaum AD, Stone MH, et al. Position statement on youth resistance training: the 2014 International Consensus. Br J Sports Med 2014;48:498-505. doi:10.1136/bjsports-2013-092952