Injury Trends and Prevention in Youth Resistance Training

Abstract

RESISTANCE TRAINING HAS BECOME A POPULAR METHOD OF CONDITIONING FOR CHILDREN AND ADOLESCENTS IN SCHOOLS, RECREATION CENTERS, AND SPORTS TRAINING FACILITIES. HOWEVER, THE GROWING POPULARITY OF YOUTH RESISTANCE TRAINING AND THE COMPLEX NATURE OF SOME TRAINING PROGRAMS RAISE NEW QUESTIONS AND CONCERNS ABOUT THE SAFETY OF THIS TYPE OF TRAINING FOR YOUTH. IN THIS ARTICLE, THE INCIDENCE, SEVERITY, AND ETIOLOGY OF YOUTH RESISTANCE TRAINING INJURIES ARE REVIEWED, RISK FACTORS FOR RESISTANCE TRAINING-RELATED INJURIES ARE IDENTIFIED, AND INJURY PREVENTION STRATEGIES FOR YOUTH WHO PERFORM RESISTANCE EXERCISE ARE DISCUSSED.

INTRODUCTION

Resistance training is a popular activity that is performed by a growing number of children and adolescents (^8,34). Current public health initiatives now aim to increase the number of youth who engage in “muscle-strengthening” activities, and contemporary physical education curricula include lessons that improve muscular strength (^31,40). Moreover, training programs specifically designed to enhance sports performance have become a popular fitness trend among young athletes (³⁹). Yet there is substantial interest from youth coaches, physical education teachers, and sports medicine professionals regarding the best techniques to maximize safety and improve the efficacy of resistance training for young lifters.

At present, there is a need to review the incidence, severity, and etiology of youth resistance training injuries and examine the relative safety of resistance training activities for children and adolescents. Furthermore, it is important to identify risk factors for resistance training injuries and discuss injury prevention strategies for youth who perform this type of training. The purposes of this article were to review the latest evidence regarding the safety of youth resistance training and provide general guidelines for reducing the risk of injury associated with resistance exercise. This information will aid professionals who instruct youth to participate in resistance training activities as part of physical education, sports training, or recreation.

In this article, the term “resistance training” refers to a specialized method of physical conditioning that uses a wide range of resistive loads, different movement velocities, and a variety of training modalities, including weight machines, free weights (barbells and dumbbells), elastic bands, medicine balls, and body weight. The terms “weightlifting” and “powerlifting” refer to sports in which athletes attempt to lift maximal amounts of weight in competition. The term “children” refers to boys and girls who have not developed secondary sex characteristics (a period of development called “preadolescence”), and the term “adolescence” refers to a period between childhood and adulthood (generally girls aged 12-18 years and boys aged 14-18 years). For ease of discussion, the term “youth” refers to both children and adolescents.

INCIDENCE AND SEVERITY OF YOUTH RESISTANCE TRAINING INJURIES

In the 1970s and 1980s, resistance training was not often recommended for children and adolescents because of the presumed high risk of injury associated with this type of exercise. A few retrospective case reports published during this era highlighted the potential for injury to the growth cartilage from resistance exercise and contributed to the misperception that this type of training was unsafe for young lifters (^{1,16,20,36,41}). However, improper lifting techniques, poorly chosen training loads, or lack of qualified supervision caused most of these injuries. For example, in a case report, a 13-year-old boy suffered a bilateral fracture of the distal radial epiphyses when he attempted to press 30 kg overhead while exercising in a “makeshift gymnasium” at home (²⁰). Others reported that a 16-year-old football player suffered a fracture of the left distal radius with dorsal displacement when he lifted 48 kg on the bench press exercise without supervision (⁴¹). It is unclear from these reports if these young lifters received any instruction on proper lifting techniques or training procedures from qualified professionals.

Injury to the growth cartilage has not been reported in any prospective youth resistance training study that provided qualified guidance and instruction (^10,23). Although growth cartilage is “prebone” and is weaker than adjacent connective tissue (²⁵), the perception that resistance training is inherently injurious to the developing musculoskeletal system is not consistent with clinical observations and research findings (^10,23). Furthermore, no scientific evidence indicates that resistance training will negatively impact growth at any stage of development during childhood and adolescence (^12,23). Paradoxically, most of the forces that youth are exposed to in various sports (e.g., gymnastics and martial arts) and recreational activities (e.g., running and tag games) are likely to be greater both in exposure time and in magnitude than competently supervised and sensibly progressed resistance exercise. For example, jumping and landing activities during competitive sports and play have been found to induce ground reaction forces of up to 5-7 times body mass (^7,24).

Myer et al. (²⁹) recently queried the U.S. Consumer Product Safety Commission to evaluate resistance training-related injuries presenting to U.S. emergency rooms by age, type, and mechanism of injury. They found that as age-group increased (8-13, 14-18, 19-22, and 25-30 years), the number of accidental injuries decreased significantly for each successive age-group. In this report, the mechanism of injury was considered accidental if it resulted from dropped weights, improper use of equipment, or tripping over equipment. Of note, 77% of the reported injuries in the 8- to 13-year-old age-group were categorized as accidental (²⁹).

These researchers also noted that two-thirds of the injuries sustained by 8- to 13-year-old patients were to the hand and foot and were most often related to “dropping” and “pinching” in the injury descriptions (Figure 1) (²⁹). These observations are supported by epidemiological findings from Kerr et al. (²²), who reported that children aged 12 years and younger suffered a larger proportion of hand and foot injuries than older resistance training participants. In the aforementioned report (²²), 65% of the reported injuries were caused by weights falling on the person and in 10% of the cases a body part was smashed or crushed between weights. Although many factors need to be considered when examining these data, the importance of proper exercise technique, gradual progression of training loads, and qualified instruction should not be overlooked.

Figure 1: Percentage of injuries in the youngest and oldest age categories. Note that the small prevalence of leg injuries in the 8-13 years age categories provides invalidated results and should be interpreted with caution. Reprinted from Myer et al. (²⁹).

Although the majority of youth resistance training injuries are the result of accidents that appear to be preventable with increased supervision and adherence to stricter safety guidelines, resistance training as with all physical activities does carry some degree of injury risk. A retrospective survey of resistance training injuries in 354 adolescent American football players found 27 injuries (causing more than 7 days of missed participation), which resulted in estimated injury rates in junior high school athletes (mean age, 13.3 years), high school freshman/junior varsity athletes (mean age, 15.6 years), and high school varsity athletes (mean age, 17.2 years) of 0.11, 0.091, and 0.51 per person year, respectively (³⁵). In that study (³⁵), only 36% of the training sessions performed by junior high school athletes were supervised by a coach. Brown and Kimball (³) estimated an injury rate of 0.29 per 100 participant hours in adolescent powerlifters who presumably trained with maximal or near-maximal loads on the bench press, deadlift, and back squat exercises. Of potential relevance, the average powerlifter in this report trained 4.1 times per week (99 minutes per training session), and a majority of the training sessions were performed without supervision from a strength and conditioning coach (³).

Although data comparing the relative safety of resistance training, weightlifting, and other sports are limited, in a retrospective evaluation of injury rates in adolescents, it was noted that resistance training and weightlifting were markedly safer than many other sports and activities (¹⁷). In that study (¹⁷), the overall injury rates per 100 participant hours were 0.8000, 0.0035, and 0.0017 for rugby, resistance training, and weightlifting, respectively. In support of these findings, Pierce et al. (³²) followed 70 competitive weightlifters (aged 7-16 years) over a 1-year period (1,224 lifts were performed in competition) and reported no injuries that limited training or required medical attention. Other researchers reported significant gains in muscular strength without any report of injury when weightlifting movements (e.g., snatch, clean and jerk, modified cleans, and pulls and presses) were incorporated into youth training programs (^9,14).

At present, little if any scientific evidence indicates that properly performed and sensibly progressed weightlifting movements performed during practice or competition are riskier than other sports and activities in which youth regularly participate (^10,17). However, these lifts involve more complex neural activation patterns than other resistance exercises; professionals should be knowledgeable of the progression from basic exercises (e.g., front squat) to skill transfer exercises (e.g., overhead squat) and finally to the competitive lifts (e.g., snatch). Youth should learn proper exercise technique with a wooden dowel or a lightweight aluminum barbell under the watchful eye of a strength and conditioning professional to enhance fundamental movement patterns (Figure 2).

Figure 2: A strength and conditioning coach reinforcing proper barbell position during the first pull of the power clean.

Regardless of the type of resistance exercise, all professionals who work with youth need to be aware of proper resistance training procedures because the lack of qualified supervision and the improper use of exercise equipment can be injurious (^2,3,22,29). Of note, there is an increased risk of injury to children and adolescents who use exercise equipment at home (^15,21). It has been reported that young children are more likely to be injured from home exercise equipment than older age-groups due, in part, to unsafe behavior, equipment malfunction, and lack of supervision (¹⁵). There is also the potential for a catastrophic injury if safety standards for youth resistance training are not followed. In a case study report, a 9-year-old boy died when a 23-kg barbell rolled off a bench press support and fell on his chest after he had jarred the supports while trying to get up (¹³). These findings underscore the risk of injury in the unsupervised and informal setting of a child's home; fortunately, this risk is removed with qualified instruction of youth.

A related concern regards the performance of plyometric exercises for children and adolescents. This type of training typically includes hops and jumps that exploit the muscles' cycle of lengthening and shortening to increase muscle power. Although most playground activities, such as hop scotch and jumping rope, can be characterized as plyometric, some observers have a very narrow view of plyometric training and suggest that this type of exercise can “wreak havoc” on the skeletal system of young athletes (³⁷).

Although advanced plyometric exercises should be reserved for trained strength/power athletes to increase speed of movement and power production, there are many examples of plyometric exercises, such as double-leg hops and throws with a lightweight medicine ball, that can be part of a youngster's fitness program. Indeed, regular participation in an age-appropriate resistance training program that includes plyometric exercises has been found to enhance movement biomechanics, improve functional abilities, and decrease the number of injuries in youth sports (^6,18,27,28). However, the focus of plyometric training should be on learning proper jumping and landing techniques along with a sensible progression from double-leg to single-leg exercises.

Nonetheless, injury or illness can result if the intensity, volume, or frequency of plyometric training exceeds the ability of the participants. In a case report (⁴), a 12-year-old boy developed exertional rhabdomyolysis after he was instructed to perform more than 250 repetitive squat jumps in physical education class. Clearly, the volume of plyometric training needs to be carefully prescribed and consistent with the needs, goals, and abilities of the participants. Efforts made to improve instruction and jumping mechanics during plyometric training can reduce the risk of injury to youth who may have limited, if any, experience participating in this type of structured training. Specific guidelines for designing youth strength and conditioning programs are beyond the scope of this article but are available elsewhere (^11,30).

RISK FACTORS AND PREVENTION

Although data from the pediatric literature indicate a relatively low risk of injury in children and adolescents who follow age-appropriate resistance training guidelines (^10,23), professionals who prescribe and supervise youth resistance training programs should be cognizant of the potential for injury with this type of training and should attempt to reduce injuries through the identification of risk factors and injury patterns in young lifters. For example, Quatman et al. (³⁴) reported that the trunk was the most frequently injured body part for both men and women between the ages of 14 and 30 years who presented to U.S. emergency rooms because of an injury related to resistance exercise.

In support of these observations, others reported that low back pain was the most frequent injury in adolescent athletes who participated in a resistance training program (^2,3,35). Because low back pain among adolescents has become a significant public health issue, with prevalence rates in adolescents approaching those in adults (¹⁹), there appears to be a role for preventative interventions that specifically strengthen the trunk and posterior chain musculature (e.g., erector spinae, gluteus maximus, and hamstrings). From our experience, young lifters who do not receive instruction from qualified professionals on proper program design spend too much time training their so-called mirror muscles (i.e., biceps and chest) and not enough time (or no time at all) strengthening the musculature on the posterior side of their body. Of potential relevance, neuromuscular training protocols that target deficits in trunk and hip control may alleviate high-risk biomechanics in adolescent female athletes (²⁶).

In addition to the aforementioned concerns regarding poor posterior chain strength, other risk factors that have been associated with resistance training injuries in youth are outlined in the Table. A recurring theme in most youth resistance training-related injuries is the lack of qualified adult supervision. All professionals who work with youth need to be aware of age-appropriate resistance training procedures because improper exercise technique and the aggressive progression of training loads can be injurious (^2,3). Without qualified supervision and instruction, youth are more likely to attempt to lift weights that exceed their abilities or perform an excessive number of repetitions with improper exercise technique (^15,21,29). Because children are more susceptible to central (i.e., nervous system) fatigue than adults (³⁸), the volume of resistance training needs to be carefully prescribed and sensibly progressed over time to avoid overtraining. Modifiable risk factors associated with youth resistance training injuries, which can be reduced or eliminated with qualified supervision and instruction, are outlined in the Table.

Table: Modifiable risk factors associated with resistance training injuries in children and adolescents, which can be reduced (or eliminated) with qualified supervision and instruction

Although there have not been any preventive trials that have focused specifically on measures to prevent resistance training-related injuries in youth, it seems reasonable to suggest that qualified professionals who understand pediatric resistance training guidelines and genuinely appreciate the physical and psychosocial uniqueness of children and adolescents should provide supervision and instruction. Ideally, professionals who teach and coach youth should have a level of knowledge commensurate with a college degree in physical education, exercise science, or a related field. Furthermore, if youth participate in advanced training programs (e.g., weightlifting classes), professionals should have additional knowledge and practical experience to properly teach young lifters this type of training. Although respected certifications are available from the National Strength and Conditioning Association, the United Kingdom Strength and Conditioning Association and USA Weightlifting, professionals who work with children and adolescents should be able to properly instruct and sensibly prescribe or advance resistance training programs for youth with different needs, goals, and abilities.

Basic education on weight room etiquette, proper exercise technique, and fundamental training principles should be part of all youth resistance training programs. Although there is no minimum age for participation in a youth resistance training program, all participants must be able to follow coaching instructions and undergo the stress of a resistance training program (⁸). In general, most 7- and 8-year-old children are ready for some type of resistance exercise. However, regardless of the starting age, all youth should receive safety instructions on appropriate starting weights, proper spotting, the correct use of collars, and the proper handling of barbells, dumbbells, and plates. This is particularly important in schools and recreation centers because untrained youth tend to overestimate their physical abilities and this may increase their risk of injury (³³). This type of instruction not only enhances participant safety and enjoyableness of the training experience, but direct supervision of youth resistance training programs can improve program adherence and optimize strength gains (⁵).

The available data suggest that well-designed educational interventions are needed to enhance participant safety and create an enjoyable exercise experience so youth can feel good about their performances (e.g., the ability to properly perform a back squat or power clean). Because there is evidence to suggest that most of the injuries related to youth resistance training are preventable, efforts are needed to minimize this risk with qualified supervision, sensible progression of training loads, and a safe exercise environment. Additional efforts toward the development of specific methods for teaching multijoint lifts and prescribing the optimal training volume are needed to enhance the safety and efficacy of youth resistance training. Specifically, qualified professionals who possess the required knowledge to safety and effectively teach topics related to youth resistance training may provide the most effective interventional approach to reduce resistance training-related injuries in youth. Continuing education seminars, in-service training, and a nationally recognized certification in pediatric strength and conditioning may help alleviate high-risk behaviors and enhance the training experience for children and adolescents.

ACKNOWLEDGMENT

The authors thank Jim McFarland from the Hillsborough High School in New Jersey for his contributions to this article.