Can Resistance Training Reduce Injuries in Youth Sports?
This paper examines the potential health-related benefits of youth resistance training, specifically the role of resistance training in injury reduction. Because the total elimination of injuries is an unrealistic goal, the role of resistance training in reducing the injury potential in young athletes will be discussed. Scientific evidence supporting the injury-reducing potential of youth resistance training will be examined, and important program-design variables for enhancing a young athlete's resistance to injury will be discussed. This information is particularly relevant because millions of children and adolescents are seen in hospital emergency rooms and sports medicine clinics each year for sports-related injuries. This treatment can lead to significant health care costs and other health-related problems (21). In addition, there is a renewed interest in health promotion in many schools, clinics, and community centers.
For the purpose of this paper, the term resistance training (or strength training) is broadly defined as a method of physical conditioning that involves the progressive use of a wide range of resistive loads (light manual resistance to high intensity plyometrics) designed to enhance or maintain muscular strength, muscular power, local muscular endurance, and proprioception (sense of position). Resistance training encompasses an assortment of training modalities, such as body weight, free weights (barbells and dumbbells), weight machines, elastic tubing, medicine balls, and wobble boards, and it is applicable to exercises performed in weight-room settings, sports performance centers, athletic training rooms, and rehabilitation clinics. We use the term weight training to describe a method of resistance training using only free weights or weight machines. The subjects we discuss in this paper range from boys and girls who have not reached puberty (children) and boys and girls between 13 and 18 years of age (adolescents). For ease of discussion, the term youth refers to children and adolescents.
Evidence of Injury Reduction in Youth
Because many of the injuries that occur in sports involve connective tissues, it is reasonable to believe that changing the size, density, or mechanical properties of the connective-tissue framework will help reduce the risk of injury (29, 30). These changes in tissue makeup form the foundation upon which the rehabilitation of musculoskeletal injuries is based and thus may also play a role in the reduction of injuries. A limited number of prospective studies involving adolescents suggest that regular participation in a conditioning program that includes resistance training can reduce the incidence of injury (Table 1) . Whereas clinical evidence and practice seem to support the use of resistance training for this purpose in children (12), the effectiveness of this type of intervention during childhood has not been evaluated.
One of the first trials involving adolescents to investigate the impact of a conditioning program on sports injuries was by Cahill and Griffith (5). They compared high school injury data over a 4-year period when preseason conditioning was used with the previous 4-year period without preseason conditioning. They demonstrated that 5–6 weeks of total-body conditioning, which included weight training, cardiovascular exercises, stretching, and agility drills, decreased the number and severity of knee injuries in high school football players. These findings were supported by Hejna et al. (15), who noted that the injury rate in male and female high school athletes who participated regularly in a multifaceted conditioning program was 26.2% (61 of 232) compared to 72.4% (20 of 29) for athletes who did not use resistance training. Furthermore, the rehabilitation ratio (a ratio of the time lost to rehabilitation because of injury per number of athletes in a group) was 4.82 days for the athletes who did not participate in resistance training versus 2.02 days for those athletes who did. Whereas these data support the injury-reducing potential of youth resistance training, details regarding the training programs are limited, and it is unclear which components of the intervention were effective and which were not.
More recently, Wedderkopp et al. (31) investigated the effects of resistance training on female European team handball players (16–18 years of age). In this randomized, controlled trial, players in the intervention group performed 10–15 minutes of ankle disc training followed by upper- and lower-body plyometric training throughout one 10-month season. The results indicated that the resistance-training program significantly reduced the incidence of acute injuries and those caused by overuse in these young athletes during games and practice. The players who did not participate in the conditioning program had a 5.9 times higher risk of injury than players who participated in the training program.
Because of the increasing incidence of knee injuries in young female athletes (4), researchers have conducted more investigations concerning this group of athletes and the effects of resistance training on injury rates. Hewett et al. (17) evaluated the effects of a 6-week jump-training program on landing mechanics and lower-extremity strength in female high school volleyball players. The training program progressed through 3 phases and included instruction on proper jumping and landing techniques. Stretching was performed immediately before jump training, and weight training came immediately after. After the athletes completed the training program, it was reported that potentially dangerous landing forces significantly decreased because of an improvement in body mechanics and an increase in hamstring muscle power.
In a follow-up nonrandomized, controlled trial involving 1,263 athletes, Hewett et al. (16) evaluated the effects of a 6-week training program on the incidence of knee injury in female athletes. The structured training program, which included plyometric exercises, weight training, and stretching 3 times a week, significantly decreased the incidence of serious knee injuries in high school female athletes. Ten of the untrained female athletes sustained a serious knee injury, whereas only 2 of the trained athletes sustained such an injury. The incidence of injury in untrained women was not significantly different from untrained men. As noted by Hewett et al. (16), the decreased incidence of serious knee injuries was probably caused by a combination of factors, including an improvement in jumping technique and lower-extremity strength.
In another controlled trial, Heidt et al. (14) examined the impact of a 7-week multi-factorial preseason conditioning program on female high school soccer players. The training program included weight training, plyometric exercises, cardiovascular conditioning, speed drills, and flexibility exercises. After the soccer season, players who participated in the conditioning program had a significantly decreased incidence of injury compared with the untrained group (14.7% versus 33.7%, respectively). The trained group also had a smaller percentage (2.4%) of anterior cruciate ligament injuries compared with the untrained group (3.1%), although this finding was not statistically significant. Whereas data from this study, as well as other reports, provide supporting evidence regarding the protective effect of resistance training, it is difficult to assess how much the different features of the conditioning program contributed to the total affect.
Collectively, these data suggest that sports-related injuries in adolescent athletes are amenable to preventive strategies, which include different types of resistance training, cardiovascular conditioning, and flexibility exercises. Although resistance training seems to be the bedrock of injury-reduction programs, different modes of conditioning may each make a unique contribution to the overall reduction in sports-related injuries. Also, whereas intensity or volume of training has not been established as a factor in reducing injuries in young athletes, a training frequency of 3 days per week and a training duration of at least 6 weeks seem necessary to elicit the desired effect. However, the results of exercise interventions need to be interpreted carefully because athletic injuries can be caused by several factors including field conditions, rules enforcement, equipment modifications, inadequate supervision, and intensity of play.
Special Concerns for Young Athletes
Whereas some observers may question the need for preparatory fitness programs, fewer athletes are exposed to physical education than in the past, and most youth spend a significant amount of time watching television, playing video games, or surfing the Internet (8, 22). Owing to this apparent decline in free-time physical activity, the bodies of boys and girls may be ill-prepared to handle the demands of sports training and competition. Thus, one of the most significant benefits of resistance-training fitness conditioning may be its ability to prepare boys and girls for the demands of sports practice and competition. Preliminary findings from Mediate (20) suggest that conditioning programs that include resistance training may better prepare young athletes for sports participation by developing general athleticism and enhancing self-confidence. According to Smith et al. (28), the incidence of overuse injuries sustained by young athletes could be reduced by 50% if more emphasis was placed on the development of fundamental fitness abilities before sports participation. In accordance with that view, the National Athletic Trainers' Association suggests that high school athletes engage in conditioning activities at least 6 weeks before the start of practice (23).
Based on scientific evidence and clinical impressions, professionals who work with youth need to pay special attention to the choice of exercise and the amount of rest and recovery between exercise sessions if injury reduction is a primary training objective. In short, a resistance-training program should not simply be added to a young athlete's weekly exercise program, but rather it should be incorporated into a multi-factorial conditioning program that varies throughout the year. In some cases, young athletes may need to decrease the amount of time they spend practicing sport-specific skills to allow time for fitness conditioning with qualified instruction. Sports-medicine professionals are frequently treating young athletes who have been injured because of their lack of conditioning, improper exercise techniques, or inappropriate progression of training loads (24).
Choice of Exercise
Plyometric exercises have been sensibly incorporated into resistance-training programs designed to reduce the incidence of injury in young athletes. With qualified instruction and an appropriate progression of training intensity and volume, children and adolescents can benefit from this type of conditioning (7, 19). Although plyometric exercises are often associated with high intensity drills, such as depth jumps (i.e., jumping from a box to the ground and then immediately jumping upward), common activities such as jumping, skipping, hopping, and throwing can also be considered plyometrics. In fact, jumping jacks and hop scotch can be characterized as plyometrics because they exploit the muscles' cycle of lengthening and shortening to increase power.
Researchers who incorporated plyometric training into their injury-reduction program started with lower-intensity drills and gradually progressed to higher-intensity drills over time. Researchers also focused on developing proper jumping technique, as evidenced by Hewett et al. (16), who required all subjects to participate in a 2-week technique phase, during which time proper jumping technique was demonstrated and practiced. This is an important concept to keep in mind when training or rehabilitating athletes or nonathletes of any level. Other considerations for plyometric training include proper warm-up, appropriate footwear, sufficient space, adequate recovery between training sessions, and a shock-absorbing landing surface (e.g., wrestling mat, suspended floor, or grass playing field). The floors of training rooms and clinics typically consist of concrete flooring with carpeting. This type of surface is not ideal for plyometric training, and therefore, modifications should be made to decrease joint stress and the increased risk of injury.
Rest and Recovery
Although far more data have been published on how to prepare young athletes for sports than on how to best recover from sports training and competition, it is noteworthy that most prospective resistance-training trials that significantly reduced injuries had a training frequency of 3 days per week on nonconsecutive days. A downfall of many youth resistance-training programs is not allowing for adequate recovery between workouts. Many children and adolescents (as well as some coaches) do not value the importance of rest and recovery and believe in the more-is-better philosophy of sports training. A reduction in performance and an increased risk of injury can result from muscle strain caused by frequent training sessions without adequate rest and recovery in between (13, 18).
It has been estimated that 10–20% of adult athletes who train intensely experience overtraining, which is characterized by chronic decreases in performance and an impaired ability to train (26). Because children and adolescents are still growing and developing, it is likely that they may need even more time for rest and recovery between exercise sessions than adults. Even simple methods of restoration (e.g., self-massage, contrast [hot and cold] showers, and recovery beverages) can influence an adult's ability to recover from physical training and avoid injury (27, 32), and it is possible that younger athletes could benefit from these methods as well. Because the need for rehabilitation sometimes stems from inadequate restoration, future research should examine the impact of restorative methods on a young athlete's ability to recover from training and competition.
Providing an opportunity for physical and mental recovery should be considered an integral component of an injury-reduction program. Whereas the amount of rest and recovery needed between exercise sessions may vary depending upon the intensity of the training program and individual needs, adequate restoration will accelerate the ability to adapt to physical training and thus reduce the risk of injury. Furthermore, whereas it is tempting to focus only on resistance-training variables such as sets, repetitions, and exercise choice, it is important to realize that what is done between exercise sessions can have a significant impact on what is done during exercise sessions. Proper nutrition (including adequate hydration), adequate recovery, and sufficient sleep are all particularly important for young athletes who are training harder and longer than ever before (11, 33).
Is it possible to reduce the incidence of injury by participating in a youth resistance-training program? The answer is a qualified yes, because the effects of the resistance-training program seem to be dependent on the program design. A limited number of controlled studies suggest that regular participation in a broad-based training program that includes resistance training can significantly reduce sports-related injuries in adolescents. However, additional randomized, controlled trials are required to further examine the effectiveness of different resistance training protocols and interventions on reducing the incidence of injury in competitive (sport) and noncompetitive activities (recreation and fitness).
Important future goals should be to elucidate the mechanisms responsible for injury and to establish the optimal mixture of training activities that help reduce the risk of injury. In addition, investigations are required to explore the influence of other strategies, including coaching education, preseason fitness evaluations, and select restorative procedures (proper nutrition and stress management), on reducing the incidence of injury in children and adolescent athletes. By continuing our efforts to better prepare young athletes for sports training and competition, we will decrease the dropout rate from youth athletic programs caused by frustration, embarrassment, failure, or injury.
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Avery D. Faigenbaum is an Associate Professor in the Department of Exercise Science and Physical Education at the University of Massachusetts Boston
Jaynie Bjornaraa Schram is currently pursuing her PhD in Rehabilitation Science at the University of Minnesota and has served on the NSCA Certification Commission and on the Board of Directors for the NSCA
Table 1 Prospective Controlled Studies Involving Adolescents: Resistance Training and Injury Reduction
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