Injuries sustained under the influence of alcohol or other recreational drugs as reported by the hospital staff or subjects who left without seeing a physician were eliminated from the analyses. All data were quality controlled by cross referencing the specific comments to the CPSC category code. In addition, each injury was classified into a mechanism of injury termed “nonaccident” or “accident” based on the specific comments to the CPSC category. The mechanism of injury was considered nonaccidental if it resulted from exertion (sprain/strain, fatigue failure, headache), overuse (e.g., tendonitis), or from equipment malfunction (cable snapping, resistance bands breaking). The mechanism of injury was considered accidental if it resulted from dropped weights, improper use of equipment, or tripping over equipment. The mechanism of injury was categorized by 2 separate authors blinded to both the age and sex of the subjects. One author performed the initial categorization, and the second author quality controlled the data and performed a separate, independent categorization. If the authors were unable to reach an agreement about the mechanism of injury or if they were unable to determine the injury mechanism from the description, the data were eliminated from the analysis. Frequency of resistance training injury estimates and data analyses were based upon the sample fulfilling the inclusionary criteria (age 8-30 yr, the mechanism of injury could be determined from the comments, no drug or alcohol use during injury, and patient was seen by a physician). The differences between age categories (8-13, 14-18, 19-22, and 23-30 yr) were determined for mechanism of injury (accident or nonaccident), type of injury (sprain/strain or fracture), and body part injured (head, trunk, arm, leg, foot). In addition, comparisons of injuries classified as “accidental” versus “nonaccidental” were made to further characterize the sample population.
Statistical analyses were performed using SAS, version 9.1 (SAS Institute, Cary, NC, USA). To account for the survey design and use the appropriate standard errors, the survey-specific procedures, which incorporated the sample weights and design clusters, were used for analysis. The independent variable of interest, age group, had 4 categories. Multiple logistic regression was initially used to assess the overall age effect, in which the 23 to 30 year age group was used as the reference category. Comparisons between successive age categories were also made using logistic regression, and a Bonferrroni correction was used to adjust for the multiple comparisons. The level of significance was established a priori at p ≤ 0.05.
The sample consisted of 4,111 patients for inclusion in the analysis. The distribution of injuries classified as caused by “weightlifting” are presented in Table 1. Table 2 shows the comparison of age group for accidental injury, and each category shows a statistically significant difference by age (p < 0.0001). After Bonferrroni correction for multiple comparisons, the percentage of the injuries that were accidental decreased significantly (p < 0.05) for each successive age group: 8 to 13 > 14 to 18 > 19 to 22 years; those 23 to 30 years of age were not different from the 19 to 22 year group. For sprain/strain injuries, the effect went in the opposite direction, and each successive age group was different (p < 0.05) after Bonferroni correction. Sprains and strains were 18.2% of injuries in the 8 to 13 age group, 43.9% in the 14 to 18 age group, 59.6% in the 19 to 22 age group, and 66.1% in the 23 to 30 age group. Evaluation of only the nonaccidental injuries (n = 2565) revealed that the oldest categories (19-22 and 23-30 yr) demonstrated a greater percentage (85% and 89%, respectively) of injuries categorized as sprains and strains relative to the other age categories (p < 0.001).
The oldest age groups demonstrated the greatest percentage of trunk-related injuries. Figure 2 represents the anthropometric location breakdown of weighted percentages of injuries for the youngest and oldest age categories. Two thirds of the injuries sustained in the 8 to 13 age group were to the hand and foot and were most often related to “dropping” and “pinching” in the injury descriptions. Consequently, when comparing injury type, there was an increased percentage of injuries classified as a fracture in the 8 to 13 group relative to all other groups (p < 0.001).
In addition to increased evidence on the safety of supervised resistance training in young athletes and adolescents, there is evidence that resistance training may reduce injury in a young athlete's chosen sport (6,22,29). This evidence is based on the beneficial adaptations that occur in bones, ligaments, and tendons after training and is further supported by epidemiology-based reports (18,28). Lehnhard and colleagues (29) reported significant reductions in injury rates with the addition of a strength training regimen with a male soccer team. Cahill and Griffith (6) incorporated weight training into their preseason conditioning for adolescent football teams and reported a reduction in knee injuries as well as a reduction in knee injuries that required surgery over 4 competitive seasons. Hejna et al. (23) reported that young athletes (13-19 yr) who included resistance training as part of their exercise regimen demonstrated decreased injuries and recovered from injuries with less time spent in rehabilitation when compared with their teammates. Training regimens that incorporated resistance training into preseason and in-season conditioning reduced injury risk factors and anterior cruciate ligament injuries in female athletes (25,26,30,35,36,38). Thus, there is evidence that indicates that resistance training is not only a relatively safe activity for young athletes but that it may also be useful to reduce injuries during competitive play (21,37).
The positive effects of a sound resistance training regime on increases in strength in adult athletes have been widely documented in the literature (3,5,7,19,47). Strength improvements achieved from resistance training occur by way of muscle hypertrophy (increases in muscular cross-sectional area), muscle fiber structural changes (pennation angle changes), and neuromuscular (increased motor unit synchrony and recruitment) and metabolic (improved energy delivery) adaptations (2,27,32,33,43,46,47). In contrast, earlier reports on resistance training in children purported that no similar adaptations would occur, mainly because of lack of circulating androgens in young children (9,48).
Although earlier studies suggested an absence of significant effect of resistance training in youth, subsequent studies that incorporated more rigorous experimental designs demonstrated marked improvements in strength measures for prepubescent and pubescent subjects after resistance training regimens (13,15-17,41,42,44,45,49). The measured benefits from resistance training are now considered to be greater than those attributable to normal growth and development in children and adolescents (37). These gains stem largely from neural adaptations (more complete and synchronous firing of muscle units) associated with the training. Faigenabum and Bradley (10,11) listed the potential benefits of resistance training for young athletes to range from increased muscle strength and power to enhancement of mental health as well as a stimulation of positive attitude that can foster a lifelong activity of resistance training.
Physical maturity and size, which may limit the use of certain resistance machines, should not limit participation in appropriately designed and supervised resistance training protocols. However, mental maturity level could limit participation (37). Faigenbaum and colleagues (14) demonstrated that with appropriate supervision children can be safely tested and trained even with applied maximum effort resistance. In general, if young athletes maintain sufficient emotional maturity to accept and follow directions, then they should be ready for strength training. If they are unable to follow supervision, then participation should be limited. All children and adolescents should be closely supervised and provided with competent and consistent feedback related to their exercise performance. Although injuries during resistance training are less frequent than in actual sport performance, they can occur and may be related to maturity level (21). The current study indicated that two thirds of the injuries sustained in the younger aged patients were to the hand and foot and were most often related to “dropping” and “pinching” in the injury descriptions. Appropriate attention to teaching weight room etiquette and equipment safety, combined with precautions to prevent horseplay and attention to proper handling of heavy objects in the weight room, may limit the risk of accidental weight room injuries (12,37).
To reduce the occurrence of nonaccidental injuries in children and adolescents, an emphasis should be placed on safe equipment use and perfecting proper technique. If the athlete is allowed to perform the exercise maneuvers improperly at low resistance levels, then the risk of injury will be amplified as resistance is increased. To improve exercise techniques, instructors should give continuous and immediate feedback to the young athlete, both during and after each exercise bout (37). This will make them aware of proper form and technique, as well as undesirable and potentially dangerous positions. In addition, visual feedback can be useful to help make young weightlifters cognizant of exercise techniques performed with visually identifiable poor biomechanics (34). Instructors can use mirrors or video equipment to help provide visual feedback. Visual and verbal feedback may help young athletes to match their perceived technique performance to their actual technique. Beyond the obvious benefit of appropriate supervision to decreasing injury risk in the weight room, direct supervision increases the efficacy of resistance training. Coutts and colleagues (8) demonstrated that supervised resistance training improved strength gains and exercise adherence in young athletes versus unsupervised training. Mazzetti et al. (31) corroborated these findings when they found similar results in male athletes who had moderate experience with resistance training. Cumulatively, there is strong evidence to support the benefits of direct supervision to improve both the efficacy and safety of resistance training applied to young athletes.
Our study limitations are mainly associated with the NEISS dataset sampling techniques. The manner in which these data were categorized based on the mechanism of injury (accident or nonaccident) is limited by the accuracy of recording of each injury by the separate treating clinicians and by the interpretation of the authors who reviewed each injury description. However, before individual categorization, the authors defined the methods of categorization to improve the systematic nature of the processes. In addition, emergency room technicians provided specific comments linked to each injury mechanism in the NEISS database. This afforded the investigators a secondary assessment of the injury mechanism and “weightlifting” activity to confirm the data quality control. Future prospective investigations should be used that attempt to objectify injury categorization to further diminish this study design limitation. In addition, the authors were blinded to the age and the CPSC sampling weights during the categorization process. It is also not known whether multiple visits were made to the emergency room by the same patient related to the same isolated “weightlifting” injury. If this occurred, an artificial inflation of the overall injury frequency may be reflected in the data. To control for overestimations, the NEISS coding manual instructs hospital workers to record only the first emergency room visit for any specific injury (CPSC NEISS coding manual), and thus it is unlikely that multiple visits by the same person for a specific injury were recorded. The NEISS coding manual instructs hospital workers to record only the most severely affected body part associated with an injury incident. In some cases, the frequency of additional minor injuries accompanying an injury incident may be underrepresented.
Another potential limitation is that the dataset does not include all “weightlifting” injuries because we cannot account for injuries that may not have resulted in an emergency room visit, perhaps because treatment was available at the setting of injury (e.g., athletic trainers or team physicians), treatment was sought at other medical facilities, or treatment was not sought out for an injury. Finally, this data cannot be generalized to specific populations based on athletic participation, skill level, or physical fitness because the NEISS database does not distinguish between recreational, high school, and collegiate athletes. More importantly, we cannot accurately determine whether the “weightlifting” injury occurred during “structured” (developed programs monitored by coaches, teachers, or trainers) or “unstructured” (no formal program or supervision) activities or any level of supervision that was available at the time of injury to the athlete. Despite these limitations, the results presented in this study provide important information on resistance training injury patterns in young children and adolescents relative to adults. Future work should focus on determining whether technique training, proper supervision, stricter safety guidelines, or other modifications can make resistance training safer for all ages and levels of participation.
On the basis of the current report, there is an increased risk of joint sprain and muscle strain injury in adults compared with children during resistance training activities. Younger children tend to sustain more accidental injuries, especially fractures, during resistance training activities than older children and adults. If appropriately supervised, resistance training may be safe and effective and may also facilitate injury risk reduction during sports participation. Resistance training programs for young children should focus primarily on the safe use of equipment to avoid accidental injury, then on the acquisition of proper resistance training techniques, and finally on the appropriate intensity progression that allows the development of strength and power. Unsupervised resistance training should be avoided in both preadolescent and adolescents athletes.
Financial support was provided from the National Institutes of Health/NIAMS Grant R01-AR049735. The authors also acknowledge Jensen Brent for his assistance with the literature review and Jane Kirwan with her help with the database management.
1. Adirim, TA and Cheng, TL. Overview of injuries in the young athlete. Sports Med
33: 75-81, 2003.
2. Alway, SE, Grumbt, WH, Gonyea, WJ, and Stray-Gundersen, J. Contrasts in muscle and myofibers of elite male and female bodybuilders. J Appl Physiol
67: 24-31, 1989.
3. Ben-Sira, D, Ayalon, A, and Tavi, M. The effect of different types of strength training on concentric strength in women. J Strength Cond Res
9: 143-148, 1995.
4. Bernhardt, DT, Gomez, J, Johnson, MD, Martin, TJ, Rowland, TW, Small, E, LeBlanc, C, Malina, R, Krein, C, Young, JC, Reed, FE, Anderson, SJ, Griesemer, BA, and Bar-Or, O. Strength training by children and adolescents. Pediatrics
107: 1470-1472, 2001.
5. Boyer, BT. A comparison of the effects of three strength training programs on women. J Appl Sport Sci Res
4: 88-94, 1990.
6. Cahill, BR and Griffith, EH. Effect of preseason conditioning on the incidence and severity of high school football knee injuries. Am J Sports Med
6: 180-184, 1978.
7. Chilibeck, PD, Calder, AW, Sale, DG, and Webber, CE. A comparison of strength and muscle mass increases during resistance training in young women. Eur J Appl Physiol Occup Physiol
77: 170-175, 1998.
8. Coutts, AJ, Murphy, AJ, and Dascombe, BJ. Effect of direct supervision of a strength coach on measures of muscular strength and power in young rugby league players. J Strength Cond Res
18: 316-323, 2004.
9. Docherty, D, Wenger, HA, Collis, ML, and Quinney, HA. The effects of variable speed resistance training on strength development in prepubertal boys. J Hum Move Stud
13: 377-382, 1987.
10. Faigenbaum, AD. Youth resistance training. President's Council on Physical Fitness and Sports Research Digest
11. Faigenbaum, AD and Bradley, DF. Strength Training for the Young Athlete. Orthopaed Phys Ther Clin North Am
7: 67-90, 1998.
12. Faigenbaum, AD, Kraemer, WJ, Cahill, B, Chandler, J, Dziados, J, Elfrink, LD, Forman, E, Gaudiose, M, Micheli, LJ, Nitka, M, and Roberts, S. Youth resistance training: position statement paper and literature review. J Strength Cond Res
18: 62-75, 1996.
13. Faigenbaum, AD, Loud, RL, O'Connell, J, Glover, S, and Westcott, WL. Effects of different resistance training protocols on upper-body strength and endurance development in children. J Strength Cond Res
15: 459-465, 2001.
14. Faigenbaum, AD, Milliken, LA, and Westcott, WL. Maximal strength testing in healthy children. J Strength Cond Res
17: 162-166, 2003.
15. Faigenbaum, AD, Westcott, WL, Micheli, LJ, Outerbridge, AR, Long, CJ, LaRosa-Loud, R, and Zaichkowsky, LD. The effects of strength training and detraining on children. J Strength Cond Res
10: 109-114, 1996.
16. Faigenbaum, AD, Zaichkowsky, LD, Westcott, WL, Micheli, LJ, and Fehlandt, AF. The effects of a twice-a-week strength training program on children. Pediatr Exerc Sci
5: 339-345, 1993.
17. Falk, B and Mor, G. The effects of resistance and martial arts training in 6 to 8 year old boys. Pediatr Exerc Sci
8: 48-56, 1996.
18. Fleck, SJ and Falkel, JE. Value of resistance training for the reduction of sports injuries. Sports Med
3: 61-68, 1986.
19. Fry, AC, Kraemer, WJ, Weseman, CA, Conroy, BP, Gordon, SE, Hoffman, JR, and Maresh, CM. The effects of an off-season strength and conditioning program on starters and non-starters in women's intercollegiate volleyball. J Appl Sport Sci Res
5: 174-181, 1991.
20. George, D, Stakiw, K, and Wright, C. Fatal accident with weight-lifting equipment: implications for safety standards. Can Med Assoc J
140: 925-926, 1989.
21. Hamill, BP. Relative safety of weightlifting and weight training. J Strength Cond Res
8: 53-57, 1994.
22. Hejna, W, Rosenberg, A, Buturusis, D, and Krieger, A. The prevention of sports injuries in high school students through strength training. Natl Strength Cond Assoc J
4: 28-31, 1982.
23. Hejna, WF, Rosenberg, A, Buturusis, DJ, and Krieger, A. The prevention of sports injuries in high school students through strength training. Natl Strength Coaches Assoc J
4: 28-31, 1982.
24. Herring, SA, Bergfeld, JA, Boyd, JL, Brolinson, PG, Chang, CJ, Glover, DW, Grana, WA, Indelicato, P, Johnson, RJ, Kibler, WB, Kraemer, WJ, McNerney, JP, Pallay, RM, and Tanji, JL. The team physician and conditioning of athletes for sports. American Academy of Family Physicians Consensus Statement. 2000.
25. Hewett, TE, Myer, GD, Ford, KR, Heidt, RS, Jr, Colosimo, AJ, McLean, SG, van den Bogert, AJ, Paterno, MV, and Succop, P. Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: a prospective study. Am J Sports Med
33: 492-501, 2005.
26. Hewett, TE, Riccobene, JV, and Lindenfeld, TN. The effect of neuromuscular training on the incidence of knee injury in female athletes: a prospective study. Am J Sports Med
27: 699-706, 1999.
27. Kawakami, Y, Abe, T, and Fukunaga, T. Muscle-fiber pennation angles are greater in hypertrophied than in normal muscles. J Appl Physiol
74: 2740-2744, 1993.
28. Kraemer, WJ, Duncan, ND, and Volek, JS. Resistance training and elite athletes: adaptations and program considerations. J Orthop Sports Phys Ther
28: 110-119, 1998.
29. Lehnhard, R, Lehnhard, HR, Young, R, and Butterfield, SA. Monitoring injuries on a college soccer team: the effect of strength training. J Strength Cond Res
10: 115-119, 1996.
30. Mandelbaum, BR, Silvers, HJ, Watanabe, D, Knarr, J, Thomas, S, Griffin, L, Kirkendall, DT, and Garrett, WJ. Effectiveness of a neuromuscular and proprioceptive training program in preventing the incidence of ACL injuries in female athletes: two-year follow up. Am J Sport Med
33: 1003-1010, 2005.
31. Mazzetti, SA, Kraemer, WJ, Volek, JS, Duncan, ND, Ratamess, NA, Gomez, AL, Newton, RU, Hakkinen, K, and Fleck, SJ. The influence of direct supervision of resistance training on strength performance. Med Sci Sports Exerc
32: 1175-1184, 2000.
32. McCall, GE, Byrnes, WC, Dickinson, A, Pattany, PM, and Fleck, SJ. Muscle fiber hypertrophy, hyperplasia, and capillary density in college men after resistance training. J Appl Physiol
81: 2004-2012, 1996.
33. Milner-Brown, HS, Stein, RB, and Lee, RG. Synchronization of human motor units: possible roles of exercise and supraspinal reflexes. Electroencephalogr Clin Neurophysiol
38: 245-254, 1975.
34. Myer, GD, Ford, KR, and Hewett, TE. Rationale and clinical techniques for anterior cruciate ligament injury prevention among female athletes. J Athl Train
39: 352-364, 2004.
35. Myer, GD, Ford, KR, McLean, SG, and Hewett, TE. The effects of plyometric versus dynamic stabilization and balance training on lower extremity biomechanics. Am J Sports Med
34: 490-498, 2006.
36. Myer, GD, Ford, KR, Palumbo, JP, and Hewett, TE. Neuromuscular training improves performance and lower-extremity biomechanics in female athletes. J Strength Cond Res
19: 51-60, 2005.
37. Myer, GD and Wall, EJ. Resistance training in the young athlete. Oper Tech Sports Med
14: 218-230, 2006.
38. Myklebust, G, Engebretsen, L, Braekken, IH, Skjolberg, A, Olsen, OE, and Bahr, R. Prevention of anterior cruciate ligament injuries in female team handball players: a prospective intervention study over three seasons. Clin J Sport Med
13: 71-78, 2003.
39. NFHS. 2006 High School Participation Survey
. Indianapolis, IN: National Federation of State High School Associations, 2006.
40. Pediatrics, A. A.o. Weight training and weight lifting: information for the pediatrician. Phys Sports Med
11: 157-161, 1983.
41. Pfeiffer, R and Francis, R. Effects of strength training on muscle development in prepubescent, pubescent, and postpubescent males. Phys Sports Med
14: 134-143, 1986.
42. Ramsay, J, Blimkie, C, Smith, K, Garner, S, MacDougall, J, and Sale, D. Strength training effects in prepubescent boys. Med Sci Sports Exerc
22: 605-614, 1990.
43. Rooney, KJ, Herbert, RD, and Balnave, RJ. Fatigue contributes to the strength training stimulus. Med Sci Sports Exerc
26: 1160-1164, 1994.
44. Sailors, M and Berg, K. Comparison of responses to weight training in pubescent boys and men. J Sports Med Phys Fitness
27: 30-37, 1987.
45. Sewall, L and Micheli, L. Strength training for children. J Pediatr Orthop
6: 143-146, 1986.
46. Smith, RC and Rutherford, OM. The role of metabolites in strength training. I. A comparison of eccentric and concentric contractions. Eur J Appl Physiol Occup Physiol
71: 332-336, 1995.
47. Staron, RS, Karapondo, DL, Kraemer, WJ, Fry, AC, Gordon, SE, Falkel, JE, Hagerman, FC, and Hikida, RS. Skeletal muscle adaptations during early phase of heavy-resistance training in men and women. J Appl Physiol
76: 1247-1255, 1994.
48. Vrijens, F. Muscle strength development in the pre and post-pubescent. Med Sport
11: 152-158, 1978.
49. Weltman, A, Janney, C, Rians, CB, Strand, K, Berg, B, Tippitt, S, Wise, J, Cahill, BR, and Katch, FI. The effects of hydraulic resistance strength training in pre-pubertal males. Med Sci Sports Exerc
18: 629-638, 1986.