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Extremity Conditions

Risk Factors for Overuse Injuries in Runners

Wen, Dennis Y. MD

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Current Sports Medicine Reports: October 2007 - Volume 6 - Issue 5 - p 307-313
doi: 10.1097/01.CSMR.0000306493.61271.a9
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Abstract

Introduction

Running has become a popular form of exercise over the past three decades not only in this country, but worldwide. The numerous health benefits of running and other forms of exercise are well documented [1,2]. However, injuries frequently occur as a result of running. Depending on the definition of injury used and the type of population studied, various reports have estimated yearly incidence rates of 37% to 79% [3,4]. Although traumatic injuries do occur with running (acute muscle strains, ankle sprains, motor vehicle traumas), the vast majority of running injuries are due to what we consider “overuse.” Some of the more common clinical conditions that are often considered related to running include patellofemoral knee pain, shin splints or lower leg pain, Achilles tendinopathy, iliotibial band tendinopathy, plantar fasciitis, metatarsal stress fractures, and tibial stress fractures [3].

Treatment methods and, more importantly, prevention methods, would be enhanced by an understanding of the cause of each type of running injury. Unfortunately, risk factors for individual running conditions as well as for running injuries in general are poorly defined; very few well-controlled studies exist in the literature. Most of the purported risk factors are based on opinion, case series, and uncontrolled studies.

The various purported risk factors for running injuries are commonly divided into intrinsic and extrinsic risk factors. Intrinsic risk factors include mostly anatomic and other variables that are innate to the individual, such as gender, age, height, weight, personality type (eg, aggressive, passive), and anatomic factors such as femoral anteversion, genu varus or valgus, pes planus or cavus, bone density, muscular flexibility, and leg-length discrepancies [3]. Extrinsic risk factors include training variables such as mileage, hill running, pace, interval training, equipment (shoes, shoe inserts), and training surfaces. This article reviews the existing literature concerning risk factors for running injuries, summarizes our current knowledge, and highlights the shortcomings in our understanding of this issue.

Anatomic Risk Factors

Retrospective studies

In one of the earlier case series that looked at running injuries, James et al. [5] identified anatomic malalignment factors that were thought to contribute to the injuries in a group of injured runners. Lysholm and Wiklander [6] made similar observations in another case series. However, case series such as these lack control groups and, therefore, causality cannot be established.

Several case control studies have been performed evaluating the association between anatomic alignment risk factors and various overuse injuries (Table 1). Viitasalo and Kvist [7] found greater subtalar pronation in a group of runners with shin splints compared with a group of healthy controls. Sommer and Vallentyne [8] similarly found a greater propensity toward subtalar pronation in subjects with shin splints among a group of 25 athletes and dancers. Messier and Pittala [9] compared runners with iliotibial band syndrome, shin splints, and plantar fasciitis with a healthy control group. The shin splints group had greater maximum pronation compared with the control group; the plantar fasciitis group had greater plantar-flexion range of motion compared with the control group. Using discriminant analysis, Warren [10] and Warren and Jones [11] could not find a set of predictor anatomical variables between groups with plantar fasciitis and control groups.

T1-10
Table 1:
Retrospective studies of anatomic risk factors

In a group of 304 runners, Wen et al. [12] measured arch heights, heel varus or valgus, knee tubercle-sulcus angles, knee varus or valgus, and leg-length discrepancies. Low as well as high arch heights were associated with shin injuries compared with average arch heights; heel varus was associated with back injuries; lower knee tubercle-sulcus angles were associated with ankle injuries; high and low knee varus groups had more hip injuries compared with the average group; and less leg-length discrepancy was associated with back and ankle injuries.

Kibler et al. [13] found plantar-flexion strength and dorsiflexion range of motion deficits in a group of 43 athletes with plantar fasciitis compared with a healthy control group. van Mechelen et al. [14] evaluated 16 injured runners, looking at their hip and ankle ranges of motion compared with healthy controls. They found the injured group to have more restricted hip range of motion compared with controls.

Messier et al. [15] found knee quadriceps-angles (Q-angles) to be greater in a group of 16 runners with patellofemoral pain compared with a healthy control group. Similarly, Moss et al. [16] noted that a group of high school athletes with patellofemoral pain had greater Q-angles compared with healthy controls. In contrast to these studies, Caylor et al. [17] found no differences in measured Q-angles between a group of patients with anterior knee pain and asymptomatic controls. Fairbank et al. [18] also measured Q-angle, along with generalized joint laxity, genu valgus, and femoral neck anteversion, in a group of 446 adolescents, and found that these factors were not statistically different between those with and without anterior knee pain. Galanty et al. [19] found no association between Q-angles and anterior knee pain in high school students.

Dahle et al. [20] classified 77 high school football players and cross country runners into three groups based on whether they had pronated, supinated, or neutral foot types. Knee pain was more common in the groups with pronated and supinated foot types compared with the group with neutral foot type. Williams et al. [21] compared a group of 20 high-arched runners with a group of 20 low-arched runners. They found that the high-arched runners tended to have more ankle, lateral-sided, and bony injuries. The low-arched runners had more knee, medial-sided, and “soft tissue” injuries.

Niemuth et al. [22] compared 30 previously injured recreational runners with 30 noninjured runners and found that the previously injured runners had weaker hip abductors and flexors but stronger adductors on their injured side compared with their uninjured side.

Cause and effect usually cannot be determined based on retrospective studies, whether case-control or cohort. It is possible that some of the risk factors found in these retrospective studies were a result of the running injuries rather than an actual cause of the injuries. Furthermore, retrospective studies suffer from selection bias, known as the “healthy runner effect” [23,24], in which injured or injury-prone runners stop running and are, therefore, not included in the study population, thereby biasing the study towards “healthier” runners.

Prospective studies

Fewer prospective studies exist concerning anatomical risk factors for running injuries (Table 2). Although cause and effect is more easily determined with prospective studies, they can still be biased by the healthy runner effect.

T2-10
Table 2:
Prospective studies of anatomic risk factors

Walter et al. [25] measured femoral neck anteversion, pelvic obliquity, knee and patellar alignment, rearfoot valgus, and pes cavus/planus in 1000 runners and found that none of these variables was associated with increased risk of running injuries. Similarly, Montgomery et al. [26] measured hip and ankle range of motion, knee range of motion and alignment, and foot arch type in 505 Navy SEAL recruits. During a subsequent 6-month training period, no associations between these measurements and injuries were found.

Cowan et al. [27] performed another prospective study in which measures of foot morphology were performed on 246 Army recruits prior to a 12-week training course. In this study, injury risk increased with increasing arch heights. This same group of investigators measured knee varus/valgus, knee Q-angle, knee recurvatum, and leg-length differences in 294 Army recruits prior to their 12-week training course [28]. Those with the most valgus knees had a higher risk of injury, whereas those with the highest Q-angles had a higher risk of stress fractures.

Wen et al. [29] measured arch heights, heel and knee varus/valgus, knee tubercle-sulcus angles, and leg-length discrepancy in 255 runners. During a subsequent 32-week marathon training program, a few statistical associations were found: higher arches were protective of overall injuries and knee injuries; greater heel valgus was protective of knee and foot injuries; higher knee tubercle-sulcus angles were associated with shin injuries; and less leg-length discrepancy was associated with more overall injuries.

In a group of 295 Israeli army recruits, Giladi et al. [30] measured ankle dorsiflexion and plantar-flexion, hindfoot inversion and eversion, and in-toeing or out-toeing gait, and classified arches as low, average, or high. During a subsequent 14-week training period, stress fracture incidence was higher with increasing arch heights.

Kaufman et al. [31] measured arch characteristics in 449 Navy SEAL recruits. During a 25-week training program, stress fractures were associated with pes planus and cavus. Restricted hindfoot inversion was associated with more femoral stress fractures, whereas increased hindfoot inversion was associated with tarsal and metatarsal stress fractures.

Reinking and Hayes [32] performed a retrospective and prospective study of exercise-related leg pain in collegiate cross-country runners. Ankle dorsiflexion and navicular drop was measured in 63 runners, and neither measure was associated with leg pain. Reinking [33] prospectively measured foot pronation and calf muscle length in 76 collegiate athletes. The athletes who later developed lower leg pain had greater navicular drop compared with those in the control group.

Lun et al. [4] measured hip range of motion, knee recurvatum and Q-angle, ankle range of motion, and subtalar and forefoot varus/valgus in 87 recreational runners. During a 6-month observation period, no associations between the measurements and overall injuries were noted. However, patellofemoral pain was associated with ankle dorsiflexion, knee varus, and forefoot varus.

Burns et al. [34] measured foot alignment in 131 triathletes. A 6-month retrospective analysis was performed, along with a 10-week prospective follow-up. The prospective portion of the study showed an association between supinated foot type and injuries.

Dynamic variables

Although static alignment measures may be related to dynamic variables, more recent thinking suggests that dynamic factors are likely the more important risk factors for injuries. Several recent studies have investigated these factors.

Messier et al. [15] evaluated several kinetic and strength measures in a group of 16 runners with patellofemoral pain. Compared with noninjured controls, rearfoot movement variables of maximal pronation and pronation velocity showed no differences between the groups. Support time, maximum vertical propulsive force, maximum braking force, and braking impulse did discriminate between the groups. Muscular endurance, but not strength, was also different between the groups.

Moss et al. [16] studied several kinematic measures in 14 high school female athletes with patellofemoral pain, comparing them with 15 noninjured girls. Shorter time to minimum dynamic Q-angle was associated with patellofemoral pain.

Stefanyshyn et al. [35] conducted a retrospective study comparing 20 subjects with patellofemoral pain with 20 asymptomatic control subjects. Higher knee abduction impulses were found in the group with patellofemoral pain. In a prospective follow-up to this study, 6 of 80 subjects developed patellofemoral pain, and these six had higher knee abduction impulses compared with matched control subjects.

Willems et al. [36] prospectively measured static alignment and gait kinematics of 400 students in a barefoot condition, and then repeated the measurements with subjects wearing shoes [37•]. Forty-six subjects developed lower leg pain, and this group, while barefoot, had a more central heel strike, increased pronation with more pressure under the medial foot, and more lateral roll-off compared with uninjured controls [36]. Similar results were found when the subjects wore shoes [37•]. Those with lower leg pain had increased pronation with increased pressure underneath the medial foot, delayed maximal eversion, and accelerated reinversion compared with control subjects.

In a retrospective case control study, Hreljac et al. [38] evaluated kinetic and rearfoot kinematic variables in a group of runners with overuse injuries and in a group of uninjured controls. Injury-free runners demonstrated lower vertical force impact peak and maximal vertical loading rate.

Several studies have evaluated the relationship between dynamic factors and stress fractures. Bennell et al. [39] measured ground reaction force parameters, bone densities, and tibial bone geometry in a cross-sectional group of running athletes. They found no differences between the measured variables in those athletes with a history of tibial stress fractures compared with control subjects. Milner et al. [40] compared 20 runners with a history of tibial stress fractures with 20 healthy control subjects. They measured vertical impact peak, instantaneous and average vertical loading rates, instantaneous and average loading rates during braking, knee flexion excursion, ankle and knee stiffness, and peak tibial shock. They found that the tibial stress fracture group had greater instantaneous and average vertical loading rates and tibial shock than the control group. The same group of investigators measured peak adduction, braking peak, and absolute peak free moment and impulse in 25 runners with a history of tibial stress fractures and 25 control subjects [41]. Greater peak adduction, braking peak, and absolute peak free moment was found in the group with tibial stress fractures. Finally, Zifchock et al. [42] found no differences in gait symmetry between a group of runners with a history of unilateral tibial stress fractures and a control group.

Nonalignment Risk Factors for Running Injuries

Several nonalignment factors for running injuries have been proposed, including height, weight, age, gender, running experience, excessive mileage, excessive pace, interval-type training, hill running, running on hard or banked surfaces, previous injuries, type of shoes worn, and “training errors.” Many studies implicating these factors are uncontrolled case series. Some cross-sectional and retrospective studies do exist, but even fewer prospective studies have examined many of these factors. Studying or controlling for many of the training-type variables is very difficult.

Age and gender have generally not been found to be risk factors for running injuries in retrospective [12,23,24] or prospective studies [25,29,43]. The exception to this is that several studies of stress fracture implicate female gender as a risk factor [41,44]. Running experience may decrease the risk of injury [24,43], although this factor is highly susceptible to the healthy runner bias [3,24] and not every study corroborates this theory [12,25,29]. In regard to height and weight, although at least one study implicates these as risk factors [16], most do not [12,24,25,29,43].

In a case control study specifically looking at stress fractures, Myburgh et al. [45] has implicated menstrual dysfunction in females as a risk factor. Similarly, Shaffer et al. [44] and Rauh et al. [46], in separate prospective studies, have shown that menstrual dysfunction and poor aerobic fitness are risk factors for stress fractures among female military recruits. Bennell et al. [47] noted lower bone mineral density, menstrual disturbance, and less lean lower limb mass to be risk factors for stress fractures in female track and field athletes.

The data concerning the practice of stretching are quite sparse, conflicting, and inconclusive [29,48]. Many runners stretch because of the ingrained belief that it will help prevent injuries. They may be more likely to stretch if they believe that they are injury prone. This preexisting belief among runners, coaches, trainers, therapists, and physicians makes this a very difficult area to adequately study.

Many, but not all, studies, whether retrospective or prospective, implicate the volume of running as a risk factor for injuries [5,6,23–25,43]. Higher injury risk occurs with higher volumes of running; however, studies evaluating other training parameters such as pace, interval training, hill training, and running surfaces are not conclusive [12,23–25,29,43]. Training errors are difficult to define and even more difficult to actually study; no well-controlled studies have adequately addressed this variable.

Several studies, both retrospective and prospective, have noted that previous injuries are a risk factor for future injuries [12,24,25,29,43,49]. The wearing of improper or worn running shoes has also been implicated as a risk factor; however, there have been inconclusive findings in the literature [12,29]. Marti et al. [24] showed a higher injury risk in runners who wore more expensive shoes. Wen et al. [29] showed no clear relationship between shoe habits and injury risk. Because of the commonly held belief that shoes are somehow protective of injuries, this is a difficult area to adequately study.

Summary and Discussion

A myriad of potential risk factors for running injuries have been proposed, including anthropometric variables, anatomic alignment variables, dynamic kinematic variables, and training variables. Many of these are considered risk factors based simply on intuition, conjecture, and expert opinion. While studies evaluating several of these factors now exist in the literature, the study methodologies, definition of injuries, and populations have varied greatly. Often conflicting results are noted from one study to another, possibly attributable to these differing methods and populations. Most, but not all, studies seem to implicate training volume as a consistent risk factor for running injuries. Similarly, most, but not all, studies implicate previous injuries as a risk factor for development of future injuries. The proposed mechanisms include the possibility that the previous injury has not completely healed, that the previously injured tissue functions inferiorly, or that the risk factors for the first injury remain [50].

Although there are trends in the literature implicating pronation, statically or dynamically, as a risk factor for lower leg pain (shin splints) [7–9,33,36,37•], not every study is in agreement [4,12,25–29,32,34]. Similarly, some studies suggest Q-angle as a risk factor for patellofemoral pain [15,16], whereas others do not [4,17–19]. Overall, the literature is inconclusive in regard to anatomic alignment risk factors. Similarly, the literature is inconclusive concerning nonanatomic risk factors, such as training variables. Several recent studies have concentrated on dynamic variables, but reproducibility of their results has not been established.

Despite the variety of differing results found in the various studies, most proposed risk factors appear to have some sound intuitive logic. The proposed model by Meeuwisse et al. [51], whereby certain anatomic and other intrinsic factors interact with training factors to produce injury, may hold true. One drawback of several studies, however, is a lack of control for the myriad of possible confounding variables, both intrinsic and extrinsic.

In particular, with the exception of some military studies and laboratory kinematic studies, many studies have not adequately controlled for the running shoe. Although no studies exist on this matter, it is possible that the shoe interacts with anatomic factors and training factors to either decrease, or possibly increase, the injury risk [36,37]. Similar arguments apply to shoe inserts such as orthotics.

Studies also differ widely with regard to the specific injuries being studied. Some studies have looked at running injuries in general, whereas others have more specifically studied shin splints, patellofemoral pain, or stress fractures. It can certainly be speculated that different risk factors exist for different injuries, and that this is not always accounted for in the studies. Furthermore, even among the stress fracture studies, it is possible that different risk factors exist for different stress fractures even within the same bone.

Conclusions

Despite the amount of speculation and opinion regarding a variety of proposed risk factors for running-related overuse injuries, the available studies in the literature do not allow any firm conclusions to be made. Due to the difficulty associated with controlling for multiple risk factors and confounding variables, inconsistent results are found among the various studies. The risk factors of training volume and previous injury are the most consistently implicated factors cited in epidemiologic studies. Most likely, the risk factors for running injuries are multifactorial, with some underlying risk associated with various anatomic factors, but with the need for certain training factors, such as high volume, to manifest that underlying risk. Future prospective studies controlling for multiple variables and performed in relatively novice runners to reduce the healthy runner selection bias may shed more light on this confusing area.

References and Recommended Reading

Papers of particular interest, published recently, have been highlighted as: • Of importance •• Of major importance

1. Paffenbarger, RS Jr, Hyde RT, Wing AL, et al.: The association of changes in physical-activity level and other lifestyle characteristics with mortality among men.N Engl J Med 1993, 328:538–545.
2. Thompson PD, Franklin BA, Balady GJ, et al.: Exercise and acute cardiovascular events: placing the risks into perspective. A scientific statement from the American Heart Association Council on Nutrition, Physical Activity, and Metabolism and the Council on Clinical Cardiology.Circulation 2007, 115:2358–2368.
3. van Mechelen W: Running injuries: a review of the epidemiological literature.Sports Med 1992, 14:320–335.
4. Lun V, Meeuwisse WH, Stergiou P, Stefanyshyn D: Relation between running injury and static lower limb alignment in recreational runners.Br J Sports Med 2004, 38:576–580.
5. James SL, Bates BT, Osternig LR: Injuries to runners.Am J Sports Med 1978, 6:40–50.
6. Lysholm J, Wiklander J: Injuries in runners.Am J Sports Med 1987, 15:168–171.
7. Viitasalo JT, Kvist M: Some biomechanical aspects of the foot and ankle in athletes with and without shin splints.Am J Sports Med 1983, 11:125–130.
8. Sommer HM, Vallentyne SW: Effect of foot posture on the incidence of medial tibial stress syndrome.Med Sci Sports Exerc 1995, 27:800–804.
9. Messier SP, Pittala KA: Etiologic factors associated with selected running injuries.Med Sci Sports Exerc 1988, 20:501–505.
10. Warren BL: Anatomical factors associated with predicting plantar fasciitis in long-distance runners.Med Sci Sports Exerc 1984, 16:60–63.
11. Warren BL, Jones CJ: Predicting plantar fasciitis in runners.Med Sci Sports Exerc 1987, 19:71–73.
12. Wen DY, Puffer JC, Schmalzried TP: Lower extremity alignment and risk of overuse injuries in runners.Med Sci Sports Exerc 1997, 29:1291–1298.
13. Kibler WB, Goldberg C, Chandler TJ: Functional biomechanical deficits in running athletes with plantar fasciitis.Am J Sports Med 1991, 19:66–71.
14. van Mechelen W, Hlobil H, Zijlstra WP, et al.: Is range of motion of the hip and ankle joint related to running injuries? A case control study.Int J Sports Med 1992, 13:605–610.
15. Messier SP, Davis SE, Curl WW, et al.: Etiologic factors associated with patellofemoral pain in runners.Med Sci Sports Exerc 1991, 23:1008–1015.
16. Moss RI, DeVita P, Dawson ML: A biomechanical analysis of patellofemoral stress syndrome.J Athl Train 1992, 27:64–69.
17. Caylor D, Fites R, Worrell TW: The relationship between quadriceps angle and anterior knee pain syndrome.J Orthop Sports Phys Ther 1993, 17:11–16.
18. Fairbank JC, Pynsent PB, van Poortvliet JA, Phillips H: Mechanical factors in the incidence of knee pain in adolescents and young adults.J Bone Joint Surg Br 1984, 66:685–693.
19. Galanty HL, Matthews C, Hergenroeder AC: Anterior knee pain in adolescents.Clin J Sport Med 1994, 4:176–181.
20. Dahle LK, Mueller M, Delitto A, Diamond JE: Visual assessment of foot type and relationship of foot type to lower extremity injury.J Orthop Sports Phys Ther 1991, 14:70–74.
21. Williams DS, McClay IS, Hamill J: Arch structure and injury patterns in runners.Clin Biomech 2001, 16:341–347.
22. Niemuth PE, Johnson RJ, Myers MJ, Thieman TJ: Hip muscle weakness and overuse injuries in recreational runners.Clin J Sport Med 2005, 15:14–21.
23. Jacobs SJ, Berson BL: Injuries to runners: a study of entrants to a 10,000 meter race.Am J Sports Med 1986, 14:151–155.
24. Marti B, Vader JP, Minder CE, Abelin T: On the epidemiology of running injuries: the 1984 Bern Grand-Prix study.Am J Sports Med 1988, 16:285–294.
25. Walter SD, Hart LE, McIntosh JM, Sutton JR: The Ontario cohort study of running-related injuries.Arch Intern Med 1989, 149:2561–2564.
26. Montgomery LC, Nelson FR, Norton JP, Deuster PA: Orthopedic history and examination in the etiology of overuse injuries.Med Sci Sports Exerc 1989, 21:237–243.
27. Cowan DN, Jones BH, Robinson JR: Foot morphologic characteristics and risk of exercise-related injury.Arch Fam Med 1993, 2:773–777.
28. Cowan DN, Jones BH, Frykman PN, et al.: Lower limb morphology and risk of overuse injury among male infantry trainees.Med Sci Sports Exerc 1996, 28:945–952.
29. Wen DY, Puffer JC, Schmalzried TP: Injuries in runners: a prospective study of alignment.Clin J Sport Med 1998, 8:187–194.
30. Giladi M, Milgrom C, Stein M, et al.: The low arch, a protective factor in stress fractures: a prospective study of 295 military recruits.Orthop Rev 1985, 14:709–712.
31. Kaufman KR, Brodine SK, Shaffer RA, et al.: The effect of foot structure and range of motion on musculoskeletal overuse injuries.Am J Sports Med 1999, 27:585–593.
32. Reinking MF, Hayes AM: Intrinsic factors associated with exercise-related leg pain in collegiate cross-country runners.Clin J Sport Med 2006, 16:10–14.
33. Reinking MF: Exercise-related leg pain in female collegiate athletes: the influence of intrinsic and extrinsic factors.Am J Sports Med 2006, 34:1500–1507.
34. Burns J, Keenan AM, Redmond A: Foot type and overuse injury in triathletes.J Am Podiatr Med Assoc 2005, 95:235–241.
35. Stefanyshyn DJ, Stergiou P, Lun VMY, et al.: Knee angular impulse as a predictor of patellofemoral pain in runners.Am J Sports Med 2006, 34:1844–1851.
36. Willems TM, De Clercq D, Delbaere K, et al.: A prospective study of gait related risk factors for exercise-related lower leg pain.Gait Posture 2006, 23:91–98.
37.• Willems TM, Vitvrouw E, De Cock A, De Clercq D: Gait-related risk factors for exercise-related lower-leg pain during shod running.Med Sci Sports Exerc 2007, 39:330–339.

Well-done, elaborate study that evaluates several potential risk factors with modern laboratory techniques.

38. Hreljac A, Marshall RN, Hume PA: Evaluation of lower extremity overuse injury potential in runners.Med Sci Sports Exerc 2000, 32:1635–1641.
39. Bennell K, Crossley K, Jayarajan J, et al.: Ground reaction forces and bone parameters in females with tibial stress fracture.Med Sci Sports Exerc 2004, 36:397–404.
40. Milner CE, Ferber R, Pollard CD, et al.: Biomechanical factors associated with tibial stress fracture in female runners.Med Sci Sports Exerc 2006, 38:323–328.
41. Milner CE, Davis IS, Hamill J: Free moment as a predictor of tibial stress fracture in distance runners.J Biomech 2006, 39:2819–2825.
42. Zifchock RA, Davis I, Hamill J: Kinetic asymmetry in female runners with and without retrospective tibial stress fractures.J Biomech 2006, 39:2792–2797.
43. Macera CA, Pate RR, Powell KE, et al.: Predicting lower-extremity injuries among habitual runners.Arch Intern Med 1989, 149:2565–2568.
44. Shaffer RA, Rauh MJ, Brodine SK, et al.: Predictors of stress fracture susceptibility in young female recruits.Am J Sports Med 2006, 34:108–115.
45. Myburgh KH, Hutchins J, Fataar AB, et al.: Low bone density is an etiologic factor for stress fractures in athletes.Ann Intern Med 1990, 113:754–759.
46. Rauh MJ, Macera CA, Trone DW, et al.: Epidemiology of stress fracture and lower-extremity overuse injury in female recruits.Med Sci Sports Exerc 2006, 38:1571–1577.
47. Bennell KL, Malcolm SA, Thomas SA, et al.: Risk factors for stress fractures in track and field athletes: a twelve-month prospective study.Am J Sports Med 1996, 24:810–818.
48. van Mechelen W, Hlobil H, Kemper HCG, et al.: Prevention of running injuries by warm-up, cool-down, and stretching exercises.Am J Sports Med 1993, 21:711–719.
49. Jones BH, Cowan DN, Tomlinson JP, et al.: Epidemiology of injuries associated with physical training among young men in the army.Med Sci Sports Exerc 1993, 25:197–203.
50. Powell KE, Kohl HW, Caspersen CJ, Blair SN: An epidemiological perspective on the causes of running injuries.Phys Sportsmed 1986, 14:100–114.
51. Meeuwisse WH: Assessing causation in sport injury: a multifactorial model.Clin J Sport Med 1994, 4:166–170.
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