**1. Introduction**

The injury rate is high in children and adolescents participating in sports activities [1–4]. Radelet et al. [4] reported that the injury rate ranged from 1.0 to 2.3 per 100 athlete exposures in 7 to 13-year-old children in community sports. In 12 to 15-yearold students, the injury rate in sports activities was 60.85 injuries/100 students/year [1]. Compared to adults, children and adolescents are more vulnerable to sports injuries due to the stage of maturation in growth cartilage and the musculoskeletal system [4,5]. Both acute and overuse injuries in growth cartilage may result in the permanent alteration of bone and muscle growth, which may have a long-term impact such as disability in later life if the injury is not properly treated [6,7].

A number of survey studies have investigated sports injury and related risk factors in children and adolescents [1–4,8,9], demonstrating that the most common sport injuries occur to the lower limbs, with the ankle and knee the most frequently injured locations [1,2,8].

**Citation:** Guan, Y.; Bredin, S.S.D.; Taunton, J.; Jiang, Q.; Wu, N.; Li, Y.; Warburton, D.E.R. Risk Factors for Non-Contact Lower-Limb Injury: A Retrospective Survey in Pediatric-Age Athletes. *J. Clin. Med.* **2021**, *10*, 3171. https://doi.org/ 10.3390/jcm10143171

Academic Editors: Emmanuel Andrès and David Rodríguez-Sanz

Received: 9 June 2021 Accepted: 16 July 2021 Published: 19 July 2021

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Although contact injuries account for the majority of sport injuries [8,10], some non-contact injuries (e.g., ankle sprains and muscle strains) are found to be the most common injuries across sports [2,10]. Further, non-contact injuries are often associated with modifiable risk factors such as neuromuscular disorders, overtraining, and being unfit [11]. However, there is a lack of survey-based research investigating the risk factors for non-contact lower-limb injury in pediatric-age athletes. This is an important cohort to focus research on, especially considering that children as young as 6 years of age (or even younger) engage in competitive sport training [12].

Regardless of the mechanism (contact vs. non-contact) of injury, studies have reported a range of risk factors for sports injury in children and adolescents, including training duration [8], impact [4,8], age [13], sex [13], previous injury [2,13], amount of physical activity [3], and stage of maturity [3]. To date, there is a lack of research examining the potential effects of lateral dominance in sport (laterally dominant vs. non-laterally dominant sport) on the risk of injury in the lower limbs. Laterally dominant sports (or asymmetric sports, e.g., fencing, badminton, and soccer) are characterized by the two sides of the lower limbs frequently performing in different patterns [14] or performing movements that are directed towards one side [15]. For example, in the lunge movement, which is frequently performed in fencing, tennis, and badminton, the dominant leg performs as the leading leg while the non-dominant leg performs as the supporting leg [14]. This asymmetric movement may cause lateral dominance and relative adaptions of the dominant leg in the long-term [14]. In contrast, non-laterally dominant sports (or symmetric sports, e.g., running, swimming) are characterized by both sides of the lower limbs equally involved in the movements, requiring equal mastery of techniques with the dominant and non-dominant leg [15]. Compared with non-laterally dominant sports, long-term training in laterally dominant sports may cause greater inter-limb asymmetry which has been associated with an increased risk of lower-limb injury [16,17]. To date, there is no evidence available in the literature reporting the injury rate between athletes specialized in laterally dominant vs. non-laterally dominant sports. Therefore, it is unknown empirically whether the laterally dominant moving pattern in laterally dominant sports will increase the risk of lower-limb injury.

The purpose of this study was to examine the effects of lateral dominance in sports (laterally dominant vs. non-laterally dominant sports) on non-contact lower-limb injury, and to identify risk factors of non-contact lower-limb injury in pediatric-age athletes. It was hypothesized that pediatric-age athletes specialized in laterally dominant sports would sustain a greater risk of non-contact lower-limb injury compared to those specialized in non-laterally dominant sports.

#### **2. Method**

#### *2.1. Participants*

Parents and/or legal guardians of pediatric-age athletes training in sports clubs and/or school teams were eligible to participate in the online survey, if the athletes met the following criteria: (1) were between the ages of 6 and 17 years, (2) specialized in only one sport, and (3) maintained regular training in the preceding 12 months. The levels of competition of the athletes were not limited. Informed consent was received upon completion and submission of the survey. The investigation received approval from, and was executed in exact accordance with, the ethical guidelines set forth by the University of British Columbia's Clinical Research Ethics Board and the Shandong Sport University's Human Ethics Committee for research involving human participants according to the standards established by the Declaration of Helsinki.

#### *2.2. Questionnaire*

The content of the questionnaire (Supplementary File) was developed based on previous surveys [4,5]. The parents and/or legal guardians were asked to answer 10 questions, reporting their child's age (y), sex, sport, dominant leg (right, left leg), length of training (y), training frequency (1, 2, 3, 4, 5 or more sessions/wk), training intensity (low, moderate, high), whether their children suffered any non-contact lower-limb injury (during training or competition) causing time loss for at least one day from participation in sports activities during the preceding 12 months, and the location and type of the injury. The question types included fill-in-the-blank questions (age, sex, sport, length of training), single-choice questions (dominant leg, training frequency, training intensity, presence or absence of injury), and multiple-choice questions (location and type of injury). A day lost due to injury was any day (including the day in which the participant was injured) where the participant was not permitted to or not able to participate in sporting activities in an unrestricted manner [18]. Participants were not asked about lower-limb injuries that occurred at a time other than during training or competition, or were caused by contact with equipment or another player. If the athlete sustained more than one injury during the preceding 12 months, participants were asked to report all the injuries [19]. Survey development included examination of the validity of the content. The questionnaire was reviewed by a sports medicine researcher, an athletic trainer, a physical education teacher, a sport psychologist, and three professors in the area of kinesiology. A pilot test was conducted in a taekwondo club before the actual large-scale survey was disseminated.
