Which Factors Influence Running Gait in Children and Adolescents? A Narrative Review

ent years, running has dramatically increased in children and adolescents, creating a need for a better understanding of running gait in this population; however, research on this topic is still limited. During childhood and adolescence multiple factors exist that likely in uence and shape a child's running mechanics and contribute to the high variability in running patterns. The aim of this narrative review was to gather together and assess the current evidence on the different factors that in uence running gait throughout youth development. Factors were classi ed as organismic, environmental, or task-related. Age, body mass and composition, and leg length were the most researched factors, and all evidence was in favour of an impact on running gait. Sex, training, and footwear were also extensively researched; however, whereas the ndings concerning footwear were all in support of an impact on running gait, those concerning sex and training were inconsistent. The remaining factors were moderately researched with the exception of strength,

length were the most researched factors, and all evidence was in favour of an impact on running gait. Sex, training, and footwear were also extensively researched; however, whereas the ndings concerning footwear were all in support of an impact on running gait, those concerning sex and training were inconsistent. The remaining factors were moderately researched with the exception of strength, perceived exertion, and running history for which evidence was particularly limited. Nevertheless, all were in support of an impact on running gait. Running gait is multifactorial and many of the factors discussed are likely interdependent. Caution should therefore be taken when interpreting the effects of different factors in isolation. Keywords:biomechanics; running; growth; maturation; children; adolescents 1. Introduction Over the last few decades participation in running as a sport has greatly increased in children and adolescents. Running distances in this population have also increased with an exponential rise in marathon and even ultramarathon participation in youth (under 19 years of age) [1]. Although exercise and physical activity is of great importance for a healthy development, there is a concern that increased running will result in an increase in running-related injuries [2]. In particular, the increase in running distance could present a health risk for growth and development as the bone–muscle–tendon complex is still immature [3]. Children's increased participation in running calls for further investigation of their running gait as it is likely in uenced by a multitude of different factors during childhood and adolescence. These factors may be intrinsic to individuals, such as genetics, growth, maturation, and sex, or of an extrinsic nature such as footwear or surfaces. An understanding of how these factors in uence running gait is essential in order to know how children's gait will change under a variety of conditions and to be prepared to make informed decisions that will bene t development and minimise injury risk. Running gait can be de ned as the movement patterns and mechanical strategies that individuals adopt in order to run. It is generally studied by measuring kinematic variables (joint or segment angles), kinetic variables (ground reaction forces, joint forces Int.

variety of conditions and to be prepared to make informed decisions that will bene t development and minimise injury risk. Running gait can be de ned as the movement patterns and mechanical strategies that individuals adopt in order to run. It is generally studied by measuring kinematic variables (joint or segment angles), kinetic variables (ground reaction forces, joint forces Int. J. Environ. Res. Public Health2023,20, 4621.

Int. J. Environ. Res. Public Health2023,20, 4621 2 of 17 and moments), and spatiotemporal variables (step rate, step length, etc). Amongst healthy individuals there is a high variability in running patterns, and it is recognised that runners can be separated into biomechanically distinct groups [4]. This high variability is likely a result of different gait strategies; however, the explanation as to why individuals employ different strategies is complex and multifactorial. Running gait has been well studied in adults [5–7], and a recent review has even proposed a simple model enabling the categorisation into one of ve different running styles by identi cation of certain key characteristics that differentiate between running patterns [8]. There is, however, a paucity of research examining running biomechanics in children and adolescents. Differences in running gait between healthy and pathological children have been investigated [9–11], but few studies have explained the reasons for changes occurring in running gait in typically developing youth. To date, the existing studies seem to have focused on describing the mechanics behind the developmental process of running[12–17] as opposed to identifying the factors responsible for the changes in running patterns during growth and maturation. It is likely that the in uence of these factors contributes to the shaping of an individual's unique running style. Furthermore, knowledge of these factors and their effects could contribute to a better understanding of the high variability in running patterns and could also provide information on potential risk factors for running- related injuries. The aim of this narrative review was to examine the existing literature and critically assess the key information concerning the factors that in uence running gait during childhood and adolescence. In order to group factors together in a consistent manner, the Grand Uni ed Theory of sports performance proposed by Glazier [18] was used. The proposed model stipulates that patterns of coordination and control, re ected here by running gait, are in uenced by organismic, environmental, and task-related factors and their interactions. Organismic factors can be described as physical, physiological, morphological, or psychological; environmental factors are external to the movement system; and task-related factors

Theory of sports performance proposed by Glazier [18] was used. The proposed model stipulates that patterns of coordination and control, re ected here by running gait, are in uenced by organismic, environmental, and task-related factors and their interactions. Organismic factors can be described as physical, physiological, morphological, or psychological; environmental factors are external to the movement system; and task-related factors are speci c to the task being performed. The factors discussed hereafter have therefore been classi ed in this manner. 2. Organismic Factors 2.1. Genetics An in-depth review of the genetics of sport and exercise is not the aim of the current analysis; however, a few areas must be addressed on this topic as many of the ensuing factors owe a certain proportion of their effects to an individual's genetic makeup. Indeed, genes have been said to have an important part to play in the explanation of individual variation in the growth and development of children and adolescents [19]. Height, weight, body size, and even strength all have a certain amount of heritability [20] and are therefore genetically predetermined to a certain extent. Of course, many of these variables, such as body mass and strength, are also susceptible to behavioural in uences including dietary intake, energy expenditure, and physical activity. Furthermore, the timing and rate of both growth and maturation are also subject to a strong genetic in uence [20]. It is therefore important to bear in mind that certain factors in uencing the development of running gait are indirectly controlled and determined by genetic expression. However, to date, no studies exist regarding the in uence of genetics on youth running gait, probably due to the need for very large cohorts and both expensive and complex analyses. 2.2. Biological Age Age has an indirect effect on running gait, particularly during childhood and adoles- cence. With advances in time there are multiple changes in a child's characteristics that subsequently in uence their running pattern. Indeed, numerous studies have reported differences in running gait variables at different chronological ages [15,21–26]. However, a more insightful analysis can be obtained by taking biological age

Age has an indirect effect on running gait, particularly during childhood and adoles- cence. With advances in time there are multiple changes in a child's characteristics that subsequently in uence their running pattern. Indeed, numerous studies have reported differences in running gait variables at different chronological ages [15,21–26]. However, a more insightful analysis can be obtained by taking biological age into account. Biological age refers to both growth and maturity status at a given chronological age [20]. With increasing biological age changes in bone, tendon, and muscle growth may impact running

Int. J. Environ. Res. Public Health2023,20, 4621 3 of 17 gait in children and adolescents [27]. Indeed, these changes will affect factors, such as body mass, body composition, leg length, and strength, with subsequent effects on running gait. It is also important to bear in mind that the timing and rate of growth and maturation vary considerably among individuals, leading to differences in gait regardless of chronological age [12]. Therefore, it is more relevant to assess biological age when studying running gait in children and adolescents as most intrinsic factors that in uence running gait are in fact dependent on biological age. Advances in growth and maturity (i.e., biological age) also lead to an increase in sex differences due to the associated changes in anthropometrics and body composition. The timing of these differences between boys and girls are also subject to the timing and rate of growth and maturation and in general do not occur at similar chronological ages. 2.3. Sex Throughout childhood and adolescence, multiple sex differences appear leading to differences in running gait between boys and girls. Indeed, from early to late childhood, sex differences in both step rate and step length are negligible as leg length between girls and boys remains similar [28,29]. The fact that peak height velocity (PHV) occurs earlier in girls is likely a contributing factor. However, from the onset of PHV in boys, their leg length surpasses that of girls [28] and contrasts in spatiotemporal parameters become increasingly apparent, especially during adolescence [30]. For more information concerning the in uence of leg length on running gait see 2.5. Prior to female puberty, boys and girls of similar chronological age are also similar in body mass, body composition, and strength [31]. However, from the onset of puberty, sex differences occur, primarily attributed to differences in the levels of circulating hormones and eventually leading to increased strength in adolescent boys compared with adolescent girls [32]. These sex differences in body composition affect running kinetics during sprint- ing, resulting in greater mass-speci c force production in boys, not only due to greater gains in muscle mass

onset of puberty, sex differences occur, primarily attributed to differences in the levels of circulating hormones and eventually leading to increased strength in adolescent boys compared with adolescent girls [32]. These sex differences in body composition affect running kinetics during sprint- ing, resulting in greater mass-speci c force production in boys, not only due to greater gains in muscle mass compared with girls but also due to the higher gains in body fat in the latter [25,26]. These contrasts in mass-speci c force production also result in spatiotemporal differences at maximal velocity, notably greater step length in boys [25,26]. At submaximal speeds, sex differences in relative force production and the in uence on spatiotemporal parameters is not apparent, or at least does not seem to have been investigated, in children and adolescents. Sex differences in kinematic variables during running have not been demonstrated in children but do exist between boys and girls during jumping tasks [33,34]. Furthermore, dif- ferences have been demonstrated during running between adult men and women[35–37] . It is likely that kinematic differences between sexes accompany the increasingly appar- ent differences in body size, composition, and strength previously reported [31,38,39]. However, from exactly what age or development phase running kinematics start to differ signi cantly between boy and girls is uncertain and could be joint speci c. Other sex differences that could lead to differences in running gait include those concerning ankle joint range of motion (ROM). Indeed, a greater ROM about the ankle could lead to sex differences in foot strike pattern (FSP). Grimston et al. [40] reported that ankle ROM at rest was generally greater in girls compared with boys aged 9 to 20 years. However, a causal relationship between ankle joint ROM at rest and FSP during running has not been demonstrated. Moreover, to date, multiple studies have indicated no differences in FSP between sexes throughout youth [22,41,42]. Many of the sex differences mentioned previously can in fact be attributed to differ- ences in size as opposed to sex differences per se after appropriate normalisation or scaling. It is therefore likely that most of

and FSP during running has not been demonstrated. Moreover, to date, multiple studies have indicated no differences in FSP between sexes throughout youth [22,41,42]. Many of the sex differences mentioned previously can in fact be attributed to differ- ences in size as opposed to sex differences per se after appropriate normalisation or scaling. It is therefore likely that most of these differences become apparent from puberty onwards. However, in adults certain differences in joint motion (ankle, pelvis, and torso) between men and women have been shown to persist even after normalisation, suggesting that some sex differences are not simply size related [35].

Int. J. Environ. Res. Public Health2023,20, 4621 4 of 17 2.4. Body Mass and Composition Body mass has been reported to affect running gait in children. At moderate speeds, heavier adolescents tend to have lower step rates and longer step lengths compared with lighter individuals [30]. At maximal speeds, greater mass is also associated with lower step rates; it is suggested that amongst other factors this could be due to additional mass leading to increased contact times [23,24]. The increases in contact times with additional mass have been observed to stabilize around and after PHV but do not naturally decrease with further maturation [23,24]. When considering body mass, the ratio of lean mass to fat mass should also be taken into account. Indeed, increases in body mass due to increases in muscle mass are likely to result in greater step lengths when sprinting as a result of greater force production [25,43]. On the contrary, increases in body mass due to greater levels of fat mass have been hypothesised to have a negative effect on mass-speci c force production, leading to decreases in step length and even greater increases in contact time [24,25,43]. Increases in both muscle and fat mass occur as individuals advance in maturity, with a marked increase observed at the onset of puberty in healthy children. However, abnormal increases in fat mass in pre- and post-pubertal children can also arise in cases of obesity. Overweight prepubescent children have been reported to display signi cantly greater contact times and step lengths when running at low speeds compared with normal weight children [44]. Children with this condition also manifest larger contact areas and higher peak pressure at multiple foot regions compared with healthy children [44,45]. Furthermore, the changes in running patterns due to the bearing of excessive weight is thought to predispose these individuals to injury (overuse or musculoskeletal) and exercise-related pain [46,47]. Body mass clearly has an in uence on running gait in children, but the effects differ with body composition. Multiple studies have investigated these effects at maximal velocity, but there appears to be a lack of studies

patterns due to the bearing of excessive weight is thought to predispose these individuals to injury (overuse or musculoskeletal) and exercise-related pain [46,47]. Body mass clearly has an in uence on running gait in children, but the effects differ with body composition. Multiple studies have investigated these effects at maximal velocity, but there appears to be a lack of studies concerning the effects observed at low to moderate speeds and in healthy and overweight youth. 2.5. Leg Length One of the main anthropometric parameters affecting running gait during growth is leg length. In general, taller children display lower step rates and longer step lengths than those that are shorter [15,30]. Independent of running velocity, increases in leg length during growth affect spatiotemporal variables such as step rate and step length. Increases in leg length lead to a decrease in step rate and a corresponding increase in step length [15]. However, the effect of leg length on step rate is not always straightforward. When sprinting, step rate or cadence has been observed to increase in early childhood, decrease during the years preceding PHV, and nally stabilise around and post PHV despite continual increases in leg length throughout this entire period [23,25,43,48]. It has been reported that the multiple changes in sprinting cadence with increasing maturity are associated with the phenomenon of “adolescent awkwardness” [23,25,43]. This phenomenon has been described as a temporary disruption of motor coordination during periods of rapid growth and is said to occur primarily in males [20,49]. During this period, step rate during sprinting decreases and contact time increases, provoking a certain delay in maximal speed development [23,25]. Although many of the factors accounting for adolescent awkwardness are not apparent, recent research suggests that the rapid changes in body proportions (e.g., somatotype) during the adolescent growth spurt could disturb proprioceptive abilities leading to the changes observed in spatiotemporal variables [50]. Adolescent awkwardness may also in uence running gait at submaximal speeds, but results only seem to have been reported in relation to sprinting. In adults, voluntary increases in cadence reduced foot strike angle (FSA) and even led to

body proportions (e.g., somatotype) during the adolescent growth spurt could disturb proprioceptive abilities leading to the changes observed in spatiotemporal variables [50]. Adolescent awkwardness may also in uence running gait at submaximal speeds, but results only seem to have been reported in relation to sprinting. In adults, voluntary increases in cadence reduced foot strike angle (FSA) and even led to changes from rearfoot strike (RFS) to mid or forefoot strike (MFS or FFS) [51]. In growing children, the natural decrease in step rate due to increasing leg length could therefore provoke an increase in FSA and a progressive shift from FFS to RFS. Indeed, this could partially explain the results observed in the study by Latorre Rom¡n et al. [22] in which the

The review examines various factors affecting running gait in youth.