Running skill develops substantially in preschool-age children (1). The first running stride cycle occurs approximately at 20 months of age, and 70%–75% of children achieve mastery of running level within preschool age (2,3). Although we can find extensive previous literature dedicated to development of walking (3–5), little attention has been paid to running, which is the most commonly reported specific physical activity in preschool children (6). As children develop during preschool age, their gait patterns also change due to physical growth, central nervous maturation, accrual of strength and time of participation in physical activity (7–9). Gait pattern development also has an association with morphological changes in toddlers (10,11).
Some important and widely discussed characteristics of gait pattern are the running footstrike pattern and sagittal plane joint angles at footstrike, which can consequently determine tissue loading of the lower limb (12,13). There are different approaches to classify or quantify the running footstrike patterns. Nominal classification differentiates runners as rearfoot, midfoot, and forefoot strikers or as rearfoot and non-rearfoot (14,15). Numerous studies have reported strong evidence that the running footstrike pattern is affected by different types of footwear in different ethnic and age populations (16–22). However, no universal recommendation exists regarding footwear or footstrike and their effect on overall incidence of running-related injuries (15,21,23).
Barefoot and footwear condition have also been investigated in relation to morphological differences of the foot structural properties in children. Some researchers found that the habitually barefoot children had a lower prevalence of flat foot (24) and a higher foot arch than habitually shod (25), which could be seen as beneficial from the health perspective. However, the long-term effect of footwear on development of children’s bodies or health-related outcomes in older individuals remains currently unknown, as there is very limited evidence (23,25,26).
People of all ages in economically developed countries have been wearing shoes for most of their lives (18,25,27). Previous studies suggested the importance of investigating the effect of footwear on running biomechanics in children (17,27). They found a similar acute effect of footwear on footstrike pattern as was reported by authors focusing on adult runners (18). The children’s tendency was to use a forefoot strike when they ran barefoot (17). However, Hollander et al. (17) focused on preadolescent children (older than 6 yr), and from our perspective, it is essential to focus on preschool children, the period in which running develops.
A recent study by Latorre-Román et al. (20) studied the effect of footwear on footstrike pattern during overground running in preschool children. They reported that 54% of preschool children displayed a non-rearfoot strike in the shod condition, which is far greater than in adult runners. The authors explained the higher prevalence of non-rearfoot strike pattern in preschoolers by morphological/biomechanical changes associated with growth or due to habit of wearing shoes (20). However, Latorre-Román et al. (20) did not account for the preschool age–related changes during this important growth period for running skill development.
In 2020, the more recent youth running consensus statement, the authors suggested that footstrike mechanics in youth runners seem to be influenced by footwear and age (22). However, previous studies have been based on research evidence concerning footstrike pattern in adolescents and children older than 6 yr. Footstrike pattern may be associated with injury risk in mature athletes, requiring an understanding of its development and contributing factors when young, especially in the crucial developmental period of preschool age. Therefore, the purpose of this study was to compare footstrike patterns among different age groups of preschool children running in different footwear conditions. We hypothesized that children in younger age groups would demonstrate fewer differences in footstrike pattern in different footwear conditions than children in older groups who would show greater differences.
An a priori sample size estimation power analysis was performed in G*Power. The experimental sample was estimated based on a key variable (sagittal ankle angle at footstrike) in different footwear conditions (barefoot–standard running shoes and uncushioned minimalist shoes–standard running shoes) from a previous study (28). To detect an effect of partial η2 = 0.168 with minimal statistical power 80% in a repeated-measures between-within ANOVA (four age groups, three footwear condition, α level = 0.05, nonsphericity correction = 1), G*Power indicated a total sample size of 44 participants. In the current cross-sectional study, 48 participants (12 participants per group) were recruited because of random counterbalanced order of footwear conditions in each group (six possible combinations of the order). The total sample consisted of 48 healthy children without any motor developmental disabilities and without any serious musculoskeletal injuries as reported by their parents. Exclusion criteria for this study included developmental coordination disorders or any lower limb abnormalities diagnosed by podiatrist or orthopedist (e.g., flatfoot, leg length discrepancy, genu varum, and genu valgum). Children between 3 and 6 yr of age were divided into four groups according to their age. No stratification for sex was required because a recent study showed no differences in footstrike pattern between preschool boys and girls (20). However, both sexes in each age group were included in the current study. All preschoolers were Caucasian and came from Moravian-Silesian Region in Czech Republic. All of them attended preprimary educational child care institution or first grade of primary education. Participants were recruited via social networks and flyers and consequently by snowball sampling method (e-mails, phone calls, friends, colleagues). Data collection began in November 2017 and was completed in August 2019. Ethical approval for this study was obtained from the ethical board of the University of Ostrava. All parents of the children signed a written informed consent form with the child’s assent before the start of the study.
Children were tested using the Movement Assessment Battery for Children—Second Edition (MABC-2) to disclose possible developmental coordination disorders. As an inclusion criterion, the limit for this study was set over the 15th percentile for a certain age according to Czech norms of the MABC-2. This limit was created by using the same statistical approach based on the original UK norms (29). Before biomechanical measurements were taken, all parents of the children returned the short Early Years Physical Activity Questionnaire (EY-PAQ). The aforementioned questionnaire measured the extent of the average daily sedentary and percent physically active time during a typical week in the last 4 wk before measurement (30). The parents also completed a six-item Barefoot Questionnaire (BFQ) assessing how often their children wore shoes in two different weather conditions (cold, warm) and environments (daycare/nursery/kindergarten, sports, in and around the house) on a 3-point Likert scale (very barely/almost never, 1 point; half of the time/often, 2 points; most of time/always, 3 points). Total score of BFQ could range from minimal 6 points (almost always barefoot) to maximal 18 points (almost always shod). Children were considered as habitually barefoot when they had 3 points at least in warm weather condition (always barefoot in and around the house, always in nursery or during sports) and habitually shod ≥4 points. This BFQ was modified for preschoolers in the current study (31). Both questionnaires (BFQ, EY PAQ) served as control variables because level of barefootness could directly affect footstrike pattern and level of physical activity showed an association with motor skill performance (9,16). In addition, the MABC-2 was used to control the level of motor competences by converting total standardized score to percentile for each age (29).
Body height and body mass as basic anthropometric parameters were measured using a stadiometer (In Body 370; Biospace, Seoul, South Korea) and body composition analyzer (Inbody 770; Biospace). Body mass index (BMI) was calculated by dividing body mass (in kilograms) by body height2 (in meters squared), and consequently, BMI percentile (Czech Republic norms) was assessed for each child according to their age (32).
The biomechanics laboratory in the Human Motion Diagnostic Centre at University of Ostrava consists of runway with 10 optoelectronic cameras sampling at 240 Hz (Oqus; Qualisys, Gothenburg, Sweden) and three force platforms (Kistler, Winterthur, Switzerland) synchronized with the camera system. Kinetic data were recorded by 0.9 × 0.9 m (9287CCAQ02) and two 0.6 × 0.4 m (9286AA and 9281CA) force platforms sampling at 1200 Hz. The force platforms were arranged as in Figure 1.
Retroreflective markers (6.4-mm diameter) and rigid clusters were placed on the body of each participant according to the marker placement suggested by Hamill and colleagues (33). Specifically, 18 markers were placed on the right lower limb, 4 on pelvis, 1 on the left greater trochanter, and 1 marker at the heel of left foot. Calibration markers on the right limb were placed on the lateral and medial malleoli, the medial and lateral femoral condyles, the greater trochanters, and on the shoe/foot over the first and fifth metatarsal heads. Tracking markers were attached on the pelvis (left and right posterior superior iliac spines and the left and right anterior superior iliac spines), the right thigh and shank (light-weight rigid plates each with four markers), a right foot/shoe (a triad of markers on the heel over the calcaneus or intact shoe). Standing calibrations were always recorded before each footwear condition (three times in total during whole protocol). Marker placement was performed by experienced expert in biomechanical 3D movement analysis.
Children were asked to perform a simple running game in three different footwear conditions. The footwear conditions barefoot (B), minimalist shoes (M), and standard running shoes (SRS) were presented to each group in a random counterbalanced order (17). The shod running conditions consisted of minimalist shoes (M) with 0-mm heel–forefoot offset (no drop) and scoring 96% on minimalist index (Leguano; Leguanito, Buchholz, Germany) and cushioned SRS with a minimalist index of 30% (Forta Run CF I and K; Adidas, Herzogenaurach, Germany). The minimalist index score ranges from 0% (least minimalist) to 100% (most minimalist) (34). Parents of children choose the appropriate shoe size to fit their child’s feet. The sizes of shoes used in the current study ranged from 24 to 35 EU (8K to 3.5 US).
A game with balls and a shuttle run was invented to maintain the external focus attention and motivation of child. The leg length of 4-yr-old children has previously been determined to be 88% of the 6-yr-old children (1). The distances on the runway for each age group were determined according to leg length, with distances increasing by 6%–8% for each year of age. The children performed shuffle running game on hard, flat, and nonslippery surface of runway with distance approximately 10, 11, 12, and 13 m from stage to stage according to age, respectively.
Before each footwear condition, each child was instructed about the continuous movement motor task based on running between two ends of a runway (to run inside the band created by blue cones) placing four tennis balls from the red to the green cones at the same end of the runway (during one running trial, only one ball was relocated). For familiarization and warm-up, four running trials were performed before the first condition in which the child ran following either the investigator or their parent. After familiarization, children were asked to run between two ends of runway by instruction “Run comfortable straight in the middle of the blue cones back and forth.” Each child ran from one end to another (from cones to cones with the balls) at their self-selected speed in each condition. The running trials were divided into two stages (1 stage = 8 runs), which were recorded (16 recorded runs in total per footwear condition). Each stage was started by instruction “Ready, set, go!” The completion time of one stage varied between 60 and 90 s (younger children had usually longer time because the task of relocation balls was sometimes more difficult for them). Between the first and second stages, a 3-min break was allowed to avoid fatigue followed by question “Do you feel tired?” If the answer was negative, then the second stage was started. All biomechanical data collection was completed during morning and afternoon hours (from 8 am to 6 pm).
Both kinematic and kinetic data were processed by using Qualisys Track Manager (Qualisys) and Visual 3D software (C-Motion, Germantown, MD). The threshold for the ground reaction forces was set at 15 N. Six successful trials were chosen and analyzed based on pelvis velocity (the closest six trials to the median). A successful running trial was determined when the entire right foot of the child contacted the force plate. A low-pass Butterworth filter using cutoff frequencies of 50 and 10 Hz was used for the kinetic and kinematic data, respectively.
The key dependent variables for this study included strike index and sagittal plane ankle angle at footstrike (15). As a secondary outcome for the current study, knee angle and hip angle also at footstrike were analyzed. To avoid the effects of running speed on the aforementioned dependent variables, we calculated a Froude number as control variable based on pelvic velocity and lower extremity length (35). We also calculated a coefficient of speed variation from six trials/footwear condition per child. Strike index was determined as the center of pressure location during the first initial foot contact with the force plate and reported as a percentage of foot length from the posterior calcaneus (14). For strike index, boundary zones were determined: 1) rearfoot–midfoot at 33.3% and 2) midfoot-forefoot at 66.6% of the shoe/foot length measured from the heel (13). Ankle angle was determined as relative position of foot to shank, knee angle as relative position of shank to thigh, and hip angle as relative position of thigh to pelvis during the first initial foot contact with force plate.
A one-way ANOVA was used to compare characteristics (height, weight, BMI, MABC-2, BFQ) of participants among the age groups. A two-way mixed ANOVA (footwear (3, within)–age groups (4, between)) was performed to determine possible footwear condition and age differences in strike index and ankle angle (footstrike pattern), knee angle, hip angle, pelvis velocity, Froude number, and coefficient of speed variation. If Mauchly’s sphericity tests were found to be significant and ε ≥ 0.75, then Huynt–Feldt correction was applied (36). If a significant interaction was found, then one-way repeated-measures (within factors) ANOVA was performed to test differences between three footwear conditions separately in each age. A one-way ANOVA was applied to reveal differences between age groups for each footwear condition (between factor). A Bonferroni adjustment was used for all pairwise comparisons in post hoc analysis. The α level was set at 0.05 for all statistical tests. Practical significance for main effect and interaction was assessed using the partial η2 and Cohen’s d for pairwise comparison. Effect size (ES) values represented by η2 were considered as small (0.01–0.06), medium (0.07–0.14), and large (>0.14) and by Cohen’s d as small (0.2–0.5), medium (0.5–0.8), and large (>0.8) (37). All statistical analyses were conducted in SPSS 24 (IBM, Armonk, NY).
There were significant differences in height and mass among age groups (P < 0.05; Table 1). No significant differences were found in BMI, BMI percentile (CZ norms), MABC-2 percentile (CZ norms), BFQ, EY-PAQ sedentary time, and EY-PAQ moderate-to-vigorous physical activity time among age groups (P ≥ 0.05).
TABLE 1 -
|BMI (percentile), CZ norms
|EY-PAQ ST, %
|EY-PAQ MVPAT, %
Data are presented as a mean (SD).
M/F, male/female; MVPAT, moderate-to-vigorous physical activity time; ST, sedentary time.
Table 2 presents means and SD of the control variables. To assess footstrike pattern, strike index and ankle angle were used as key dependent variables for this study (Fig. 2). For ankle angle, there was a significant interaction (footwear condition and age group; P = 0.030, η2 = 0.145). Pairwise comparisons showed statistical differences in ankle angle with large ES for 6-yr-old children between barefoot condition and standard running shoes (P = 0.005, d = 1.20) and also between minimalist and standard running shoes (P = 0.006, d = 1.09), respectively. There were no footwear condition differences in ankle angles in the younger age groups (3-, 4-, and 5-yr-old children; P > 0.05). Moreover, the pairwise comparison between age groups showed that ankle angle differs with large ES between 3- and 6-yr-old children when they ran barefoot (6-yr-old children had more plantar flexed ankle; P = 0.008, d = 1.24). No age differences were found in minimalist and standard running shoes.
TABLE 2 -
Control variables according to age groups and footwear conditions.
||3 yr old
||4 yr old
||5 yr old
||6 yr old
|Pelvis velocity*, m·s−1
|Froude number (1)
|Coefficient of speed variation, %
Data are presented as mean (SD). Post hoc tests for pairwise comparison between age groups across all footwear condition used in the first column (Significant differences: *3 × 6 yr).
No interaction was found for strike index (Table 3). There was only main effect within footwear condition across all age groups for strike index (P = 0.001, η2 = 0.337). Further pairwise comparison showed that preschool children in barefoot condition had a significantly higher value of strike index than in minimalist with small ES (P = 0.028, d = 0.28), but with large ES in comparison with standard running shoes (P = 0.001, d = 1.04). In addition, they also have a higher strike index in minimalist shoes compared with standard running shoes with medium ES (P = 0.001, d = 0.69).
TABLE 3 -
Two-way mixed ANOVA (3 × 4): tests of within-subject and between-subject effect.
|Strike index, %
|Ankle angle, °
|Knee angle, °
|Hip angle, °
|Pelvis velocity, m·s−1
|Froude number (1)
|Coefficient of speed variation, %
Data (P value) are represented as main effect or interaction. Bolded values represent significant difference between footwear conditions across age groups, significant difference between groups across conditions, and interactions (P < 0.05). η2 represents partial η2: trivial effects were considered having values <0.01; small, 0.01–0.06; medium, 0.07–0.14, and large, >0.14.
We found a significant interaction in knee angle (P = 0.002, η2 = 0.278; Fig. 3). Pairwise comparison showed that 4-yr-old children had more flexed knee in minimalist than in standard running shoes (P = 0.046, d = 0.73). In terms of age differences, it was found that 3-yr-old children had more flexed knee than 4-, 5-, and 6-yr-old in minimalist (P = 0.048, d = 0.98; P = 0.004, d = 1.50; P = 0.036, d = 1.23) and 4- and 5-yr-old in standard running shoes (P = 0.001, d = 1.49; P = 0.031, d = 1.05), respectively. No differences were found in hip angle.
There were differences between the age groups across footwear conditions in pelvis velocity (3 vs 6 yr) but no differences in Froude number, which is a dimensionless number representing the speed of running relative to leg length (Tables 2, 3). In addition, no differences were found in the coefficient of speed variation between footwear condition or among age groups.
The purpose of this study was to compare footstrike patterns among age groups of preschool children while running in different footwear conditions. We hypothesized that younger children would show fewer differences than older children in their footstrike patterns with different footwear. This hypothesis was confirmed because the youngest children (especially 3- and 4-yr-old) did not change their ankle angle at footstrike as much as older children depending on footwear condition. Footwear condition altered the footstrike patterns of preschool children. The main finding of our study is that the children’s footstrike patterns represented by ankle angle are different during running in response to changing footwear conditions at certain ages. If we look at preschool age as one specific life period or population, we can confirm that footwear affects the footstrike pattern during running. Previously, this has been seen in preschoolers (20) or in older populations such as primary (16,17), secondary school-age children, adolescents (16), or adults (18).
Preschool children in standard running shoes display footstrike pattern close to rearfoot–midfoot boundary, and it remains stable across age groups
Based on the current findings, we can conclude that preschoolers are not dominantly rearfoot strikers such as has been shown in older populations during running in standard running shoes (18); however, they are not dominantly forefoot strikers either. Our study showed that 94% preschool children displayed a rearfoot–midfoot strike pattern (54% rearfoot, 40% midfoot, 6% forefoot), with the average strike index close to the rearfoot–midfoot boundary zone (close to 33.3% SI). This seems to agree with Latorre-Román et al. (20) and Wei et al. (38). These authors reported a predominant rearfoot–midfoot strike in preschoolers (77% and 80%, respectively) (20,38). In addition, a study by Hollander et al. (16) showed that the prevalence of rearfoot strikers in habitually shod 6-yr-old children during shod running is 63% (16).
There are only a few studies that investigated age-related changes (differences) of running footstrike pattern in a shod condition with including preschoolers (38,39). Latorre-Román et al. (39) showed significantly fewer rearfoot strikers in preschoolers (47%) compared with 15- to 16-yr-old children (92%). Surprisingly, Wei et al. (38) did not find any differences in footstrike angle between preschoolers and adults. Moreover, in a latter study, the authors stated, as important limitations, a small sample that divided preschoolers into age subgroups (38).
To the best of our knowledge, no study exists comparing footstrike pattern in each year of the preschool age. Because running skill and the central nervous system develop in that period, running footstrike pattern may change from age 3 to 6 yr (1,2,7). Furthermore, the categorization of footstrike patterns in one rather wide age group (3–6 yr) may not be sufficiently insightful. Therefore, we analyzed footstrike pattern as continuously changing phenomenon (variable) in the multiple narrower age groups. Albeit, we can conclude that strike index and ankle angle did not change over preschool years during running in standard running shoes.
Preschool children in barefoot and minimalist shoes display a trend of shifting over age from midfoot to forefoot footstrike pattern
Prior literature has shown that 65% of preschool children are non-rearfoot strikers when they run barefoot (20). The present findings seem to be consistent with the previous research, which found that habitually shod 6-yr-old children are in 75% non-rearfoot strikers when they ran barefoot (16). The results of our study indicate that preschoolers in barefoot and minimalist footwear conditions, in average, run with a midfoot footstrike pattern. However, there is a trend that footstrike patterns shift from midfoot to forefoot during preschool age and percentage of forefoot strikers increased with age in both barefoot (3 yr, 25%; 4 yr, 33%; 5 yr, 33%; and 6 yr, 58%) and minimalist footwear condition (3 yr, 17%; 4 yr, 25%; 5 yr, 42%; and 6 yr, 58%). For better understanding of footstrike pattern development, we should look at their footstrike pattern and joint kinematics in different years of preschool age and in different footwear condition, concurrently.
Footstrike pattern and joint kinematics changed differently in certain age according to footwear condition
Generally, when 3-yr-old children run, footwear did not affect their joint (ankle, knee, hip) kinematics at footstrike. In the 4 yr of investigation in the current study, children’s knee angle significantly decreased in minimalist and standard running shoes and did not change until the end of preschool age. Furthermore, the knee is significantly more extended in standard running shoes than in minimalist shoes in 4-yr-old children. One can speculate that standard running shoes for 4-yr-old children could impose greater loading to lower limb joints indicated by rearfoot strike index, lower ankle plantar flexion, and lower flexion in the knee at footstrike (13). In 5-yr-old children, both barefoot and minimalist shoes should promote a more plantar flexed position compared with standard running shoes, although the results in 5-yr-old children were not statistically significant after the Bonferroni adjustment for multiple comparisons. On the other hand, Rothman (40) suggested that multiple comparisons for biological data are not reasonable or the least significant difference could be safely used for three treatments groups (40,41). Moreover, this trend was significant in 6-yr-old children in the current study.
From our perspective, there are three possible explanations of more posterior footstrike pattern represented by strike index and ankle angle (greater dorsiflexion position) in each footwear condition in 3- and 4-yr-old children compared with the older groups. First, as running development stages are delayed in comparison to walking, younger children may have transferred their rearfoot strike skill from more proficient stage of walking to elementary stage of running development (42,43). In addition, it has been shown that, with increasing speed of locomotion, footstrike pattern in children, adolescent, or adults shift from rearfoot to forefoot strike (1,42,44). Second, younger children are unable to adapt to the change in footwear because they were not as experienced in wearing shoes as were the older children and tended to display the same footstrike pattern in all footwear conditions. However, questionnaires used in this study showed that their habit of wearing shoes (all children were habitually shod) was similar as well as quantity of physical activity (movement behavior). Third, younger children do not yet have a capacity (strength and balance) for forefoot strike landing because of a less developed musculoskeletal and central nervous system. At that young age, the eccentric force of ankle plantar flexors and dynamic balance, necessary in forefoot running, are limited, and children would not have a sufficient capacity to land safely only on the ball of the foot and kinesthetic differentiation ability are not able to adapt to the different footwear conditions (7,8,45,46).
Although we hypothesized fewer differences in younger children because we expected them to be less experienced in using shoes and, concurrently, we expected 3- and 4-yr-old children to be forefoot strikers and not rearfoot strikers (20,27), we expected barefoot or minimalist shoes to be stable over preschool age with an increasing rearfoot strike from ages 3 to 6 yr in standard running shoes. However, the results of the current study showed an opposite trend. Therefore, we suggest that this trend may be due to the limitation of the central nervous and musculoskeletal systems in younger children to perform a forefoot strike. We can state that children did not differ in the level of motor competences represented by percentile for each age (all typically developing). From this perspective, it might be beneficial if children at least in the age 5 or 6 yr spend some time barefoot or in true minimalist shoes during running because this could lead to improvement of their balance ability, proprioception, and/or foot morphological characteristics (18,21,24,25,47–49).
When children begin to attend school, physical activity significantly declines (50). Understanding that running is the most frequent physical activity in preschool age and skill develops at this period of life (1,6,42), some recommendations regarding footwear would be very important for healthy development of preschoolers. From the results of our research, it is evident that it would be highly inappropriate if coaches or teachers would promote only one type of footstrike pattern as correct (e.g., forefoot strike). All who work with preschool children should respect age and footwear influence on footstrike patterns. Particularly, younger preschool-age children (3–4 yr) could be limited in their footstrike pattern running development perspective. For better understanding to changes in footstrike pattern, future research should adopt a longitudinal study design with focus on joint kinetics during stance phase and foot morphological changes.
Strengths and limitations of the study
The strength of the current study is that we used an appropriately designed movement task with a submaximal running velocity for preschool children adjusted for age and external focus of attention. Both a strength and a limitation could be observed using of uniform footwear (controlled footwear).
In terms of limitations, the main limitation of this study could be found in the cross-sectional design. Each child may not have had a previous experience with the standard running shoes. Although strike index is considered as gold standard for assessing footstrike pattern in adults (15), there seems to be no study in the literature using this method in children. Particularly in preschoolers, it could potentially bring about some difficulties with accuracy in the center of pressure assessment at footstrike because of the small feet sizes and lower body mass of children. In addition, the current study focused on only discrete kinematic parameters (footstrike at initial contact) and did not include the analysis of ground reaction forces.
Footstrike pattern may be affected by a child’s age and the use of different types of footwear in habitually shod preschool children. When children get older, their footstrike pattern may use a more non-rearfoot pattern with a more plantar flexed ankle during barefoot and minimalist shoe running. On the contrary, the footstrike pattern did not change over age when they wore standard running shoes. Coaches and teachers should be very careful with their footstrike pattern recommendations in preschool age because children may react differently to changing footwear condition at these ages.
This research was cofounded by Czech Ministry of Education, Youth and Sport and European Union structural funds by the grant “Healthy Aging in Industrial Environment” (program 4 HAIE CZ.02.1.01/0.0/0.0/16_019/0000798) and student’s grant (SGS14/PdF/2017-18), internal funding of the Faculty of Education at University of Ostrava. We would also like to thank Matthew Zimmermann for his helpful advice in the writing of this manuscript.
The authors declare that the results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. The authors declare no conflicts of interest. The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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