Pathare, Neeti PT, PhD; Haskvitz, Esther M. PT, PhD, ATC; Selleck, Marjane PT, DPT, MS, PCS
In the United States, more than 23 million children are either overweight (OW) or obese, placing them at increased risk for serious health conditions such as knee osteoarthritis, heart disease, and type 2 diabetes. For children, 6 to 11 years of age, the rate of obesity has quadrupled in the past 3 decades,1 with an estimated 30% of children who are OW or at risk of being OW.2 Few children and adolescents get the 60 minutes of moderate to vigorous physical activity per day, recommended by the Centers for Disease Control and Prevention, for healthy growth and development.3 Essential to engaging in physical activity are weight-bearing activities. Children who are OW/obese may have altered biomechanics during weight-bearing activities.4–7 These alterations may contribute to their difficulty performing exercise and negatively affect their desire to exercise.
Being OW/obese has been linked to various changes in musculoskeletal structures and mobility. Studies have proposed various spatiotemporal differences in the gait pattern of children who are obese.4–7 Specifically, children, 8 to 13 years of age, who are obese have a longer gait cycle duration and stance phase, decreased cadence and gait velocity,5,6 and use more mechanical energy compared with children of healthy weight (HW).8 Also, children with obesity may experience foot discomfort during weight-bearing activities.9,10 Gushue et al4 further report that children who are obese have abnormal knee loading during walking, which can increase the risk of developing osteoarthritis. These findings suggest that children who are obese redistribute forces, which can predispose them to greater soft tissue and skeletal injury with repetitive loading tasks. This may negatively affect their desire to engage in physical activity. Despite various studies of the gait pattern of children who are obese, most of the previous work included very small sample sizes and some conflicting findings. Moreover, literature is lacking on young children (younger than 9 years) who are OW/obese.
Apart from gait disturbances, being obese may have a detrimental effect on postural balance.11,12 Using standardized field tests and other static and dynamic tasks, obesity has been shown to lead to significant constraints on adolescents' (12-18 years) functional balance.11 Other studies provide evidence that children who are OW/obese might be at greater risk in tasks that require a narrow base of support, such as the 1 leg stance test (OLST)13,14 and sit to stand.12,14 Limited research exists on balance in young children who are OW/obese.
Muscle strength is intricately linked to functional tasks. Handgrip strength is regarded as one of the most reliable clinical measures of strength and an important indicator of general health.15 It is considered to closely represent total body strength.16,17 An understanding of differences in muscular strength in children who are OW/obese and HW is also essential when designing safe and effective interventions for children who are OW/obese. This emphasizes the need to further elucidate whether balance and strength differ in young children who are OW/obese.
Childhood obesity is associated with lifelong health concerns, which are a financial burden to the individual as well as to the health care system.18 Children who are OW/obese may exhibit limitations in their activities as well as restrictions in their participation levels that are a direct result of the impairments in body structures and functions as a consequence of being OW/obese. Young children who are OW may be unable to fully engage in physical activities in school physical education programs and after-school recreational programs. Some of this may be readily preventable by early identification and intervention. Therefore, it is imperative to act when children are younger. To date, very limited data could be found on the effect of being OW/obese on gait, balance, and strength in young children. Clearly these data are needed.
In summary, the enormity of the problem and limited research leads to an immediate need to answer key questions related to gait, balance, strength, and physical activity in young children who are OW/obese. Valid and reliable measurements, which are feasible, portable, and can be easily administered in a school setting, should be used. Therefore, the primary purpose of this study was to determine the differences in gait, balance, and muscle strength between young children, 5 to 9 years of age, who were classified as HW and OW/obese. A secondary purpose was to characterize the socioeconomic status of young children, 5 to 9 years of age, who were classified as HW and OW/obese.
We conducted a cross-sectional study in which 70 children in kindergarten to grade 3 and their parents/guardians participated. Convenience sampling was used. Height and weight (Health-O-Meter Professional Dial Scale, Sunbeam Products, Inc, Boca Raton, Florida), without shoes, were measured to calculate the body mass index (BMI) for each child. BMI was calculated using the Centers for Disease Control and Prevention's BMI Percentile Calculator for Child and Teen.19 Overweight/obesity was determined on the basis of BMI. Children with a BMI of equal to or greater than the 85th percentile were classified as OW/obese, and those with a BMI between the 5th percentile and the 85th percentile were classified as HW.20 Demographic and anthropometric characteristics of the participants are presented in Table 1.
Instrumentation/Tests and Measures
Spatiotemporal gait data were collected using a GAITRite portable walkway system (CIR Systems, Inc, Sparta, New Jersey). The GAITRite is an electronic walkway with embedded pressure-activated sensors along one side that capture temporal and spatial parameters of gait.21 Specifically, the variables measured in this study included velocity (cm/s), cadence (steps per minute), stride length (cm), heel-to-heel base of support (cm), and stance cycle (%). The GAITRite has been shown to have good reliability for measuring step length (interclass correlation coefficient [ICC] = 0.99), stride length (ICC = 0.99), stance time (ICC = 0.92), and velocity (ICC = 0.99) in healthy adults, aged 21 to 71 years, with no underlying neurological or orthopedic condition.22,23
Balance was measured using the OLST in the eyes-open condition. This is a widely used clinical tool with good reliability and validity to measure balance in children.24,25
Handgrip strength is an objective method of evaluation of upper extremity strength.26 Handgrip strength was measured with a JAMAR handgrip dynamometer (Sammons Preston Rolyan, Chicago, IL). The dynamometer is regarded as a reliable and valid instrument to measure the grip strength of children.27,28 The Just Jump mat (Probotics, Inc, Huntsville, Alabama), a valid and reliable measure of vertical jump (VJ) height,29 was used as a measure of lower body explosive strength.
A self-reported questionnaire was designed to elicit information on parent/guardian's socioeconomic status and health status (Appendix, Supplemental Digital Content 1, http://links.lww.com/PPT/A43). This study was approved by the Institutional Review Board at The Sage Colleges. Each child provided assent and the parent/guardian provided written consent for the child to participate in the study.
To examine gait, each participant was asked to walk at a comfortable and typical pace on the GaitRite walkway. Three trials of walking on the GaitRite mat were recorded for each child. Participants were given detailed instructions to promote consistency and reproducibility.
For balance, each child was asked to perform the OLST in the eyes-open condition with hands placed on the hips. The criteria to stop timing included movement of the supporting foot, hooking the free leg behind the supporting leg, dropping the free leg below 45° of knee flexion, moving arms from the start position, tilting the trunk, or looking away from the visual target.
For the handgrip dynamometer, hand dominance was first determined by asking the child to pick up a coin. Hand dominance was confirmed by asking the child whether the hand used to pick up the coin was the same hand used to write or draw. Each child was seated on a straight back chair with feet flat on the floor, shoulders adducted and neutrally rotated, the elbow flexed to 90°, and the forearm in the neutral position. The handle was adjusted so it rested in the middle of the 4 fingers. Following a demonstration by the researcher, each child performed 3 trials on each hand alternating between sides with 1 minute between each trial. For each trial, the child was instructed, “Squeeze as hard as you can … harder … harder … relax.”
For the VJ, each child was instructed to stand with both feet shoulder width apart on the mat. Again, a researcher demonstrated the test and then the child was asked to jump straight up as high as he or she could, without tucking his or her legs, and land with both feet on the mat. The VJ height (in cm) was recorded as an average of 3 trials.
All tests were administered in a randomized order. Also, measures were taken to ensure interrater reliability by providing standardized instructions and adequate training to the researchers. When possible, the same researcher(s) collected data for a given test and measure on all children.
Descriptive statistics were calculated for each variable. To examine differences between children classified as HW and OW/obese, independent t tests and Mann-Whitney U tests (for categorical data) were used. An analysis of covariance (ANCOVA) was used to evaluate differences in stride length while controlling for leg length of each child. All analyses performed were 2-tailed, with the α level set at 0.05. Statistical analyses were performed using the Statistical Package for Social Sciences for Windows (version 19.0; SPSS Inc, Chicago, IL).
Descriptive characteristics of the participants are presented in Table 1. The entire sample was 64.8% white, 24.2% black, 9.2% Hispanic, and 1.8% other ethnic groups. No significant differences in racial makeup or other measures of socioeconomic status were noted (Table 2).
During walking, significant differences in heel-to-heel base of support distance as well as left and right step and stride length were noted between the 2 groups (Table 3). Further analysis with an ANCOVA, however, revealed no significant differences in step or stride length when leg length was controlled (Table 3). All other spatiotemporal gait parameters of velocity, cadence, percent single and double support stance and left/right percent stance of the gait cycle were not significantly different between the 2 groups (Table 3).
Being OW/obese resulted in poorer performance on the OLST (HW 14.0 ± 7.2 seconds vs OW/obese 8.3 ± 4.2 seconds; P < .05).
Lower Extremity Explosive Strength
Lower extremity explosive strength, as measured by VJ height, was lower in the children who were OW/obese than in their counterparts (HW 30.1 ± 4.5 cm vs OW/obese 25.4 ± 6.5 cm; P < .01).
Upper Extremity Strength
With regard to muscle strength, both groups had similar values for handgrip strength (dominant hand: HW 11.2 ± 3.9 kg vs OW/obese 12.1 ± 3.1 kg, P > .05; nondominant hand: HW 10.7 ± 3.7 kg vs OW/obese 11.3 ± 3.1 kg, P > .05).
The aim of this study was to examine differences in measures of physical performance between young children classified as OW/obese and HW. The findings of this study indicate that differences in physical performance in children who are OW/obese and HW exist primarily in their heel-to-heel base of support during walking, performance in the OLST, and lower extremity explosive strength.
In this study, we did not detect any significant links between being OW/obese and ethnicity, socioeconomic status, and parent's education/health status. A recent review on the disparities observed in obesity prevalence among various groups nationally shows these differences to be complex and more importantly to have changed over time.30 The commonly held belief of higher prevalence of obesity in minority groups and those with lower socioeconomic status is intricate because of the interactions of various factors.30 Studies conducted on socioeconomic status reveal that the influence of this factor has attenuated over the last decade.30 Also, low socioeconomic status is associated with obesity only among certain population groups.30
To date, the published literature on the effects of obesity on the spatiotemporal parameters of gait, balance, and measures of strength in children is primarily limited to children aged 8 years and older.4,7,31,32 Furthermore, many of these studies compared children who were HW with those who were obese (BMI > 95th percentile) and did not include children who were OW (BMI > 85th and <95th percentile).
This study showed significant differences with respect to the base of support during gait with an increased heel-to-heel width in children in the OW/obese group compared with the children in the HW group. This is consistent with prior research on step width/base of support in both adults33 and children and adolescents (8-16 years).34,35 The explanations proposed to account for increased base of support include increased adipose tissue in the thighs and a need to increase postural stability. McGraw et al31 have suggested that future research should address whether obesity results in postural instability or whether postural instability is a primary contributor to a more sedentary activity level that contributes to obesity.
Consistent with the findings of Nantel et al,36 we did not find significant differences in cadence between children who were OW/obese and those who were HW. This differs from the findings of McGraw et al,31 who found cadence to be increased, and Hill and Parker,5 who found cadence to be decreased in children (aged 8-11 years) who were obese. Our study and the work of Nantel et al37 in children, 8 to 13 years of age, used similar distances to measure cadence, which may account for the difference in these findings from those of other researchers. However, there is variability among these studies with respect to the conditions under which cadence was measured. Future research with consistent methods, distances, and conditions for measuring cadence is warranted.
In this study, we found no significant differences in single-limb, double-support phases, step length, or stride length between the 2 groups. This is different from the previously reported research.31,37 McMillan et al38 have proposed that gait characteristics may change at some threshold of BMI that is related to age. If this is true, the different findings related to cadence, single-limb and double-support phases, and step and stride length between our study and the findings of other researchers may be explained by the differences in ages of the children in our study and those in previous studies. Also, we compared children who were OW/obese and not solely those who were obese. Further research with consistent walking distances, conditions, and ages of children that explores the differences in the spatiotemporal gait parameters between young children who are OW and obese is needed. Although the children in this study who were OW/obese may not have been exhibiting alterations in the spatiotemporal gait parameters found in older children who are obese, further exploration of effective interventions to prevent gait deviations and the potential musculoskeletal impairments associated with obesity is important.
Using the OLST as a measure of balance, we found that the children who were OW/obese were not able to maintain single limb stance as long as the children of HW. This is similar to the findings of Deforche et al34 when they tested unilateral stance on a balance beam in prepubertal boys and D'Hondt et al39 when testing balance in 5- to 10-year-old children using the Movement Assessment Battery for Children. Whether impaired balance is due to inadequate muscle function or altered joint torque needed to stabilize the body over a reduced base of support is not known. Future work using more objective measures may provide insight into the mechanisms that may differ between children who are HW and OW/obese.
Our data on measures of upper and lower extremity strength are in agreement with what is reported in the literature for older children. Our results suggest no significant differences between the groups in handgrip strength with a trend for the OW/obese group to have greater handgrip strength than their peers. This is supported by similar findings by Raudsepp and Jurimae40 in prepubertal girls. Studies by Suzuki and Tatsumi41 in 9- to 10-year-old children and Deforche et al11 in 12- to 18-year-old adolescents report that those who are obese have a higher grip strength than their counterparts. A proposed explanation for this is that children who are OW/obese develop more fat-free mass with increased adiposity that could help support extra load.42,43
Contrary to the findings for upper extremity strength, our results suggest that children who were HW had a significantly greater VJ height than those who were OW/obese. This finding is consistent with other studies that used the VJ as a measure of lower extremity explosive strength.12,44 These findings suggest that even in young children, who are OW/obese, muscle performance is impaired when the body mass is moved against gravity.
This study is not without limitations. One limitation of this study was the small sample size and the number of children in the obese category. Of the total 29 children who were classified in the OW/obese category, only 7 were obese. This may also have led to the smaller or lack of differences noted in our study, between the 2 groups of children.
Future work is needed to further elucidate differences in performance of weight-bearing activities to promote greater participation of young children with an aim to combat obesity. Studies that include data from an urban underserved population to better represent the prevalence of obesity are necessary. Also, future studies should include sensitive measures of balance and strength to allow greater insight into impairments in children who are OW/obese. Work to identify the effect of being OW on levels of physical activity and participation in physical education classes and community recreational/athletic activities is needed.
Our findings suggest that children who are OW/obese have an increased base of support while walking, decreased one-leg stance balance, and decreased lower extremity explosive strength in comparison with children who are HW. This study provides new clinical data on gait, balance, and muscle strength in young children, which is especially important, given the need for early detection and treatment of impairments in children who are OW/obese.
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