Joint kinematics and SPM analysis of gait in children with and without Down syndrome.

BACKGROUND: Individuals with Down syndrome (DS) walk with altered gait patterns compared to their typically developing (TD) peers. While walking at faster speeds and with external ankle load, preadolescents with DS demonstrate spatiotemporal and kinetic improvements. However, evidence of joint kinematic adjustments is unknown, which is imperative for targeted rehabilitation design. RESEARCH QUESTION: How does increasing walking speed and adding ankle load affect the joint kinematics of children with and without DS during overground walking? METHODS: In this cross-sectional observational study, thirteen children with DS aged 7-11 years and thirteen age- and sex-matched TD children completed overground walking trials. There were two speed conditions: normal speed and fast speed (as fast as possible without running). There were two load conditions: no load and ankle load (2% of body mass added bilaterally above the ankle). A motion capture system was used to register the ankle, knee, and hip joint angles in the sagittal plane. Peak flexion/extension angles, range of motion, and timing of peak angles were identified. In addition, statistical parametric mapping (SPM) was conducted to evaluate the trajectory of the ankle, knee, and hip joint angles across the entire gait cycle. RESULTS AND SIGNIFICANCE: SPM analysis revealed the DS group walked with greater ankle, knee, and hip flexion compared to the TD group for most of the gait cycle, regardless of condition. Further, increasing walking speed led to improved ankle joint kinematics in both groups by shifting peak plantarflexion closer to toe-off. However, knee extension during stance was challenged in the DS group. Adding ankle load improved hip and knee kinematics in both groups but reduced peak plantarflexion around toe-off. The kinematic adjustments in the DS group suggest specific motor strategies to accommodate their neuromuscular deficits, which can provide a foundation to design targeted gait-based interventions for children with DS.

Dynamic gait stability in children with and without Down syndrome during overground walking.

BACKGROUND: Challenging children with Down syndrome to walk fast and with external ankle load has demonstrated acute adjustments, such as increased step length and decreased step width, and improved joint stability. However, it is unknown to what extent these task constraints affect gait stability. Assessing dynamic gait stability through margin-of-stability not only quantifies adjustments related to balance control, but also informs safety considerations. METHODS: Twenty-four children with and without Down syndrome participated in this study. Subjects walked overground at two speed conditions: self-selected (normal) and as fast as possible (fast); and two ankle load conditions: no load and ankle load of 2% body mass. We assessed margin-of-stability in the anteroposterior and mediolateral directions, separately, at three gait events of toe-off, mid-swing, and heel strike. FINDINGS: Children with Down syndrome walked with greater mediolateral margin-of-stability than typically developing children. Children with Down syndrome demonstrated less anteroposterior margin-of-stability than typically developing children only before heel-strike at normal speed but increased anteroposterior margin-of-stability at fast speed. The ankle load increased the mediolateral margin-of-stability in both groups but did not impact the anteroposterior margin-of-stability. In addition, children with Down syndrome took shorter and wider steps for more lateral placement of mediolateral margin-of-stability. INTERPRETATION: Children with Down syndrome were capable of adjusting their margin-of-stability for fast walking and ankle-load conditions. However, children with Down syndrome walked with less mediolateral stability and anteroposterior mobility than typically developing children. Children with Down syndrome overcompensate the mediolateral foot placement to recapture their margin-of-stability and maintain gait stability.

Parental perceptions of nutritional intake, cooking skills, and food skills among preschoolers.

Objective: To determine parents' perceptions of cooking skills, food skills, and nutritional status of children ages 3 to 5 years. Methods: Parents of preschoolers aged 3 to 5 years completed two questionnaires, a Nutri-STEP questionnaire, assessing nutritional status, and a cooking exposure questionnaire. This parent recall questionnaire assessed cooking skills and food skills children possessed. Results: Willingness to try a new vegetable, parental confidence of child's cooking skills, total food skills possessed, and the covariates of gender, age, and ethnicity significantly predicted child dietary quality grouping p = 0.04. Conclusions and Implications: Trying new vegetables was a significant predictor of dietary behavior, with children more likely to try new vegetables demonstrating better dietary behavior (odds ratio= .43, p = 0.03). Trends showed that children with more cooking skills had better diets. Empirical data are needed through experimental designs to examine the integration of cooking skills in the home on child dietary behaviors and long-term cooking development.

Self-directed kinematic adjustments when learning the kettlebell swing in young adults.

The kettlebell swing is a complex exercise shown to provide cardiovascular and strength benefits. However, novice kinematic pattern differences might limit the effectiveness of the kettlebell swing to fully realise those benefits. The purpose of this study was to assess how novices self-directed their learning of the kettlebell swing using only an instructional video. Twelve young adults performed kettlebell swings sets over one week. We captured kinematic data of their first sets without practice, sets within-day following practice, and sets one week later following practice. The subjects received no augmented feedback. Ankle, knee, hip, and shoulder mean and variability kinematics were compared. In addition, the relative timing of peak sagittal plane angular velocity of the hip and shoulder was evaluated to determine whether the hips led to the shoulders. Within-day subjects reduced hip and shoulder peak extension, knee and hip peak flexion, and hip peak flexion velocity. Between-day subjects reduced mean hip peak flexion and range of motion, as well as peak knee flexion. Our results suggest novices prioritised improving consistency early in practice and then adjusted their kinematic pattern over the week. Moreover, most subjects transitioned to the hips leading shoulders, suggesting this is a perceivable coordination pattern by intrinsic feedback.

Lower Limb Joint Functions during Single-Leg Hopping in-Place in Children and Adults.

Children often display different whole-body dynamics compared to adults during locomotion such as walking and hopping. However, it is unknown whether these differences result in diverging functional usage of the lower limb joints. This study aimed to compare the mechanical functions of the ankle, knee, and hip joints between children and adults during single-leg hopping in-place at different frequencies. Children aged 5-11 years and adults aged 18-35 years performed hopping at their preferred frequency and slower and faster frequencies. Function of the joint was modeled as a combination of a strut, spring, motor, and damper. At the preferred frequency, children hopped equally with strut and spring functions at the ankle and knee joints while adults primarily used the spring function. When increasing frequency, both children and adults decreased the spring index and increased the strut index at the ankle and knee joints. Across all conditions, both children and adults used the strut function primarily at the hip joint. Results suggest that preadolescent children are still developing the adult-like spring function of their ankle and knee joints during hopping in-place. Quantification of spring function during hopping in-place may present an innovative approach to understand the maturation of the stretch-shortening cycle in children.

Muscle activation pattern during two-legged hopping in children with and without down syndrome.

This study aimed to characterize muscle activation and its variability during two-legged hopping in children with and without Down syndrome (DS). Seventeen typically developing (TD) children and 15 children with DS were recruited. As only 6 children with DS (4F/2M, 9.95 (1.71) years) completed the test, we used a 2(TD):1(DS) ratio to age- and sex-match 12 TD children. Subjects first hopped at a self-selected free frequency and then three metronome-cued conditions: slow, preferred, and moderate (80%, 100%, and 120% of free frequency, respectively). Across conditions, children with DS exhibited greater pre-activation before landing and greater shape and timing variability in gastrocnemius, vastus lateralis, and biceps femoris than TD children. However, this compensatory strategy limited their ability to change movement speed.

Coordination dynamics of hopping on a mini-trampoline in adults and children.

BACKGROUND: While mini-trampolines have been used among a variety of groups including children as an intervention tool, the motor behavior children adopt while hopping on this soft, elastic surface is unknown. Identifying coordinative structures and their stability for hopping on a mini-trampoline is imperative for recommending future interventions and determining appropriateness to populations with motor dysfunctions. RESEARCH QUESTION: Do children demonstrate similar biomechanical and coordination patterns as adults while hopping on a mini-trampoline? METHODS: Fifteen adults aged 18-35 years and 14 children aged 7-12 years completed bouts of continuous two-legged hopping in-place on a stiff surface for 10 s at a time and on a mini-trampoline for 30 s at a time. 3-D motion capture tracked whole-body movement. We evaluated whole-body vertical stiffness as a ratio of peak vertical force and peak vertical displacement, as well as spatiotemporal parameters of hopping. Coordinative structures were evaluated as continuous relative phase angles of the foot, shank, thigh, and pelvis segments. RESULTS AND SIGNIFICANCE: Adults did not modify whole-body vertical stiffness on a mini-trampoline, while children increased whole-body vertical stiffness to compensate for the reduced surface stiffness. Both groups conserved the coordinative structure for hopping on a mini-trampoline by modulating hopping cycle timing. Moreover, children hopped with an adult-like coordinative structure, but required greater shank-thigh and thigh-pelvis out-of-phase motion. However, the consistency of their coordination was diminished compared to adults. Children aged 7-12 years old have formed a stable coordinative structure for spring-mass center-of-mass dynamics that is preserved on this soft, elastic surface. However, children might be developing control strategies for preferred whole-body vertical stiffness, particularly when required to dampen peak vertical forces. These results highlight the importance of evaluating the emerging motor behavior to manipulated environmental constraints, particularly when considering the utility and appropriateness of mini-trampoline interventions for children with motor dysfunctions.

Acute effect of whole-body vibration on acceleration transmission and jumping performance in children.

BACKGROUND: Whole-body vibration (WBV) has emerged as a potential intervention paradigm for improving motor function and bone growth in children with disabilities. However, most evidence comes from adult studies. It is critical to understand the mechanisms of children with and without disabilities responding to different WBV conditions. This study aimed to systematically investigate the acute biomechanical and neuromuscular response in typically developing children aged 6-11 years to varying WBV frequencies and amplitudes. METHODS: Seventeen subjects participated in this study (mean age 8.7 years, 10 M/7F). A total of six side-alternating WBV conditions combining three frequencies (20, 25, and 30 Hz) and two amplitudes (1 and 2 mm) were randomly presented for one minute. We estimated transmission of vertical acceleration across body segments during WBV as the average rectified acceleration of motion capture markers, as well as lower-body muscle activation using electromyography. Following WBV, subjects performed countermovement jumps to assess neuromuscular facilitation. FINDINGS: Vertical acceleration decreased from the ankle to the head across all conditions, with the greatest damping occurring from the ankle to the knee. Acceleration transmission was lower at the high amplitude than at the low amplitude across body segments, and the knee decreased acceleration transmission with increasing frequency. In addition, muscle activation generally increased with frequency during WBV. There were no changes in jump height or muscle activation following WBV. INTERPRETATION: WBV is most likely a safe intervention paradigm for typically developing children. Appropriate WBV intervention design for children with and without disabilities should consider WBV frequency and amplitude.

Spring-like leg dynamics and neuromuscular strategies for hopping on a mini-trampoline in adults and children.

Improved balance control is an often-cited potential benefit for trampoline interventions. However, it is unknown whether the soft, elastic surface of a trampoline elicits different motion and neuromuscular strategies between adults and children. Therefore, the purpose of the study was to evaluate the center-of-mass (COM) dynamics and neuromuscular strategies for hopping on a mini-trampoline in adults and children. Fourteen children aged 7-12 years and 15 adults aged 18-35 years hopped on a stiff surface and a mini-trampoline. We evaluated the vertical displacement of COM and leg length, as well as the horizontal displacements between hops. We also assessed muscle activation from tibialis anterior, lateral gastrocnemius, biceps femoris, and vastus lateralis during time periods surround landing and estimated fatigue across the hopping cycles. Our results indicated both groups used spring-like leg dynamics to regulate the COM movement while hopping on a mini-trampoline. Children increased horizontal displacements between hops on the mini-trampoline, requiring greater muscle activation during time-periods associated with proprioceptive input. Moreover, children might not have developed the adult-like ability to appropriately adjust muscle pre-activation for feedforward control. Hopping on a mini-trampoline might increase proprioceptive information and postural demand compared to a stiff surface while reducing neuromuscular fatigue.

The patterning of local variability during the acquisition of a novel whole-body continuous motor skill in young adults.

There is increasing evidence that movement variability during motor skill acquisition plays a functional role. Specifically, initial variability might represent exploration of the possible motor space for solutions and error identification. Following practice, individuals might exploit a reduced amount of motor solutions to execute the task. While this variability pattern has been supported during discrete upper limb and multi-finger force tasks, there is a paucity of evidence for continuous whole-body motor tasks. Therefore, the purpose of this study was to characterize the role of variability during the acquisition of a whole-body continuous motor task across practice sessions in young adults. Twelve young adults aged 18-35-years participated in this study. Subjects practiced a novel, sagittal plane task, the kettlebell swing, using an online training video. We conducted an uncontrolled manifold analysis to partition local variability of the configuration of the kettlebell and body segments based on their impact on the position of the center-of-mass (COM) in the sagittal plane. Our results demonstrated that following initial practice, variability that did not affect the COM position remained elevated, suggesting sustained exploration of motor solutions. Following multiple practice sessions, variability related to motor solutions decreased, potentially indicating exploitation. The results from this study support the proposal that young adults initially utilize a range of motor solutions when acquiring a whole-body motor skill, followed by exploitation of stereotypic movement.

Improvement in Overground Walking After Treadmill-Based Gait Training in a Child With Agenesis of the Corpus Callosum.

BACKGROUND: Agenesis of the corpus callosum (ACC) is a rare congenital brain defect that produces a wide variety of cognitive and motor impairments. Literature regarding the response of pediatric populations with ACC to physical rehabilitation is scarce. Treadmill-based gait training (TT) has been shown to improve walking ability in some pediatric populations but has not been investigated in children with ACC. OBJECTIVE: The purpose of this study was to investigate the effect of a novel treadmill intervention paradigm on the gait parameters of a child with ACC. DESIGN: A single-participant design with 2 phases was used. METHODS: The settings were the participant's home and the laboratory. The participant was a 13-year-old girl who had ACC and cortical visual impairment and who ambulated independently using a reverse walker for household and short community distances. A home-based TT intervention (2 phases of 3 months of training over 6 months) was implemented, and a laboratory-based gait analysis was conducted at 4 time points: baseline, after each of the 2 training phases, and 3 months after the cessation of training. The intervention consisted of weekly bouts of TT. Phase I incorporated forward, backward, and incline walking for 15 minutes each; in phase II, this protocol was continued, but short-burst interval training for 10 minutes was added. Data collected at each laboratory visit included spatiotemporal parameters and kinematics (joint angles) during overground and treadmill walking. RESULTS: After both phases of training, increased step length, decreased step width, and foot progression angle and decreased variability of most spatiotemporal parameters were observed for the participant. Further, after phase II, increased peak extension at the hip, knee, and ankle, decreased crouched gait, and improved minimum foot clearance during overground walking were observed. Most gait improvements were retained for 3 months after the cessation of the intervention. LIMITATIONS: The small sample size of this study and wide variety of presentations within individuals with ACC limit the generalizability of our findings. CONCLUSIONS: TT may be a safe and effective treatment paradigm for children with ACC. Future research should investigate the effect of intervention dosage on gait improvements and generalization in individuals with ACC.

Neuromechanical control of leg length and orientation in children and adults during single-leg hopping.

Adult-like fine control of cyclical motor patterns found in locomotion develops into adolescence. Single-leg hopping in place is one such motor pattern where children have demonstrated a reduced capacity to control horizontal motion and match metronome cues. These developmental differences might arise from immature inter-segment coordination strategies and variability regulation. Therefore, the purpose of this study was to use an uncontrolled manifold (UCM) analysis to evaluate the control of segment angle variance (i.e., local variables) to stabilize leg length and leg orientation (i.e., task variables) in the sagittal plane between young adults and children aged 5-11 years old while hopping at different frequencies. The UCM space and its orthogonal space were constructed and segment angle variance was partitioned into these two spaces. Increased variance in the UCM space represents the stabilization of a task variable, while increased variance in its orthogonal space indicates a greater deviation of a task variable from its mean value. Our results indicated that children have developed an adult-like inter-segment coordination strategy of stabilizing leg length at mid-stance and leg orientation during flight. However, children might have an underdeveloped capacity to modulate leg length at take-off from cycle-to-cycle. Moreover, when increasing hopping frequency, children showed limited capacity to selectively increase leg-length stabilization. When decreasing hopping frequency, children illustrated an increased stabilization of leg orientation over the entire stance phase. Mid-stance leg-length stabilization might emerge with the motor skill; however, other inter-segment coordination strategies might continue to develop beyond 11-years of age.

Variability of spatiotemporal gait parameters in children with and without Down syndrome during treadmill walking.

BACKGROUND: Increasing walking speed and including bilateral external ankle load have been shown to improve aspects of the gait pattern of children with Down syndrome (DS). However, it is unknown if speed and ankle load improves the cycle-to-cycle variability in a similar way. RESEARCH QUESTION: How do changes of walking speed and external ankle load impact spatiotemporal variability during treadmill walking in children with and without DS? METHODS: Thirteen children with DS (aged 7-10 years) and thirteen age- and sex-matched typically developing (TD) children participated in this study. Subjects completed two bouts of 60-second treadmill walking at two different speeds (slow and fast) and two load conditions (no load and ankle load equaling to 2% bodyweight at each side). Kinematic data was captured using a Vicon motion capture system. Mean and coefficient of variance of spatiotemporal gait variables were calculated and compared between children with and without DS. RESULTS AND SIGNIFICANCE: Across all conditions, the DS group took shorter and wider steps than the TD group, but walked with a similar swing percentage, double support percentage, and foot rotation angle. Further, the DS group demonstrated greater variability of all spatiotemporal parameters, except for step width and foot rotation angle. Our results indicated that children with DS can modulate their spatiotemporal gait pattern accordingly like their TD peers when walking faster on a treadmill and/or with an external ankle load. Smaller step width variability in the DS group suggests that mediolateral stability may be prioritized during treadmill walking to safely navigate the treadmill and complete walking tasks. Similar temporal parameters but distinct spatial parameters in the DS group suggest that they may have developed similar rhythmic control but are confined by their spatial movement limitations.

Biomechanical analysis of the timed up-and-go (TUG) test in children with and without Down syndrome.

BACKGROUND: The timed up-and-go (TUG) test consists of multiple functional activities of daily living performed in a sequence, with the goal to complete the test as quickly as possible. Considering children with Down syndrome (DS) have been shown to take longer to complete the TUG test, it is imperative to identify which tasks are problematic for this population in order to individualize physical interventions. RESEARCH QUESTION: Is the biomechanical pattern of each functional task during the TUG test different between children with DS and typically developing (TD) children? METHODS: Thirteen children with DS and thirteen TD children aged 5-11 years old completed the TUG test. Kinematic data was captured using a Vicon motion capture system. We visually coded the TUG test into five phases: sit-to-stand, walk-out, turn-around, walk-in, and stand-to-sit. We focused on the center-of-mass (COM) movement in the sit-to-stand phase, spatiotemporal parameters in the walk-out phase, and intersegmental coordination in the turn-around phase. RESULTS AND SIGNIFICANCE: Children with DS took longer to complete the entire test, as well as each of the five phases. During the sit-to-stand phase, children with DS produced smaller peak vertical COM velocity, medial-lateral COM excursion, and peak knee and hip extension velocity compared to TD peers. Children with DS walked at a slower velocity during the walk-out phase. Both groups demonstrated a similar intersegmental coordination pattern between the head, thorax, and pelvis during the turn-around phase although children with DS had slower average and peak angular velocity at the head, thorax, and pelvis. Our results suggest that children with DS were less able to anticipate transitioning between motor tasks and took longer to initiate motor tasks. Our TUG analysis provides the detailed insights to help evaluate individual motor tasks as well as the transition from one task to another for clinical populations.

Vertical stiffness and balance control of two-legged hopping in-place in children with and without Down syndrome.

BACKGROUND: Children with Down syndrome (DS) are known for their reduced balance control, and typically take longer to develop motor skills and display less coordinated movement patterns. Hopping in-place is a gross motor skill requiring whole-body vertical stiffness and horizontal movement control, particularly when attempting to modify hopping frequency. However, there is a lack of knowledge of the hopping capacity of children with DS. RESEARCH QUESTION: The purpose of this study was to assess the ability of children with DS aged 5-11 years old to continuously hop in-place on two legs and compare their biomechanical patterns to those of typically developing (TD) children. METHODS: This observational study included 14 children with DS and 16 TD children. Subjects were asked to complete 20 s trials of two-legged hopping in-place at a self-selected frequency, and four metronome guided conditions: preferred (self-selected frequency), moderate (20% increase), fast (40% increase) and slow (20% decrease). Two sample independent t-tests were conducted on whole-body vertical stiffness, horizontal center-of-mass movement, and toe displacement between hops for the self-selected hopping condition and two-way ANOVAs were used for the metronome conditions. RESULTS AND SIGNIFICANCE: Our findings suggest that children with DS might not be able to continuously hop in-place until the age of 7 years old, and were unable to hop for as long in duration as their TD peers. Children with DS self-selected a faster hopping frequency, and demonstrated an increased medial-lateral center-of-mass movement during the stance phase of hopping, suggesting reduced balance control. Moreover, children with DS were unable to correctly modify their hopping frequency when cued by a metronome and exhibited an inability to modulate whole-body vertical stiffness and constrain horizontal or vertical movement. These results demonstrate the utility of a future hopping intervention to improve whole-body vertical stiffness and balance control in children with DS.

Effect of whole-body vibration on center-of-mass movement during standing in children and young adults.

Whole body vibration (WBV) can affect postural control and muscular activation. The purpose of this study was to investigate the center-of-mass (COM) movement of children and young adults before, during, immediately after, and 5min after 40-s WBV in quiet standing. Fourteen young adults (mean age 24.5 years) and fourteen children (mean age 8.1 years) participated in the study. A full-body 35-marker set was placed on the participants and used to calculate COM. Forty-second standing trials were collected before, during, immediately after, and 5min after WBV with an frequency of 28Hz and an amplitude of <1mm. Two visual conditions were provided: eyes-open (EO) and eyes-closed (EC). COM variables included time-domain measures (average velocity, range, sway area and fractal dimension), frequency-domain measures (total power and median frequency), and detrended fluctuation analysis (DFA) scaling exponent in both anterior-posterior (AP) and medial-lateral (ML) directions. Results show that during WBV both children and adults increased average velocity and median frequency, but decreased range and the DFA scaling exponent. Immediately after WBV both groups increased the range, but showed pre-vibration values for most of the COM variables. Comparing to adults, children displayed a higher COM velocity, range, fractal dimension, and total power, but a lower DFA scaling exponent at all phases. The results suggest that both children and adults can quickly adapt their postural control system to WBV and maintain balance during and after vibration. Children display some adult-like postural control during and after WBV; however, their postural development continues into adolescence.

Comparison of whole-body vertical stiffness and leg stiffness during single-leg hopping in place in children and adults.

In the hopping literature, whole-body vertical stiffness and leg stiffness are used interchangeably, due to most of the movement occurring in the vertical direction. However, there is some anterior/posterior movement of the center of mass and displacements of the foot during hopping in place in both children and adults. Further it is not understood if leg stiffness show a similar pattern as whole-body vertical stiffness when increasing hopping frequency. The purpose of this study was to test if whole-body vertical stiffness and leg stiffness are different during single-leg hopping in-place in children and adults, across a range of frequencies. Seventeen children aged 5-11years and 16 young adults participated in this study. The subjects hopped at their preferred frequency as well as 20% below, 20% above and 40% above preferred frequency. Our results demonstrate that both whole-body vertical stiffness and leg stiffness increase when increasing hopping frequency for children and adults. However, whole-body vertical stiffness consistently overestimates leg stiffness due to a similar peak force but a greater leg length change compared to vertical COM displacement. This suggests a considerable horizontal COM movement from landing to mid-stance during hopping. Children aged 5-11years old showed lower absolute values but higher normalized values of two stiffness measures than adults. This suggests somewhat adult-like stiffness control in children, but a reduced ability to manipulate the horizontal movement during single-leg hopping in place when compared to adults.

Vertical stiffness and center-of-mass movement in children and adults during single-leg hopping.

Single-leg hopping in-place can be typically modeled using a spring-mass model. Within this model, the leg acts as a spring whose stiffness can be regulated to hop at different heights and frequencies. The control of vertical stiffness has been shown to be important for running and jumping performance, as well as injury prevention. It is known that adults increase vertical stiffness to hop at frequencies higher than preferred, but it is unknown if children younger than 11 years have a similar ability to control vertical stiffness. Further, little is known about the horizontal movement of the center-of-mass (COM) and foot positioning during hopping in both children and adults. The purpose of this study was to evaluate the validity of the spring-mass model in 5-11 years old children and compare horizontal COM and foot movement between children and adults. We found that single-leg hopping in children generally follows a spring-mass model and children are able to increase vertical stiffness with hopping frequency. Moreover, children demonstrate adult-like control strategies of decreasing the COM range and toe displacement but maintaining the COM positioning with increasing frequency. However, children showed a faster preferred frequency, elevated vertical stiffness normalized by body weight, a greater toe displacement between hops and a greater toe range within a trial. Together, single-leg hopping in place can generally be modeled in 5-11 years old children as a spring-mass model; however, children at this age are still developing their motor ability to control the COM and foot placement during hopping.

Children Display Adult-Like Kinetic Patterns in the Time Domain, But Not in the Frequency Domain, While Walking With Ankle Load.

This study used both time and frequency domain analyses to investigate walking patterns with ankle load in children and adults. Twenty-two children aged 7-10 years and 20 young adults participated in this study. Three levels of ankle load were manipulated: no load, low load (2% of body mass on each side), and high load (4% of body mass on each side). An instrumented treadmill was used to register vertical ground reaction force (GRF) and spatiotemporal parameters, and peak vertical GRFs were determined. A frequency domain analysis was conducted on the vertical GRF data. Results demonstrate that, in the time domain, children showed adult-like spatiotemporal parameters and adult-like timing and magnitude of the 2 peak vertical GRFs under each load. In the frequency domain, children produced a lower power from the second harmonic than young adults, although both groups showed the highest power from this harmonic and increased this power with ankle load. It was concluded that children aged 7-10 years may start showing adult-like neuromuscular adaptations to increasing ankle load and display similar spatiotemporal control of foot falls and foot-floor kinetic interaction; however, a frequency domain analysis is effective in revealing different kinetic and neuromuscular characteristics between children and adults.

Walking dynamics in preadolescents with and without Down syndrome.

BACKGROUND: A force-driven harmonic oscillator (FDHO) model reveals the elastic property of general muscular activity during walking. OBJECTIVE: This study aimed to investigate whether children with Down syndrome (DS) have a lower K/G ratio, a primary variable derived from the FDHO model, compared with children with typical development during overground and treadmill walking and whether children with DS can adapt the K/G ratio to walking speeds, external ankle load, and a treadmill setting. DESIGN: A cross-sectional study design was used that included 26 children with and without DS, aged 7 to 10 years, for overground walking and 20 of them for treadmill walking in a laboratory setting. METHODS: During overground walking, participants walked at 2 speeds: normal and fastest speed. During treadmill walking, participants walked at 75% and 100% of their preferred overground speed. Two load conditions were manipulated for both overground and treadmill walking: no load and an ankle load that was equal to 2% of body mass on each side. RESULTS: Children with DS showed a K/G ratio similar to that of their healthy peers and increased this ratio with walking speed regardless of ankle load during overground walking. Children with DS produced a lower K/G ratio at the fast speed of treadmill walking without ankle load, but ankle load helped them produce a K/G ratio similar to that of their healthy peers. LIMITATIONS: The FDHO model cannot specify what muscles are used or how muscles are coordinated for a given motor task. CONCLUSIONS: Children with DS show elastic property of general muscular activity similar to their healthy peers during overground walking. External ankle load helps children with DS increase general muscular activity and match their healthy peers while walking fast on a treadmill.