Optimization of walking in children

Walking around the preferred speed: examination of metabolic, perceptual, spatiotemporal and stability parameters

Walking is the most accessible and common type of physical activity. Exercising at one's self-selected intensity could provide long-term benefits as compared to following prescribed intensities. The aim of this study was to simultaneously examine metabolic, perceptual, spatiotemporal and stability parameters at an absolute 3 km·h-1 speed range around the individual preferred walking speed (PWS). Thirty-four young sedentary adults (18 women) volunteered to walk at seven speeds relative to their PWS in 3-min trials interspaced with 3-min rest intervals. Results indicated a significant main effect of speed on all studied variables. While metabolic, perceptual and spatiotemporal values were sensitive to the smallest change in speed (i.e., 0.5 km·h-1), a significant increase in the rate of carbohydrate oxidation and decrease in %fat oxidation were only observed at speeds above PWS. Results also revealed significantly higher coefficients of variation for stride characteristics at speeds below PWS only. Moreover, analyses of best fit models showed a quadratic relationship between most variables and speed, with the exceptions of metabolic cost of transport, rating of perceived exertion and stride duration that changed exponentially with speed. PWS coincided with optimized mechanical efficiency, fuel oxidation and gait stability. This indicated that walking below PWS decreased both mechanical efficiency and stability of gait, while walking above PWS increased carbohydrate oxidation. Those factors seem to play an important role as determinants of PWS. We suggest that walking at PWS may provide benefits in terms of fat oxidation while optimizing gait stability.

Early spontaneous movements and spatiotemporal gait characteristics in preterm children

This study aimed to analyze spatiotemporal gait characteristics of preterm children from 3 to 4 years of age according to different gestational age groups and to examine the relationship between the detailed general movements assessment and spatiotemporal gait characteristics. A total of 74 preterm children, 32 extremely preterm and very preterm (EP-VP, < 32 weeks gestational age) and 42 moderate to late preterm (MLP, 32 to < 37 weeks gestational age), were included in this prospective study, along with 38 term children. Early spontaneous movements of preterm children were assessed from videos at 9-20 weeks post-term according to the general movements assessment, which determines the Motor Optimality Score-Revised (MOS-R). The spatiotemporal gait characteristics of all children were evaluated using the GAITRite^®electronic walkway at self-selected walking speeds. EP-VP children walked with shorter step lengths (p = 0.039), and MLP children walked with greater step length variability (p = 0.003) than their term peers. The MOS-R results were related to step length (r = 0.36, p = 0.042), step length variability (r =  -0.56, p = 0.001), and base of support (r =  -0.37, p = 0.038) in EP-VP children. The MOS-R subcategories, age-adequate movement repertoire, and postural patterns were related to some of the spatiotemporal gait characteristics, including step length, step length variability, and base of support (p < 0.05).  Conclusion: EP-VP and MLP children might catch up to their term peers at 3 to 4 years of age in terms of most gait parameters. In addition to the MOS-R, age-adequate movement repertoire and postural patterns of preterm children without cerebral palsy in early life may be a marker of later neurodevelopmental dysfunction. What is Known: • Preterm children walk with a wider step width, a greater step length asymmetry and step time, and a shorter stride length at 18 to 22 months of age compared with term children at a self-selected speed, while these differences disappear in children 4.5-5 years old and older. What is New: • Early spontaneous movements were related to some spatiotemporal gait characteristics. • Preterm children might catch up to term children at 3-4 years of age in spatiotemporal gait characteristics while walking at a self-selected speed.

Glycine receptor subunit-ß -deficiency in a mouse model of spasticity results in attenuated physical performance, growth and muscle strength

Spasticity is the most common neurological disorder associated with increased muscle contraction causing impaired movement and gait. The aim of this study was to characterize the physical performance, skeletal muscle function, and phenotype of mice with a hereditary spastic mutation (B6.Cg-Glrb^spa/J). Motor function, gait, and physical activity of juvenile and adult spastic mice and the morphological, histological, and mechanical characteristics of their soleus and gastrocnemius medialis muscles were compared with those of their wild-type (WT) littermates. Spastic mice showed attenuated growth, impaired motor function, and low physical activity. Gait of spastic mice was characterized by a typical hopping pattern. Spastic mice showed lower muscle forces, which were related to the smaller physiological cross-sectional area of spastic muscles. The muscle-tendon complex length-force relationship of adult gastrocnemius medialis was shifted toward shorter lengths, which was explained by attenuated longitudinal tibia growth. Spastic gastrocnemius medialis was more fatigue resistant than WT gastrocnemius medialis. This was largely explained by a higher mitochondrial content in muscle fibers and relatively higher percentage of slow-type muscle fibers. Muscles of juvenile spastic mice showed similar differences compared with WT juvenile mice, but these were less pronounced than between adult mice. This study shows that in spastic mice, disturbed motor function and gait is likely to be the result of hyperactivity of skeletal muscle and impaired skeletal muscle growth, which progress with age.

Objectively measured movement asymmetry in yearling Standardbred trotters

BACKGROUND

Lameness evaluation of Standardbred trotters can be challenging due to discrepancies in observed movement asymmetry between in-hand and track exercise, and between different trotting speeds. There are few studies on objective measurement of movement in Standardbreds, and little knowledge regarding biological variation and clinical significance of measured movement asymmetry in this breed.

OBJECTIVES

To quantify the prevalence and magnitude of objectively measured movement asymmetry in young Standardbred trotters, and identify associations with trainer, sex, height, track type and in-hand measurement prior to or after track trials.

STUDY DESIGN

Cross-sectional, observational study.

METHODS

A total of 114 Standardbred yearlings were evaluated with a wireless inertial sensor system during trot in-hand and when driven on a track. After exclusions relating to lameness or technical difficulties, 103 horses were included in the study; 77 were evaluated in-hand and on the track, 24 only in-hand and 2 only on the track.

RESULTS

Front and/or hindlimb parameters were above asymmetry thresholds previously established for other breeds during in-hand trials for 94 (93%) horses and during track trials for 74 (94%) horses. Most horses showed mild asymmetry. A minority of horses (20%) switched side of the asymmetry for one or more parameters between in-hand and track trials. Mixed model analyses revealed no significant effects of trial mode (in-hand or track trial, in-hand trial pre- or post-track trial, straight or oval track), trainer or horse height. Females had a significant but small reduction in asymmetry in one front limb parameter (HD_max ) compared with males (1.7 mm, 95% CI 0.18-3.28, P = .03).

MAIN LIMITATIONS

High data variability, reflected in large trial standard deviations, relating mainly to a lack of horse compliance.

CONCLUSIONS

A high proportion of Standardbred yearlings showed movement asymmetries. There was no group-level effect between in-hand and track trials, however, considerable individual variation was observed.

Gait Characteristics of Children Born Preterm

Walking is a central skill of daily living. A delay in the onset of walking can be a sign of abnormal motor development. Further, abnormalities in gait can also affect physical functioning. Children born preterm are at significant risk for neurodevelopmental impairments; however, little is known about how preterm birth affects walking. This review describes current evidence of walking in children born preterm with a focus on the age at onset of walking and comparisons of gait characteristics of children born preterm with those born full-term.

Gait analysis on force treadmill in children: comparison with results from ground-based force platforms

Gait analysis (GA) typically includes surface electromyographic (sEMG) recording from several lower limb muscles, optoelectronic measurement of joint rotations, and force recordings from ground-based platforms. From the latter two variables, the muscle power acting on the lower limb joints can be estimated. Recently, gait analysis on a split-belt force treadmill (GAFT) was validated for the study of adult walking. It showed high reliability of spatiotemporal, kinematic, dynamic, and sEMG parameters, matching those obtainable with GA on the basis of ground walking. GAFT, however, still needs validation in children. Potential differences with respect to adult GAFT relate to (a) possible high signal-to-noise ratio, given the lower forces applied; (b) higher differences between treadmill and over-ground walking; and (c) limited compliance with the experimental setup. This study aims at investigating whether GAFT provides results comparable with those obtainable from ground walking in children and consistent with results from GAFT in adults. GAFT was applied to three groups of healthy children aged 5-6 years (n=6), 7-8 years (n=6), and 9-13 years (n=8) walking at the same average speed spontaneously adopted overground. The results were compared with those obtained from another study applying GA to an age-matched and speed-matched sample of 47 children, and with those obtained from GAFT in adults. The reliability (as indicated by the SD) of both spatiotemporal and dynamic parameters was higher in GAFT compared with GA. In the 5-6-, 7-8-, and 9-13-year-old groups, at average speeds of 0.83, 1.08, and 1.08 m/s, step length was shorter by 9.19, 3.57, and 2.30% compared with GA in controls at comparable speeds, respectively. For the youngest group, a lower power generation from the plantar flexors (peak power: 1.35±0.32 vs. 2.11±1.02 W/kg) and a slightly more flexed posture of the hip, knee, and ankle joints were observed during GAFT compared with GA in controls. The other gait parameters were very similar between the GAFT and the GA groups. The shortening of step length during GAFT, relative to GA at superimposable speed, was on average of all children 6.8%, in line with the 8% decrease found in adults. The profiles of sEMG and joint rotations, and all of the weight-standardized joint power parameters, matched those recorded in adults. The entire experimental session lasted about 1 h. All children complied with the experimental setting and easily completed the requested tests. In conclusion, GAFT seems to be a promising alternative to conventional GA in children.

Uncontrolled manifold hypothesis: Organization of leg joint variance in humans while walking in a wide range of speeds

This study aimed at investigating the organization of joint angle variability during walking by using the uncontrolled manifold (UCM) theory. We tested two hypotheses: i. the coordinative mechanism underlying joint angle variance during the stance phase is compatible with a kinematic synergy that stabilizes the centre of mass (CoM) position; ii. the walking speed affects the variance components onto and orthogonal to the UCM. Eight healthy subjects (26.0±2.0years old) steadily walked on a treadmill at five normalised speeds (from 0.62±0.03m/s to 1.15±0.07m/s). Joint angles and foot orientation, and components of the CoM position were, respectively, used as elemental variables and task performance for the UCM implementation. The effect of speed, time events, and variance components on the distribution of data variance in the space of joint angles was analyzed by the ANOVA test. Results corroborated the hypothesis that the variance of elemental variables is structured in order to minimize the stride-to-stride variability of the CoM position, at all speeds. Noticeably, both variance components increase during the propulsive phase, albeit that parallel to the UCM was always grater than the orthogonal one. Accordingly, the observed kinematic synergy is supposed to contribute to accomplishing an efficient transition between two steps. Results also revealed that the walking speed does not affect the partitioning of elemental variables-related variance onto and orthogonal to the UCM. Accordingly, the organization of leg joint variance underlying the stabilization of CoM position remains almost unaltered across speeds.

The Spanish version of the Alberta Infant Motor Scale: Validity and reliability analysis

OBJECTIVES

Validity and reliability of the cross-cultural adaptive translation of the Alberta Infant Motor Scale (AIMS), to monitor gross motor development in infants from 0 to 18 months of age, were evaluated.

METHODS

A cross-cultural translation was used to generate a Spanish version of the AIMS. Fifty infants at risk or with diagnosis of motor delay, 0-18 months of age, participated in this study. Two independent physical therapists scored infants on the AIMS. Concurrent validity was tested using the AIMS and the Bayley Scales of Infant and Toddler Development - III (Bayley - III).

RESULTS

Reliability and the internal consistency were high (ICCs ranged from 0.94 to 1.00 and KR-20 ranged from 0.90 to 0.98, respectively). AIMS and Bayley - III scores correlated strongly (r = 0.97).

CONCLUSION

The Spanish version of the AIMS presented excellent validity and reliability. Further studies are suggested in order to assess the AIMS in preterm babies.

Developmental differences in dynamic muscle-tendon behaviour: implications for movement efficiency

Children perform cyclic motor tasks less efficiently than adults; however, the mechanisms underlying such differences are not fully understood. One mechanism that may contribute to these age-related differences is a differential contribution of muscles and tendons to a given muscle-tendon unit (MTU) excursion. The aims of this study were to (i) compare muscle and tendon excursion between children and adults performing vertical hopping, and (ii) determine whether children and adults choose a hopping frequency that maximizes movement efficiency, based on the utilization of energy-saving mechanisms. Twelve children (8.8±0.3 years) and 12 adults (26.0±2.1 years) performed 20 s of two-legged hopping at a self-selected frequency and at 1.33, 2.00, 2.67 and 3.33 Hz. Gastrocnemius medialis MTU excursion was estimated from kinematic data and muscle and tendon excursions were derived using a combination of 3D-motion capture and ultrasonography. Optimum hopping frequency was determined as the frequency that maximized surrogate measures of elastic energy storage potential of the tendon and minimized muscle excursion. Adults presented a significantly greater potential for elastic energy storage in combination with lower muscle excursion than children at their self-selected frequency, suggesting that children do not utilize these energy-saving mechanisms as effectively as adults. However, tendon elastic energy storage was maximized and muscle excursion minimized at the preferred frequency in both children and adults, indicating that children may select their preferred hopping frequency based on the same criteria as adults. These findings increase our understanding of the mechanisms contributing to the higher energy cost of movement performance in children, and have implications for the interpretation of age-related differences in complex task performance.

Exercise training modifies walking kinematics and energy cost in obese adolescents: A pilot controlled trial

The aim of this study was to investigate the effects of a weight loss intervention based on physical exercise on the relationship between energy cost and stride frequency during walking in obese teenagers. Participants aged 13-16 years old were assigned to a training (n = 14) and control (n = 10) groups. During eight weeks, the training group performed three 60-min weekly sessions of high-intensity intermittent activities coupled with aerobic training. Body composition, gait parameters and energy cost during 4-min walking bouts at participants' most comfortable speed and preferred stride frequency (PSF), PSF-10%, PSF + 10%, PSF-20% and PSF + 20% were measured before and after intervention. The effects of training and stride frequencies on the energy cost of walking were analysed by an ANOVA with repeated measures. The main results showed that the exercise intervention induced a significant increase in walking speed (+23.2%), and significant decreases in body mass (-1.4%), body fat percentage (-2.1%) and energy cost of walking at various frequencies (decreases ranging from -10.5% to -20.4%, p < .05). In addition, significantly greater decreases were shown at high frequencies (p < .05). No significant differences were shown in the control group (p > .05). These results suggest that this type of training is beneficial to reduce walking energy cost of obese teenagers, in particular at high frequencies. This should improve their well-being during daily activities.

The influence of cognitive load and walking speed on gait regularity in children and young adults

The dual-process account of sensorimotor-cognitive interactions postulates that easy cognitive tasks can lead to performance improvements in the motor domain (e.g., an increased stability while walking or balancing) across the lifespan. However, cross-domain resource competition can lead to performance decrements in motor tasks when the concurrent cognitive task is very difficult, and older adults have shown performance decrements in their motor functioning under such circumstances. Resource limitations are particularly pronounced not only in old adulthood, but also in childhood. The current study investigates the relationship of walking speed and cognitive load on walking regularity in 7- and 9-year olds and young adults, with 18 participants in each group. Participants were walking on a treadmill at their preferred speed, and with speeds that were 30% faster and 30% slower than preferred. Regularity of lower-body coordination was operationalized as the residual variance of principal component analyses performed on the data of a motion analysis system. All age groups showed a more regular gait with increasing walking speed. Young adults' gait regularity was not influenced by cognitive load, whereas children showed a U-shaped relationship of cognitive load and walking regularity, with the highest regularity when performing an easy cognitive task. It can be concluded that children are also influenced by cross-domain resources competition in challenging cognitive-motor dual-task situations.

Measurement of children's physical activity using a pedometer with a built-in memory

OBJECTIVES

We evaluated the accuracy of the Accusplit AH120 pedometer (built-in memory) for recording step counts of children during treadmill walking against (1) observer counted steps and (2) concurrently measured steps using the previously validated Yamax Digiwalker SW-700 pedometer.

DESIGN

This was a cross-sectional validation study performed under controlled settings.

METHODS

Forty five 9-12-year-olds walked on treadmills at speeds of 42, 66 and 90m/min to simulate slow, moderate and fast walking wearing Accusplit and Yamax pedometers concurrently on their right hip. Observer counted steps were captured by video camera and manually counted. Absolute value of percent error was calculated for each comparison. Bland-Altman plots were constructed to show the distribution of the individual (criterion-comparison) scores around zero.

RESULTS

Both pedometers under-recorded observer counted steps at all three walk speeds. Absolute value of percent error was highest at the slowest walk speed (Accusplit=46.9%; Yamax=44.1%) and lowest at the fastest walk speed (Accusplit=8.6%; Yamax=8.9%). Bland-Altman plots showed high agreement between the pedometers for all three walk speeds.

CONCLUSIONS

Using pedometers with built-in memory capabilities eliminates the need for children to manually log step counts daily, potentially improving data accuracy and completeness. Step counts from the Accusplit (built-in memory) and Yamax (widely used) pedometers were comparable across all speeds, but their level of accuracy was dependent on walking pace. Pedometers should be used with caution in children as they significantly undercount steps, and this error is greatest at slower walk speeds.

Effect of stride frequency on the energy cost of walking in obese teenagers

The aim of this study was to compare the energy cost of obese and non-obese teenagers while walking at their preferred speed and different stride frequencies. Twelve obese and twelve non-obese teenagers walked continuously on the treadmill at their most comfortable speed for 6 periods of 4 min each. Each period corresponded to a specific stride frequency: preferred (PSF), force-driven harmonic oscillator (FDHO), PSF+10%, PSF+20%, PSF-10% and PSF-20%. Cardiorespiratory parameters were collected between the 3rd and 4th minute of each stage, and used to calculate the energy cost of walking (EC). The main results showed a significantly higher cost of walking expressed relative to lean body mass. In addition, a U-shaped relationship between EC and stride frequency was shown in both groups, with PSF and FDHO leading to a significantly lower value compared to all other frequencies. This showed first, that FDHO is a good predictor of PSF and minimal energy cost of walking in both groups, and second, that excess body fat does not affect the relationship between energy expenditure and stride frequency. Walking at lower or higher than preferred frequencies could be used as an exercise mode to promote weight loss in obese teenagers.

Within- and between-day repeatability and variability in children's physiological responses during submaximal treadmill exercise

The purpose of this study was to verify within- and between-day repeatability and variability in children's oxygen uptake (VO2), gross economy (GE; VO2 divided by speed) and heart rate (HR) during treadmill walking based on self-selected speed (SS). Fourteen children (10.1 +/- 1.4 years) undertook three testing sessions over 2 days in which four walking speeds, including SS were tested. Within- and between-day repeatability were assessed using the Bland and Altman method, and coefficients of variability (CV) were determined for each child across exercise bouts and averaged to obtain a mean group CV value for VO2, GE, and HR per speed. Repeated measures analysis of variance showed no statistically significant differences in within- or between-day CV for VO2, GE, or HR at any speed. Repeatability within- and between-day for VO2, GE, and HR for all speeds was verified. These results suggest that submaximal VO2 during treadmill walking is stable and reproducible at a range of speeds based on children's SS.

The effects of femoral derotation osteotomy in children with cerebral palsy: an evaluation using energy cost and functional mobility

BACKGROUND

The effect of femoral derotation osteotomy (FDO) in children with cerebral palsy (CP) has hitherto been examined using various outcome measures including range of motion of lower extremity joints and gait parameters. However, functional ambulation following this procedure has been scarcely investigated.

OBJECTIVE

To evaluate the effect of FDO on energy cost during stair climbing and functional mobility in children with CP.

METHOD

A prospective case series study was conducted on 18 children with CP, 11 at Gross Motor Functional Classification System (GMFCS) II and 7 with GMFCS III, aged 8.5 +/- 1.24 years (range, 6.9-11 years) who underwent FDO to correct hip internal rotation. The energy cost was measured using the heart beat cost index (HBCI) during stair climbing test, whereas functional mobility was assessed using the Gillette Functional Assessment Questionnaire (FAQ). Tests were administered before surgery (P0), 6 months (P1), and at approximately a year postoperatively (P2).

RESULTS

Compared with P0, significant changes in hip rotation were observed at P1 and P2. There was a significant improvement in HBCI from P0 to P2, whereas FAQ improved significantly from P1 to P2. A moderate correlation was found between HBCI and GMFCS at all times (r = 0.61-0.78). Negative correlations were found between the HBCI and FAQ and between GMFCS and FAQ at all times (r = -0.5).

CONCLUSION

This study indicates that children with CP may benefit functionally from FDO as judged by HBCI and functional mobility rating.

Neuromechanical stabilization of leg length and orientation through interjoint compensation during human hopping

Evidence for the simplification of motor control of the limbs through a reduction in the number of degrees of freedom exists in areas of research such as neuroscience, robotics, and biomechanics. Human hopping in place can be modeled well with spring-mass dynamics and provides a tractable model by which to study how the locomotor system compensates through inter-joint coordination to achieve stability of performance variables, leg length and orientation. This study provides the first evidence for how the redundancy of human leg joints may be simply coordinated to stabilize spring-mass dynamics throughout the hopping cycle using an uncontrolled manifold (UCM) analysis. We use a UCM analysis to quantify the structure of joint variance that stabilizes the hypothesized performance variables, leg length and leg orientation. For one-legged human hopping in place, we hypothesized that leg length and orientation would each be stabilized throughout the entire hopping cycle. We also hypothesized that hopping at non-preferred frequencies would be more difficult for subjects and stabilization of leg length and orientation would increase. Kinematic data from eleven subjects hopping at three frequencies (2.2, 2.8, and 3.2 Hz) were collected and analyzed within the framework of the UCM. Maximum leg length stabilization was observed at mid-stance when leg length was most susceptible to small changes in joint angles. Overall stabilization of leg length increased as subjects hopped at higher frequencies, reflecting the increased demands on the control system. The stabilization of leg orientation during aerial phase acted to position the foot at initial contact to determine velocity and trajectory of the center of mass during the stance phase. Because hopping in place does not require a change in forward velocity, the control strategy for leg orientation remained the same across frequencies. We conclude that stabilization of leg length and orientation may signify a reduction in degrees of freedom in the control system.

Prediction of mechanical efficiency from heart rate during stair-climbing in children with cerebral palsy

Measuring mechanical efficiency (ME) is potentially useful to assess motor performance in individuals with physical disabilities. The purpose of this study was to determine the accuracy of predicting ME from heart rate (HR) during a self-paced stair-climbing test in children with a range of motor abilities. The participants were 12 normally developed children (ND) and 24 with cerebral palsy (CP), ranging in age from 5 to 15 years (mean: 8 years). Five were at level II, 11 at level III and 8 at level IV according to the gross motor function classification system. ME was calculated as the ratio of external work to O(2) uptake (VO(2) ml/min) measured or predicted from HR. The absolute values of VO(2) and HR during stair-climbing were not significantly correlated. However, the correlation between values above resting (dVO(2) and dHR) was significant (r=0.61). Furthermore, when including body weight as a second variable the prediction of dVO(2) was significantly improved (r=0.85). This resulted in a high correlation (r=0.96) between measured and predicted net ME (ME(net)). Predicted ME(net) for 25 stair-climbing tests repeated after an average of 6 months resulted in an r-value of 0.92 with predicted ME(net) of the first test. This study demonstrates that ME(net) during stair-climbing can be predicted in children with a broad range of motor abilities from dHR and may be a simple tool to help define developmental stages or evaluating intervention efficacy.

Development of walking in preterm and term infants: age of onset, qualitative features and sensitivity to resonance

An increasing number of studies have examined the development of walking in preterm infants; however, the results concerning those who had no major neonatal disease were inconclusive. This study was therefore aimed to examine the age of onset, the quality of early walking movement, and the sensitivity to resonant period of the force-driven harmonic oscillator (FDHO) model in preterm infants who had no major neonatal disease and normal term infants. Twenty-nine preterm infants and 29 term infants were prospectively examined for their age of onset of independent walking and were subsequently assessed the qualitative features of walking at 18 months of corrected age using kinematic analysis. Kinematic variables examined included spatio-temporal organization, inter-joint coordination, and inter-limb coordination. The anthropometric data were used to calculate the resonant period. The results demonstrated that the preterm infants attained independent walking at significantly older ages than the term infants when corrected for prematurity. The preterm infants manifested similar walking characteristics, except for shorter stride lengths, at 18 months of corrected age compared with the term infants. Furthermore, the stride periods of both groups were accurately predicted by the resonant period of the FDHO model. We conclude that preterm birth without accompanied major neonatal disease may affect infants' age of onset and spatial organization but not their sensitivity to resonance during the early stage of walking development.

The effect of community-prescribed ankle-foot orthoses on gait parameters in children with spastic cerebral palsy

PURPOSE

To evaluate the efficacy of ankle foot orthoses (AFOs) prescribed in the community for children with cerebral palsy (CP).

METHODS

Fifty-six children (32 boys and 24 girls, mean age 8.9 years, range 4-17) who were diagnosed as having CP were enrolled. They were grouped according to the type of CP, diplegic (n = 38) and hemiplegic (n = 18). Three-dimensional gait analyses while patient were barefoot and with AFOs were obtained and analyzed.

RESULTS

The spatio-temporal findings were the most significantly changed as a result of AFO use. In the hemiplegic group, stride length was 11.7% (p = 0.001) longer with AFOs in both affected (10.2%) and non-affected (12.4%) legs, and cadence was reduced by 9.7%; walking speed was not affected. In the diplegic group, stride length with AFOs was 17.4% longer compared to barefoot (p < 0.001) and walking velocity improved by 17.8% (p < 0.001); cadence was unchanged. AFOs also increased ankle dorsiflexion at initial contact in both groups. In the hemiplegic group, AFOs produced an average 9.4 degrees increase of dorsiflexion at initial contact (IC) on the affected side (p < 0.001) and 5.87 degrees on the unaffected side (p = 0.007), and an increase of 9.9 degrees (p < 0.001) dorsiflexion at swing, on the affected side. In the diplegic group, dorsiflexion at IC was increased by 13.4 degrees on the right side and 7.8 degrees on the left side (p = 0.05; p > 0.001, respectively) and an increase of 6 degrees (p = 0.005) at swing. In the hemiplegic group of patients, knee flexion at initial contact on the affected side was reduced by 8.5 degrees (p = 0.032) while in the diplegic group we found no influence. The number of patients that reached symmetry at initial double support tripled (from 5.6 to 16.7%) with the use of AFOs.

CONCLUSIONS

Our results showed that the use of AFOs improves spatio-temporal gait parameters and gait stability in children with spastic cerebral palsy. It has a lesser effect on proximal joint kinematics. Children with spastic hemiplegia display greater improvement than those with spastic diplegia.

Effects of age, walking speed, and body composition on pedometer accuracy in children

The objective of this study was to investigate the effects of age group, walking speed, and body composition on the accuracy of pedometer-determined step counts in children. Eighty-five participants (43 boys, 42 girls), ages 5-7 and 9-11 years, walked on a treadmill for two-minute bouts at speeds of 42, 66, and 90 m x min(-1) while wearing a spring-levered (Yamax SW-200) and a piezoelectric (New Lifestyles NL-2000) pedometer. The number of steps taken during each bout was also recorded using a hand counter Body mass index (BMI) was calculated from height and mass, and percentage of body fat (%BF) was determined using hand-to-foot bioelectrical impedance analysis. The tilt angle of the pedometer was assessed using a magnetic protractor. Both pedometers performed well at 66 and 90 m x min(-1), but undercounted steps by approximately 20% at 42 m x min(-1). Although age group, BMI, waist circumference, and %BF did not affect pedometer accuracy, children with large pedometer tilt angles (> or =10 degrees) showed significantly greater percent bias than those with small tilt angles (< 10 degrees). We suggest that the style of waistband on the child's clothing is a more important determinant of tilt angle and thus pedometer accuracy than body composition. Our results also indicate that the NL-2000 pedometer provides similar accuracy and better precision than the SW-200 pedometer, especially in children with large tilt angles. We conclude that fastening pedometers to a firm elastic belt may improve stability and reduce undercounting in young people.

Age-related differences in adaptation during childhood: the influences of muscular power production and segmental energy flow caused by muscles

Acquisition of skillfulness is not only characterized by a task-appropriate application of muscular forces but also by the ability to adapt performance to changing task demands. Previous research suggests that there is a different developmental schedule for adaptation at the kinematic compared to the neuro-muscular level. The purpose of this study was to determine how age-related differences in neuro-muscular organization affect the mechanical construction of pedaling at different levels of the task. By quantifying the flow of segmental energy caused by muscles, we determined the muscular synergies that construct the movement outcome across movement speeds. Younger children (5-7 years; n = 11), older children (8-10 years; n = 8), and adults (22-31 years; n = 8) rode a stationary ergometer at five discrete cadences (60, 75, 90, 105, and 120 rpm) at 10% of their individually predicted peak power output. Using a forward dynamics simulation, we determined the muscular contributions to crank power, as well as muscular power delivered to the crank directly and indirectly (through energy absorption and transfer) during the downstroke and the upstroke of the crank cycle. We found significant age x cadence interactions for (1) peak muscular power at the hip joint [Wilks' Lambda = 0.441, F(8,42) = 2.65, p = 0.019] indicating that at high movement speeds children produced less peak power at the hip than adults, (2) muscular power delivered to the crank during the downstroke and the upstroke of the crank cycle [Wilks' Lambda = 0.399, F(8,42) = 3.07, p = 0.009] indicating that children delivered a greater proportion of the power to the crank during the upstroke when compared to adults, (3) hip power contribution to limb power [Wilks' Lambda = 0.454, F(8,42) = 2.54, p = 0.023] indicating a cadence-dependence of age-related differences in the muscular synergy between hip extensors and plantarflexors. The results demonstrate that in spite of a successful performance, children construct the task of pedaling differently when compared to adults, especially when they are pushed to their performance limits. The weaker synergy between hip extensors and plantarflexors suggests that a lack of inter-muscular coordination, rather than muscular power production per se, is a factor that limits children's performance ranges.

A comparison of resonance tuning with positive versus negative sensory feedback

We used a computational model of rhythmic movement to analyze how the connectivity of sensory feedback affects the tuning of a closed-loop neuromechanical system to the mechanical resonant frequency (omega(r)). Our model includes a Matsuoka half-center oscillator for a central pattern generator (CPG) and a linear, one-degree-of-freedom system for a mechanical component. Using both an open-loop frequency response analysis and closed-loop simulations, we compared resonance tuning with four different feedback configurations as the mechanical resonant frequency, feedback gain, and mechanical damping varied. The feedback configurations consisted of two negative and two positive feedback connectivity schemes. We found that with negative feedback, resonance tuning predominantly occurred when omega(r) was higher than the CPG's endogenous frequency (omega(CPG)). In contrast, with the two positive feedback configurations, resonance tuning only occurred if omega(r) was lower than omega(CPG). Moreover, the differences in resonance tuning between the two positive (negative) feedback configurations increased with increasing feedback gain and with decreasing mechanical damping. Our results indicate that resonance tuning can be achieved with positive feedback. Furthermore, we have shown that the feedback configuration affects the parameter space over which the endogenous frequency of the CPG or resonant frequency the mechanical dynamics dominates the frequency of a rhythmic movement.

Resonance tuning of a neuromechanical system with two negative sensory feedback configurations

Resonance tuning in a model of rhythmic movement is compared when the central pattern generator (CPG) consists of two endogenously bursting or two tonically spiking neurons that are connected with reciprocally inhibitory synapses. The CPG receives inhibitory and/or excitatory position feedback from a linear, one-degree-of-freedom mechanical subsystem. As with previously published results [5, 15], resonance tuning is limited to frequencies that are greater than the intrinsic CPG frequency with endogenously bursting neurons. In contrast, with tonically spiking neurons, the resonance tuning range is expanded to frequencies that are below the intrinsic CPG frequency.

Original investigation correlated joint fluctuations can influence the selection of steady state gait patterns in the elderly

This investigation utilized a Markov model to investigate the relationship of correlated lower extremity joint fluctuations and the selection of a steady state gait pattern in the young and elderly. Our model simulated the neuromuscular system by predicting the behavior of the joints for the next gait cycle based on the behavior exhibited in the preceding gait cycles. Such dependencies in the joint fluctuations have been noted previously in the literature. We speculated that compared to the young model, the characteristics of the correlated fluctuations in the elderly model would result in the selection of a different steady state gait pattern. The results of our simulation support the notion that correlated fluctuations in the joint kinematics influence the selection of a steady state gait pattern. The steady state gait pattern for the elderly model was dependent the ankle and hip. Conversely, the steady state gait pattern for the young control model was dependent on the behavior of the knee and hip. Based on our model, we suggested that the altered steady state gait patterns observed in the elderly may be due to an altered neuromuscular memory of prior joint behaviors.

A comparison of kinetic gait parameters for 3-13 year olds

BACKGROUND

Normative gait data is essential for diagnosing and treating abnormal gait patterns. The examination of the onset of adult-like kinetic gait patterns in children has generated inconsistent results. The purpose of this study was to identify age-related differences in kinematic and kinetic gait parameters across children aged 3-13 years old.

METHODS

A motion capture system and three force plates were employed to compute sagittal joint angles and joint kinetics during walking and compare results between children aged 3-4 years (n=13), 5-6 years (n=10), 7-8 years (n=12), and 9-13 years (n=12). Anthropometric data was estimated using a mathematical model (elliptical cylinder method). Peak flexion and extension joint angles and moments, and peak concentric and eccentric joint powers were analyzed using multivariate analyses of variance.

FINDINGS

For most of the variables examined, similar results were obtained across age groups. Reduced peak hip flexion moments and knee extension moments were observed in the 3-4 year olds compared to the oldest group of walkers. Compared to the 9-13 year olds, reduced ankle joint moments and power were observed in most age groups.

INTERPRETATION

The results suggest that adult-like kinetic patterns for the hip and knee were attained by 5 years of age. However, for the ankle joint, adult-like patterns are not achieved until nine years of age or older. These findings stress the importance of using age-matched normative data for clinical gait analysis.

The biomechanics of restricted movement in adult obesity

In spite of significant advances in the knowledge and understanding of the multi-factorial nature of obesity, many questions regarding the specific consequences of the disease remain unanswered. In particular, there is a relative dearth of information pertaining to the functional limitations imposed by overweight and obesity. The limited number of studies to date have mainly focused on the effect of obesity on the temporospatial characteristics of walking, plantar foot pressures, muscular strength and, to a lesser extent, postural balance. Collectively, these studies have implied that the functional limitations imposed by the additional loading of the locomotor system in obesity result in aberrant mechanics and the potential for musculoskeletal injury. Despite the greater prevalence of musculoskeletal disorders in the obese, there has been surprisingly little empirical investigation pertaining to the biomechanics of activities of daily living or into the mechanical and neuromuscular factors that may predispose the obese to injury. A better appreciation of the implications of increased levels of body adiposity on the movement capabilities of the obese would afford a greater opportunity to provide meaningful support in preventing, treating and managing the condition and its sequelae. Moreover, there is an urgent need to establish the physical consequences of continued repetitive loading of major structures of the body, particularly of the lower limbs in the obese, during the diverse range of activities of daily living.

Adapting to changing task demands: variability in children's response to manipulations of resistance and cadence during pedaling

Reduction in performance variability is characteristic of skill acquisition during childhood. Less understood is the role of variability in adaptive skill. The purpose of this study was to determine children's capacity for adapting to changing task requirements. Children ages 4-14 years and adults rode a stationary ergometer at different levels of cadence and resistance. Younger children were less successful in meeting task requirements. When they did succeed, the younger children were more variable. However, no interactions were found. Variability did not change with resistance, and all groups showed increasing variability as cadence increased. It was concluded that in spite of a weaker synergy (more variability), children were adept to changes in task demand within tested limits.

Nonlinear dynamics indicates aging affects variability during gait

OBJECTIVE

To investigate the nature of variability present in time series generated from gait parameters of two different age groups via a nonlinear analysis.

DESIGN

Measures of nonlinear dynamics were used to compare kinematic parameters between elderly and young females.

BACKGROUND

Aging may lead to changes in motor variability during walking, which may explain the large incidence of falls in the elderly.

METHODS

Twenty females, 10 younger (20-37 yr) and 10 older (71-79 yr) walked on a treadmill for 30 consecutive gait cycles. Time series from selected kinematic parameters of the right lower extremity were analyzed using nonlinear dynamics. The largest Lyapunov exponent and the correlation dimension of all time series, and the largest Lyapunov exponent of the original time series surrogated were calculated. Standard deviations and coefficient of variations were also calculated for selected discrete points from each gait cycle. Independent t-tests were used for statistical comparisons.

RESULTS

The Lyapunov exponents were found to be significantly different from their surrogate counterparts. This indicates that the fluctuations observed in the time series may reflect deterministic processes by the neuromuscular system. The elderly exhibited significantly larger Lyapunov exponents and correlation dimensions for all parameters evaluated indicating local instability. The linear measures indicated that the elderly demonstrated significantly higher variability.

CONCLUSIONS

The nonlinear analysis revealed that fluctuations in the time series of certain gait parameters are not random but display a deterministic behavior. This behavior may degrade with physiologic aging resulting in local instability.

RELEVANCE

Elderly show increased local instability or inability to compensate to the natural stride-to-stride variations present during locomotion. We hypothesized that this may be the one of the reasons for the increases in falling due to aging. Future efforts should attempt to evaluate this hypothesis by making comparisons to pathological subjects (i.e. elderly fallers), and examine the sensitivity and specificity of the nonlinear methods used in this study to aid clinical assessment.

The spanning set indicates that variability during the stance period of running is affected by footwear

Sensory information the foot receives appears to be related to kinematic variability. Since footwear material densities affect sensory information, footwear may be an important factor that dictates variability. This study hypothesized that modifications in footwear would result in changes in kinematic variability during the running stance period. Subjects ran on a treadmill for three conditions: hard shoe, soft shoe and barefoot. The spanning sets of the mean ensemble curves of the knee and ankle changes for each condition were used to define variability. Variability was significantly larger in the barefoot condition in comparison with the two footwear conditions for both joints. These results suggest that variability can be affected by peripheral sensory information. The spanning set methodology can be utilized to examine changes in variability.

Spanning set defines variability in locomotive patterns

The purpose of the investigation was to use the spanning set methodology to quantify variability in locomotive patterns and to compare this method with traditional measures of variability. Subjects ran on a treadmill while sagittal plane kinematic data were collected with a high-speed (180 Hz) camera. Changes in variability were evaluated as the subject ran barefoot and in shoes. Mean ensemble curves for the knee angle during the stance period were created for each condition. From these curves, traditional measures of variability were calculated using the coefficients of variation (CVs), and the mean deviation (MD). Spanning set vectors were defined from the coefficients of polynomials that were fitted to the respective standard deviation curves. The magnitude of the spanning set was determined by calculating the norm of the difference between the two vectors. The normalised difference between the two conditions was 6.6%, 6.9% and 98%, for the MD, CV and spanning sets, respectively. The results indicated that the spanning set was capable of statistically (p < 0.05) determining differences in variability between the two conditions. CV and MD measures were unable to detect statistical differences (p > 0.05) between the two conditions. The spanning set provides an alternative, and sensitive measure for evaluating differences in variability from the mean ensemble curve.

Optimization characteristics of walking with and without a load on the trunk of the body

Previous work showed that subjects naturally adopt a walking speed which optimizes energy cost of locomotion and stability of stride; however, no studies have examined whether these criteria are affected by carrying an external load. The purpose of this study was to compare optimization characteristics during loaded or unloaded walking. Energy cost and stride characteristics were measured for 10 subjects with and without a load on the trunk of the body of 10% of the body weight during 4 sessions. The first 2 sessions represent free walking at 2.5, 3, 3.5, 4, 4.5, and 5 km x hr.(-1). The last sessions represent free vs forced walking at constant speed (preferred frequency and +/- 10 PF and +/-20% of preferred frequency). Results show an effect of load on energy cost of walking but no effect on the optimal speed for stability. Furthermore, when carrying a load the subject does not adopt systematically the speed that minimizes physiological cost. Our findings suggest the necessity to consider this effect to prevent gait disturbance and maintain the health benefits of walking.

Neural control of human motor development

It has been possible to expand considerably our understanding of human motor development by making a detailed analysis of various types of movement and muscular activation patterns during different stages of development. Alterations in development subsequent to the appearance of brain lesions have enabled valuable information to be collected about the underlying neural mechanisms, in addition to new information concerning the pathophysiology of cerebral palsy. Studies on the development of the corticospinal system indicate that plastic changes can take place after perinatal brain damage.