Fatigue-related gait adaptations in children with cerebral palsy.

AIM: To obtain insights into the effects of fatigue on the kinematics, kinetics, and energy cost of walking (ECoW) in children with cerebral palsy (CP). METHOD: In this prospective observational study, 12 children with CP (mean age 12 years 9 months, SD 2 years 7 months; four females, eight males) and 15 typically developing children (mean age 10 years 8 months, SD 2 years 4 months; seven females, eight males) followed a prolonged intensity-based walking protocol on an instrumented treadmill, combined with gas analysis measurements. The protocol consisted of consecutive stages, including a 6-minute walking exercise (6MW) at comfortable speed, 2 minutes of moderate-intensity walking (MIW) (with a heart rate > 70% of its predicted maximal), and 4 minutes walking after MIW. If necessary, the speed and slope were incremented to reach MIW. Outcomes were evaluated at the beginning and end of the 6MW and after MIW. RESULTS: With prolonged walking, Gait Profile Scores deteriorated slightly for both groups (p < 0.01). Knee flexion increased during early stance (p = 0.004) and ankle dorsiflexion increased during late stance (p = 0.034) in children with CP only. Negligible effects were found for kinetics. No demonstrable change in ECoW was found in either group (p = 0.195). INTERPRETATION: Kinematic deviations in children with CP are progressive with prolonged walking. The large variation in adaptations indicates that an individual approach is recommended to investigate the effects of physical fatigue on gait in clinical practice.

Energy cost of gait in children and the effect of speed, age, and body size.

BACKGROUND: Energy cost (EC) of comfortable walking is often used in clinical evaluation of children with altered gait function. EC is presented as energy expenditure per kg bodyweight per meter, either in total (grossEC) or in addition to resting energy expenditure (netEC). GrossEC is considered more reliable and netEC less affected by between-subject variations in speed, age, and body size. However, the effect of the individual child's speed on EC is rarely considered, while altered gait function may affect both speed and EC. RESEARCH QUESTION: To what extent are grossEC and netEC affected by within-subject variation in speed and between-subject variations in speed, age, and body size? METHODS: Forty-two typically developing children (7-15 y) were included in this cross-sectional study. Age, height, and bodyweight were obtained. Breath-to-breath gas-exchange measures of VO2 and VCO2 were conducted during rest and five over-ground gait conditions: walking at slow, comfortable, and fast speed, jogging and running. All conditions lasted 3-5 min. Body surface area, non-dimensional speed, grossEC, and netEC were calculated. Regression analyses and mixed model analyses were conducted to explain the effect of speed, age, and body size on variations in EC. RESULTS: GrossEC showed a non-significant, concave up relation to within-subject variation in speed, with a minimum around comfortable/fast walking speed. NetEC had a strong positive linear relation to within-subject variation in speed. For each gait condition, grossEC was more affected by between-subject variations in speed, age, and body size compared to netEC. However, the effect of age and body size was not eliminated for netEC but was quadratic. SIGNIFICANCE: Although normalised to speed and bodyweight, grossEC and netEC are still affected by those factors. However, they are affected differently for within- and between-subject variations. This must be considered when interpreting EC in children in relation to gait function.

The relationship between energy cost of walking, ankle push-off and walking speed in persons with multiple sclerosis.

BACKGROUND: The energy cost of walking (ECw) is an important indicator of walking dysfunction in persons with multiple sclerosis (PwMS). However, its underlying causes and its relation with ankle push-off and walking speed are not well understood. RESEARCH QUESTION: What is the contribution of ankle push-off and walking speed to increased ECw in PwMS? METHODS: Ten PwMS with walking limitations and 10 individually gender- and age-matched healthy controls (HC) were included. All participants performed two 6-min walking trials on a treadmill at comfortable walking speed (CWS of PwMS) and fast walking speed (FWS, 130 % of CWS of PwMS). Kinetics and metabolic cost were evaluated. Generalized estimating equations were performed to investigate effects of group and walking speed, and their interaction. Spearman correlations were conducted to examine whether ECw was related to ankle push-off in PwMS, controlling for differences in walking speed in PwMS. RESULTS: ECw at matched walking speed was significantly higher in PwMS compared to HC. Kinetic parameters were not different between the most impaired leg in PwMS and HC at matched walking speed, but asymmetry between both legs of PwMS was observed. At FWS, ECw reduced and ankle push-off increased similarly in both groups. ECw was inversely related to peak ankle power of the most impaired leg in PwMS at CWS. SIGNIFICANCE: Slow walking speed is one factor that contributes to increased ECw in PwMS. Furthermore, PwMS who had a higher ECw showed a lower peak ankle power, independent of walking speed. This indicates that ankle push-off could be a contributor to increased ECw.

The effect of prolonged walking on muscle fatigue and neuromuscular control in children with cerebral palsy.

BACKGROUND: Muscle fatigue of the lower limbs is considered a main contributor to the perceived fatigue in children with cerebral palsy (CP) and is expected to occur during prolonged walking. In adults without disabilities, muscle fatigue has been proposed to be associated with adaptations in complexity of neuromuscular control. RESEARCH QUESTION: What are the effects of prolonged walking on signs of muscle fatigue and complexity of neuromuscular control in children with CP? METHODS: Ten children with CP and fifteen typically developing (TD) children performed a standardised protocol on an instrumented treadmill consisting of three stages: six-minutes walking at preferred speed (6 MW), moderate-intensity walking (MIW, with two minutes at heart rate > 70% of predicted maximal heart rate) and four-minutes walking at preferred speed (post-MIW). Electromyography (EMG) data were analysed for eight muscles of one leg during three time periods: 6 MW-start, 6 MW-end and post-MIW. Signs of muscle fatigue were quantified as changes in EMG median frequency and EMG root mean square (RMS). Complexity of neuromuscular control was quantified by total variance accounted for by one synergy (tVAF1). Muscle coactivation was assessed for antagonistic muscle pairs. RESULTS: EMG median frequency was decreased at 6 MW-end and post-MIW compared to 6 MW-start in children with CP (p < 0.05), but not in TD children. In both groups, EMG-RMS (p < 0.01) and muscle coactivation (p < 0.01) were decreased at 6 MW-end and post-MIW compared to 6 MW-start. tVAF1 decreased slightly at 6 MW-end and post-MIW compared to 6 MW-start in both groups (p < 0.05). Changes were most pronounced from 6 MW-start to 6 MW-end. SIGNIFICANCE: Children with CP presented signs of muscle fatigue after prolonged walking, while no effects were found for TD. Both groups showed minimal changes in tVAF1, suggesting signs of muscle fatigue are not associated with changes in complexity of neuromuscular control.

How does a systematic tuning protocol for ankle foot orthosis-footwear combinations affect gait in children in cerebral palsy?

PURPOSE: To investigate the effects of a systematic tuning protocol for ankle foot orthosis footwear combinations (AFO-FC) using incrementing heel height on gait in children with cerebral palsy (CP). METHODS: Eighteen children with CP (10.8 ± 3 years, Gross Motor Function Classification System (GMFCS) I-II) underwent 3D gait analysis on a treadmill, while the AFO heel surface was systematically incremented with wedges. Children were subdivided based on their gait pattern, i.e., knee hyperextension (EXT) and excessive knee flexion (FLEX). Outcome measures included sagittal hip and knee angles and moments, shank to vertical angle (SVA), foot to horizontal angle, and gait profile score (GPS). RESULTS: For both groups, incrementing heel height resulted in increased knee flexion, more inclined SVA, and increased knee extension moments. This resulted in gait improvements for some children of the EXT-group, but not in FLEX. High variation was found between individuals and within-subject effects were not always consistent for kinematic and kinetics. CONCLUSIONS: A systematic AFO-FC tuning protocol using incremented heel height can be effective to improve gait in children with CP walking with EXT. The current results emphasise the importance of including kinematics as well as kinetics of multiple instances throughout the gait cycle for reliable interpretation of the effect of AFO tuning on gait.Implications for rehabilitationA systematic ankle foot orthosis footwear combinations (AFO-FC) tuning protocol using incremented heel height can improve gait in children walking with knee hyperextension.Tuning results in changes throughout the gait cycle.Little evidence is found for an optimal SVA of 10-12° at midstance.For clinical interpretation, both joint kinematic and kinetic parameters should be considered throughout the gait cycle and evaluation should not be based on SVA only.

Effects of functional power training on gait kinematics in children with cerebral palsy.

BACKGROUND: Muscle weakness is one of the most prevalent symptoms in children with cerebral palsy (CP). Although recent studies show that functional power training can improve strength and functional capacity in young children with CP, effects on specific gait parameters have not previously been reported. RESEARCH QUESTION: What are the effects of functional power training on gait in children with CP? Specifically, we investigated effects of training on gait kinematics and spatiotemporal parameters, and whether these were dependent on walking speed. METHODS: Ten children with CP (age 5-10 years, GMFCS I-II) participated in a functional power training program. At the start and end of the program, children underwent 3D gait analysis on a treadmill at a gradual range of walking speeds (70-175% of their comfortable walking speed). Multilevel (linear mixed model) analysis was used to evaluate effects pre-post training at different walking velocities. RESULTS: Although children's self-chosen comfortable walking speed improved (0.71 ±â€¯0.25 to 0.85 ±â€¯0.25 m/s, p < .05), effects on gait kinematics at similar speed were limited and only exceeded statistical and clinically meaningful thresholds when children walked at higher walking speed. At fast speeds, improvements up to 5° were found in knee and hip extension during stance (p < .01). SIGNIFICANCE: This study demonstrates that gait kinematics can improve after functional power training, but the magnitude of effects is dependent on walking speed. In this light, improvements are underestimated when evaluating gait at pre-training comfortable walking speed only.

Factors Associated With Long-Term Improvement of Gait After Selective Dorsal Rhizotomy.

OBJECTIVE: To identify factors associated with long-term improvement in gait in children after selective dorsal rhizotomy (SDR). DESIGN: Retrospective cohort study. SETTING: University medical center. PARTICIPANTS: Children (N=36) (age 4-13y) with spastic diplegia of Gross Motor Function Classification System (GMFCS) level I (n=14), II (n=15), and III (n=7) were included retrospectively from the database of our hospital. Children underwent SDR between January 1999 and May 2011. Patients were included if they received clinical gait analysis before and 5 years post-SDR, age >4 years at time of SDR and if brain magnetic resonance imaging (MRI) scan was available. INTERVENTION: Selective dorsal rhizotomy. MAIN OUTCOME MEASURES: Overall gait quality was assessed with Edinburgh visual gait score (EVGS), before and 5 years after SDR. In addition, knee and ankle angles at initial contact and midstance were evaluated. To identify predictors for gait improvement, several factors were evaluated including functional mobility level GMFCS, presence of white matter abnormalities on brain MRI, and selective motor control during gait (synergy analysis). RESULTS: Overall gait quality improved after SDR, with a large variation between patients. Multiple linear regression analysis revealed that worse score on EVGS and better GMFCS were independently related to gait improvement. Gait improved more in children with GMFCS I and II compared to III. No differences were observed between children with or without white matter abnormalities on brain MRI. Selective motor control during gait was predictive for improvement of knee angle at initial contact and midstance, but not for EVGS. CONCLUSION: Functional mobility level and baseline gait quality are both important factors to predict gait outcomes after SDR. If candidates are well selected, SDR can be a successful intervention to improve gait both in children with brain MRI abnormalities as well as other causes of spastic diplegia.

Evolution of gait in adolescents and young adults with spastic diplegia after selective dorsal rhizotomy in childhood: A 10 year follow-up study.

BACKGROUND: Short-term benefit on gait of selective dorsal rhizotomy (SDR) surgery, which relieves spasticity of the lower extremities has been demonstrated in children with cerebral palsy (CP). However very little is known of the evolution of gait when patients become adolescents and young adults. RESEARCH QUESTION: How does the gait pattern evolve in adolescents and young adults who underwent SDR during childhood? METHODS: A longitudinal study was performed including 19 ambulant patients with spastic diplegia due to CP or other causes (mean age at SDR: 6.6 ±â€¯1.6 years) who were assessed four times: pre-SDR, 2 years post- SDR, 5 years post-SDR and at least 10 years post-SDR. From 2D video recordings, Edinburgh Visual Gait Score and lower limb joint kinematic parameters were calculated. RESULTS: Our data show that the improvement in the gait pattern obtained short-term after SDR continues during into adolescence and adulthood. Ten years after SDR all patients improved compared to baseline. Considering the lower limb joint kinematics, most notable improvements were found at knee and ankle joints. Compared to the evaluation before SDR, the range of motion of the knee increased: the knee was more extended at initial contact and knee flexion in midswing improved. Excessive ankle plantar flexion was reduced during the entire gait cycle. Only minor changes were found at hip and pelvis. Eight patients underwent additional orthopaedic surgery in the years after SDR, and the present findings should be considered as a combination of SDR, development and additional treatment. SIGNIFICANCE: We demonstrate lasting improvement of gait quality in ambulant patients with spastic diplegia who underwent SDR during childhood when they become adolescents and young adults.

Regulation of step frequency in transtibial amputee endurance athletes using a running-specific prosthesis.

Running specific prostheses (RSP) are designed to replicate the spring-like behaviour of the human leg during running, by incorporating a real physical spring in the prosthesis. Leg stiffness is an important parameter in running as it is strongly related to step frequency and running economy. To be able to select a prosthesis that contributes to the required leg stiffness of the athlete, it needs to be known to what extent the behaviour of the prosthetic leg during running is dominated by the stiffness of the prosthesis or whether it can be regulated by adaptations of the residual joints. The aim of this study was to investigate whether and how athletes with an RSP could regulate leg stiffness during distance running at different step frequencies. Seven endurance runners with an unilateral transtibial amputation performed five running trials on a treadmill at a fixed speed, while different step frequencies were imposed (preferred step frequency (PSF) and -15%, -7.5%, +7.5% and +15% of PSF). Among others, step time, ground contact time, flight time, leg stiffness and joint kinetics were measured for both legs. In the intact leg, increasing step frequency was accompanied by a decrease in both contact and flight time, while in the prosthetic leg contact time remained constant and only flight time decreased. In accordance, leg stiffness increased in the intact leg, but not in the prosthetic leg. Although a substantial contribution of the residual leg to total leg stiffness was observed, this contribution did not change considerably with changing step frequency. Amputee athletes do not seem to be able to alter prosthetic leg stiffness to regulate step frequency during running. This invariant behaviour indicates that RSP stiffness has a large effect on total leg stiffness and therefore can have an important influence on running performance. Nevertheless, since prosthetic leg stiffness was considerably lower than stiffness of the RSP, compliance of the residual leg should not be ignored when selecting RSP stiffness.

Biomechanical organization of gait initiation depends on the timing of affective processing.

Gait initiation (GI) from a quiet bipedal posture has been shown to be influenced by the emotional state of the actor. The literature suggests that the biomechanical organization of forward GI is facilitated when pleasant pictures are shown, as compared to unpleasant pictures. However, there are inconsistencies in the literature, which could be due to the neural dynamics of affective processing. This study aimed to test this hypothesis, using a paradigm whereby participants initiated a step as soon as they saw an affective picture (i.e., onset), or as soon as the picture disappeared from the screen (i.e., offset). Pictures were a priori categorized as pleasant or unpleasant, and could also vary in their arousing properties. We analyzed center-of-pressure and center-of-gravity dynamics as a function of emotional content. We found that gait was initiated faster with pleasant images at onset, and faster with unpleasant images at offset. Also, with offset GI the peak velocity of the COG was reduced, and subjects took smaller steps, with unpleasant images relative to pleasant images. The results are discussed in terms of current knowledge regarding temporal processing of emotions, and its effects on GI.