A 'Fingerprint' of locomotor maturation: Motor development descriptors, reference development bands and data-set.

BACKGROUND: When aiming at studying and monitoring locomotor development in childhood, innovative indexes for the characterization of motor control performance and wearable technologies have highlighted the potential of significant advances. In particular, quantitative assessment of motor performance during natural walking (NW) and tandem walking (TW) has been proposed to highlight manifestations of motor automaticity and complexity, respectively. RESEARCH QUESTION: This work aims at providing a quantitative overview of metrics characterizing locomotor maturation in a typically developing population, by analysing NW and TW. The final goal is to propose a novel graphical representation of motor development from childhood to adulthood, providing metrics for quantitative assessment with reference bands and data-set, supporting data interpretation and longitudinal assessment. METHODS: 112 typically developing participants (age groups: 6-, 7-, 8-, 9-, 10-, 15-, and 25 years) walked in NW and in TW at self-selected speed. 3D acceleration and angular velocity of lower trunk and shanks were collected. Temporal parameters, their variability, and nonlinear metrics characterizing human movement (harmonic ratio, short-term Lyapunov exponents, multiscale entropy, and recurrence quantification analysis) were calculated. Effect of age was analysed on the different parameters and a graphical polar plot was defined to represent parameters that showed age effect in at least one of the two tasks. RESULTS: Age effect was shown on temporal parameters, their variability, multiscale entropy and recurrence quantification analysis. These parameters were selected for monitoring locomotor development and presented on an ad-hoc designed polar plot showing age-group reference bands. SIGNIFICANCE: Graphic results outline locomotor differences with maturation at first glance. The patterns in NW and TW allow to characterize specific aspects of locomotor maturation, to evaluate in which area changes occur and towards which direction, depending on the task. The novel database containing participants' raw collected data is made available as additional result of the present study.

Changes of human movement complexity during maturation: quantitative assessment using multiscale entropy.

Movement complexity can be defined as the capability of using different strategies to accomplish a specific task and is expected to increase with maturation, reaching its highest level in adulthood.Multiscale Entropy (MSE) has been proposed to estimate complexity on different kinematic signals, at different time scales. When applied on trunk acceleration data during natural walking (NW) at different ages, MSE decreased from childhood to adulthood, apparently contradicting the premises. On the contrary, authors hypothesised that this decrease was dependent on the specific task analysed and resulted from the concurrent increase in gait automaticity.This work aims to test this hypothesis, applying MSE on a non-paradigmatic task (tandem walking, TW), in order to exclude aspects related to automaticity.MSE was estimated on trunk acceleration data, collected on children, adolescents, and young adults during TW and NW. As hypothesized, MSE increased significantly with age in TW and decreased in NW on the sagittal plane. Assuming the development of complexity in TW as reference, MSE in NW showed a reduction to half of the complexity of TW with maturation on the sagittal plane. These results indicate MSE as sensitive to differences in performance due to maturation and to expected changes in complexity related to the specific performed task.

Towards an objective assessment of motor function in sub-acute stroke patients: Relationship between clinical rating scales and instrumental gait stability indexes.

The assessment of walking function alterations is a key issue to design effective rehabilitative interventions in sub-acute stroke patients. Nevertheless, the objective quantification of these alterations remains a challenge. Clinical rating scales are commonly used in clinical practice, but have been proven prone to errors associated to the evaluator subjective perception. On the other hand, instrumental measurement of trunk acceleration can be exploited for an objective quantitative characterization of gait function, but it is not applied in routine clinical practice, because the resulting quantitative indexes have not been related to the clinically information, conventionally provided by the rating scales. To overcome this limitation, the relationship between the indexes, in specific clinical conditions, and rating scale must be better investigated, to support their exploitability in the clinical practice as a fast and reliable screening tool. Thirty-one sub-acute stroke patients (17 with and 14 without cane) participated in the study. All were assessed with 6 rating scales (MI, TCT, MRI, FAC, WHS, CIRS) and 2 functional tests (2MWT and TUG). Sample Entropy (SEN) and Recurrence Quantification Analysis (RQA) in AP, ML and V directions were calculated over 2MWT and walking section of TUG. The influence of assessment task and cane was analysed, as well as correlation of SEN and RQA indexes with clinical rating scales. SEN and RQA on the medio-lateral plane resulted influenced by the use of the cane, while the correlations between indexes and clinical scales showed that SEN and RQA for antero-posterior direction correlate positively with WHS.

Objective assessment of movement competence in children using wearable sensors: An instrumented version of the TGMD-2 locomotor subtest.

Movement competence (MC) is defined as the development of sufficient skill to assure successful performance in different physical activities. Monitoring children MC during maturation is fundamental to detect early minor delays and define effective intervention. To this purpose, several MC assessment batteries are available. When evaluating movement strategies, with the aim of identifying specific skill components that may need improving, widespread MC assessment is limited by high time consumption for scoring and the need for trained operators to ensure reliability. This work aims to facilitate and support the assessment by designing, implementing and validating an instrumented version of the TGMD-2 locomotor subtest based on Inertial Measurement Units (IMUs) to quantify MC in children rapidly and objectively. 45 typically developing children, aged 6-10, performed the TGMD-2 locomotor subtest (six skills). During the tests, children wore five IMUs mounted on lower back, on ankles and on wrists. Sensor and video recordings of the tests were collected. Three expert evaluators performed the standard assessment of TGMD-2. Using theoretical and modelling approaches, algorithms were implemented to automatically score children tests based on IMUs' data. The automatic assessment, compared to the standard one, showed an agreement higher than 87% on average on the entire group for each skill and a reduction of time for scoring from 15 to 2min per participant. Results support the use of IMUs for MC assessment: this approach will allow improving the usability of MC assessment, supporting objectively evaluator decisions and reducing time requirement for the evaluation of large groups.

Complexity of human gait pattern at different ages assessed using multiscale entropy: From development to decline.

Multiscale entropy (MSE) has been applied in biomechanics to evaluate gait stability during human gait and was found to be a promising method for evaluating fall risk in elderly and/or pathologic subjects. The hypothesis of this work is that gait complexity is a relevant parameter of gait development during life, decreasing from immature to mature gait and then increasing again during old age. In order to verify this hypothesis, MSE was applied on trunk acceleration data collected during gait of subjects of different ages: toddlers at the onset of walking, pre-scholar and scholar children, adolescents, young adults, adults and elderlies. MSE was estimated by calculating sample entropy (SEN) on raw unfiltered data of L5 acceleration along the three axes, using values of τ ranging from 1 to 6. In addition, other performance parameters (cadence, stride time variability and harmonic ratio) were evaluated. The results followed the hypothesized trend when MSE was applied on the vertical and/or anteroposterior axis of trunk acceleration: an age effect was found and adult SEN values were significantly different from children ones. From young adults to elderlies a slight increase in SEN values was shown although not statistically significant. While performance gait parameters showed adolescent gait similar to the one of adults, SEN highlighted that their gait maturation is not complete yet. In conclusion, present results suggest that the complexity of gait, evaluated on the sagittal plane, can be used as a characterizing parameter of the maturation of gait control.

Evaluation of toddler different strategies during the first six-months of independent walking: a longitudinal study.

Twenty infants (age 10-16 month) were analyzed using inertial sensors over a 6-month period after the onset of independent walking. Changes in gait temporal parameters, coordination and gait strategies were evaluated. Gait temporal parameters showed a developmental shift at 2 months of walking experience: after this period, a change in the developmental trend was present in most of the analyzed parameters. Cadence results showed that the increased velocity is more due to an increase in step length than to an increase in cadence, after the first two months of independent walking. Different gait strategies were identified during the first month of independent gait based on collected data; after one month, characteristics of the pendulum mechanism were present in each examined toddler.

Gait variability and stability measures: minimum number of strides and within-session reliability.

BACKGROUND: Several methods are proposed in the literature for the quantification of gait variability/stability from trunk accelerations. Since outputs can be influenced by implementation differences, reliability assessment and standardization of implementation parameters are still an issue. The aim of this study is to assess the minimum number of required strides and the within-session reliability of 11 variability/stability measures. METHOD: Ten healthy participants walked in a straight line at self-selected speed wearing two synchronized tri-axial Inertial Measurement Units. Five variability measures were calculated based on stride times namely Standard deviation, Coefficient of variation, Inconsistency of variance, Nonstationary index and Poincaré plot. Six stability measures were calculated based on trunk accelerations namely Maximum Floquet multipliers, Short term/long term Lyapunov exponents, Recurrence quantification analysis, Multiscale entropy, Harmonic ratio and Index of harmonicity. The required minimum number of strides and the within-session reliability for each measure were obtained based on the interquartile range/mean ratio. Measures were classified in five categories (namely excellent, good, average, poor, and very poor) based on their reliability. RESULTS: The number of strides required to obtain a reliable measure was generally larger than those conventionally used. Variability measures showed average to poor reliability, while stability measures ranged from excellent to very poor reliability. CONCLUSION: Recurrence quantification analysis and multiscale entropy of trunk accelerations showed excellent reliability and a reasonable number of required strides. Based on these results, these measures should be taken into consideration in the assessment of fall risk.

Estimating fall risk with inertial sensors using gait stability measures that do not require step detection.

Falls have major consequences both at societal (health-care and economy) and individual (physical and psychological) levels. Questionnaires to assess fall risk are commonly used in the clinic, but their predictive value is limited. Objective methods, suitable for clinical application, are hence needed to obtain a quantitative assessment of individual fall risk. Falls in older adults often occur during walking and trunk position is known to play a critical role in balance control. Therefore, analysis of trunk kinematics during gait could present a viable approach to the development of such methods. In this study, nonlinear measures such as harmonic ratio (HR), index of harmonicity (IH), multiscale entropy (MSE) and recurrence quantification analysis (RQA) of trunk accelerations were calculated. These measures are not dependent on step detection, a potentially critical source of error. The aim of the present study was to investigate the association between the aforementioned measures and fall history in a large sample of subjects (42 fallers and 89 non - fallers) aged 50 or older. Univariate associations with fall history were found for MSE and RQA parameters in the AP direction; the best classification results were obtained for MSE with scale factor τ = 2 and for maximum length of diagonals in RQA (72.5% and 71% correct classifications, respectively). MSE and RQA were found to be positively associated with fall history and could hence represent useful tools in the identification of subjects for fall prevention programs.

Orbital stability analysis in biomechanics: a systematic review of a nonlinear technique to detect instability of motor tasks.

Falls represent a heavy economic and clinical burden on society. The identification of individual chronic characteristics associated with falling is of fundamental importance for the clinicians; in particular, the stability of daily motor tasks is one of the main factors that the clinicians look for during assessment procedures. Various methods for the assessment of stability in human movement are present in literature, and methods coming from stability analysis of nonlinear dynamic systems applied to biomechanics recently showed promise. One of these techniques is orbital stability analysis via Floquet multipliers. This method allows to measure orbital stability of periodic nonlinear dynamic systems and it seems a promising approach for the definition of a reliable motor stability index, taking into account for the whole task cycle dynamics. Despite the premises, its use in the assessment of fall risk has been deemed controversial. The aim of this systematic review was therefore to provide a critical evaluation of the literature on the topic of applications of orbital stability analysis in biomechanics, with particular focus to methodologic aspects. Four electronic databases have been searched for articles relative to the topic; 23 articles were selected for review. Quality of the studies present in literature has been assessed with a customised quality assessment tool. Overall quality of the literature in the field was found to be high. The most critical aspect was found to be the lack of uniformity in the implementation of the analysis to biomechanical time series, particularly in the choice of state space and number of cycles to include in the analysis.

Sensitivity analysis of an energetic muscle model applied at whole body level in recumbent pedalling.

Musculoskeletal models are used in order to describe and analyse the mechanics of human movement. In order to get a complete evaluation of the human movement, energetic muscle models were developed and were shown to be promising. The aim of this work is to determine the sensitivity of muscle mechanical and energetic model estimates to changes in parameters during recumbent pedalling. Inputs of the model were electromyography and joint angles, collected experimentally on one participant. The sensitivity analysis was performed on muscle-specific tension, physiological cross-sectional area, muscle maximal force, tendon rest length and percentage of fast-twitch fibres using an integrated sensitivity ratio. Soleus, gastrocnemius, vasti, gluteus and medial hamstrings were selected for the analyses. The energetic model was found to be always less sensitive to parameter changes than the mechanical model. Tendon slack length was found to be the most critical parameter for both energetic and mechanical models even if the effect on the energetic output was smaller than on muscle force and joint moments.

Can Patellar Tendon Angle reveal sagittal kinematics in total knee arthroplasty?

The Patellar Tendon Angle is strongly correlated with both patello-femoral and tibio-femoral joint kinematics. Thus, the Patellar Tendon Angle might be regarded as a concise indicator of the antero-posterior translation of the femur with respect to the tibia. Twelve subjects, who had undergone total knee arthroplasty, were investigated by video-fluoroscopy during step-up/down. The kinematics at the replaced knee was reconstructed by means of 3D fluoroscopy. The Patellar Tendon Angle and the knee-flexion angle were measured on sagittal fluoroscopic images with software designed for the purpose. The slope of the linear trend of the Patellar Tendon Angle versus knee-flexion angle relationship correlated significantly with the mean (p = 0.001), most anterior (p = 0.001), and most posterior (p = 0.016) position reached by the femur over the tibia. The Patellar Tendon Angle versus knee-flexion angle relationship provides relevant information about the anterior or posterior positioning of the femur over the tibia, but it cannot be interpreted as quantification of the actual antero-posterior translation of the femur over the tibia.

Mobility of the subtalar joint in the intact ankle complex.

A previous study by these authors showed that the calcaneus follows a unique path of unresisted coupled motion relative to the tibia during passive flexion and that most of this motion occurred at the ankle level. Subtalar motion in the intact ankle complex was observed only when perturbations from this path were induced by the application of force to the calcaneus. Relative motion of the bones of the ankle complex was tracked by stereophotogrammetry in seven specimens. Anatomical landmarks, reference frames and joint angles were defined by standard techniques. Sequential moments were applied to the calcaneus about the long axis of the tibia. Measured movements at subtalar level demonstrated plantarflexion coupled to supination and internal rotation (inversion) and dorsiflexion coupled to pronation and external rotation (eversion). These movements were resisted and were fully recovered when the external load was removed. Subtalar motion diminished as the ankle approached maximal dorsi- and plantarflexion. Two clearly distinguished mean axes of rotation were observed for inversion and eversion runs. The axes of inversion and eversion of the subtalar complex changed orientation along a preferred and repeatable path. The subtalar joint complex occupied only a single stable position in the unloaded state and with no range of unresisted motion. It is inferred that mobility was possible only by the stretching and lengthening of the ligaments and the indentation of the articular surfaces, requiring the application of loads. The subtalar joint complex behaves like a flexible structure.

Effects of hip joint centre mislocation on gait analysis results.

Methods to determine the hip joint centre (HJC) location are necessary in gait analysis. It has been demonstrated that the methods proposed in the literature involve large mislocation errors. The choice should be made according to the extent by which HJC location errors distort the estimates of angles and resultant moments at the hip and knee joints. This study aimed at quantifying how mislocation errors propagate to these gait analysis results. Angles and moments at the hip and knee joint were calculated for five able-bodied subjects during level walking. The nominal position of the HJC was determined as the position of the pivot point of a 3D movement of the thigh relative to the pelvis. Angles and moments were then re-calculated after having added to HJC co-ordinates errors in the range of +/-30 mm. Angles and moments at both hip and knee joints were affected by HJC mislocation. The hip moments showed the largest propagation error: a 30 mm HJC anterior mislocation resulted in a propagated error into flexion/extension component of about -22%. The hip abduction/adduction moment was found the second largest affected quantity: a 30 mm lateral HJC mislocation produced a propagated error of about -15%. Finally, a 30 mm posterior HJC mislocation produced a delay of the flexion-to-extension timing in the order of 25% of the stride duration. HJC estimation methods with minimum antero-posterior error should therefore be preferred.

Comparison of the myocardial effects of desflurane and isoflurane in healthy patients: assessment by continuous oesophageal aortic blood flow echo-Doppler.

Experimentally, desflurane causes a moderate positive inotropic effect and a transient increase in arterial pressure with rapid increases in concentration compared with isoflurane. We used a continuous oesophageal aortic blood flow echo Doppler device to study the myocardial effects of equi-anaesthetic concentrations of isoflurane and desflurane in 32 healthy patients undergoing superficial surgery. After induction of anaesthesia with midazolam, etomidate and fentanyl general anaesthesia was maintained in 16 patients with 0.6% end-expired concentration of isoflurane and in 16 patients with 3% end expired concentration of desflurane. Isoflurane induced a rapid decrease in aortic blood flow (ABF) which remained almost stable whereas desflurane induced an early, moderate and transient increase in ABF (1 min after introduction of the halogenated agent, mean ABF was 107 (SD 3)% in the desflurane group vs 95 (9)% in isoflurane group compared with control values before introduction of the inhalation agent; P = 0.005), followed by a marked secondary decrease in ABF. The maximal decrease in ABF reached 71 (15)% of its initial value in the desflurane group compared with 80 (14)% in the isoflurane group (ns). Neither agent caused significant changes in other variables except for PE'CO2 which decreased in both groups. Continuous ABF echo-Doppler monitoring demonstrated an early transient positive inotropic effect of desflurane.