Postmortem fetal imaging: prospective blinded comparison of two-dimensional ultrasound with magnetic resonance imaging.

OBJECTIVE: To compare the diagnostic rate and accuracy of 3-Tesla (T) postmortem magnetic resonance imaging (PM-MRI) and postmortem ultrasound (PM-US) in an unselected fetal population. METHODS: We performed prospectively, in a blinded manner, 3-T PM-MRI and PM-US on 160 unselected fetuses at 13-41 weeks of gestation. All imaging was reported according to a prespecified template, for five anatomical regions: brain, thorax, heart, abdomen and spine. The rates of non-diagnostic results for PM-US and PM-MRI were compared and, for results that were diagnostic, we calculated sensitivity, specificity and concordance rates for each anatomical region, using conventional autopsy as the reference standard. RESULTS: 3-T PM-MRI performed significantly better than did PM-US overall and in particular for fetuses ≥ 20 weeks' gestation. Specifically, the non-diagnostic rates for PM-MRI vs PM-US were 4.4% vs 26.9% (7/160 vs 43/160; P < 0.001) for the brain, 5.2% vs 17.4% (8/155 vs 27/155; P < 0.001) for the thorax, 3.8% vs 30.6% (6/157 vs 48/157; P < 0.001) for the heart and 3.2% vs 23.6% (5/157 vs 37/157; P < 0.001) for the abdomen. For the spine, both techniques showed an equally low non-diagnostic rate. When both postmortem imaging techniques were diagnostic, they had similar accuracy, with no difference in sensitivity or specificity, and similar concordance with autopsy (PM-US, 79.5-96.5%; PM-MRI, 81.6-99.1%). CONCLUSIONS: PM-MRI performed significantly better than PM-US in this unselected population, due mainly to a lower non-diagnostic rate. PM-MRI should remain the first-line imaging investigation for perinatal autopsy, but PM-US could be considered if MRI is not available, albeit with a higher non-diagnostic rate. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Postmortem examination of human fetuses: comparison of two-dimensional ultrasound with invasive autopsy.

OBJECTIVE: To assess the diagnostic accuracy of postmortem ultrasound performed by operators blinded to prenatal findings and to invasive autopsy results in fetuses at different gestational ages and to investigate the effect of various parameters on its diagnostic success. METHODS: We performed postmortem two-dimensional ultrasound examination, blinded to clinical details, on 163 fetuses at 13-42 weeks' gestation. Logistic regression analysis was used to investigate the effect of: (i) gestational age at postmortem ultrasound, (ii) presence of maceration and (iii) mode of death, on whether the exam succeeded or failed to reach a diagnosis. In 123 cases in which invasive autopsy was available, the diagnostic accuracy of ultrasound in detecting major organ abnormalities was evaluated, using invasive autopsy as the gold standard. RESULTS: For the fetal brain, postmortem ultrasound exam was non-diagnostic in significantly more fetuses with maceration (39.5%; 17/43) vs those without maceration (20.0%; 24/120) (P = 0.013). For the fetal thorax, the exam was non-diagnostic in 34.1% (15/44) of fetuses < 20 weeks of gestation and in 10.9% (13/119) of fetuses ≥ 20 weeks (P < 0.001). For the heart and abdominal organs, there was no association between non-diagnostic postmortem ultrasound and the variables tested. For fetuses < 20 weeks, specificity of postmortem ultrasound examination was 83.3% for detection of anomalies of the brain, 68.6% for the thorax and 77.4% for the heart. For fetuses ≥ 20 weeks, sensitivity and specificity were, respectively, 61.9% and 74.2% for detection of anomalies of the brain, 29.5% and 87.0% for the thorax and 65.0% and 83.1% for the heart. For the fetal abdominal organs, sensitivity was 60.7% and specificity 75.8%, and postmortem ultrasound was particularly useful for detection of abnormalities of the kidneys, irrespective of gestational age. CONCLUSION: Although maceration may lead to failure of postmortem ultrasound examination in some cases, this technique achieves diagnostically acceptable levels of accuracy for fetal brain and abdominal organs, compared with conventional autopsy. It may therefore play a role as a first-line examination before other virtual autopsy techniques are indicated. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Minimally invasive fetal autopsy using ultrasound: a feasibility study.

OBJECTIVES: To evaluate postmortem ultrasound (PM-US) for minimally invasive autopsy, and to demonstrate its feasibility, sensitivity and specificity, as compared with conventional autopsy, in detecting major congenital abnormalities. METHODS: Over a 19-month study period from 1 March 2012 to 30 September 2013, we recruited from a referral hospital 88 consecutive fetuses, at 11-40 weeks' gestation, which had undergone termination, miscarriage or intrauterine fetal death. We performed PM-US using different transducers and compared the data with those from conventional autopsy. The latter was performed, according to the Societé Francaise de Foetopathologie (France) guidelines, by experienced perinatal pathologists who were blinded to the ultrasound data. RESULTS: Complete virtual autopsy by ultrasound was possible in 95.5% of the cases. The sensitivity of PM-US for detecting brain abnormalities was 90.9% (95% CI, 58.7-99.8%) and the specificity was 87.3% (95% CI, 75.5-94.7%). In 20% of cases, a neuropathological examination was not possible due to severe maceration. The sensitivity for detection of thoracic abnormalities was 88.9% (95% CI, 65.3-98.6%) and the specificity was 92.8% (95% CI, 84.1-97.6%), and the sensitivity for detection of abdominal anomalies was 85.7% (95% CI, 57.2-98.2%) and the specificity was 94.6% (95% CI, 86.7-98.5%). CONCLUSION: This pilot study confirms the feasibility of PM-US for virtual autopsy as early as 11 weeks' gestation. This new technique shows high sensitivity and specificity in detecting congenital structural abnormalities as compared with conventional autopsy. Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.

[Diagnosis and management of a particular caseof intractable constipation]. / Diagnostic et gestion d'un cas particulier de constipation opiniâtre.

Constipation is a very common pattern in childhood. There are multiple reasons for constipation including one very rare : chronic intestinal pseudo-obstruction syndrome. We report the case of a young patient monitored for multiple incidents of intestinal pseudo- obstruction with intractable constipation. The patient underwent several surgical interventions to relieve his symptoms because the non operative treatments, based on liquid diet and laxatives, didn't show great effectiveness. We will review the differential diagnosis of chronic constipation and we will discuss the particular diagnostic entity of this patient. We will also discuss the different treatments that allowed to provide tolerance to oral feeding.

La constipation est un motif de consultation pédiatrique très courant. Les étiologies sont multiples mais le syndrome de pseudo- obstruction intestinale chronique, une cause de constipation chronique, est très rare. Nous rapportons le cas d'un jeune patient suivi pour de multiples épisodes de pseudo- obstruction intestinale avec une constipation opiniâtre. Le patient a subi plusieurs interven- tions chirurgicales pour soulager ses symptômes car les traitements à base de diète liquide et de laxatifs ne se sont pas toujours montrés efficaces. Nous reverrons les diagnostics différentiels d'une constipation chronique et nous discuterons de l'entité diagnostique particulière de ce jeune patient. Nous discuterons également des différents traitements entrepris pour lui permettre de continuer à s'alimenter normalement.

Talent in Female Gymnastics: a Survival Analysis Based upon Performance Characteristics.

This study investigated the link between the anthropometric, physical and motor characteristics assessed during talent identification and dropout in young female gymnasts. 3 cohorts of female gymnasts (n=243; 6-9 years) completed a test battery for talent identification. Performance-levels were monitored over 5 years of competition. Kaplan-Meier and Cox Proportional Hazards analyses were conducted to determine the survival rate and the characteristics that influence dropout respectively. Kaplan-Meier analysis indicated that only 18% of the female gymnasts that passed the baseline talent identification test survived at the highest competition level 5 years later. The Cox Proportional Hazards Model indicated that gymnasts with a score in the best quartile for a specific characteristic significantly increased chances of survival by 45-129%. These characteristics being: basic motor skills (129%), shoulder strength (96%), leg strength (53%) and 3 gross motor coordination items (45-73%). These results suggest that tests batteries commonly used for talent identification in young female gymnasts may also provide valuable insights into future dropout. Therefore, multidimensional test batteries deserve a prominent place in the selection process. The individual test results should encourage trainers to invest in an early development of basic physical and motor characteristics to prevent attrition.

Kinematics and dynamics of burst transitions.

Subjects (N = 14) were instructed to walk at comfortable walking speed and to start sprinting on an external (visual) stimulus. This is a burst transition. To accelerate maximally, different strategies can be used. The choice for a strategy was hypothesized to be (a) dependent of the body's dynamical status, which is in its turn dependent on the signal timing within the gait cycle; and (b) influenced by the performance and efficacy of the different strategies. Three-dimensional kinematics and ground reaction forces were used to discriminate between strategies and to calculate work (W(total)). Distance laser data yielded performance measures and the work related to the forward acceleration (W(objective)). Efficacy was calculated as the ratio of W(objective) to W(total). Subjects mainly used 2 strategies among others depending on the timing of the stimulus: (a) subjects placed their body center of mass (BCOM) in front of their center of pressure (COP) by tilting the trunk forward and flexing the knee, resulting in a sudden forward acceleration but a relatively fair efficacy; (b) subjects placed their COP behind their BCOM by placing the foot of the swing leg backward. This led to a high performance with high efficacy and was therefore the most ecologically relevant.

Postmortem examination of human fetal hearts at or below 20 weeks' gestation: a comparison of high-field MRI at 9.4 T with lower-field MRI magnets and stereomicroscopic autopsy.

OBJECTIVES: To compare the diagnostic usefulness of high-field with low-field magnetic resonance imaging (MRI) and stereomicroscopic autopsy for examination of the heart in fetuses at or under 20 weeks' gestation. METHODS: Prior to invasive stereomicroscopic autopsy, MRI scans at 9.4, 3.0 and 1.5 T were performed on 24 fetuses between 11 and 20 weeks' gestation, including 10 fetuses with cardiac abnormalities. The ability to visualize different heart structures was evaluated according to the different field strength MRI magnets used and gestational age at examination. RESULTS: On 1.5- and 3.0-T MRI, only the heart situs and four-chamber view could be visualized consistently (in 75% or more of cases) when the fetus was beyond 16 weeks' gestation, but other heart structures could not be visualized for fetuses at any gestational age. In contrast, using high-field MRI at 9.4 T, the heart situs, four-chamber view and the outflow tracts could be visualized in all fetuses irrespective of gestational age. Using high-field MRI, the sensitivity for detecting an abnormality of the four-chamber view was 66.7% (95% CI, 30.1-92.1%) with a specificity of 80.0% (95% CI, 51.9-95.4%). For abnormalities of the outflow tracts, sensitivity was 75.0% (95% CI, 20.3-95.9%) and specificity 100.0% (95% CI, 83.3-100.0%). Eight fetuses out of 10 with congenital heart disease (CHD) were classified as having major CHD. High-field MRI at 9.4 T was able to identify seven out of the eight cases of major CHD. CONCLUSION: High-field MRI at 9.4 T seems to be an acceptable alternative approach to invasive stereomicroscopic autopsy for fetuses with CHD at or below 20 weeks' gestation.

Virtual autopsy by computed tomographic angiography of the fetal heart: a feasibility study.

OBJECTIVE: To determine the feasibility of postmortem computed tomographic (pm-CT) angiography for fetal heart evaluation. METHODS: Following termination of pregnancy (TOP) or intrauterine fetal death (IUFD) beyond 18 weeks' gestation, 33 fetuses were examined by pm-CT; in eight contrast medium was injected through the umbilical cord and in 25 contrast medium was injected directly into the heart. Logistic regression analysis was used to investigate the effect on the ability to visualize cardiac structures on pm-CT angiography of gestational age at TOP or delivery following IUFD, the time delay between fetal death and examination, the technique used for contrast-medium injection, the presence of cardiac abnormalities and whether or not there was IUFD. The diagnostic accuracy of pm-CT angiography for the evaluation of fetal cardiac structures was also evaluated. RESULTS: Cardiac anatomy including heart situs, the four-chamber view and great vessels could be visualized on pm-CT angiography in 29 out of 33 fetuses (87.9%). Logistic regression analysis showed that the ability to visualize cardiac structures on pm-CT angiography was positively correlated only with contrast medium injected directly into the heart. Twenty-five out of the 33 fetuses underwent conventional autopsy. There were five cases with suspected major cardiac abnormality at prenatal ultrasound and one with a minor cardiac abnormality. In one of these cases, severe leakage into the pleural cavity did not allow for visualization of any heart structure on pm-CT angiography and in another invasive autopsy was declined. In two of the remaining four cases, the findings on pm-CT angiography and invasive autopsy were in agreement, while in two a ventricular septal defect was found on invasive autopsy but not on pm-CT. None of the 27 cases with normal hearts was falsely classified as abnormal using pm-CT angiography. CONCLUSION: Pm-CT angiography by direct injection into the heart seems to be a feasible method for its evaluation. The extent to which such a technique could be used for the evaluation of congenital heart disease as an alternative to classical postmortem autopsy remains to be determined.

Fetal organ weight estimation by postmortem high-field magnetic resonance imaging before 20 weeks' gestation.

OBJECTIVE: To ascertain whether high-field magnetic resonance imaging (MRI) allows accurate estimation of the weight of various fetal organs at postmortem before 20 weeks' gestation. METHODS: From 23 fetuses at 9-20 weeks, following termination of pregnancy or in-utero fetal death (IUFD), 207 assorted fetal organs were evaluated by high-field MRI at 9.4 T prior to conventional autopsy. Fetal organ density was calculated by correlating volume and weight at autopsy using linear regression analysis, and this was used to estimate fetal organ weight by MRI. The relative error in MRI estimation of organ weight was calculated as follows: (|MRI weight - autopsy weight|/autopsy weight) × 100 (%). Multiple regression analysis was used to investigate the effect on the relative error of MRI organ weight estimates of gestational age at TOP or delivery following IUFD, autopsy weight, fetal organ examined, IUFD and fetal maceration. RESULTS: Of the 207 organs evaluated, 133 (64%) were examined for fetal organ density and 155 (75%) for fetal organ weight. Fifty-two organs were excluded from our analysis; 41 of these were from fetuses with IUFD, with 39 organs macerated. In 32 cases, exclusion was due to an inability to assess the organ both on MRI and on conventional autopsy. Volume and weight at autopsy correlated significantly, following the linear equation: autopsy volume = (0.9947 × autopsy weight) - 4.7556, where autopsy volume is in mm(3) and weight is in mg (r = 0.99, P < 0.001). Overall the mean relative error in the MRI estimation of organ weight was 68%. Multiple regression analysis showed that the relative error in the MRI estimation of organ weight was significantly associated with gestational age at TOP or delivery following IUFD and fetal maceration, but not with autopsy weight, fetal organ examined or IUFD. In the subgroup of non-macerated organs and for fetuses above 14 weeks' gestation, the mean relative error in the MRI estimation of organ weight was 34%. CONCLUSION: In fetuses before 20 weeks' gestation, noninvasive estimation of organ weight is feasible using high-field MRI, but there is a mean overestimation. Limitations of the technique occur mainly in cases of small macerated fetuses before 14 weeks' gestation.

Acceptance, reliability and confidence of diagnosis of fetal and neonatal virtuopsy compared with conventional autopsy: a prospective study.

OBJECTIVES: To compare prospectively maternal acceptance of fetal and neonatal virtuopsy with that of conventional autopsy and to determine the confidence with which magnetic resonance (MR) virtuopsy can be used to diagnose normality/abnormality of various fetal anatomical structures. METHODS: MR and/or computed tomography virtuopsy and conventional autopsy were offered to 96 women (102 fetuses/neonates) following termination of pregnancy (TOP), intrauterine fetal death (IUFD) or neonatal death. Multivariable logistic regression analysis was used to investigate the effect on maternal acceptance of virtuopsy and/or conventional autopsy of the age of the mother, gestational age at TOP or delivery after IUFD, order of pregnancy, parity, religion, type of caregiver obtaining consent and reason for death. When parents consented to both MR virtuopsy and conventional autopsy of fetuses ≥ 20 weeks of gestation or neonates, the confidence with which MR virtuopsy could be used to diagnose normality/abnormality of various anatomical structures was determined on a scale in which conventional autopsy was considered gold standard. On autopsy we classified fetuses/neonates as having either 'normal' or 'abnormal' anatomical structures; these groups were analyzed separately. At virtuopsy, we indicated confidence of diagnosis of normality/abnormality of every anatomical structure in each of these two groups defined at autopsy, using a scale from 0 (definitely abnormal) to 100 (definitely normal). RESULTS: Of the 96 women, 99% (n = 95) consented to virtuopsy and 61.5% (n = 59) to both conventional autopsy and virtuopsy; i.e. 36 (37.5%) consented to virtuopsy alone. Maternal acceptance of conventional autopsy was independently positively related to singleton pregnancy, non-Moslem mother, earlier gestation at TOP or delivery afer IUFD and a maternal-fetal medicine specialist obtaining consent. Thirty-three fetuses ≥ 20 weeks of gestation had both conventional autopsy and MR virtuopsy, of which 19 had a full autopsy including the brain. In fetuses with normal anatomical structures at conventional autopsy, MR virtuopsy was associated with high diagnostic confidence (scores > 80) for the brain, skeleton, thoracic organs except the heart, abdominal organs except the pancreas, ureters, bladder and genitals. In fetuses with abnormal anatomical structures at autopsy, MR virtuopsy detected the anomalies with high confidence (scores < 20) for these same anatomical structures. However, in three cases, virtuopsy diagnosed brain anomalies additional to those observed at conventional autopsy. CONCLUSION: MR virtuopsy is accepted by nearly all mothers while conventional autopsy is accepted by about two-thirds of mothers, in whom refusal depends mainly on factors over which we have no control. Although conventional autopsy remains the gold standard, the high acceptance of virtuopsy makes it an acceptable alternative when the former is declined.

A cross-sectional study about the relationship between morphology and kinematic parameters in children between 15 and 36 months.

Morphology and kinematic parameters were recorded for 31 children between 15 and 36 months to investigate the relation between morphology and the walking pattern. A full 3D gait analysis using a VICON motion system was performed to gather kinematic data. Next, the differences in kinematic parameters between four morphological classes were assigned with a multiple analysis of variance, with a correction for walking experience. Also stepwise linear regressions were performed, to examine the relation between detailed morphological measurements and kinematic parameters. The regression models showed relationships between kinematic parameters of the ankle, hip, thorax and morphology. All results indicated that the upper body played an important role in the coordination of the walking pattern, especially in the frontal plane.

Antenatal ultrasound prediction of pulmonary hypoplasia in congenital diaphragmatic hernia: correlation with pathology.

OBJECTIVE: To examine the relationship between observed to expected (o/e) lung to head circumference ratio (LHR) and lung-to-body weight ratio (LBWR) in fetuses with congenital diaphragmatic hernia (CDH). METHODS: All consecutive fetuses with CDH and termination of pregnancy for which a postmortem examination was available, examined at three institutions between 2000 and 2010, were included in the study. Contralateral fetal lung area was measured by two-dimensional ultrasonography using the longest axis method and the o/e-LHR was calculated based on the appropriate normal mean for gestational age (GA). Regression analysis was used to determine the significance of association between the LBWR and the o/e-LHR for left and right-sided cases, and subsequently the predicted LBWR in left-sided CDH was calculated using the regression equation. Regression analysis was used to investigate the effect on the proportional difference between the predicted and observed LBWR of GA at o/e-LHR, time gap between o/e-LHR and LBWR measurement, proportional weight of the ipsilateral compared with total lung weight, presence of associated anomalies and intrathoracic herniation of the liver. RESULTS: There were 23 fetuses with left-sided and seven fetuses with right-sided CDH. In left-sided CDH, the LBWR and the o/e-LHR correlated significantly, following the linear equation: LBWR = 0.0043 + (0.0134 × o/e-LHR) (r = 0.52, P = 0.012), but this was not the case for right-sided CDH, for which LBWR followed the equation: LBWR = 0.0107 - (0.0014 × o/e-LHR) (r = 0.08, P = 0.862), where o/e-LHR is expressed as percentage. Regression analysis showed that the proportional difference between predicted and observed LBWR in left-sided CDH was significantly and independently associated with GA at o/e-LHR measurement and proportional weight of ipsilateral vs. total lung weight. CONCLUSION: In left-sided CDH, o/e-LHR correlates well with LBWR irrespective of the length of time between o/e-LHR and LBWR measurement, presence of associated anomalies and intrathoracic herniation of the liver. Inconsistencies between the two measurements are mainly attributable to the contribution of the ipsilateral lung to the total lung weight. In right-sided CDH, o/e-LHR does not correlate with LBWR.

Overground vs. treadmill walk-to-run transition.

Determination of the walk-to-run transition (WRT) speed is a crucial aspect of gait transition research, which has been conducted on treadmill as well as overground. Overground WRT-speeds were reported to be higher than on treadmill. Part of this difference could be related to the lower acceleration magnitudes on treadmill. In this study, spontaneous WRT overground was compared to WRT at a comparable acceleration on treadmill. In addition, calculation procedures correcting for movement in the lab reference frame on treadmill were implemented. As such, this study was, in contrast to previous treadmill studies, able to detect a speed jump. This speed jump was until now a typical feature of overground WRT and contributed to the higher transition speed. By incorporating horizontal movements of the COM, a speed jump was also detected on treadmill. Yet, treadmill WRT-speed (2.61 ms(-1)) remained lower than overground (2.85 ms(-1)). Nevertheless, this difference was much smaller than assumed in the literature. The remaining difference could be explained by a larger speed jump (treadmill: 0.40 ms(-1); overground: 0.51 ms(-1)), and a higher speed at the start of the transition step overground (treadmill: 2.21 ms(-1); overground: 2.34 ms(-1)). In conclusion, even when controlling for effects of acceleration and movement in the lab reference frame a treadmill influence on WRT was visible.

Splenogonadal fusion: a case report.

Splenogonodal fusion is a rare congenital abnormality. We present the case of a continuous splenogonadal fusion diagnosed in the course of a laparoscopy for left non-palpable testis in a 1-year-old boy. This case illustrates that even though testicular salvage is the recommended approach, various anatomical features might preclude conservation.

Influence of treadmill acceleration on actual walk-to-run transition.

When accelerating continuously, humans spontaneously change from a walking to a running pattern by means of a walk-to-run transition (WRT). Results of previous studies indicate that when higher treadmill accelerations are imposed, higher WRT-speeds can be expected. By studying the kinematics of the WRT at different accelerations, the underlying mechanisms can be unravelled. 19 young, healthy female subjects performed walk-to-run transitions on a constantly accelerating treadmill (0.1, 0.2 and 0.5 m s(-2)). A higher acceleration induced a higher WRT-speed, by effecting the preparation of transition, as well as the actual transition step. Increasing the acceleration caused a higher WRT-speed as a result of a greater step length during the transition step, which was mainly a consequence of a prolonged airborne phase. Besides this effect on the transition step, the direct preparation phase of transition (i.e. the last walking step before transition) appeared to fulfil specific constraints required to execute the transition regardless of the acceleration imposed. This highlights an important role for this step in the debate regarding possible determinants of WRT. In addition spatiotemporal and kinematical data confirmed that WRT remains a discontinuous change of gait pattern in all accelerations imposed. It is concluded that the walk-to-run transition is a discontinuous switch from walking to running which depends on the magnitude of treadmill belt acceleration.

Experimental study on the role of the ankle push off in the walk-to-run transition by means of a powered ankle-foot-exoskeleton.

The goal of this study was to analyse the role of the plantarflexor muscles in the walk-to-run transition (WRT) by means of a powered ankle-foot-exoskeleton. 11 female subjects performed several WRT's on an accelerating treadmill while their plantarflexors were assisted or resisted during push off. The WRT speed was lower in the resist condition than in the control condition which reinforces hypotheses from previous simulations, descriptive and experimental studies. There was no increase in WRT speed in the assist condition which is in contrast to another study where the plantarflexor push off was assisted indirectly by a horizontal traction at waist level. The lack of effect from the assist condition in the present study is possibly due to the narrowly focused nature of the experimental manipulation.

Effects of optic flow on spontaneous overground walk-to-run transition.

Perturbations of optic flow can induce changes in walking speed since subjects modulate their speed with respect to the speed perceived from optic flow. The purpose of this study was to examine the effects of optic flow on steady-state as well as on non steady-state locomotion, i.e. on spontaneous overground walk-to-run transitions (WRT) during which subjects were able to accelerate in their preferred way. In this experiment, while subjects moved along a specially constructed hallway, a series of stripes projected on the side walls and ceiling were made to move backward (against the locomotion direction) at an absolute speed of -2 m s(-1) (condition B), or to move forward at an absolute speed of +2 m s(-1) (condition F), or to remain stationary (condition C). While condition B and condition F entailed a decrease and an increase in preferred walking speed, respectively, the spatiotemporal characteristics of the spontaneous walking acceleration prior to reaching WRT were not influenced by modified visual information. However, backward moving stripes induced a smaller speed increase when making the actual transition to running. As such, running speeds after making the WRT were lower in condition B. These results indicate that the walking acceleration prior to reaching the WRT is more robust against visual perturbations compared to walking at preferred walking speed. This could be due to a higher contribution from spinal control during the walking acceleration phase. However, the finding that subjects started to run at a lower running speed when experiencing an approaching optic flow faster than locomotion speed shows that the actual realization of the WRT is not totally independent of external cues.

Experimental study of the influence of the m. tibialis anterior on the walk-to-run transition by means of a powered ankle-foot exoskeleton.

The purpose of this study was to investigate the role of the tibialis anterior (TA) in the walk-to-run transition (WRT) by means of an experimental manipulation that allows increasing or decreasing muscular effort of the TA around heel contact. Eight subjects performed five WRTs on an accelerating treadmill wearing a powered ankle-foot exoskeleton. There was a trend towards a lower WRT-speed in the condition in which the TA was resisted (2.06+/-0.09 m s(-1)) than in the control condition (2.10+/-0.10 m s(-1)). This finding could not be extrapolated in the opposite direction, as there was no significant difference between the assist and control condition. The TA activation burst around heel contact showed a pattern that led to the hypothesis that the TA activation reaches a critical level at the fourth last heel contact before the WRT which triggers the WRT. The fact that the results comply with previous transition studies emphasises the role of the TA as a determinant of the WRT.

Spatiotemporal characteristics of spontaneous overground walk-to-run transition.

The purpose of the current study was to examine spontaneous overground walk-to-run transitions (WRT). For the first time, subjects' WRT was examined during an overground protocol that allowed them to accelerate freely. The overground speed profile prior to reaching the WRT was analysed together with the spatiotemporal characteristics of the actual transition. Nine women (height: 166.4+/-3.5 cm) performed five spontaneous WRT. Speed, step frequency (SF) and step length (SL) of the accelerating walking steps and the transition step were determined. By means of fourth degree polynomials, subjects' spatiotemporal profiles prior to reaching WRT were determined. A step length index (SLI) was used to calculate the contribution of SF and SL to the increase in walking speed. Subjects took on average 5.9+/-0.9 walking steps prior to reaching transition. When speeding up towards the transition to running, subjects chose to accelerate predominantly in the first half of the walking acceleration period, followed by smaller speed increments in the second half. The SLI values indicated that subjects tended to increase walking speed by increasing SL, more than SF, except during the first 20% of the acceleration period. WRT-speed was 2.664+/-0.230 m s(-1), which was higher than in former treadmill studies using a constant acceleration protocol (+/-2.1 m s(-1)). Subjects made a speed jump of 0.417 m s(-1) from the last walking step to the WRT-step. We can conclude that further transition studies studying the interaction between the acceleration and gait transition behaviour are necessary in order to complete the understanding of the transition phenomenon.