Effects of active and passive warming of the foot sole on vibration perception thresholds

Objective Skin temperatures are known to increase cutaneous sensitivity. However, it is unclear whether the amount of improved sensitivity differs depending on the protocol of heat application. Therefore, this study aimed to investigate the effects of active (treadmill walking) and passive (infrared radiator) warming of the foot sole on vibration perception thresholds. Methods Sixty healthy and injury-free subjects voluntarily participated in this study. Vibration perception thresholds (200 Hz) and plantar temperatures were measured at the hallux and 1st metatarsal head. In experiment 1, warming and mechanically stimulating the skin was achieved by walking on a treadmill for 30 min. In a follow-up study (experiment 2), external plantar heat was administered via an infrared radiator (30 min). Results In both experiments, increasing temperatures led to increased plantar sensitivity. However, the amount of improved sensitivity was greater in experiment 1, although plantar temperature increases were lower compared to experiment 2. Conclusions Warming in conjunction with mechanical stimulation seems to have a greater potential to enhance plantar sensitivity compared to external heat supply only. Significance The possible influence of mechanical stimulation and warming towards superior plantar afferent feedback highlights its importance regarding human posture and fall prevention

Biomechanical aspects of sensitivity in relationship with motor control

The central integration of sensory information provided by various afferent receptors is required to control human movement. Although the function of individual afferent receptors is known, the complexity and interactivity of afferent information remains unclear, especially in scenarios which involve the reduction of information provided by one or more afferent receptors. Reduced plantar sensitivity is commonly associated with postural instability, which occurs in ageing, peripheral neuropathies, and other neurological disorders like Parkinson's disease. Although there has been a great advance in understanding afferent inputs during recent years, the role of afferent information in controlling movement is still unclear. Therefore, the aim of the present thesis is to investigate the effects of reduced plantar sensitivity on quasi-static and dynamic balance control, as well as muscle reflexes. The current thesis is comprised of five experiments. Two experiments were designed as preliminary investigations, while the remaining three experiments addressed the main questions of this thesis. The first experiment investigated a basic question about subjective foot sensitivity (vibration perception) measured in two different body positions: standing and sitting. Results of Experiment I showed no differences of vibration perception between both measured conditions. Therefore, comparing data from plantar sensitivity vibration tests performed during sitting and during standing (e.g. balance) is feasible. In Experiment II, the role of afferent information from plantar mechanoreceptors on quasi-static balance was investigated using two different cooling procedures: a permanently cooling thermal platform and conventional ice pads. COP total excursions, plantar temperatures, and scores of a Visual Analogue Scale (VAS) regarding subjective pain were analyzed. Experiment II demonstrated that constant and controllable cooling via the thermal platform is the superior approach with respect to subjective pain (VAS) and to reach and maintain the desired temperature throughout the trials. Furthermore, only cooling via the thermal platform induced postural instability, revealed by increased COP values. This instability was expected due to reduced plantar input, indicating no compensation by other sensory systems. Experiment III focused on the inter- and intraday- reliability of dynamic balance responses using the Posturomed device. Generally good relative and absolute reliability were found for COP excursions. This outcome was fundamental to proceed with dynamic balance measurements using the same setup. Subsequently, effects of reduced plantar cutaneous inputs via cooling on anticipatory and compensatory balance responses (unexpected perturbations) were explored in Experiment IV. COP and EMG data were used to analyze anticipatory and compensatory balance responses. No differences in COP or EMG parameters were found for the anticipatory responses after hyper-thermia, while decreased values for compensatory balance responses were observed in response to cooling. This was interpreted as a kind of overcompensatory behavior of the central nervous system (CNS) due to more cautious behavior induced after plantar cooling. Finally, the question regarding the interaction between afferent receptors arose in Experiment V, in which the effects of reduced plantar temperatures on the Achilles tendon stretch reflex and plantar flexion were examined. Short latency responses and maximal force of plantar flexion were analyzed. Cooling resulted in decreased amplitudes of short latencies, as well as in delays in time to maximal force of plantar flexion. These findings suggest that plantar inputs participate complementarily in the Achilles stretch reflex. Collectively, the current thesis contributes to understanding how plantar receptors are involved in movement control; not only do they seem to work as independent contributors, but they also appear to interact with other afferent receptors. Furthermore, an important outcome is that the reduced plantar inputs seem to induce different alterations in the organization of CNS inputs and outputs, according to different balance tasks: quasi-static responses, anticipatory responses, and compensatory responses. For the future, the use of other methods like microneurography and electroencephalography could be helpful to gain even more understanding of afferent interactions during the control of movements. Similar protocols may also be implemented in other populations, such as elderly people or patients suffering from neurological disorders, who exhibit continued decline or degeneration of sensory receptors.Die zentrale Integration von sensorischen Informationen, die aus verschiedenen afferenten Rezeptoren zur Verfügung gestellt werden, ist erforderlich, um die menschliche Bewegung zu steuern. Obwohl die Funktion der einzelnen afferenten Rezeptoren bekannt ist, bleibt die Komplexität und Interaktivität von afferenten Information unklar, insbesondere in Szenarien, in denen die Verminderung von Informationen aus einem oder mehreren afferenten Rezeptoren eintritt. Reduzierte plantare Sensibilität wird häufig im Zusammenhang mit Haltungsinstabilität verbunden. Dies tritt häufig während des Alterns ein, bei peripheren Neuropathien und anderen neurologischen Erkrankungen, wie etwa bei der Parkinson-Krankheit. Obwohl es in den vergangen Jahren große Entwicklungen was das Verständnis afferenter Inputs gab, ist die Rolle afferenter Information bei der Bewegungskontrolle immer noch unklar. Daher ist das Ziel der vorliegenden Dissertation, den Einfluss der Beeinträchtigung der plantaren Sensibilität auf das quasi-statische und dynamische Gleichgewicht, sowie auf den Reflex der Achillessehne, zu untersuchen. Die vorliegende Dissertation ist dazu aus fünf Untersuchungen aufgebaut. Zwei Untersuchungen werden als Voruntersuchungen präsentiert, während die übrigen drei Untersuchungen auf die Kernfragen dieser Doktorarbeit gerichtet sind. Die erste Untersuchung beschäftigt sich mit der grundlegenden Fragestellung bzgl. der subjektiven Fußsensibilität (Vibrationswahrnehmung), die in zwei verschiedenen Körperpositionen gemessen wurde: Im Stehen und im Sitzen. Ergebnisse aus Untersuchung I zeigten keine Unterschiede der Vibrationswahrnehmung zwischen den beiden Körperpositionen. Daher ist es möglich, Vergleiche zwischen Daten aus plantaren Vibrationswahrnehmungstests während des Sitzens und des Stehens (z.B. bei Gleichgewichtstests) durchzuführen. In Untersuchung II wurde die Rolle afferenter Informationen plantarer Mechanorezeptoren auf das quasi-statische Gleichgewicht mittels zwei unterschiedlicher Abkühlverfahren untersucht: eine permanente Abkühlung durch eine thermische Plattform und konventionelle Eis-Pads. Es wurden der COP Gesamtweg, plantar Temperaturen und eine visuelle Analogskala (VAS) in Bezug auf subjektive Schmerzen analysiert. Untersuchung II hat gezeigt, dass eine konstante und steuerbare Abkühlung über die thermische Plattform der überlegene Ansatz in Bezug auf subjektiven Schmerz (VAS) und bzgl. des Erreichens und Erhaltens einer gewünschten Temperatur innerhalb der Messungen ist. Weiterhin wurde nur durch die Abkühlung mittels thermischer Plattform eine posturale Instabilität induziert, evident durch erhöhte COP Gesamtwege. Diese Instabilität wurde aufgrund der Beeinträchtigung der plantaren Sensibilität erwartet, was auf eine fehlende Kompensation durch andere Sinnessysteme hinzuweisen scheint. In Untersuchung III lag der Fokus auf der inter- und intra-Tag-Reliabilität dynamischer Gleichgewichtsantworten mittels des Posturomed-Trainingsgerätes. Im Allgemeinen wurden eine gute relative und absolute Reliabilität der COP Gesamtwege ermittelt. Dieses Ergebnis war von grundlegender Bedeutung, um die Nutzung des gleichen Setups für die folgenden dynamischen Gleichgewichtsmessungen (Untersuchung IV) zu ermöglichen. Anschließend wurden die Effekte einer Beeinträchtigung der plantaren Sensibilität mittels Abkühlung auf antizipatorische und kompensatorische Antworten des dynamischen Gleichgewichts (anhand unerwarteter Störungen des Gleichgewichts) in Untersuchung IV erforscht. COP und EMG Daten wurden verwendet, um die antizipatorischen und kompensatorischen Antworten des Gleichgewichts zu analysieren. Nach der Abkühlung wurden bzgl. antizipatorischer Antworten keine Unterschiede in den COP und EMG Parametern gefunden. Im Hinblick auf kompensatorische Antworten zeigten sich reduzierte COP und EMG als Reaktion auf die Abkühlung. Dies wurde wie folgt interpretiert: aufgrund eines vorsichtigen Verhaltens, ausgelöst durch die verminderten sensorischen Inputs infolge der Abkühlung, kam es zu einer Art „Überkompensierungsverhalten“ des zentralen Nervensystems (ZNS). Schließlich stellte sich die Frage der Interaktion afferenter Rezeptoren in Untersuchung V, in welcher die Effekte reduzierter plantarer Temperaturen auf den Achillessehnen-Dehnungsreflex und die Plantarflexion untersucht wurden. Kurze Latenz Antworten (short latency responses) und die maximale Kraft der Plantarflexion wurden dabei analysiert. Die Abkühlung führte zu einer verminderten Amplitude der short latency responses sowie zu Verzögerungen der Zeit bis zur maximalen Kraft der Plantarflexion. Diese Ergebnisse deuten darauf hin, dass plantare Inputs in komplementärer Weise am Achillessehnen-Dehnungsreflex beteiligt sind. Zusammenfassend lässt sich aussagen, dass die vorliegende Arbeit zum Verständnis beiträgt, wie plantare Rezeptoren an der Bewegungssteuerung beteiligt sind. Es scheint, dass diese nicht nur in unabhängiger Form zur Bewegungssteuerung beitragen, sondern dabei auch mit anderen afferenten Rezeptoren interagieren. Darüber hinaus ist ein wichtiges Resultat, dass die reduzierten plantaren Inputs scheinbar verschiedene Änderungen in der Organisation von Ein- und Ausgängen im ZNS induzieren. Dies erfolgt anhand unterschiedlicher Anforderungen an das Gleichgewicht: quasi-statische Antworten, antizipatorische Antworten und kompensatorischen Antworten. Für die Zukunft könnte die Implementierung anderer Methoden, wie Mikroneurographie und Elektroenzephalographie, hilfreich sein, um noch mehr Verständnis bezüglich afferenter Interaktionen während der Kontrolle von Bewegungen erlangen zu können. Ähnliche Protokolle könnten auch in anderen Populationen durchgeführt werden, wie ältere Menschen oder Patienten mit neurologischen Erkrankungen, die einen kontinuierlichen Rückgang oder Degenerationen sensorischer Rezeptoren zeigen

Biomechanical aspects of sensitivity in relationship with motor control

The central integration of sensory information provided by various afferent receptors is required to control human movement. Although the function of individual afferent receptors is known, the complexity and interactivity of afferent information remains unclear, especially in scenarios which involve the reduction of information provided by one or more afferent receptors. Reduced plantar sensitivity is commonly associated with postural instability, which occurs in ageing, peripheral neuropathies, and other neurological disorders like Parkinson's disease. Although there has been a great advance in understanding afferent inputs during recent years, the role of afferent information in controlling movement is still unclear. Therefore, the aim of the present thesis is to investigate the effects of reduced plantar sensitivity on quasi-static and dynamic balance control, as well as muscle reflexes. The current thesis is comprised of five experiments. Two experiments were designed as preliminary investigations, while the remaining three experiments addressed the main questions of this thesis. The first experiment investigated a basic question about subjective foot sensitivity (vibration perception) measured in two different body positions: standing and sitting. Results of Experiment I showed no differences of vibration perception between both measured conditions. Therefore, comparing data from plantar sensitivity vibration tests performed during sitting and during standing (e.g. balance) is feasible. In Experiment II, the role of afferent information from plantar mechanoreceptors on quasi-static balance was investigated using two different cooling procedures: a permanently cooling thermal platform and conventional ice pads. COP total excursions, plantar temperatures, and scores of a Visual Analogue Scale (VAS) regarding subjective pain were analyzed. Experiment II demonstrated that constant and controllable cooling via the thermal platform is the superior approach with respect to subjective pain (VAS) and to reach and maintain the desired temperature throughout the trials. Furthermore, only cooling via the thermal platform induced postural instability, revealed by increased COP values. This instability was expected due to reduced plantar input, indicating no compensation by other sensory systems. Experiment III focused on the inter- and intraday- reliability of dynamic balance responses using the Posturomed device. Generally good relative and absolute reliability were found for COP excursions. This outcome was fundamental to proceed with dynamic balance measurements using the same setup. Subsequently, effects of reduced plantar cutaneous inputs via cooling on anticipatory and compensatory balance responses (unexpected perturbations) were explored in Experiment IV. COP and EMG data were used to analyze anticipatory and compensatory balance responses. No differences in COP or EMG parameters were found for the anticipatory responses after hyper-thermia, while decreased values for compensatory balance responses were observed in response to cooling. This was interpreted as a kind of overcompensatory behavior of the central nervous system (CNS) due to more cautious behavior induced after plantar cooling. Finally, the question regarding the interaction between afferent receptors arose in Experiment V, in which the effects of reduced plantar temperatures on the Achilles tendon stretch reflex and plantar flexion were examined. Short latency responses and maximal force of plantar flexion were analyzed. Cooling resulted in decreased amplitudes of short latencies, as well as in delays in time to maximal force of plantar flexion. These findings suggest that plantar inputs participate complementarily in the Achilles stretch reflex. Collectively, the current thesis contributes to understanding how plantar receptors are involved in movement control; not only do they seem to work as independent contributors, but they also appear to interact with other afferent receptors. Furthermore, an important outcome is that the reduced plantar inputs seem to induce different alterations in the organization of CNS inputs and outputs, according to different balance tasks: quasi-static responses, anticipatory responses, and compensatory responses. For the future, the use of other methods like microneurography and electroencephalography could be helpful to gain even more understanding of afferent interactions during the control of movements. Similar protocols may also be implemented in other populations, such as elderly people or patients suffering from neurological disorders, who exhibit continued decline or degeneration of sensory receptors.Die zentrale Integration von sensorischen Informationen, die aus verschiedenen afferenten Rezeptoren zur Verfügung gestellt werden, ist erforderlich, um die menschliche Bewegung zu steuern. Obwohl die Funktion der einzelnen afferenten Rezeptoren bekannt ist, bleibt die Komplexität und Interaktivität von afferenten Information unklar, insbesondere in Szenarien, in denen die Verminderung von Informationen aus einem oder mehreren afferenten Rezeptoren eintritt. Reduzierte plantare Sensibilität wird häufig im Zusammenhang mit Haltungsinstabilität verbunden. Dies tritt häufig während des Alterns ein, bei peripheren Neuropathien und anderen neurologischen Erkrankungen, wie etwa bei der Parkinson-Krankheit. Obwohl es in den vergangen Jahren große Entwicklungen was das Verständnis afferenter Inputs gab, ist die Rolle afferenter Information bei der Bewegungskontrolle immer noch unklar. Daher ist das Ziel der vorliegenden Dissertation, den Einfluss der Beeinträchtigung der plantaren Sensibilität auf das quasi-statische und dynamische Gleichgewicht, sowie auf den Reflex der Achillessehne, zu untersuchen. Die vorliegende Dissertation ist dazu aus fünf Untersuchungen aufgebaut. Zwei Untersuchungen werden als Voruntersuchungen präsentiert, während die übrigen drei Untersuchungen auf die Kernfragen dieser Doktorarbeit gerichtet sind. Die erste Untersuchung beschäftigt sich mit der grundlegenden Fragestellung bzgl. der subjektiven Fußsensibilität (Vibrationswahrnehmung), die in zwei verschiedenen Körperpositionen gemessen wurde: Im Stehen und im Sitzen. Ergebnisse aus Untersuchung I zeigten keine Unterschiede der Vibrationswahrnehmung zwischen den beiden Körperpositionen. Daher ist es möglich, Vergleiche zwischen Daten aus plantaren Vibrationswahrnehmungstests während des Sitzens und des Stehens (z.B. bei Gleichgewichtstests) durchzuführen. In Untersuchung II wurde die Rolle afferenter Informationen plantarer Mechanorezeptoren auf das quasi-statische Gleichgewicht mittels zwei unterschiedlicher Abkühlverfahren untersucht: eine permanente Abkühlung durch eine thermische Plattform und konventionelle Eis-Pads. Es wurden der COP Gesamtweg, plantar Temperaturen und eine visuelle Analogskala (VAS) in Bezug auf subjektive Schmerzen analysiert. Untersuchung II hat gezeigt, dass eine konstante und steuerbare Abkühlung über die thermische Plattform der überlegene Ansatz in Bezug auf subjektiven Schmerz (VAS) und bzgl. des Erreichens und Erhaltens einer gewünschten Temperatur innerhalb der Messungen ist. Weiterhin wurde nur durch die Abkühlung mittels thermischer Plattform eine posturale Instabilität induziert, evident durch erhöhte COP Gesamtwege. Diese Instabilität wurde aufgrund der Beeinträchtigung der plantaren Sensibilität erwartet, was auf eine fehlende Kompensation durch andere Sinnessysteme hinzuweisen scheint. In Untersuchung III lag der Fokus auf der inter- und intra-Tag-Reliabilität dynamischer Gleichgewichtsantworten mittels des Posturomed-Trainingsgerätes. Im Allgemeinen wurden eine gute relative und absolute Reliabilität der COP Gesamtwege ermittelt. Dieses Ergebnis war von grundlegender Bedeutung, um die Nutzung des gleichen Setups für die folgenden dynamischen Gleichgewichtsmessungen (Untersuchung IV) zu ermöglichen. Anschließend wurden die Effekte einer Beeinträchtigung der plantaren Sensibilität mittels Abkühlung auf antizipatorische und kompensatorische Antworten des dynamischen Gleichgewichts (anhand unerwarteter Störungen des Gleichgewichts) in Untersuchung IV erforscht. COP und EMG Daten wurden verwendet, um die antizipatorischen und kompensatorischen Antworten des Gleichgewichts zu analysieren. Nach der Abkühlung wurden bzgl. antizipatorischer Antworten keine Unterschiede in den COP und EMG Parametern gefunden. Im Hinblick auf kompensatorische Antworten zeigten sich reduzierte COP und EMG als Reaktion auf die Abkühlung. Dies wurde wie folgt interpretiert: aufgrund eines vorsichtigen Verhaltens, ausgelöst durch die verminderten sensorischen Inputs infolge der Abkühlung, kam es zu einer Art „Überkompensierungsverhalten“ des zentralen Nervensystems (ZNS). Schließlich stellte sich die Frage der Interaktion afferenter Rezeptoren in Untersuchung V, in welcher die Effekte reduzierter plantarer Temperaturen auf den Achillessehnen-Dehnungsreflex und die Plantarflexion untersucht wurden. Kurze Latenz Antworten (short latency responses) und die maximale Kraft der Plantarflexion wurden dabei analysiert. Die Abkühlung führte zu einer verminderten Amplitude der short latency responses sowie zu Verzögerungen der Zeit bis zur maximalen Kraft der Plantarflexion. Diese Ergebnisse deuten darauf hin, dass plantare Inputs in komplementärer Weise am Achillessehnen-Dehnungsreflex beteiligt sind. Zusammenfassend lässt sich aussagen, dass die vorliegende Arbeit zum Verständnis beiträgt, wie plantare Rezeptoren an der Bewegungssteuerung beteiligt sind. Es scheint, dass diese nicht nur in unabhängiger Form zur Bewegungssteuerung beitragen, sondern dabei auch mit anderen afferenten Rezeptoren interagieren. Darüber hinaus ist ein wichtiges Resultat, dass die reduzierten plantaren Inputs scheinbar verschiedene Änderungen in der Organisation von Ein- und Ausgängen im ZNS induzieren. Dies erfolgt anhand unterschiedlicher Anforderungen an das Gleichgewicht: quasi-statische Antworten, antizipatorische Antworten und kompensatorischen Antworten. Für die Zukunft könnte die Implementierung anderer Methoden, wie Mikroneurographie und Elektroenzephalographie, hilfreich sein, um noch mehr Verständnis bezüglich afferenter Interaktionen während der Kontrolle von Bewegungen erlangen zu können. Ähnliche Protokolle könnten auch in anderen Populationen durchgeführt werden, wie ältere Menschen oder Patienten mit neurologischen Erkrankungen, die einen kontinuierlichen Rückgang oder Degenerationen sensorischer Rezeptoren zeigen

Plantar sensory vibration thresholds are not influenced by body position

Monitoring skin sensitivity is studied to clarify its relationship on balance. Measuring skin sensitivity is performed when subjects are sitting or lying, whereas balance tests are measured during standing. However, afferent signal processing and subsequent efferent responses can be altered by different body positions. Therefore, this study investigated whether vibration perception thresholds (VPTs) are influenced by body positions. Sixty-six healthy subjects (41♀; 25♂) participated in this study. Five measurements of VPTs were performed at each of the three analyzed anatomical locations (heel, first metatarsal head, hallux) of the right plantar foot under two randomized conditions: during sitting and standing. The contact force applied to the probe was measured and controlled within the five trials. Contact forces between the probe and the foot were higher during standing. However, no differences in VPTs were found between conditions. This indicates that VPTs are not different during standing compared to sitting, contrary to our expectations. We conclude that higher forces did not induce increased receptor activity. Since no differences were found between thresholds, future clinical studies can implement plantar VPT tests during sitting in association with balance tests during standing

Larger contactor area increases low-frequency vibratory sensitivity in hairy skin

Background In research, assessing vibratory cutaneous sensitivity is an important research branch to quantify various diseases or to develop devices for pattern recognition. The measured vibration perception thresholds (VPTs), however, are subjective and usually result in a large data variability. This might induce difficulties to detect differences, for example, when comparing different anatomical locations. Hence, a higher ability to detect changes is desirable. Another feature of VPTs is spatial summation, but in the literature it is controversially discussed whether or not this phenomenon is also present in the lower frequency range. For these reasons, the present study aimed to investigate whether an enlarged matrix contactor area (measured at the hairy skin) induces improvements in subjective sensitivity using high and low frequencies, and whether a large contactor area is better able to identify changes of VPTs than a small contactor area of a single contactor. For each frequency, we hypothesized an increased sensitivity for the matrix compared to the single contactor. We also hypothesized that changes can be better-detected between the anatomical locations when using the matrix than the single contactor. Methods Twenty healthy and young participants voluntarily took part in this study. Three anatomical locations at the torso were measured at the middle aspect of the lower back, middle lateral aspect of the upper arm, and the region just below the armpit. At each location, two frequencies (30, 200 Hz) and two contactor conditions (single contactor: 0.48 cm2 , contactor matrix: 9 × 0.48 cm2 = 4.32 cm2) were tested in a randomized order. Results Supporting our hypothesis, we found that improved cutaneous sensitivity after increasing the contactor size occurs not only at high, but also at low frequencies at all anatomical locations. Large contactor sizes resulted in higher sensitivity and in a superior ability to detect changes. The superior behavior of the matrix to exhibit a lower variability could not always be proven. This work may be relevant for future studies aiming to identify changes of VPTs in various patient groups, for example

Effects of hypothermically reduced plantar skin inputs on anticipatory and compensatory balance responses

Background Anticipatory and compensatory balance responses are used by the central nervous system (CNS) to preserve balance, hence they significantly contribute to the understanding of physiological mechanisms of postural control. It is well established that various sensory systems contribute to the regulation of balance. However, it is still unclear which role each individual sensory system (e.g. plantar mechanoreceptors) plays in balance regulation. This becomes also evident in various patient populations, for instance in diabetics with reduced plantar sensitivity. To investigate these sensory mechanisms, approaches like hypothermia to deliberately reduce plantar afferent input have been applied. But there are some limitations regarding hypothermic procedures in previous studies: Not only plantar aspects of the feet might be affected and maintaining the hypothermic effect during data collection. Therefore, the aim of the present study was to induce a permanent and controlled plantar hypothermia and to examine its effects on anticipatory and compensatory balance responses. We hypothesized deteriorations in anticipatory and compensatory balance responses as increased center of pressure excursions (COP) and electromyographic activity (EMG) in response to the hypothermic plantar procedure. 52 healthy and young subjects (23.6 ± 3.0 years) performed balance tests (unexpected perturbations). Subjects’ foot soles were exposed to three temperatures while standing upright: 25, 12 and 0 °C. COP and EMG were analyzed during two intervals of anticipatory and one interval of compensatory balance responses (intervals 0, 1 and 2, respectively). Results Similar plantar temperatures confirmed the successful implementation of the thermal platform. No significant COP and EMG differences were found for the anticipatory responses (intervals 0 and 1) under the hyperthermia procedure. Parameters in interval 2 showed generally decreased values in response to cooling. Conclusion No changes in anticipatory responses were found possibly due to sensory compensation processes of other intact afferents. Decreased compensatory responses may be interpreted as the additional balance threat, creating a more cautious behavior causing the CNS to generate a kind of over-compensatory behavior. Contrary to the expectations, there were different anticipatory and compensatory responses after reduced plantar inputs, thereby, revealing alterations in the organization of CNS inputs and outputs according to different task difficulties

Aspects of Dynamic Balance Responses: Inter- and Intra-Day Reliability

The Posturomed device is used as a scientific tool to quantify human dynamic balance ability due to unexpected perturbations, and as a training device. Consequently, the question arises whether such measurements are compromised by learning effects. Therefore, this study aimed to analyze inter- and intra-day reliability of dynamic balance responses using the Posturomed. Thirty healthy young subjects participated (24.3±3.2 years). The Posturomed was equipped with a triggering mechanism to enable unexpected, horizontal platform perturbations. A force platform was used to quantify Center of Pressure (COP) excursions for two time intervals: interval 1 (0–70 ms post perturbation) and interval 2 (71–260 ms post perturbation). Dynamic balance tests were performed in single leg stances in medio-lateral and anterior-posterior perturbation directions. Inter- and intra-day reliability were assessed descriptively using Bland-Altman plots and inferentially using tests for systematic error and intra-class-correlations. With regard to the mean COP excursions for every subject and all intervals, some cases revealed significant differences between measurement sessions, however, none were considered relevant. Furthermore, intra class correlation coefficients reflected high magnitudes, which leads to the assumption of good relative reliability. However, analyzing inter- and intra-day reliability using Bland-Altman plots revealed one exception: intra-day comparisons for the anterior-posterior direction in interval 2, which points towards possible learning effects. In summary, results reflected good overall reliability with the exception of certain intra-day comparisons in the anterior-posterior perturbation direction, which could indicate learning effects in those particular conditions

Vertical contact forces affect vibration perception in human hairy skin

Background Skin is the largest organ of the human body and fulfills many important functions, like detecting mechanical stimuli. Skin can be divided into glabrous (non-hairy) and hairy skin. These two skin types differ with regard to their mechanical properties and in the distribution of mechanoreceptors. Although many investigations focus on glabrous skin, hairy skin still plays a fundamental role in various activities, e.g., with regard to the perception of pleasantness or for developing wearable vibrotactile devices for pattern recognition in persons with disabilities. Unfortunately, investigations on influencing factors, like vertical contactor force, are scarce for hairy skin. Similarly, it would also be interesting to investigate whether regional vibratory sensitivity differences are present across the human torso. Hence, this study investigated the effects of vertical contactor forces and different anatomical locations on vibration perception. Four anatomical torso regions were studied. Based on findings in glabrous skin, we generally hypothesized improved vibration perception with increasing contactor forces and regional sensitivity differences between the anatomical locations. Methods Forty young and healthy individuals participated (23.0 ± 2.0 yrs), and vibration perception thresholds (VPTs) were determined at 30 Hz for three vertical force levels (0.6, 2.4, and 4.8 N) at four torso locations (sternum, deltoid/shoulder, lower back, middle lateral torso side). Results Higher contactor forces resulted in lower VPTs corresponding to improved vibration perception, regardless of anatomical location. In addition, the sternum region was more sensitive than the remaining three regions, regardless of force level. The reasons for these findings may be a varying number and activation pattern of afferents activated under the different conditions. The findings of this study complement the understanding of vibrotactile sensitivity in hairy skin and may offer implications when developing vibrotactile devices or clothing/textiles, for example

Infrared thermography as a monitoring-tool in youth elite soccer for players under 17 years of age

8th Congress of International Foot and Ankle Biomechanics Society, Bordeaux, France, April, 19 - 22, 2023. Poster presentation