Session 1: Natural Movement

Movement and Morphology in Nature: Inspiration for (future) Technology

Peter Aerts^1,2, François Druelle^1,4, Kristiaan D’Août³ & Gilles Berillon⁴

1. University of Antwerp, Biology Department, Fun-Morph lab, Belgium

2. University of Ghent, Department of Movement and Sport Sciences, Biomechanics and motor control of human movement, Belgium

3. University of Liverpool, Institute of Aging and Chronic Disease, United Kingdom

4. UPR 2147 CNRS, Dynamique de l'Evolution Humaine, France 

Ever since ancient times, the seeming ease with which animals perform in their natural habitats has been a source of wonder for man.  Aiming at the development of (future) versatile machines, able to adjust shape and movement patterns ‘on the fly’ to move through continuously changing environments and terrains (substrate, structure, complexity, slope, available space...), the diversity of animals’ morphology and behaviour is often considered the blueprint for generic design principles in robotics.  However, from the biologists’ perspective, this ‘faithfulness’ may be less evident than first expected.

Making use of examples taken from primate functional morphology, we want to address three mechanisms by which organisms may respond to changes in their environment. Each of these act on a different time scale and thus come with their own constraints, potentially interfering with the engineering goals and concepts.

1) Through a behavioural response: Based on perception of (a cue in) the environment, a proper neuro-motoric response, subject to extero- and proprioceptive feedback and exploiting the intrinsic dynamics of the system, is selected. The time-scale is ‘quasi instantaneous’. Voluntary quadrupedal-to-bipedal transitions in baboons and alternative climbing strategies in bonobos will be used as an example.

2) Through phenotypic plasticity: An environmental cue leads to morphogenetic change optimizing performance.  The time-scale is ‘life-time’. Ontogenetic changes, though not a response to new environmental cues, may enable (better) exploitation of new habitat dimensions and can, therefore, be considered an analogue of plasticity. The effect of morphometric changes on locomotor performance in infant baboons and human toddlers will be used as an example.

3) Through evolutionary adaptation (by natural selection): random (genetically based) phenotypical variation in a population results in differential individual fitness in the (changed) environment. The time-scale is an ‘evolutionary’ one. Obviously, behavioural (repertoire) and neuro-motoric features or capabilities (control), as well as the potential for plastic response, may also evolve through natural selection.  Unravelling the adaptive advantage of (morphological) characteristics is not always straight forward and requires a thoughtful and meticulous  approach.  The ‘achilles tendon’ in Hominoidea (gibbons and great apes, including humans) in relation to locomotor performance will be used as an example. 

To open the discussion, the translation towards robotics of these response classes will briefly be addressed from the naive biologists’ point of view.  

Human locomotion on “natural” and “unnatural” substrates

D’Août Kristiaan¹, Aerts Peter^2,3, Catherine Willems⁴, Alexandra Allen¹ & Robin H Crompton¹

1. University of Liverpool, Institute of Ageing and Chronic Disease, United Kingdom

2. University of Antwerp, Biology Department, Fun-Morph lab, Belgium

3. University of Ghent, Department of Movement and Sport Sciences, Biomechanics and motor control of human movement, Belgium

4. School of Arts, Ghent, Belgium

Humans have evolved on a substrate that was, from a locomotor point of view, much more varied than the typical urban substrate we typically walk and run on nowadays. Unfortunately, nearly all our insights into human locomotion are from lab-based studies. In these studies, gait is usually along a straight line, at a constant speed, and on a very simple, flat substrate. In addition, subjects tend to vary little as well (notwithstanding patients).

We have recently set out to explore variation in human gait and more specifically how gait is influenced (or not?) by the substrate. We will present examples from recent and ongoing research. The first example deals with the characterisation of “natural” substrates, both at the level of landscapes (topology) and at the level of mechanical substrate properties. The second example deals with impact (and impact coping strategies) on natural (softer) and artificial (harder) flat substrates, and with gait adjustments to substrate complexity. The third example deals with the effects of different types of footwear – a “wearable substrate” – on gait.

All data suggest that we have evolved on terrains much more complex than we habitually use currently, and we suggest that the level of compliance in the modern human foot, which has recently been found to be substantial, might allow us to deal with this complexity.

Plantar pressure distribution and foot geometry of Dutch and Malawian adults

N.L.W. Keijsers

Sint Maartenskliniek, Nijmegen, Netherlands

The foot is one of the most complex parts of the human body. It consists of 26 bones, 33 joints, and over 100 ligaments, tendons and muscles. In humans, the feet are the only part of the body that contacts the ground during gait and standing. As such, the feet are key players in the deceleration during landing, in weight bearing, maintaining balance and providing propulsion during locomotion. The plantar aponeurosis plays a key role in the function of the foot while weight bearing. Hicks (1954) was the first to describe the role of the plantar aponeurosis as a windlass mechanism explaining the relation between passive extension of the toes on the one hand and the rise of the medial arch, supination of the rearfoot and external rotation of the leg on the other hand. During gait, the windlass mechanism acts in two ways; 1) it helps to maintain the shape of the Medial Longitudinal Arch (MLA) when the foot has to manage downward forces at stance (reversed windlass mechanism) and 2) it causes a rise of the MLA and shortening of the foot at late stance, as the plantar fascia tightens at toe off due to dorsiflexion of the MTP joints.

In many western countries, many people suffer from foot complaints. Approximately 10% of the Dutch population suffers from foot complaints, increasing up to 24% in the population of above 65 years. In contrast to western countries, foot complaints are rare in Africa. This is remarkable, as many African adults walk many hours each day, often barefoot or with worn-out shoes. The reason why Africans can withstand such loading without developing foot complaints might be related to the way the foot is loaded and function. As the loading of the foot is highest during locomotion and the shape of the foot and biomechanical behavior of the foot differs between the phases of the walking cycle, it seems important to investigate the foot in a dynamic situation. Therefore, the aim of this study was to compare the static foot geometry, dynamic plantar pressure pattern and roll off of the foot between Malawian and Dutch shod adults.

Static foot geometry and dynamic plantar pressure distribution of 77 adults from Malawi were compared to 77 adults from the Netherlands. None of the subjects had a history of foot complaints. The plantar pressure pattern as well as the Arch Index (AI) and the trajectory of the center of pressure during the stance phase were calculated and compared between both groups. Plantar pressure data were normalized for foot size, width and foot progression angle.  Standardized pictures were taken from the feet to assess the height of the MLA. In principle, differences in plantar pressure between the Malawian and Dutch group could be the result of covariates such as body weight and walking velocity. Therefore, a stepwise multiple regression analysis with forward selection was performed to find the set of predictors/variables that were most effective in predicting the plantar pressure pattern.

We found that Malawian adults: 1) loaded the midfoot for a longer and the forefoot for a shorter period during roll off, 2) had significantly lower plantar pressures under the heel and a part of the forefoot and 3) had a larger AI and a lower MLA compared to the Dutch.

These findings demonstrate that differences in static foot geometry, foot loading and roll off technique exist between both groups. The advantage of the foot loading pattern as shown by the Malawian group is that the plantar pressure is distributed more equally over the foot. It is striking that these characteristics fit quite nicely with some of the main current goals of the treatment of foot problems in the west, namely to pursuit an equal distribution of pressure by insoles.

From bones to plausible (loco)motion: Palaeoanthropological point of view

Gilles Berillon¹, François Marchal², Guillaume Nicolas³ & Franck Multon³

1. UPR2147 CNRS, Paris, France

2. UMR 7268 ADES CNRS-AMU-EFS, Marseille, France

3. M2S, University Rennes 2, France

Recent discoveries of early hominins (dated up to 7 My) highlight an unexpected diversity of locomotor anatomies that lead palaeoanthropologists to hypothesize that bipedal locomotion took distinct shapes through our phylogenetic history. A much more complex scenario of hominin evolution than those proposed only few years ago is thus emerging, where knowledge on locomotor anatomy takes an increasing role. Given the fragmented nature of fossil specimens, the main challenge for palaeoanthropologists remains estimating the potential locomotor impacts of morphological differences – often very subtle compared to those between living habitual (humans) and occasional bipeds (apes) – in order to improve our knowledge on the manner hominines walked. In this talk, we first review the main approaches based on functional anatomy principles that palaeoanthropologists develop in that aim. We then introduce the multidisciplinary study we are developing toward a more specimen-specific approach of the fossils. At this stage, this approach integrates comparative anatomy and biomechanical knowledge as well as tools of motion modelling and simulation. As first results we show that it allows simulating plausible gaits for living primates (here human and chimpanzee) and fossil hominin species (here Australopithecus afarensis) based on a set of individual anatomical data.