Mechanical stimulation of the plantar foot surface attenuates soleus muscle atrophy induced by hindlimb unloading in rats.

Unloading-induced muscle atrophy occurs in the aging population, bed-ridden patients, and astronauts. This study was designed to determine whether dynamic foot stimulation (DFS) applied to the plantar surface of the rat foot can serve as a countermeasure to soleus muscle atrophy normally observed in hindlimb unloaded (HU) rats. Forty-four mature (6 mo old), male Wistar rats were randomly assigned to ambulatory control, HU alone, HU with active DFS (i.e., plantar contact with active inflation), HU with passive DFS (i.e., plantar contact without active inflation), and HU while wearing a DFS boot with no plantar contact groups. Application of active DFS during HU significantly counteracted the atrophic response by preventing approximately 85% of the reduction in type I myofiber cross-sectional area (CSA) in the soleus while preventing approximately 57% of the reduction in type I myofiber CSA and 43% of the reduction in type IIA myofiber CSA of the medial gastrocnemius muscle. Wearing of a DFS boot without active inflation prevented myofiber atrophy in the soleus of HU animals in a fashion similar to that observed in HU animals that wore an actively inflated DFS boot. However, when a DFS boot without plantar surface contact was worn during HU, no significant protection from HU-induced myofiber atrophy was observed. These results illustrate that the application of mechanical foot stimulation to the plantar surface of the rat foot is an effective countermeasure to muscle atrophy induced by HU.     

Spatial relationships between shearing stresses and pressure on the plantar skin surface during gait

Based on the hypothesis that diabetic foot lesions have a mechanical etiology, extensive efforts have sought to establish a relationship between ulcer occurrence and plantar pressure distribution. However, these factors are still not fully understood. The purpose of this study was to simultaneously record shear and pressure distributions in the heel and forefoot and to answer whether: (i) peak pressure and peak shear for anterior-posterior (AP) and medio-lateral (ML) occur at different locations, and if (ii) peak pressure is always centrally located between sites of maximum AP and ML shear stresses. A custom built system was used to collect shear and pressure data simultaneously on 11 subjects using the 2-step method. The peak pressure was found to be 362 kPa ± 106 in the heel and 527 kPa ± 123 in the forefoot. In addition, the average peak shear values were higher in the forefoot than in the heel. The greatest shear on the plantar surface of the forefoot occurred in the anterior direction (mean and std. dev.: 37.7 ± 7.6 kPa), whereas for the heel, peak shear the foot was in the posterior direction (21.2 ± 5 kPa). The results of this study suggest that the interactions of the shear forces caused greater "spreading" in the forefoot and greater tissue "dragging" in the heel. The results also showed that peak shear stresses do not occur at the same site or time as peak pressure. This may be an important factor in locating where skin breakdown occurs in patients at high-risk for ulceration.     

The extensibility of the plantar fascia influences the windlass mechanism during human running

The arch of the human foot is unique among hominins as it is compliant at ground contact but sufficiently stiff to enable push-off. These behaviours are partly facilitated by the ligamentous plantar fascia whose role is central to two mechanisms. The ideal windlass mechanism assumes that the plantar fascia has a nearly constant length to directly couple toe dorsiflexion with a change in arch shape. However, the plantar fascia also stretches and then shortens throughout gait as the arch-spring stores and releases elastic energy. We aimed to understand how the extensible plantar fascia could behave as an ideal windlass when it has been shown to strain throughout gait, potentially compromising the one-to-one coupling between toe arc length and arch length. We measured foot bone motion and plantar fascia elongation using high-speed X-ray during running. We discovered that toe plantarflexion delays plantar fascia stretching at foot strike, which probably modifies the distribution of the load through other arch tissues. Through a pure windlass effect in propulsion, a quasi-isometric plantar fascia''s shortening is delayed to later in stance. The plantar fascia then shortens concurrently to the windlass mechanism, likely enhancing arch recoil at push-off.     

Stress analysis of the standing foot following surgical plantar fascia release

Plantar fascia release is a surgical alternative for patients who suffer chronic heel pain due to plantar fasciitis and are unaffected by conservative treatment. A computational (finite element) model for analysis of the structural behavior of the human foot during standing was utilized to investigate the biomechanical effects of releasing the plantar fascia. The model integrates a system of five planar structures in the directions of the foot rays. It was built according to accurate geometric data of MRI, and includes linear and non-linear elements that represent bony, cartilaginous, ligamentous and fatty tissues. The model was successfully validated by comparing its resultant ground reactions with foot-ground pressure measurements and its predicted displacements with those observed in radiological tests. Simulation of plantar fascia release (partial or total) was accomplished by gradually removing parts of the fascia in the model. The results showed that total fascia release causes extensive arch deformation during standing, which is greater than normal deformation by more than 2.5mm. Tension stresses carried by the long plantar ligaments increased significantly, and may exceed the normal average stress by more than 200%. Since the contribution of the plantar fascia to the foot's load-bearing ability is of major importance, its release must be very carefully considered, and the present model may be used to help surgeons decide upon the desired degree of release.     

Temperature as a predictive tool for plantar triaxial loading

Diabetic foot ulcers are caused by moderate repetitive plantar stresses in the presence of peripheral neuropathy. In severe cases, the development of these foot ulcers can lead to lower extremity amputations. Plantar pressure measurements have been considered a capable predictor of ulceration sites in the past, but some investigations have pointed out inconsistencies when solely relying on this method. The other component of ground reaction forces/stresses, shear, has been understudied due to a lack of adequate equipment. Recent articles reported the potential clinical significance of shear in diabetic ulcer etiology. With the lack of adequate tools, plantar temperature has been used as an alternative method for determining plantar triaxial loading and/or shear. However, this method has not been previously validated. The purpose of this study was to analyze the potential association between exercise-induced plantar temperature increase and plantar stresses. Thirteen healthy individuals walked on a treadmill for 10 minutes at 3.2 km/h. Pre and post-exercise temperature profiles were obtained with a thermal camera. Plantar triaxial stresses were quantified with a custom-built stress plate. A statistically significant correlation was observed between peak shear stress (PSS) and temperature increase (r=0.78), but not between peak resultant stress (PRS) and temperature increase (r=0.46). Plantar temperature increase could predict the location of PSS and PRS in 23% and 39% of the subjects, respectively. Only a moderate linear relationship was established between triaxial plantar stresses and walking-induced temperature increase. Future research will investigate the value of nonlinear models in predicting plantar loading through foot temperature.     

Effect of prefabricated thermoformable foot orthoses on plantar surface temperature after running: A gender comparison

There is a lack of evidence about the effect of different type of foot orthoses on plantar surface temperature. Moreover, that effect could be different depending on gender due to anatomical and physiological differences between men and women. The aim of the study was to analyze the effect of a prefabricated thermoformable foot orthosis on plantar surface temperature after running and taking gender differences into account. Thirty recreational runners (15 males, mean (standard deviation): 28 (7) years, 69.7 (6.5) kg, 1.74 (0.05) cm and 22.9 (1.7) kg/m²; and 15 females: 35 (7) years, 55.2 (6.9) kg, 1.63 (0.06) cm and 20.6 (1.9) kg/m²) carried out a maximum incremental test as pre-test, and two running tests on a treadmill at the laboratory wearing previously randomized different foot orthoses (thermoformable and prefabricated generic). The plantar surface temperature of the dominant foot sole in ten regions of interest was assessed before and immediately after 30-min running at 75% of VO_2max. The use of thermoformable foot orthoses produced lower temperatures only in men after the run in medial heel (P = 0.033, ES = 0.7), which then disappeared in temperature variation (after – before) (P = 0.910). Regarding gender, women showed lower temperatures before the run in both orthosis conditions (P < 0.039, ES > 0.8), but no differences in temperatures after the run (P = 0.910) in comparison with men. Moreover, absolute temperatures after running were always greater than before the run (P < 0.001, ES > 5.0). In conclusion, the thermoformable foot orthoses do not modify plantar surface temperature after running in healthy runners of either gender, compared to prefabricated generic foot orthoses. Although women present lower baseline plantar temperatures than men, these differences disappear after exercise.     

A new method to normalize plantar pressure measurements for foot size and foot progression angle

Plantar pressure measurement provides important information about the structure and function of the foot and is a helpful tool to evaluate patients with foot complaints. In general, average and maximum plantar pressure of 6–11 areas under the foot are used to compare groups of subjects. However, masking the foot means a loss of important information about the plantar pressure distribution pattern. Therefore, the purpose of this study was to develop and test a simple method that normalizes the plantar pressure pattern for foot size, foot progression angle, and total plantar pressure. Moreover, scaling the plantar pressure to a standard foot opens the door for more sophisticated analysis techniques such as pattern recognition and machine learning.Twelve subjects walked at preferred and half of the preferred walking speed over a pressure plate. To test the method, subjects walked in a straight line and in an approaching angle of approximately 40°. To calculate the normalized foot, the plantar pressure pattern was rotated over the foot progression angle and normalized for foot size.After normalization, the mean shortest distance between the contour lines of straight walking and walking at an angle had a mean of 0.22 cm (SD: 0.06 cm) for the forefoot and 0.14 cm (SD: 0.06 cm) for the heel. In addition, the contour lines of normalized feet for the various subjects were almost identical.The proposed method appeared to be successful in aligning plantar pressure of various feet without losing information.     

Evaluation of potential variables contributing to the development and duration of plantar lesions in a population of aquarium-maintained African penguins (Spheniscus demersus)

Bumblefoot (pododermatitis), often described as the most significant environmental disease of captive penguins, is commonly due to excessive pressure or trauma on the plantar surface of the avian foot, resulting in inflammation or necrosis and causing severe swelling, abrasions, or cracks in the skin. Although not formally evaluated in penguins, contributing factors for bumblefoot are thought to be similar to those initiating the condition in raptors and poultry. These factors include substrate, body weight, and lack of exercise. The primary purpose of this retrospective study was to evaluate variables potentially contributing to the development and duration of plantar lesions in aquarium-maintained African penguins (Spheniscus demersus), including sex, weight, age, season, exhibit activity, and territory substrate. Results indicate that males develop significantly more plantar lesions than females. Penguins weighing between 3.51 and 4.0 kg develop plantar lesions significantly more often than penguins weighing between 2.5 and 3.5 kg, and because male African penguins ordinarily weigh significantly more than females, weight is likely a contributing factor in the development of lesions in males compared with females. Significantly more plantar lesions were observed in penguins standing for greater than 50% of their time on exhibit than swimming. Penguins occupying smooth concrete territories developed more plantar lesions compared with penguins occupying grate territories. Recommendations for minimizing bumblefoot in African penguins include training penguins for monthly foot examinations for early detection of plantar lesions predisposing for the disease, encouraging swimming activity, and replacing smooth surfaces on exhibit with surfaces providing variable degrees of pressure and texture on the feet.     

Effect of peak pressure and pressure gradient on subsurface shear stresses in the neuropathic foot

The pressure distribution on the plantar surface of the foot may provide insights into the stresses within the subsurface tissues of patients with diabetes mellitus and peripheral neuropathy (PN) who are at risk for skin breakdown. The purposes of this study were to (1) estimate the stress distribution in the subsurface soft tissue from a measured surface pressure distribution and determine any differences between values in the forefoot and rearfoot, and (2) determine the relationship between maximum shear stress (MSS) (magnitude and depth) and characteristics of the pressure distribution. The measured in-shoe pressure distributions during walking characterized by the peak plantar pressure and maximum pressure gradient on the plantar surface of the feet for 20 subjects with diabetes, PN and history of a mid foot or forefoot plantar ulcer were analyzed. The effects of peak pressure and maximum pressure gradient at the peak pressure location on the stress components in the subsurface soft tissue were studied using a potential function method to estimate the subsurface tissue stress. The calculated MSSs are larger in magnitude and located closer to the surface in the forefoot, where most skin breakdown occurs, compared to the rearfoot. In addition, the MSS (magnitude and depth) is highly correlated with the pressure gradient (r=-0.77 & 0.61) and the peak pressure (r=-0.61 & 0.91). The peak pressure and the maximum pressure gradient obtained from the surface pressure distribution appear to be important variables to identify where MSSs are located in the subsurface tissues on the plantar foot that may lead to skin break down.     

Finite element analysis of plantar fascia under stretch-the relative contribution of windlass mechanism and Achilles tendon force

Stretching plays an important role in the treatment of plantar fasciitis. Information on the internal stresses/strains of the plantar fascia under stretch is useful in enhancing knowledge on the stretch mechanisms. Although direct measurement can monitor plantar fascia changes, it is invasive and gathers only localized information. The purpose of this paper was to construct a three-dimensional finite element model of the foot to calculate the stretch effects on plantar fascia and monitor its stress/strain distributions and concentrations. A three-dimensional foot model was developed and contained 26 bones with joint cartilages, 67 ligaments and a fan-like solid plantar fascia modeling. All tissues were idealized as linear elastic, homogeneous and isotropic whilst the plantar fascia was assigned as hyperelastic to represent its nonlinearity. The plantar fascia was monitored for its biomechanical responses under various stretch combinations: three toe dorsiflexion angles (windlass effect: 15 degrees , 30 degrees and 45 degrees ) and five Achilles tendon forces (100, 200, 300, 400 and 500N). Our results indicated that the plantar fascia strain increased as the dorsiflexion angles increased, and this phenomenon was enhanced by increasing Achilles tendon force. A stress concentration was found near the medial calcaneal tubercle, and the fascia stress was higher underneath the first foot ray and gradually decreased as it moved toward the fifth ray. The current model recreated the position of the foot when stretch is placed on the plantar fascia. The results provided a general insight into the mechanical and biomechanical aspects of the influences of windlass mechanism and Achilles tendon force on plantar fascia stress and strain distribution. These findings might have practical implications onto plantar fascia stretch approaches, and provide guidelines to its surgical release.     

Surface deflection of primate fingertip under line load

A study of the biomechanics of the skin and the subcutaneous soft tissues is of fundamental importance in understanding the process of transduction at the mechanoreceptive nerve terminals responsible for the sense of touch. In the present investigation, the fingertips (distal phalanges) of three adult humans and four monkeys were indented in vivo using a line load delivered by a sharp wedge. The resulting skin surface deflection profile was photographed and used as a clue to infer the mechanical nature of the materials that make up the fingertip. It is shown that the modified Boussinesq solution used by Phillips and Johnson (1981), applicable when the fingertip is modeled as an elastic half-space in a state of plane strain, predicts a skin surface deflection profile that can only roughly approximate the empirically observed profiles. As an alternative, a simple model which views the fingertip as an elastic membrane filled with an incompressible fluid (like a 'waterbed') under plane strain conditions is proposed. It is shown that the predictions of this model, which takes into account the finite deformations that occur, agree very well with the photographed profiles in the region of interest (up to about 3 mm from the load).     

Deformation and stress distribution of the human foot after plantar ligaments release: A cadaveric study and finite element analysis

The majority of foot deformities are related to arch collapse or instability, especially the longitudinal arch. Although the relationship between the plantar fascia and arch height has been previously investigated, the stress distribution remains unclear. The aim of this study was to explore the role of the plantar ligaments in foot arch biomechanics. We constructed a geometrical detailed three-dimensional (3-D) finite element (FE) model of the human foot and ankle from computer tomography images. The model comprised the majority of joints in the foot as well as bone segments, major ligaments, and plantar soft tissue. Release of the plantar fascia and other ligaments was simulated to evaluate the corresponding biomechanical effects on load distribution of the bony and ligamentous structures. These intrinsic ligaments of the foot arch were sectioned to simulate different pathologic situations of injury to the plantar ligaments, and to explore bone segment displacement and stress distribution. The validity of the 3-D FE model was verified by comparing results with experimentally measured data via the displacement and von Mise stress of each bone segment. Plantar fascia release decreased arch height, but did not cause total collapse of the foot arch. The longitudinal foot arch was lost when all the four major plantar ligaments were sectioned simultaneously. Plantar fascia release was compromised by increased strain applied to the plantar ligaments and intensified stress in the midfoot and metatarsal bones. Load redistribution among the centralized metatarsal bones and focal stress relief at the calcaneal insertion were predicted. The 3-D FE model indicated that plantar fascia release may provide relief of focal stress and associated heel pain. However, these operative procedures may pose a risk to arch stability and clinically may produce dorsolateral midfoot pain. The initial strategy for treating plantar fasciitis should be non-operative.     

The compressive material properties of the plantar soft tissue

The plantar soft tissue is the primary means of physical interaction between a person and the ground during locomotion. Dynamic loads greater than body weight are borne across the entire plantar surface during each step. However, most testing of these tissues has concentrated on the structural properties of the heel pad. The purpose of this study was to determine the material properties of the plantar soft tissue from six locations beneath: the great toe (subhallucal), the 1st, 3rd and 5th metatarsal heads (submetatarsal), the lateral midfoot (lateral submidfoot) and the heel (subcalcaneal). We obtained specimens from these locations from 11 young, non-diabetic donors; the tissue was cut into 2 cm x 2 cm blocks and the skin was removed. Stress relaxation experiments were conducted and the data were fit using the quasi-linear viscoelastic (QLV) theory. To determine tissue modulus, energy loss and the effect of test frequency, we also conducted displacement controlled triangle waves at five frequencies ranging from 0.005 to 10 Hz. The subcalcaneal tissue was found to have an increased relaxation time compared to the other areas. The subcalcaneal tissue was also found to have an increased modulus and decreased energy loss compared to the other areas. Across all areas, the modulus and energy loss increased for the 1 and 10 Hz tests compared to the other testing frequencies. This study is the first to generate material properties for all areas of the plantar soft tissue, demonstrating that the subcalcaneal tissue is different than the other plantar soft tissue areas. These data will have implications for foot computational modeling efforts and potentially for orthotic pressure reduction devices.     

Comparison between sensitive and nonsensitive free flaps in reconstruction of the heel and plantar area

In this study, 12 cases of reconstruction of the heel and plantar area since 1982 are reviewed. Six nonsensate muscle free flaps and six sensate fasciocutaneous flaps were used, respectively. Categories assessed were the time interval for return to daily living activities, sensation to light touch, pinprick, Semmes-Weinstein monofilament test of the reconstructed area for sensory evaluation; and results of pedograms (maximal pressure, pressure distribution, and total contact area of the plantar surface). Follow-up periods were between 2 and 14 years, with an average of 6 years. Better sensory results and early return to daily living activities were observed in the sensate flap group, but the defects were smaller in this group. Despite the slightly longer time to return to daily living activities and worse sensory results, long-term follow-up showed that patients with nonsensate flaps had no difficulty in performing living activities if they continued to be careful and to use some kind of protective shoes. The results of the pedogram analyses were similar between the two groups with regard to total contact area of the reconstructed foot in relation to the healthy foot. Pressure values of the reconstructed areas in sensate flaps were found to be close to pressure values in the same weight areas of the normal foot. The differences between pressure values of the sensate and nonsensate flaps were statistically significant (p < 0.001). Therefore, in reconstruction of the weight-bearing surface of the foot, each case should be evaluated individually. The reconstructive method should be chosen according to the location and soft-tissue requirements of the defect.     

The efficacy of a pneumatic compression device in the treatment of plantar fasciitis

Plantar fasciitis is a common foot disorder that affects more than two million Americans each year. Conservative management of plantar fasciitis is the first line of treatment by the medical specialist who frequently encounters this common foot complaint. In this study, 50 patients with plantar fasciitis of 4 weeks duration but less than 12 weeks were randomized into two groups. One group of 25 patients used the AirHeel (Aircast, Inc.) and the second group of 25 used the 1st Step prefabricated foot insert (Wrymark, Inc). Standardized weight-bearing radiographs were obtained in order to categorize the foot type: normal arch, pes planus, or pes cavus. Patients were initially evaluated and at 12 weeks they returned for a subsequent visit. The contact area of the foot with the AirHeel and 1st Step insert were similar, an increase of 27% and 26%, respectively, over the contact area barefoot. There was a noted difference in force reduction with the two devices. The AirHeel reduced the midstance force by 20.19%, as compared to the 1st Step insert which showed a 1.03% increase in midstance force. Patients with a higher initial pain score seemed to respond better initially to the AirHeel (p = 0.015) than the 1st Step insert (p = 0.035). This study demonstrates the benefits of offloading the foot at midstance with two devices to relieve the discomfort associated with plantar fasciitis. The Aircast AirHeel is a new modality for dynamic, functional treatment of proximal plantar fasciitis.     

Dynamic plantar loading index: understanding the benefit of custom foot orthoses for painful pes cavus

The purpose of this study was to evaluate a new method showing how custom foot orthoses (CFO) improve dynamics of plantar loading. The method is based on the probability distribution of peak pressure time series and is quantified using the Regression Factor (RF). RF is a least square regression slope between the experimentally observed plantar pressure magnitude probability distribution and a modeled Gaussian shape. Plantar pressure data from a randomized controlled trial of 154 participants with painful Pes Cavus were retrospectively re-analyzed. The participants were randomized to an active treatment group given CFO or a control group given sham orthoses. The location of 2(nd) Peak pressure as a percentage of stance time (P(Loc2)) and its magnitude (P(M2)) was also calculated. In addition, plantar pressure data were collected on 23 healthy volunteers with normal foot alignment and no foot pain. Results demonstrated Pes Cavus had a significantly lower RF than healthy participants (0.30 v. 0.51; p<10(-7)). P(M2) was reduced in both active and control groups. However, RF and the P(Loc2) were only changed in the active group (p<0.005) without any significant change in the control group (p>0.5). This study suggests that painful Pes Cavus alters the shape of probability distribution of plantar loading during walking and CFO are an effective therapeutic solution that can significantly improve it. Further use of the RF index and 2(nd) peak pressure location as an outcome measure for treatment of foot and ankle deformities is suggested.     

A new ambulatory foot pressure device for patients with sensory impairment. A system for continuous measurement of plantar pressure and a feed-back alarm

Abnormal and excessive plantar pressure is a major risk factor for the development of foot ulcers in patients with loss of protective pain sensation. Repeated pressure with each step can result in inflammation at specific points, followed by ulcer formation. Patients with peripheral nerve disease are unable to prevent the development of such lesions, which often lead to amputation. For this reason, it has been suggested that a fundamental therapeutic intervention should be the reduction of high plantar pressure. We have developed a portable, battery-operated ambulatory foot pressure device (AFPD) which has two important functions: (1) to determine the areas of high plantar pressure, and (2) to provide an acoustic alarm, adjusted to a specific pressure load, which is triggered when weight-bearing exceeds the predetermined plantar pressure. A memory of plantar pressure parameters allows for downloading of the data and sequential analysis during the investigation period. Such an alarm device could replace the lack of pain sensation and may play an important role in the prevention of ulcer development and lower extremity amputation.     

The skin of birds' feet: Morphological adaptations of the plantar surface

The skin of the foot provides the interface between the bird and the substrate. The foot morphology involves the bone shape and the integument that is in contact with the substrate. The podotheca is a layer of keratinized epidermis forming scales that extends from the tarsometatarsus to the toe extremities. It varies in size, shape, amount of overlap and interacts with the degree of fusion of the toes (syndactyly). A study of toe shape and the podotheca provides insights on the adaptations of perching birds. Our analysis is based on micro‐CT scans and scanning electron microscopy images of 21 species from 17 families, and includes examples with different orientations of the toes: zygodactyl (toes II and III forward), anisodactyl (toes II, III, and IV forward), and heterodactyl (toes III and IV forward). We show that in these three groups, the skin forms part of a perching adaptation that involves syndactyly to different degrees. However, syndactyly does not occur in Psittacidae that use their toes also for food manipulation. The syndactyly increases the sole surface and may reinforce adherence with the substrate. Scale shape and toe orientation are involved in functional adaptations to perch. Thus, both bone and skin features combine to form a pincer‐like foot.     

Anatomic basis of plantar flap design

Safe planes exist for plantar incisions that minimize the possibility of subcutaneous nerve injury and are therefore useful in flap design. Nerve branch orientation in the plantar subcutaneous tissue is specific and guides dissection so as to avoid producing anesthesia in weight-bearing areas. An extensive proximal plantar subcutaneous plexus exists that permits elevation of plantar flaps in a superficial plane. This is due to the major contribution that the dorsal circulation makes to the skin of the plantar surface. The blood supply to the non-weight-bearing midsole area is not from the medial plantar artery exclusively. This is a watershed area with important lateral plantar artery and dorsalis pedis artery contributions as well. It is not necessary or desirable to base plantar flaps on a myocutaneous or fasciocutaneous supply with its required deep dissection. Local plantar flaps can be designed to include sensation and abundant blood supply without the need for "subfascial" dissection. Subcutaneous sensory plantar flaps designed in accordance with these principles promise a more ideal solution for the treatment of plantar defects.     

Dynamic plantar pressure distribution during terrestrial locomotion of bonobos (Pan paniscus)

We collected high-resolution plantar pressure distributions of seven bonobos during terrestrial bipedal and quadrupedal locomotion (N = 146). Functional foot length, degree of hallux abduction, and total contact time were determined, and plots, showing pressure as a function of time for six different foot regions, were generated. We also studied five adult humans for comparison (N = 13). Both locomotion types of the bonobo show a large variation in plantar pressure distributions, which could be due to the interference of instantaneous behavior with locomotion and differences in walking speed and body dimensions. The heel and the lateral midfoot typically touch down simultaneously at initial ground contact in bipedal and quadrupedal walking of bonobos, in contrast with the typical heel-strike of human bipedalism. The center of pressure follows a curved course during quadrupedalism, as a consequence of the medial weight transfer during mid-stance. Bipedal locomotion of bonobos is characterized by a more plantar positioning of the feet and by a shorter contact time than during quadrupedal walking, according to a smaller stride and step length at a higher frequency. We observed a varus position of the foot with an abducted hallux, which likely possesses an important sustaining and stabilizing function during terrestrial locomotion.