Dirk De Clercq

Biomechanical analysis of the stance phase during barefoot and shod running

This study investigated spatio-temporal variables, ground reaction forces and sagittal and frontal plane kinematics during the stance phase of nine trained subjects running barefoot and shod at three different velocities (3.5, 4.5, 5.5 m s(-1)). Differences between conditions were detected with the general linear method (factorial model). Barefoot running is characterized by a significantly larger external loading rate than the shod condition. The flatter foot placement at touchdown is prepared in free flight, implying an actively induced adaptation strategy. In the barefoot condition, plantar pressure measurements reveal a flatter foot placement to correlate with lower peak heel pressures. Therefore, it is assumed that runners adopt this different touchdown geometry in barefoot running in an attempt to limit the local pressure underneath the heel. A significantly higher leg stiffness during the stance phase was found for the barefoot condition. The sagittal kinematic adaptations between conditions were found in the same way for all subjects and at the three running velocities. However, large individual variations were observed between the runners for the rearfoot kinematics.

Intrinsic Risk Factors for Inversion Ankle Sprains in Male Subjects A Prospective Study

Background Many variables have been retrospectively associated with ankle sprains. However, very little is known about factors predisposing people to these injuries. Hypothesis Measurable intrinsic factors might predispose male athletes to ankle sprains. Study Design Cohort study; Level of evidence, 2. Methods A total of 241 male physical education students were evaluated for possible intrinsic risk factors for inversion sprains at the beginning of their academic study. The evaluated intrinsic risk factors included anthropometrical characteristics, functional motor performances, ankle joint position sense, isokinetic ankle muscle strength, lower leg alignment characteristics, postural control, and muscle reaction time during a sudden inversion perturbation. Subjects were followed prospectively for 1 to 3 years. Results A total of 44 (18%) of the 241 male subjects sustained an inversion sprain; 4 sprained both ankles. Cox regression analysis revealed that male subjects with slower running speed, less cardiorespiratory endurance, less balance, decreased dorsiflexion muscle strength, decreased dorsiflexion range of motion, less coordination, and faster reaction of the tibialis anterior and gastrocnemius muscles are at greater risk of ankle sprains. Conclusion Based on our findings, it is suggested that running speed, cardiorespiratory endurance, balance, dorsiflexion strength, coordination, muscle reaction, and dorsiflexion range of motion at the ankle are associated with the risk of ankle inversion sprains in male subjects.

A simple exoskeleton that assists plantarflexion can reduce the metabolic cost of human walking.

Background Even though walking can be sustained for great distances, considerable energy is required for plantarflexion around the instant of opposite leg heel contact. Different groups attempted to reduce metabolic cost with exoskeletons but none could achieve a reduction beyond the level of walking without exoskeleton, possibly because there is no consensus on the optimal actuation timing. The main research question of our study was whether it is possible to obtain a higher reduction in metabolic cost by tuning the actuation timing. Methodology/Principal Findings We measured metabolic cost by means of respiratory gas analysis. Test subjects walked with a simple pneumatic exoskeleton that assists plantarflexion with different actuation timings. We found that the exoskeleton can reduce metabolic cost by 0.18±0.06 W kg−1 or 6±2% (standard error of the mean) (p = 0.019) below the cost of walking without exoskeleton if actuation starts just before opposite leg heel contact. Conclusions/Significance The optimum timing that we found concurs with the prediction from a mathematical model of walking. While the present exoskeleton was not ambulant, measurements of joint kinetics reveal that the required power could be recycled from knee extension deceleration work that occurs naturally during walking. This demonstrates that it is theoretically possible to build future ambulant exoskeletons that reduce metabolic cost, without power supply restrictions.

The mechanical characteristics of the human heel pad during foot strike in running: An in vivo cineradiographic study

The compressive properties of the heel pad during the heel strike when running (barefoot and shod, two subjects, 4.5 m s-1) were studied by means of a high-speed two-dimensional cineradiographic registration (150 frames s-1) of an actual running step. Vertical ground reaction forces were measured with a force platform. In barefoot running the heel pad deforms to a maximal percentage deformation of 60.5 +/- 5.5%. In shod running the heel pad deforms only 35.5 +/- 2.5% and the nonlinear force-deformation relationship reflects an increasing stiffness when deformation rises. Although the amplitudes of the vertical ground reaction forces do not differ notably in both conditions, barefoot running implies a maximal deformation to the fatty heel tissue, reducing its functional role from shock reduction towards local protection of the heel bone. It is argued that embedding the foot in a well-fitting shoe increases the effective stiffness of the heel pad.

Intrinsic risk factors for inversion ankle sprains in females – a prospective study

Ankle sprains are extremely common. However, very little is known about the variables that predispose individuals to these injuries. The purpose of this study was to examine prospectively intrinsic risk factors for inversion sprains in a young physically active female population. One hundred and fifty‐nine female physical education students were evaluated for several possible intrinsic risk factors for inversion sprains at the beginning of their academic study. The evaluated intrinsic risk factors included anthropometrical and physical characteristics, ankle joint position sense, isokinetic ankle muscle strength, lower leg alignment characteristics, postural control and muscle reaction time during a sudden inversion perturbation. All sports injuries were registered during 1–3 years and exposure to sport was recorded (mean: 15.33±4.33 h a week). Thirty‐two (20%) of the 159 females sprained their ankle. The number of ankle sprains per 1000 h of sports exposure was 0.75. The Cox regression analysis revealed that females with less accurate passive joint inversion position sense [hazard ratio (HR): 1.08, 95% confidence interval (CI): 1.02–1.14 for absolute error at 15° inversion], a higher extension range of motion at the first metatarsophalangeal joint (HR: 1.03, 95% CI: 1.00–1.06) and less coordination of postural control (HR: 0.96, 95% CI: 0.93–1.00 for endpoint excursion; HR: 0.94, 95% CI: 0.89–0.99 for maximal endpoint excursion) are at greater risk of an ankle sprain. The findings of this study suggest that effective prevention and conservative rehabilitation of ankle inversion sprains should include attention to these variables.

The effects of habitual footwear use: foot shape and function in native barefoot walkers†

The human foot was anatomically modern long before footwear was invented, and is adapted to barefoot walking on natural substrates. Understanding the biomechanics of habitually barefoot walkers can provide novel insights both for anthropologist and for applied scientists, yet the necessary data is virtually non-existent. To start assessing morphological and functional effects of the habitual use of footwear, we have studied a population of habitually barefoot walkers from India (n = 70), and compared them with a habitually shod Indian control group (n = 137) and a Western population (n = 48). We focused on foot metrics and on the analysis of plantar pressure data, which was performed using a novel, pixel based method (Pataky and Goulermas 2008, Journal of Biomechanics, 41, 2136). Habitually shod Indians wore less often, and less constricting shoes than Western people. Yet, we found significant differences with their habitually barefoot peers, both in foot shape and in pressure distribution. Barefoot walkers had wider feet and more equally distributed peak pressures, i.e. the entire load carrying surface was contributing more uniformly than in habitually shod subjects, where regions of very high or very low peak pressures were more apparent. Western subjects differed strongly from both Indian populations (and most from barefoot Indians), by having relatively short and, especially, slender feet, with more focal and higher peak pressures at the heel, metatarsals and hallux. The evolutionary history of humans shows that barefoot walking is the biologically natural situation. The use of footwear remains necessary, especially on unnatural substrates, in athletics, and in some pathologies, but current data suggests that footwear that fails to respect natural foot shape and function will ultimately alter the morphology and the biomechanical behaviour of the foot.

Deformation characteristics of the heel region of the shod foot during a simulated heel strike: The effect of varying midsole hardness

Impact tests using a pendulum were performed on the shod heel region of nine subjects. Both soft- and hard-soled shoes were used. The deformations involved were calculated from the registered decelerations during impact. Thus, load-deformation cycles were recorded for various impact velocities. In contrast to in vivo force-platform recordings, peak loadings for the soft- and hard-soled conditions differed significantly (614 +/- 29 N vs 864 +/- 49 N, respectively), thus challenging the evidence for compensation at the level of the heel pad. Moreover, computation of the compression of the heel pad in the shoe showed an unexpected inverse relationship between shoe midsole hardness and degree of heel pad compression: the harder the midsole, the smaller the compression (soft shoe 7.6 +/- 0.9 mm; hard shoe 6.7 +/- 0.9 mm). This can be explained by assuming a loading rate dependent stiffness of the heel pad in the shod condition (stiffness in N.m-1 = 51.25x (loading rate in N.s-1)0.76; R2 = 0.90), determined by the visco-elastic nature of the heel pad and the spatial confinement of the heel counter of the shoe.

A Prospective Study on Gait-related Intrinsic Risk Factors for Patellofemoral Pain

Objective:To prospectively determine gait-related risk factors for patellofemoral pain. Design:A prospective cohort study. Setting:Male and female recruits of the Belgian Royal Military Academy during a 6-week basic military training period. Participants:Eighty-four officer cadets (65 men, 19 women), who entered the Military Academy and were without a history of any knee or lower-leg complaints, participated in the study. Interventions:Before the start of the 6-week basic military training period, plantar pressure measurements during walking were performed. During the basic military training period, patellofemoral complaints were diagnosed and registered by a sports medicine physician. Main Outcome Measurements:Plantar pressure measurements during walking were performed using a footscan pressure plate (RsScan International). Results:During the 6-week training period, 36 subjects developed patellofemoral pain (25 male and 11 female). Logistic regression analysis revealed that subjects who developed patellofemoral pain had a significantly more laterally directed pressure distribution at initial contact of the foot, a significantly shorter time to maximal pressure on the fourth metatarsal, and a significantly slower maximal velocity of the change in lateromedial direction of the center of pressure during the forefoot contact phase. Conclusions:Our findings suggest that the feet of the persons who developed anterior knee pain have a heel strike in a less pronated position and roll over more on the lateral side compared with the control group. The results of this study can be considered valuable in identifying persons at risk for patellofemoral pain.

Locomotion in bonobos (Pan paniscus): differences and similarities between bipedal and quadrupedal terrestrial walking, and a comparison with other locomotor modes.

One of the great ongoing debates in palaeo‐anthropology is when, and how, hominids acquired habitual bipedal locomotion. The newly adopted bipedal gait and the ancestral quadrupedal gait are most often considered as very distinct, with each habitual locomotor mode showing corresponding anatomical adaptations. Bonobos (Pan paniscus), along with common chimpanzees (P. troglodytes), are the closest living relatives to humans and their locomotion is valuable for comparison with other primates, and to gain an insight in the acquisition of human bipedalism. Bonobos are habitual quadrupeds, but they also engage in bipedal locomotion, both on terrestrial and in arboreal substrates. In terms of kinematics and dynamics, the contrast between bipedal and quadrupedal walking seems to be more subtle than one might expect. Apart from the trunk being approximately 37° more erect during bipedal locomotion, the leg movements are rather similar. Apart from the heel, plantar pressure distributions show subtle differences between bipedal and quadrupedal locomotion. Regardless, variability is high, and various intermediate forms of locomotion (e.g. tripedal walking) exist both in captivity and in the wild. Moreover, there is overlap between the characteristics of walking and other locomotor modes, as we show with new data of walking on an inclined pole and of vertical squat jumps. We suggest that there is great overlap between the many locomotor modes in bonobos, and that the required polyvalence is reflected in their anatomy. This may hamper the development of one highly specialized gait (i.e. bipedalism), which would constrain performance of the other types of locomotion.

A comprehensive physical activity promotion programme at elementary school: the effects on physical activity, physical fitness and psychosocial correlates of physical activity.

OBJECTIVE To evaluate the effects of a comprehensive physical activity (PA) promotion programme in elementary schools on childrens total PA levels, leisure-time PA, physical fitness and psychosocial correlates of PA. DESIGN A pre-test-post-test design over two school years. SETTING AND SUBJECTS Sixteen elementary schools (764 children, mean age: 11.2 +/- 0.7 years) were randomly assigned to the intervention condition (n = 8) and the control condition (n = 8). The intervention included a health-related physical education programme, an extracurricular PA promotion programme and classroom-based PA education lessons. In the total sample, leisure-time PA, psychosocial correlates of PA and physical fitness were measured using a PA questionnaire and the Eurofit test battery. In a sub-sample, total PA levels were measured using an accelerometer. RESULTS According to accelerometer data, childrens moderate PA and moderate-to-vigorous PA (MVPA) levels decreased less in the intervention schools than in the control schools (P < 0.01). The average time spent on MVPA decreased by 9 min per day in the intervention schools compared with 33 min per day in the control schools. Children in the intervention schools reported significantly more moderate PA in leisure time than the controls (P < 0.05). No overall improvement of physical fitness and no effects on the psychosocial correlates of PA were found. CONCLUSIONS The comprehensive PA promotion programme was successful in preventing a decline in childrens total activity levels. Furthermore, the intervention increased childrens PA engagement in leisure time. Therefore, implementation needs to be encouraged.