No abstract

SUMMARYAlthough humans appear to be specialized for endurance running, the plantigrade posture of our feet, in which the heel contacts the substrate at the beginning of a step, seems incompatible with economical running. In this study, we tested the hypothesis that plantigrade foot posture reduces the energetic cost of transport (COT) during walking in humans. When human subjects walked with their heels slightly elevated in a 'low-digitigrade' posture, COT increased by 53% above that of normal plantigrade walking. By contrast, there was no difference in COT when subjects ran with digitigrade versus plantigrade foot posture. Stride frequency increased and stride length decreased when subjects switched to digitigrade walking; however, this change did not influence the COT. Additionally, we found that possible reductions in postural stability appear not to have caused the elevated cost of digitigrade walking. Digitigrade walking, however, did (1) increase the external mechanical work performed by the limbs; (2) reduce the pendular exchange of kinetic and potential energy of the center of mass; (3) increase the average ground reaction force moment at the ankle joint; and (4) increase the recruitment of major extensor muscles of the ankle, knee, hip and back. These observations suggest that plantigrade foot posture improves the economy of walking. Relative to other mammals, humans are economical walkers, but not economical runners. Given the great distances hunter-gatherers travel, it is not surprising that humans retained a foot posture, inherited from our more arboreal great ape ancestors, that facilitates economical walking.

No abstract

Humans are known to have energetically optimal walking and running speeds at which the cost to travel a given distance is minimized. We hypothesized that "optimal" walking and running speeds would also exist at the level of individual locomotor muscles. Additionally, because humans are 60-70% more economical when they walk than when they run, we predicted that the different muscles would exhibit a greater degree of tuning to the energetically optimal speed during walking than during running. To test these hypotheses, we used electromyography to measure the activity of 13 muscles of the back and legs over a range of walking and running speeds in human subjects and calculated the cumulative activity required from each muscle to traverse a kilometer. We found that activity of each of these muscles was minimized at specific walking and running speeds but the different muscles were not tuned to a particular speed in either gait. Although humans are clearly highly specialized for terrestrial locomotion compared with other great apes, the results of this study indicate that our locomotor muscles are not tuned to specific walking or running speeds and, therefore, do not maximize the economy of locomotion. This pattern may have evolved in response to selection to broaden the range of sustainable running speeds, to improve performance in motor behaviors not related to endurance locomotion, or in response to selection for both.cost of transport | human evolution | persistence hunting | locomotor energetics | electromyography T he energetic cost to travel a given distance, the cost of transport (COT), has long been known to strongly depend on walking speed in humans (1, 2). The cost is minimized at intermediate walking speeds of 4.5-5.4 km·h −1 (1.25-1.5 m·s −1 ) and rises rapidly as speed increases above or decreases below this optimum. In contrast, the metabolic cost to run a given distance is generally recognized to be independent of speed in humans (2-6). Recently, however, a reevaluation of the COT in running humans has shown that humans also have energetically optimal speeds when running (7). This study relied on repeated measures from individual subjects, an approach that had the potential to identify the subtle relationship observed. There are at least three reasons to expect the COT to depend on locomotor speed. First, the force that a muscle generates decreases as its shortening velocity increases in a hyperbolic relationship. As a consequence of this relationship, a muscle's capacity to perform work and its energetic efficiency are highest at intermediate shortening velocities (8). Thus, if there is a relationship between locomotor speed and muscle shortening velocity, the force-velocity relationship may account for the COT being lowest at intermediate walking or running speeds. Note that this relationship is unlikely to explain energetically optimal speeds in both walking and running gaits because the shortening velocity of muscles in these two gaits will most often be very different. Second, the external mechan...

The Return to Activity Algorithm is able to support the evaluation of the functional status of the loco-motor system after injury or surgery and is furthermore capable of uncovering deficits or asymmetries, which are a proven risk for re-injury. This function-oriented individual approach is able to adequately dose the therapeutic efforts on an individual basis. With this approach, the right timing for a safe return to sports activities can be detected with high certainty.