Energetic consequences of human sociality: walking speed choices among friendly dyads

Far from the walking pace. Ecological and evolutionary consequences of the suboptimal locomotion speeds in non-adult humans

INTRODUCTION

Locomotion activities are part of most human daily tasks and are the basis for subsistence activities, particularly for hunter-gatherers. Therefore, differences in speed walking-related variables may have an effect, not only on the mobility of the group, but also on its composition. Some anthropometric parameters related to body length could affect walking speed-related variables and contribute to different human behaviors. However, there is currently little information on the influence of these parameters in nonadult individuals.

METHODS

Overall, 11 females and 17 male child/adolescents, 8-17 years of age, volunteered to participate in this cross-sectional study. Five different pace walking tests were performed on a treadmill to calculate the optimal locomotion speed (OLS) and U-shaped relationship between the walking energy expenditure and speed (χ2 cost of transport [CoT]) (i.e., energetic walking flexibility).

RESULTS

The mean OLS was 3.05 ± 0.13 miles per hour (mph), with no differences between sexes. Similarly, there were no sex differences in walking flexibility according to the χ2 CoT. Body height (p < .0001) and femur length (p < .001) were positively correlated with χ2 CoT; however, female child/adolescents mitigated the effect of height and femur length when walking at suboptimal speeds.

CONCLUSION

Consistent with prior observations in adults, our findings suggest that anthropometric parameters related to body stature are associated with reduced suboptimal walking flexibility in children and adolescents. Taken together, these results suggest that children and adolescents can adapt their pace to the one of taller individuals without a highly energetic penalty, but this flexibility decreases with increasing body size.

Understanding the influence of context on real-world walking energetics

Speeds that minimize energetic cost during steady-state walking have been observed during lab-based investigations of walking biomechanics and energetics. However, in real-world scenarios, humans walk in a variety of contexts that can elicit different walking strategies, and may not always prioritize minimizing energetic cost. To investigate whether individuals tend to select energetically optimal speeds in real-world situations and how contextual factors influence gait, we conducted a study combining data from lab and real-world experiments. Walking kinematics and context were measured during daily life over a week (N=17) using wearable sensors and a mobile phone. To determine context, we utilized self-reported activity logs, GPS data and follow-up exit interviews. Additionally, we estimated energetic cost using respirometry over a range of gait speeds in the lab. Gross and net cost of transport were calculated for each participant, and were used to identify energetically optimal walking speed ranges for each participant. The proportion of real-world steady-state stride speeds within these ranges (gross and net) were identified for all data and for each context. We found that energetically optimal speeds predicted by gross cost of transport were more predictive of walking speeds used during daily life than speeds that would minimize net cost of transport. On average, 82.2% of all steady-state stride speeds were energetically optimal for gross cost of transport for all contexts and participants, while only 45.6% were energetically optimal for net cost of transport. These results suggest that while energetic cost is a factor considered by humans when selecting gait speed in daily life, it is not the sole determining factor. Context contributes to the observed variability in movement parameters both within and between individuals.

Association of Physical Activity and Gait Speed: Does Context Matter?

Background: Physical activity (PA) is associated with gait speed, and both are recognized predictors of important health outcomes. The role of social context, such as PA of one’s spouse, in the association between PA and gait speed is largely unexplored. Methods: In our dyadic study of 69 couples, we objectively assessed each partner’s moderate to vigorous PA (MVPA) and gait speed. Associations of MVPA and gait speed were tested using actor-partner interdependence models in a structural equation modeling framework. Whether partners’ typically exercise together was examined as a moderator of these associations. Results: A nonlinear association was observed where higher MVPA was associated with faster gait speed, but only when MVPA was below average (husbands β = −.517; P = .002; wives β = −.483; P = .009). No moderating effects of exercising together were detected for husbands’ or wives’ MVPA on their own or their partners’ gait speed. Conclusions: In this investigation of couples, the association between MVPA and gait speed emerged only when nonlinear effects were considered. Findings suggest that the PA and gait speed association may be more nuanced than previously examined. Additional consideration of contextual factors that may alter the complex association between MVPA and gait speed is warranted.

Fossil footprints and what they mean for hominin paleobiology

Hominin footprints have not traditionally played prominent roles in paleoanthropological studies, aside from the famous 3.66 Ma footprints discovered at Laetoli, Tanzania in the late 1970s. This contrasts with the importance of trace fossils (ichnology) in the broader field of paleontology. Lack of attention to hominin footprints can probably be explained by perceptions that these are exceptionally rare and "curiosities" rather than sources of data that yield insights on par with skeletal fossils or artifacts. In recent years, however, discoveries of hominin footprints have surged in frequency, shining important new light on anatomy, locomotion, behaviors, and environments from a wide variety of times and places. Here, we discuss why these data are often overlooked and consider whether they are as "rare" as previously assumed. We review new ways footprint data are being used to address questions about hominin paleobiology, and we outline key opportunities for future research in hominin ichnology.

Interrupting Pedestrians in Indonesia; Effect of Climate on Perceived Steepness and Stair Climbing Behaviour

Increased activity during daily life is one public health initiative to reduce population inactivity. Increasing temperature and humidity influence walking for transport by reducing the blood supply available to exercising muscles. This study investigated effects of temperature and humidity on a perceptual cue, estimated stair slant, that can influence behaviour, and on subsequent speed of climbing. Participants (402 males, 423 females) estimated the slant of a 20.4° staircase at a university in Indonesia. Subsequently, the participants were timed covertly while climbing. As temperature and humidity increased, estimated stair slant became more exaggerated. Females estimated stair slant as steeper than males. For stair climbing, speed was reduced as temperature increased, and females climbed slower than males. Estimates of stair slant were not associated with speed of the subsequent climb. Climate influences estimates of stair slant that precede stair climbing and subsequent speed of the ascent. In this study, perception was unrelated to behaviour.

Variability and the form-function framework in evolutionary biomechanics and human locomotion

The form-function conceptual framework, which assumes a strong relationship between the structure of a particular trait and its function, has been crucial for understanding morphological variation and locomotion among extant and fossil species across many disciplines. In biological anthropology, it is the lens through which many important questions and hypotheses have been tackled with respect to relationships between morphology and locomotor kinematics, energetics and performance. However, it is becoming increasingly evident that the morphologies of fossil hominins, apes and humans can confer considerable locomotor diversity and flexibility, and can do so with a range of kinematics depending on soft tissue plasticity and environmental and cultural factors. This complexity is not built into traditional biomechanical or mathematical models of relationships between structure and kinematics or energetics, limiting our interpretation of what bone structure is telling us about behaviour in the past. The nine papers presented in this Special Collection together address some of the challenges that variation in the relationship between form and function pose in evolutionary biomechanics, to better characterise the complexity linking structure and function and to provide tools through which we may begin to incorporate some of this complexity into our functional interpretations.

Social interaction and the thermogenic response of chicken hatchlings

The aggregation of two or more individuals of the same species (huddling) is common in mammals and birds, especially in the cold. The physical contact reduces the weight-specific body surface exposed to the environment, thus lowering heat loss and the thermogenic needs. This study investigated the possibility that the mere presence of a conspecific, in absence of physical contact, may by itself influence metabolic rate during cold. The oxygen consumption (Vo₂) of pairs of chicken hatchlings was measured when the hatchlings were in isolation (individuals), together in the respirometer but kept separated by a grid (separated) or together in the respirometer free to huddle (together), in random order, in warm (ambient normothermia, 37.5 °C) and cold conditions (26 °C, 1 h). In warm, Vo₂ did not differ significantly among individuals, separated and together (~ 1.03 ± 0.04 ml O₂/min). During the whole cold period, Vo₂ of individuals exceeded the value by 23.3 ± 3.1 ml of O₂, significantly more than in separated (15.3 ± 2.0 ml O₂, P<0.01) and together (13.9 ± 3.3 ml O₂; P<0.001). Separated and together did not differ significantly. Vo₂ in the cold averaged 149 ± 7% of the value measured in normothermia in isolated, 132 ± 5% in separated and 128 ± 7% in together. By the end of the cold-exposure, Vo₂ averaged 166 ± 8% of normothermia in isolated, 146 ± 8% in separated and 140 ± 9% in together. In all cases, values of isolated significantly exceeded those of separated (P<0.01) and together (P<0.0001), while separated and together did not differ from each other (P>0.05; Two-way RM ANOVA). Hence, in this experimental model, social interaction without physical contact decreased the thermogenic response to cold as much as huddling did. Presumably, during the cold exposure, social interaction lowered the additional energetic cost of the stress of isolation.

Changes to gait speed when romantic partners walk together: Effect of age and obstructed pathway

BACKGROUND

Walking at a brisk pace is widely recommended to promote health. When partners walk together, walking activity is increased and maintained due to enhanced social support and accountability, but at least one person must adjust their gait speed. Decreased gait speed could compromise health benefits, which may be especially relevant for the aging population.

RESEARCH QUESTION

Do adults change gait speed when walking with their romantic partner, relative to walking alone, and is the change in speed affected by age or pathway conditions?

METHODS

Participants were 141 individuals from 72 romantic couples; age range 25-79 years. The three couple conditions were walking alone, walking with their partner, and walking while holding hands with their partner. The two pathway conditions were clear pathway and pathway with obstacles. Gait speed was modeled as a function of the couple conditions, pathway conditions, and covariates (gender, age, relationship duration, and physical activity) using mixed-effects (3-level) regression.

RESULTS

In both pathway conditions, both partners reduced speed when walking together (p < 0.001), and reduced speed further while holding hands (p < 0.001), when compared to walking alone. These effects were unchanged when covariates were included in the model. Further, speed was slower on the obstructed pathway for all participants, but the magnitude of slowing was greater with increasing age (p < 0.001) and in females (p=0.03).

SIGNIFICANCE

Across the adult lifespan, when walking together, both partners decreased gait speed by a clinically meaningful amount (≥0.05 m/s). While walking with a partner may increase walking activity due to social support, reduced speed when walking together may unintentionally reduce health benefits and gait quality in both partners. Future research should identify how health is impacted by the trade-off between increased walking activity and reduced gait speed when romantic partners walk together.

Snapshots of human anatomy, locomotion, and behavior from Late Pleistocene footprints at Engare Sero, Tanzania

Fossil hominin footprints preserve data on a remarkably short time scale compared to most other fossil evidence, offering snapshots of organisms in their immediate ecological and behavioral contexts. Here, we report on our excavations and analyses of more than 400 Late Pleistocene human footprints from Engare Sero, Tanzania. The site represents the largest assemblage of footprints currently known from the human fossil record in Africa. Speed estimates show that the trackways reflect both walking and running behaviors. Estimates of group composition suggest that these footprints were made by a mixed-sex and mixed-age group, but one that consisted of mostly adult females. One group of similarly-oriented trackways was attributed to 14 adult females who walked together at the same pace, with only two adult males and one juvenile accompanying them. In the context of modern ethnographic data, we suggest that these trackways may capture a unique snapshot of cooperative and sexually divided foraging behavior in Late Pleistocene humans.

Children are not like other loads: a cross-cultural perspective on the influence of burdens and companionship on human walking

A major portion of humans' activity-based energy expenditure is taken up by locomotion, particularly walking. Walking behaviors have energetic outcomes and as such can be important windows into how populations and groups adjust to different environmental and task constraints. While sex differences in the speed of paired walkers have been established by others, the dynamics of how walkers adjust their speed in more varied groups and in groups containing children remains unexplored. Furthermore, little ecological data exists to illustrate the relationships between walking speed and child-carrying. Here, we aim to determine how culture impacts the effects of group composition and infant-carrying on walking speed. Because the determinants of group dynamics and parental investment are partially cultural, we examine walking behavior in the Northwestern United States and in Central Uganda. Using an observational method, we recorded the speed, load carriage, and group composition of pedestrians in a single naturalistic urban environment within each country. Our data suggest that children are treated fundamentally differently than other loads or the presence of walking partners, and that major speed adjustments are child-dependent. Our data furthermore indicate that Ugandans walk more slowly in groups than when alone, while Americans walk more quickly in groups. Clear distinctions between the groups make large generalizations about walking behavior difficult, and highlight the importance of culturally specific contexts.

Multi-Gait Recognition Based on Attribute Discovery

Gait recognition is an important topic in biometrics. Current works primarily focus on recognizing a single person's walking gait. However, a person's gait will change when they walk with other people. How to recognize the gait of multiple people walking is still a challenging problem. This paper proposes an attribute discovery model in a max-margin framework to recognize a person based on gait while walking with multiple people. First, human graphlets are integrated into a tracking-by-detection method to obtain a person's complete silhouette. Then, stable and discriminative attributes are developed using a latent conditional random field (L-CRF) model. The model is trained in the latent structural support vector machine (SVM) framework, in which a new constraint is added to improve the multi-gait recognition performance. In the recognition process, the attribute set of each person is detected by inferring on the trained L-CRF model. Finally, attributes based on dense trajectories are extracted as the final gait features to complete the recognition. The experimental results demonstrate that the proposed method achieves better recognition performance than traditional gait recognition methods under the condition of multiple people walking together.

The Biomechanical and Energetic Advantages of a Mediolaterally Wide Pelvis in Women

Here, we argue that two key shifts in thinking are required to more clearly understand the selection pressures shaping pelvis evolution in female hominins: (1) the primary locomotor mode of female hominins was loaded walking in the company of others, and (2) the periodic gait of human walking is most effectively explained as a biomechanically controlled process related to heel-strike collisions that is tuned for economy and stability by properly-timed motor inputs (a model called dynamic walking). In the light of these two frameworks, the evidence supports differences between female and male upper-pelvic morphology being the result of the unique reproductive role of female hominins, which involved moderately paced, loaded walking in groups. Anat Rec, 300:764-775, 2017. © 2017 Wiley Periodicals, Inc.

Walking on a moving surface: energy-optimal walking motions on a shaky bridge and a shaking treadmill can reduce energy costs below normal

Understanding how humans walk on a surface that can move might provide insights into, for instance, whether walking humans prioritize energy use or stability. Here, motivated by the famous human-driven oscillations observed in the London Millennium Bridge, we introduce a minimal mathematical model of a biped, walking on a platform (bridge or treadmill) capable of lateral movement. This biped model consists of a point-mass upper body with legs that can exert force and perform mechanical work on the upper body. Using numerical optimization, we obtain energy-optimal walking motions for this biped, deriving the periodic body and platform motions that minimize a simple metabolic energy cost. When the platform has an externally imposed sinusoidal displacement of appropriate frequency and amplitude, we predict that body motion entrained to platform motion consumes less energy than walking on a fixed surface. When the platform has finite inertia, a mass- spring-damper with similar parameters to the Millennium Bridge, we show that the optimal biped walking motion sustains a large lateral platform oscillation when sufficiently many people walk on the bridge. Here, the biped model reduces walking metabolic cost by storing and recovering energy from the platform, demonstrating energy benefits for two features observed for walking on the Millennium Bridge: crowd synchrony and large lateral oscillations.

The energy costs of wading in water

Studies measuring the energy costs of wading in water have been limited to higher walking speeds in straight lines, in deep water. However, much foraging in water, by both humans and other primates, is conducted in the shallows and at low speeds of locomotion that include elements of turning, as befits searching for cryptic or hidden foods within a patch. The present study brings together data on the rate of oxygen consumption during wading by humans from previous studies, and augments these with new data for wading in shallower depths, with slower and more tortuous walking, to obtain a better understanding both of the absolute costs of wading in typical scenarios of aquatic foraging and of how the cost of wading varies as a function of water depth and speed of locomotion. Previous and present data indicate that, at low speeds, wading has a similar energetic cost to walking on land, particularly at lower water depths, and only at higher speeds is the cost of wading noticeably more expensive than when water is absent. This is probably explained by the relatively small volume of water that must be displaced during locomotion in shallow waters coupled with the compensating support to the limbs that the water affords. The support to the limbs/body provided by water is discussed further, in the context of bipedal locomotion by non-human primates during wading.