Energetic Consequences of Human Sociality: Walking Speed Choices among Friendly Dyads

<div><p>Research has shown that individuals have an optimal walking speed–a speed which minimizes energy expenditure for a given distance. Because the optimal walking speed varies with mass and lower limb length, it also varies with sex, with males in any given population tending to have faster optimal walking speeds. This potentially creates an energetic dilemma for mixed-sex walking groups. Here we examine speed choices made by individuals of varying stature, mass, and sex walking together. Individuals (N = 22) walked around a track alone, with a significant other (with and without holding hands), and with friends of the same and opposite sex while their speeds were recorded every 100 m. Our findings show that males walk at a significantly slower pace to match the females’ paces (p = 0.009), when the female is their romantic partner. The paces of friends of either same or mixed sex walking together did not significantly change (p>0.05). Thus significant pace adjustment appears to be limited to romantic partners. These findings have implications for both mobility and reproductive strategies of groups. Because the male carries the energetic burden by adjusting his pace (slowing down 7%), the female is spared the potentially increased caloric cost required to walk together. In energetically demanding environments, we will expect to find gender segregation in group composition, particularly when travelling longer distances.</p></div

Mean walking speeds of Female Partner (FP) and Male Partner (MP) alone, together, and holding hands.

<p>The average walking speed of the MPs significantly slowed to walk with the FP (by 6.3%; p = 0.009) and to hold hands (by 7.0%; p = 0.007), while the FPs’ speeds changed by <1% across all three conditions (alone, with MP, and holding hands). The error bars represent standard error.</p

Mean relationship lengths.

<p>Mean relationship lengths.</p

Mean anthropometrics.

<p>Mean anthropometrics.</p

Stroller running: Energetic and kinematic changes across pushing methods

<div><p>Objective</p><p>Running with a stroller provides an opportunity for parents to exercise near their child and counteract health declines experienced during early parenthood. Understanding biomechanical and physiological changes that occur when stroller running is needed to evaluate its health impact, yet the effects of stroller running have not been clearly presented. Here, three commonly used stroller pushing methods were investigated to detect potential changes in energetic cost and lower-limb kinematics.</p><p>Methods</p><p>Sixteen individuals (M/F: 10/6) ran at self-selected speeds for 800m under three stroller conditions (2-Hands, 1-Hand, and Push/Chase) and an independent running control.</p><p>Results</p><p>A significant decrease in speed (p = 0.001) and stride length (p<0.001) was observed between the control and stroller conditions, however no significant change in energetic cost (p = 0.080) or heart rate (p = 0.393) was observed. Additionally, pushing method had a significant effect on speed (p = 0.001) and stride length (p<0.001).</p><p>Conclusions</p><p>These findings suggest that pushing technique influences stroller running speed and kinematics. These findings suggest specific fitness effects may be achieved through the implementation of different pushing methods.</p></div

Mean walking speeds. Mean (standard deviation).

<p>Mean walking speeds. Mean (standard deviation).</p

Review of prior studies investigating stroller running.

<p>Review of prior studies investigating stroller running.</p

Kinematic and energetic values across conditions (Mean ± SD).

<p>Kinematic and energetic values across conditions (Mean ± SD).</p

The significantly different mass-specific footprint patterns of males and females.

<p>These figures are for unloaded walking at the medium (comfortable) speed, but the graphs and patterns are identical for all speed conditions. The p-values for the residuals of the sex differences of these relationships are p<0.04 for maximum foot length; p<0.04 for maximum foot width; p<0.02 for foot area.</p

A summary of significant changes (p<0.05) to footprint size and stride length during loaded walking.

<p>A summary of significant changes (p<0.05) to footprint size and stride length during loaded walking.</p