Mechanical Work as an Indirect Measure of Subjective Costs Influencing Human Movement

To descend a flight of stairs, would you rather walk or fall? Falling seems to have some obvious disadvantages such as the risk of pain or injury. But the preferred strategy of walking also entails a cost for the use of active muscles to perform negative work. The amount and distribution of work a person chooses to perform may, therefore, reflect a subjective valuation of the trade-offs between active muscle effort and other costs, such as pain. Here we use a simple jump landing experiment to quantify the work humans prefer to perform to dissipate the energy of landing. We found that healthy normal subjects (N = 8) preferred a strategy that involved performing 37% more negative work than minimally necessary (P<0.001) across a range of landing heights. This then required additional positive work to return to standing rest posture, highlighting the cost of this preference. Subjects were also able to modulate the amount of landing work, and its distribution between active and passive tissues. When instructed to land softly, they performed 76% more work than necessary (P<0.001), with a higher proportion from active muscles (89% vs. 84%, P<0.001). Stiff-legged landings, performed by one subject for demonstration, exhibited close to the minimum of work, with more of it performed passively through soft tissue deformations (at least 30% in stiff landings vs. 16% preferred). During jump landings, humans appear not to minimize muscle work, but instead choose to perform a consistent amount of extra work, presumably to avoid other subjective costs. The degree to which work is not minimized may indirectly quantify the relative valuation of costs that are otherwise difficult to measure

STATE AND SOCIETY AT TEOTIHUACAN, MEXICO

Between 100 BCE and 200 CE, the city of Teotihuacan grew rapidly, most of the Basin of Mexico population was relocated in the city, immense civic-religious structures were built, and symbolic and material evidence shows the early importance of war. Rulers were probably able and powerful. Subsequently the city did not grow, and government may have become more collective, with significant constraints on rulers\u27 powers. A state religion centered on war and fertility deities presumably served elite interests, but civic consciousness may also have been encouraged. A female goddess was important but probably not as pervasive as has been suggested. Political control probably did not extend beyond central Mexico, except perhaps for some outposts, and the scale and significance of commerce are unclear. Teotihuacan\u27s prestige, however, spread widely in Mesoamerica, manifested especially in symbols of sacred war, used for their own ends by local elites