Ivanenko further states that there are variables that the experiment cannot account for. As water refills the air cavity sooner on Earth than on the Moon, Mars, Titan or other planets and satellites with reduced gravity, participants had to adopt a higher stride frequency than people would normally adopt in true hypogravity. Liquid density is one of the parameters that affect slap and stroke impulses, so it is more difficult to run on less dense liquids.
Physics of Walking: How and Why Do We Walk The Way We Do?
It may seem strange, even funny, that anyone would want to strap volunteers into a harness just to see if they could run on water. In many ways, this piece of research is worthy of the Ig Nobel Prize as, on the surface it seems silly but attempts to answer questions pertaining to the Glasheen and McMahon model and whether it applies to humans running on water at different gravity levels.
Ivanenko says there are reasons for doing this type of research and that, “Understanding locomotor adaptions in a heterogravity condition may help us understand what happens here on Earth.”
Research like this may help answer questions as to why different animals developed different gaits during evolution, and whether we would walk or run differently if we lived in different gravity conditions. This in turn will help us understand the principles of gait adaptions and what we need to do to construct robots that can run on different planets.
There is interplay in this area between several parameters such as body mass, foot size, stride frequency, liquid density and gravity. By understanding and manipulating these factors we may be able to find or estimate the most optimal solution for running on water and other liquids in specific environments.
Physical Limitations on Walking on Water
This doesn’t mean there aren’t physical limitations: Running on water requires endurance and a robust musculoskeletal system for producing force and power. Ivanenko noted that the largest animal that can run on water is possibly the Western Grebes and can only do so for a few seconds as force production is anaerobic. Participants in the experiment could only run for about ten seconds. In a reduced gravity, these birds could run for a longer time.
Ivanenko speculates that one day humans could run on alien lakes and oceans for leisure and sport. Who knows? This experiment by Minetti and others certainly meets the Ig Noble’s aims of making us laugh as it makes us ask some very important questions regarding gait and locomotion.
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Minetti, Alberto E. et al. Humans Running in Place on Water at Simulated Reduced Gravity. (2012). PLoS ONE 7.7: PLoS Journals. Accessed October 16, 2013.
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