Humans Running in Place on Water at Simulated Reduced Gravity

PLoS ONE 7(7): e37300
DOI: 10.1371/journal.pone.0037300
Received: August 1, 2011; Accepted: April 19, 2012; Published: July 18, 2012

Alberto E. Minetti
Department of Human Physiology, University of Milan, Milan, Italy

Yuri P. Ivanenko, Germana Cappellini, Nadia Dominici, Francesco Lacquaniti
Laboratory of Neuromotor Physiology, IRCCS Santa Lucia Foundation, Rome, Italy

Nadia Dominici, Francesco Lacquaniti
Center of Space BioMedicine, University of Rome
Tor Vergata, Rome, Italy

Francesco Lacquaniti
Department of Systems Medicine, Neuroscience Section, University of Rome
Tor Vergata, Rome, Italy


Background

On Earth only a few legged species, such as water strider insects, some aquatic birds and lizards, can run on water. For most other species, including humans, this is precluded by body size and proportions, lack of appropriate appendages, and limited muscle power. However, if gravity is reduced to less than Earth’s gravity, running on water should require less muscle power. Here we use a hydrodynamic model to predict the gravity levels at which humans should be able to run on water. We test these predictions in the laboratory using a reduced gravity simulator.

Methodology/Principal Findings

We adapted a model equation, previously used by Glasheen and McMahon to explain the dynamics of Basilisk lizard, to predict the body mass, stride frequency and gravity necessary for a person to run on water. Progressive body-weight unloading of a person running in place on a wading pool confirmed the theoretical predictions that a person could run on water, at lunar (or lower) gravity levels using relatively small rigid fins. Three-dimensional motion capture of reflective markers on major joint centers showed that humans, similarly to the Basilisk Lizard and to the Western Grebe, keep the head-trunk segment at a nearly constant height, despite the high stride frequency and the intensive locomotor effort. Trunk stabilization at a nearly constant height differentiates running on water from other, more usual human gaits.

Conclusions/Significance

The results showed that a hydrodynamic model of lizards running on water can also be applied to humans, despite the enormous difference in body size and morphology.

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0037300