Imagine this scene. A young woman walks into a gym wearing a pink tank top and tight black pants. Athletic and blonde, she waves a quick hello to someone at the front desk. She ignores a few sweaty guys on the weights machines who stare as she passes by and makes her way towards a line of treadmills. Flinging a towel over the bars of one she takes a small sip of water before placing down her bottle of brand-name water. She pauses, adjusting her ponytail and flicking through her iPod to choose the perfect workout song. She pokes at a few buttons on the treadmill display causing it to whir to life. As the sound of the latest pop music superstar blares in her ears she works into a rhythm as she has done many times before.
Suddenly we hear ominous music as the view changes to one several metres behind her near ground level, the camera rising and falling in time as if in time with something’s breath. The camera goes back to the girl who is completely oblivious to the world outside, hearing only the saccharine refrain of her pop idol. Whatever is behind her starts slowly moving forwards as the ominous music gets faster. We see a glimpse of a foot armed with razor sharp claws. A long scaly tail swings from side to side. The nostrils flare on a pointed snout full of glistening teeth. As the creature nears the girl we see one final glimpse, a dark brown eye staring coldly back. The eye of a killer.
This probably sounds like the opening scene to the latest C-grade horror movie, a companion to the likes of Sand Sharks. However, this story is inspired by (although no way similar to) a recent piece of research that required the researchers to do something out of the ordinary. They trained crocodiles to run on treadmills.
It all comes down to the question of how crocodile’s breathe. Crocs are unique in that they have a muscle that runs between their pelvis and their liver, which is in turn attached to the bottom of their lungs. This muscle is called the diaphragmaticus, also known as ‘the hepatic piston pump’. When the muscle contracts it causes the lungs to expand and the crocodile breathes in, similar to the way in which the human diaphragm works. It has long been thought that this was the primary method that crocodiles used to breathe in, instead of using the intercostal muscles between the ribs like most other animals. But sometimes a group of scientists comes along and asks “is this actually true?”
An international team of scientists performed tests on the young crocodiles approximately 50cm long and 1.5kg. They measured breathing, metabolism and the amount of oxygen and carbon dioxide in the blood of the crocs in various conditions, including after exercising on a modified treadmill. They then compared the results of healthy crocs against crocs with disabled pump muscles.
The team found that the hepatic piston pump muscle wasn’t actually necessary for the crocodiles to breath and that they instead used their rib muscles for normal breathing like most other animals. The pump muscle only played a big role in breathing after exercise when they needed much more oxygen. Previous studies in alligators suggest that the diaphragmaticus is actually more important for diving and moving about in the water.
This study has done what great science has always done, finding a unique way to look at and test what is a unique situation. But don’t worry; there is no need to be on the lookout for crocodiles the next time you go to the gym. But just to play it safe, maybe use the exercise bikes instead.
Munns, S. L., Owerkowicz, T., Andrewartha, S. J., & Frappell, P. B. (2012). The accessory role of the diaphragmaticus muscle in lung ventilation in the estuarine crocodile Crocodylus porosus. The Journal of Experimental Biology, 215(5), 845-852. doi:10.1242/jeb.061952