A domesticated helmeted guinea fowl (Numida meleagris) in Hampshire, UK. Photo credit: Andy Morffew, Itchen Abbas, Hampshire, UK, CC BY 2.0, via Wikimedia Commons.

A domesticated helmeted guinea fowl (Numida meleagris) in Hampshire, UK. Photo credit: Andy Morffew, Itchen Abbas, Hampshire, UK, CC BY 2.0, via Wikimedia Commons.

Walking on two legs is a remarkable feat which requires an incredible amount of balance just to walk on a flat surface. Chances are that when you walk down the street, you don't even register all of the little pebbles that you walk across and have no problem stepping on even larger obstacles that are in your way as well. That is all thanks to your muscles, which respond to these little hurdles without getting your brain involved in the process. This is even more impressive when considering that no two steps are exactly the same. The differences in how strongly the muscle contracts or how much weight each part of the muscle is lifting during each step is very apparent when biologists measure these in running animals. However, these differences in each part of the muscle are very rarely seen in the simplified experiments that are usually undertaken in the lab. This realization led Nicole Rice, Caitlin Bemis and Kiisa Nishikawa of Northern Arizona University, USA, and Monica Daley of the University of California Irvine, USA, to propose a solution to this problem that comes straight from the world of video games.

The team realized that the problem with lab experiments is that they are done under very artificial conditions that you rarely see in the real world. For instance, muscles are almost never contracted for minutes at a time like they are during some laboratory experiments. So, Rice and colleagues developed an ‘avatar’ system based on data from a previous study that measured not only the electrical signals but also the length of the calf muscles of helmeted guineafowl (Numida meleagris) running over some obstacles on a treadmill. The researchers used these same signals to stimulate a different muscle (the extensor digitorum longus) of a mouse. In this case, the mouse muscle is an avatar of the guineafowl's.

Surprisingly, when the researchers gave mouse muscles the same signals as a guineafowl running over obstacles on a treadmill, they responded just like the bird's did, contracting with more force when lifting their bodies over an obstacle (acting like a motor) and less forcefully when stepping down from the obstacle (acting like a shock absorber). Not only is this impressive given that the researchers were using different muscles from very different species but also the muscle from the guinea fowl is over 600,000 times larger than the muscle from the mouse. This, then, could open a whole new world to biologists as one of the limits of laboratory muscle studies is the size of the muscles that can be used. This technique could allow researchers to work on much larger animals or animals that are highly endangered and provide a look into some truly wonderous feats such as running in cheetahs or flight in hummingbirds.

For nearly 75 years, many researchers have looked at muscles as a motor that propels you forward as you walk, without taking into account that your muscles also act as brakes, shock absorbers or struts under different circumstances. This new technique allows researchers to look at all of these different aspects and discover how remarkable muscles truly are.

Rice
,
N.
,
Bemis
,
C.
,
Daley
,
M.
and
Nishikawa
,
K.
(
2023
).
Understanding muscle function during perturbed in vivo locomotion using a muscle avatar approach
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226
,
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