They found two reasons for this: First, the muscles produce little force; second, they don't rely exclusively on oxygen for fuel. The researchers also believe--though they've been unable to prove--that rattlesnakes shake not by shortening the muscles on the side of the tail toward which the rattle is moving, as one might expect, but by using their muscles as a brake.
Producing force in a lengthening muscle, they found, requires much less energy than in one that is shortening. That's why a backpacker hiking into the Grand Canyon, using most of her muscles as a brake, burns fewer calories than she does coming back out. She's moving the same amount of weight around, but the muscles that do the bulk of the work are primarily lengthening rather than shortening as she descends. Lengthening a muscle also produces at least twice as much force as shortening it.
A weightlifter who can bench-press pounds knows that the challenge comes in lifting the barbell up; he can easily let down much more weight than that. It was this combination of low energy consumption and high force production that really captured the researchers' attention. When muscles produce high force, they grow stronger. Yet most exercise regimens focus on aerobic activity or making muscles stronger through contractions that shorten them. Many people, such as the elderly or heart patients, don't have the energy to expend on such conventional weightlifting and thus cannot avoid muscle wasting.
Even if you're elderly your muscles are responsive. You can still build muscle mass. The job of the person sitting on it is to resist that motion.
Even a few minutes of resistance causes the sitter's muscles to work hard. That causes them to grow not faster, but stronger. When elderly patients tried out the device, their muscle mass increased, as did their balance.
That translated into a lower risk of falling. Rattlesnakes are one of the most discernible snakes in the animal kingdom, not only because of their appearance, but also because of how they shake their tails at threats to warn them to stay away. When a rattlesnake shakes its tail, it makes the sound of a high-pitched baby rattle, hence their name. Instead, the sound comes from loosely packed keratin chunks that make an audible sound as they rub together when shaken.
Keratin is the same stuff that makes up hair and fingernails; in fact, if you were to flick one fingernail against another in rapid succession, you might hear a similar sound. This nub multiplies as the snake sheds its skin, so a snake that has shed its skin several times will have more nubs than a youngling, and consequently, it will make more noise too. On the other hand, rattles are fragile, and one that grows too large can break off just as a long fingernail would.
Login here. Register Free. Anthony Bouchard. Fascinated by scientific discoveries and media, Anthony found his way here at LabRoots, where he would be able to dabble in the two. Anthony is a technology junkie that has vast experience in computer systems and automobile mechanics, as opposite as those sound. SEP 17, Ancient families that lived together were unlikely to have mated with one another, new research has suggested. Written By: Carmen Leitch. SEP 19, It is possibly one of the most terrifying sounds in the animal kingdom, but how the rattlesnake evolved its chilling warning signal is a mystery.
Now a study suggests the rattle evolved long after the tail-shaking behaviour. The evolution of the rattle has baffled scientists because, unlike other complex physical traits like eyes or feathers, it has no obvious precursor or intermediate stage.
One theory is that ancestral snakes shook their tails to warn off predators, and the noise-making rattle — which is made of a series of hollow, modified keratin scales — evolved later as a more effective signal that took advantage of the pre-existing behaviour. This may be why many rattle-less snakes also shake their tails. To test the idea, Pfennig and his colleague prodded 56 species of venomous and non-venomous snakes with a fake rat on a stick and recorded their defensive tail shakes.
0コメント