Bear Strength

[brotherbear]

#2....Blaire Van Valkenburgh
professor of ecology and evolutionary biology

www.ioes.ucla.edu/person/blaire-van-valkenburgh/

SPEED AND STRENGTH
All bears have a large head with small ears followed by massive shoulders and a short back and | tail, all of which are supported on thick limbs and broad paws. Compared with big cats, bears have longer snouts and shorter, stiffer backs. Relative to large dogs, bears have bulky legs and much more spreading feet. Unlike these other carnivores, and more like humans, bears walk on the soles of their hindfeet, with their ankle joint positioned just above the ground. This condition is called plantigrade, and differs from the digitigrade posture of cats and dogs, in which the “soles” of the feet are elevated, along with the ankle, and only the toes touch the ground. To understand why bears are built so differendy from cats and dogs, it is essential to explain the benefits of digitigrade feet.

Running around on your toes in a digitigrade posture is advantageous if speed is important. Speed is the product of stride length and stride frequency. Raising the ankle adds length to the part of the limb that determines stride length, that is from the shoulder or hip to the point of contact with the ground. Longer limbs take bigger strides, and digitigrade posture is therefore typical of mammals designed to run. Digitigrade animals also tend to have relatively long bones, or metapodials, making up the sole of the foot, adding further to total limb length. In addition, their limb muscles are much thicker close to the hip or shoulder joint, and taper towards the toes as long, elastic tendons. This construction reduces muscle mass near the ankles and feet, where the limb travels farthest during locomotion, and thus reduces inertial effects. 

A The skeletons of a bear and a domestic dog illustrate the difference between plantigrade and digitigrade postures. The dog is digitigrade, standing on its toes with the soles of its feet (metapodials) off the ground. By contrast, the soles of the bear's hindfeet are flat to the ground, as in humans, giving it a plantigrade posture. 

If one imagines the additional energy required to walk or run with ankle weights or heavy shoes, then the drawbacks of heavy feet become clear. There are yet further benefits to runners in having long tendinous muscle attachments. Tendons are elastic and act as energy-saving springs when running. They are stretched as the limb is flexed under the weight of the animal and then rebound, propelling the body forward and upward. So, digitigrade posture, long metapodials, and compact muscles with stretchy tendons are typical of carnivores built for speed. 
 
Bears are clearly not built for speed. Although their forefeet are semi-digitigrade, their hind-feet are plantigrade. Moreover, their metapodials are short and their muscles thick throughout the length of the limb. In many ways, bears are built more like badgers than other similar-sized carnivores, such as tigers, and it shows in their speed. The top speed recorded for both black and brown bears is 50 kilometers (30 miles) per hour, whereas the range for the fully digitigrade lion and wolf is 55 to 65 kilometers (35 to 40 miles) per hour.


If bears are not built for speed, then what does the combination of massive limbs, plantigrade hindfeet, cumbersome paws, and a short back provide? Strength and mobility of limb movement are the answers. The stout limbs of bears are capable of producing large forces over a much greater range of motion than those of dogs or even cats. Bears use these capabilities when digging for food or shelter, fishing for salmon, climbing to escape danger, and battling with members of their own species as well as other predators. Imagine a wolf trying to perform a bear hug or climb a tree. Dogs have forfeited these abilities in favor of speed. Cats are more like bears in their range of possible movements, but lack strength. Bears may not be able to outrun danger, but can successfully defend themselves through brute force. 
 
*Quote: Cats are more like bears in their range of possible movements, but lack strength. Bears may not be able to outrun danger, but can successfully defend themselves through brute force.  Reply