Exploring the Speed: Why the Fastest Creatures Aren’t Either Small or Large

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<p>Cheetahs dash across the savanna while impalas, antelopes, and other prey flee. All these animals are designed for speed. Indeed, <a href="https://www.nature.com/articles/s41467-024-52924-z" rel="noopener">medium-sized terrestrial animals tend to be faster than their larger or smaller counterparts</a>. Recent studies are beginning to uncover the reasons behind this phenomenon.</p>

<p>Leading the research is Christofer Clemente, who specializes in biomechanics (the study of animal movement) at Sunshine Coast University in Shippy Downs, Australia.</p>

<p>To analyze how size impacts speed, he and his team compared the movements of various animals like elephants, cheetahs, and mice. However, the muscles and leg mechanics of these species show significant variations.</p>

<p>"There are too many variables at play," says Clemente. Identifying the specific factors that limit an animal’s running speed proves to be quite challenging.</p>

<aside class="wp-block-sciencenews-inline-related-post alignleft"><h4>Description: What is a computer model?</h4></aside>

<p>Instead of making direct comparisons, Clemente and his team utilized computer models of a single species (humans) at various sizes. They simulated humans ranging from a mouse size of 100 grams (0.2 pounds) to an elephant size of 2,000 kilograms (4,400 pounds).</p>

<p>The model indicated that larger animals can sustain longer strides. However, there are limitations. As an animal grows, its mass increases more rapidly than its muscular strength. This imbalance can lead to reduced speed. In fact, the scaled-up models of humans were so heavy that the muscles couldn't function effectively.</p>

<p>While small animals are proportionally stronger, this doesn't necessarily make them the fastest. The miniature model of a human illustrated this point. The muscles of smaller creatures generate enough force to lift them off the ground quickly with each step, which limits their forward propulsion.</p>

<p>"When they generate sufficient power, they tend to lift off the ground," says Clemente, comparing this to how astronauts walk on the moon.</p>

<p>To limit their airtime, smaller animals tend to squat more than their larger counterparts, bending their feet and maintaining contact with the ground longer during their strides. However, this also means they cannot move as quickly as more upright animals.</p>

<p>Clemente describes an optimal zone for speed: "Your muscles remain strong, but your weight is just right to effectively utilize that strength." He shared these findings last October in <em>Nature Communications</em>, suggesting potential applications for engineering robots designed for movement.</p>

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<h2 class="wp-block-heading">When muscles can't keep up with mass</h2>

<p>As animals grow taller, their mass increases at a rate faster than their strength due to the relationship between mass and volume. In contrast, strength correlates with the area of muscle cross-sections. For example, envision a cube with a height of 1 centimeter. Its volume amounts to 1 cubic centimeter, and the area of one cross-section is 1 square centimeter. If the cube's height increases to 2 centimeters, its volume now expands to 8 cubic centimeters, but the cross-sectional area is only 4 square centimeters.</p>

<figure class="wp-block-image size-full"><img width="1030" height="1122" src="https://www.snexplores.org/wp-content/uploads/2025/04/1030_Speed_Size_graph_rev.png" alt="Graph showing how to stack size and speed to run animals" class="wp-image-3153984" /><figcaption class="wp-element-caption"><span class="caption wp-caption-3153984">The researchers analyzed the relationship between size and speed in running animals. The X-axis depicts the animal's weight in relation to volume, while the Y-axis shows speed. Figure A compares the size and speed of various four-legged animals, revealing that the fastest species typically fall within specific size ranges. The team also modeled human figures of different sizes, resulting in similar graphs as illustrated in Figure B.</span><span class="credit wp-credit-3153984">CJ Clemente <em>et al</em>/<em>Nature Communications</em> 2024</span></figcaption></figure>
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<h2 class="wp-block-heading">Data Dive:</h2>

<ol class="wp-block-list">
<li>Examine Figure A. What size category contains the fastest animals? What speeds do those animals achieve?</li>
<li>How does that speed compare to that of a 1 kilogram animal? What about an animal weighing approximately 1,000 kilograms?</li>
<li>Refer to Figure B. What is the speed of the smallest modeled human? How fast does the largest modeled human move?</li>
<li>What is the peak speed of a human? How does this compare to the peak speed of a four-legged animal?</li>
</ol>

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<h2 class="wp-block-heading has-text-align-center">Do you have any science questions? We can help!</h2>

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