Usain Bolt and the limits of human speed

How fast might human beings ultimately run?

Usain Bolt's recent assault on the track and field record book – running 9.58 in the 100m and reaching a top speed of nearly 28 mph – has raised this question at a crucial crossroads for organized athletics. While specific predictions by modern science are not precise, the general influence of scientific advancement is poised to overwhelm human performance and organized athletics as we have known them.

Although we can readily quantify the forces acting on the body and predict the motion they produce using classical Newtonian mechanics, we still have an incomplete understanding of the process of force production within the body, and how the body's internal forces eventually translate into motion.

Conceivably, the secret to blazing running speeds might be explained by either of two abilities: repositioning the limbs quickly through the air, or hitting the ground forcefully with each step. Contrary to intuition, fast runners achieve their greater speeds, not by repositioning their legs any more rapidly, but rather by hitting the ground with greater force and quickness than slower runners do.

How hard and how quickly do elite sprinters hit the ground? Once up to speed, an athlete like Usain Bolt will hit the ground with a force equivalent to roughly 1,000 pounds, and do so within five 100ths of a second of the first instant of foot-ground contact.

To better appreciate the extreme athleticism involved in attaining world-class sprinting speeds, imagine the weight-lifting equivalent of a sprinter's limb-ground mechanics. Try to envision heading to your local gym and lifting four or five times your body weight with one leg in one-20th of a second. If this performance seems superhuman, it should. There is no way that Usain Bolt today, or Michael Johnson or Carl Lewis previously, could perform this weight-lifting task either. The maximum forces muscles produce during lifting exercises, or even when stimulated artificially, are dramatically lower than those they produce during sprint running for reasons that are poorly understood.

However, incomplete understanding does not preclude scientifically reasonable considerations of the ultimate human running speeds. Much of the secret to running speed is explained by what we do know about muscles as force-producing machines. A critical factor is the contractile speed limits of the muscle fibers themselves.

Slow pokes cannot hit the ground as hard and as quickly as speed demons do because their slower muscle fibers do not contract quickly enough to allow them to. To date, efforts to identify training, diet, supplementation, or other methods that overcome this critical, cellular-level limit have been marginally successful at best.

Although we may not be able to precisely predict the world records of 2012 or 2050, we can predict that speed barriers of today will be long gone. Consider the once-hallowed marks of 4 minutes for the one mile run and 61 home runs in a single baseball season. They are quaint relics now; the first overcome by modern training, professionalism, and globalization; and the second by widespread pharmaceutical and training interventions.

The speed barrier as we have known it could be shattered by scientific progress on any one of a number of fronts: molecular biological interventions that speed up muscular contraction, engineering advances in shoes or prosthetic limbs, dietary, supplement or training techniques that push biological adaptations beyond previous boundaries.

The history of modern athletics prompts two conclusions that are germane to considerations of the ultimate performance limits of humans. First, predicting when advances in knowledge-based enhancement methods will occur is a fool's mission. Second, scientific and technical knowledge that can be used to enhance performance will be used.

The obliteration of world swimming records within the past year occurred not because the swimmers improved, but rather because their swimsuits did. Similarly, a speed-skating record spree occurred in the 1990s when innovative hinged skates emerged that prolonged the push-off phase of each skating stride. The scientific and technical challenges posed by the mechanics of running have thus far proven more obstinate than those of swimming or skating, but they are not by any means insurmountable.

So, when we head into the post-Bolt era, the barriers to human speed will no longer lie within the traditional limits of human biology. Rather, new barriers will be repeatedly broken by inevitable advances in knowledge and the methods of performance improvement they spawn. How – and how well – the sporting authorities regulate the imminent scientific and technical advances is the question that now hangs heavily over the future of human performance and organized athletics.

At this juncture, one prediction is clear: The future limits of human speed are likely to lie largely where we decide to set them.

Peter Weyand is an associate professor of applied physiology and biomechanics in the Annette Caldwell Simmons School of Education and Human Development at Southern Methodist University in Dallas.