September 24, 2015 | David F. Coppedge

Talk the Walk

Upright walking—that distinctive human form of locomotion—is more complex than putting one foot in front of the other. Let’s talk the walk.

Why do we walk the way we walk? “Walk this way” is more than a classic comedian gag (YouTube). John E. A. Bertram seeks to explain how special human locomotion is in a Dispatch in Current Biology. Here’s the summary of his report:

The way we walk determines the energetic investment needed. Humans spontaneously alter their walking style to exploit energetic opportunities. New research demonstrates the sensitivity and timing of this optimization and opens the door to discovering the underlying mechanisms.

Over a decade ago, we reported on Daniel Lieberman’s remarkable analysis of human endurance running, a unique human trait requiring multiple specializations to the body (11/18/04). But walking upright is no less complex. Scientists are only beginning to understand the processes involved:

Locomotion is initiated by the motor control centers of the brain, and is subsequently influenced by various ascending and descending features of the neuromuscular and mechanical systems of the body. However, our bodies move in a manner that cannot neglect the influence of the physical environment. This is a complex issue, doubtless with a variety of key inputs. How does the brain choose the best strategy to drive the motion and placement of the limbs? Even for constant speed locomotion, such as walking or running on a treadmill, this question currently remains open. Although an interesting and fundamental basic question, finding the answer to this will have many practical implications. Understanding how the brain integrates its control program with changes in the function or circumstances in which the body operates will influence our ability to predict the outcomes of various interventions, whether surgical, rehabilitative or prosthetic. The ever-growing field of enhanced function and performance provided by artificial bio-integrated ‘exoskeleton’ devices will depend on understanding how the body will react to such influence.

Indeed, trying to design robots and exoskeletons has underscored the complexity of human walking. Bertram describes challenges to designing artificial knee joints and other parts that can stay upright and move without falling over, let alone optimize their actions for best energy utilization. It’s a challenge to explain, in evolutionary terms, a human’s fast, responsive method of optimizing walking for best metabolic efficiency.

We observe that healthy humans generally walk in a similar manner [as experimental subjects]. Is this because of species-level evolutionary adaptation, because our coordination systems develop and learn in the same way or because we are all solving basically the same energetic problem? Certainly all these factors (and more) have their influence. The Selinger et al. study conclusively demonstrates that humans do solve at least part of the problem by coordinating their movements to optimize immediate metabolic energy expenditure. At this point, the mechanisms through which this is accomplished are not clear, but it is impossible to identify mechanisms unless their effects are recognized. This study adds a new dimension (and a novel technique) to our understanding of how humans move the way they do in walking.

The paper referred to by Selinger et al. in Current Biology is titled, “Humans Can Continuously Optimize Energetic Cost during Walking.” It reports on experiments where subjects were outfitted with robotic exoskeletons that altered their normal walking styles. The researchers found that “people readily adapted gait patterns to minimize energy use” and were able, within minutes, to converge on new energetic optima, even for small cost savings. After the next change, they could re-converge on the optimum within seconds. “Our collective findings indicate that energetic cost is not just an outcome of movement, but also plays a central role in continuously shaping it.” The body of their paper says almost nothing about evolution, other than noting that “Much theorizing has focused on optima being established over evolutionary timescales, through changes to body shape, muscle action, and the hardwiring of neural circuitry.” They were apparently more interested in the empirical, measurable results from experiments on real people.

Restoring the Art

Evolutionary theorizing about the unobservable past seems far less valuable than helping people in the here and now. Live Science reports on exciting developments that are allowing a 26-year-old man, paralyzed for five years, to walk again under his mind’s control. Doctors channeled his brain waves to a computer that interpreted the signals, and sent them to devices on his leg muscles. The man trained his mind to control an avatar in the computer, learning how to control it in the same way required for moving his legs. After practice moving his legs while suspended above ground, he has just been able to walk 12 feet under his own power, with a walker and harness for safety.

Even after years of paralysis, the brain can still generate robust brain waves that can be harnessed to enable basic walking,” study co-author Dr. An Do, an assistant professor of neurology at the University of California, Irvine, said in a statement. “We showed that you can restore intuitive, brain-controlled walking after a complete spinal cord injury.

This is a quantum leap over previous methods like electrically controlled exoskeletons that allowed a veteran to walk again (Science Daily), and even a paraplegic to make the first kick of the 2014 World Cup (Live Science).

Growing into the Optimal Walk

Kids can seem like clumsy walkers and runners, Medical Xpress notes. That’s because they are not just miniature adults. Their body proportions are different. Jim Usherwood of the Royal Veterinary College (UK) decided to look into the reasons for the childhood waddle, with fresh experience from his two young daughters. He put reflective dots on their limbs and recorded the energetic costs as they walked and ran.

Building a model that represented the moving people as a single piston that was the length of the individual’s leg, Usherwood calculated the amount of muscle required to produce the power necessary to propel the individuals along at the speeds that he and Hubel had measured. The new model successfully reproduced the youngsters’ and adults’ movements.

So kids move the way that they do simply because they are smaller than adults and their short limbs do not have enough time to produce the high powers needed to lift them into the air when running, not because they are training to be as good as adults.

Who doesn’t treasure videos of their baby’s first steps? Humans are born to walk. Toddlers may start out a little awkward, but with a little growth and practice, they can take after Mom and Dad at full speed when told, “Walk this way.”

Read this piece in Evolution News & Views about Optimization as an intelligent design science. When you see your own body performing high-quality optimization rapidly, you have to conclude that good design went into the hardware and software. The more detail we learn, the more difficult it is to believe that a supposed evolutionary transition from ape knuckle-dragging to upright walking and endurance running reduced to random mutations (Stuff Happens Law).

We are glad to see progress in robotic exoskeletons that are starting to let paralyzed persons enjoy the freedom of walking again, and hope this wonderful technology will become rapidly available to those who have been confined to wheelchairs for years.  We who can walk, in the meantime, should value this ability while we have it.

Because walking is usually associated with purposeful activity, it is a frequent metaphor in the Bible for lifestyle choices. “Be careful how you walk,” Paul says in Ephesians 5, “making the best use of the time, because the days are evil.” He also says in the same passage to “walk in love” and “walk as children of light.” Both in spiritual and physical senses, walking the talk and talking the walk require intelligent design.

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