By Bob Nelson, P.T.
If you read any of the thousands books and articles about cycling technique, what you read about is body position, biomechanical efficiency, aerodynamic resistance and muscle activation, among other imponderables. Nobody talks about how the brain controls movement. But the brain is where movement gets started, and there’s plenty to learn about cycling if you just think about the brain.
Neurologists are the folks who think about the brain, and the field of neurology has been abuzz with news of a Dutch man in his late 50s who checked in to a clinic for Parkinson’s disease in Nijmegen, the Netherlands. Parkinson’s is one of several movement disorders directly traceable to the brain, and patients typically have trouble initiating movement. A common symptom is freezing in place, at inopportune moments like crossing a busy city street. Patients also display what’s called postural instability, meaning they fall easily. They also have tremors in the arms and legs and sometimes the face.
This Dutch man had severe Parkinson’s and was unable to take more than a few steps without falling over. The case was reported in 2010 in the New England Journal of Medicine, which has a video on its website (http://www.nejm.org/doi/full/10.1056/NEJMicm0810287) that shows both his heartbreaking physical condition walking down a hospital corridor – and his amazing ability to ride a bicycle with no trace whatever of a movement disorder.
Neurologists, not least among them at the Dutch clinic, have been stunned at this news. How could a man with advanced degenerative brain disease be able to ride a bicycle, which does, after all, require balance and some degree of motor coordination?
Bastiaan Bloem, the Dutch neurologist who wrote up the case for NEJM, asked 20 more of his Parkinson’s patients to ride bicycles, and every one of them could. (Remember, this is the Netherlands, where everyone, but everyone, rides a bike.) He suggests that the rotary motion of the pedals may provide an external pacing cue that keeps the Parkinson’s patients on track. Or, he writes, maybe bicycling doesn’t require very much input from the part of the brain that’s diseased in Parkinson’s patients.
There’s a famous cartoon of Homer Simpson’s brain that shows major partitions for sleep, doughnuts, sex and beer. It’s tough to argue with this insight, but brain anatomists divvy the gray matter up into regions for consciousness, movement, sensation and emotion. Movement circuits start in a slice across the midbrain called the motor cortex. Those motor neurons take several detours before they reach the spinal cord and the neurons, or nerve cells, that will carry the brain’s movement orders to the muscles. (Homer’s brain is the same, but smaller.)
One of the brain organs that our brains and Homer’s share is called the basal ganglia. They look like two lumps with ram’s horns on the underside (“basal” side) of the brain. The brain’s orders to move go through the basal ganglia, which are essentially signal processing units that help figure out motor strategies. Given a voice, the basal ganglia would say: So you’re going to ride a bike? Better know where to put your foot! And then what are you going to do?
In patients with Parkinson’s, it’s precisely this region, the basal ganglia, that is impaired, and it’s the reason why Parkinson’s patients freeze, because the part of the brain that tells them what to do next isn’t functioning. It’s certainly possible that one of the reasons the Dutch patient wasn’t showing any sign of Parkinson’s while riding a bike is that riding a bike doesn’t require a lot of signal processing in the basal ganglia. Nurses helped the patient onto the bike and got him going, and once he was going, he could keep doing the same thing without much thought about motor strategies.
It’s thought that different kinds of guidance use different parts of the brain. For example, if you’re learning to ride a bike without anyone’s help, you have to figure things out on your own, which requires a lot of conscious attention to the task. That uses the frontal lobe of the cerebral cortex. If you’ve got someone telling you where to put your foot and what to do next, you don’t need much conscious effect, but you do need balance and coordination, which reside mostly in the cerebellum, a lobe at the back of the brain. And if you’ve got things figured out but you’re playing with muscle activation (push with the foot? lift the toes? flex then extend the hip?), you’re refining a motor strategy, and the basal ganglia are doing it.
Australian researchers in 2005 did electromyographic studies of novice and experienced cyclists, in which they stuck electrodes into thigh muscles to determine which muscles were getting the most juice and therefore which were being used and how often. Experienced cyclists had less variability in muscle recruitment than novices, presumably the result of their long practice. Working on bicycling – practicing on different bikes, riding on varied terrain, thinking of different ways of pulling up on the pedals and pushing down – creates new nerve connections and reinforces old ones among the different parts of the brain and with the spinal cord and with muscles. Scientists think that those connections, once made, persist, which is why you never forget how to ride a bike.
Bob Nelson is a physical therapist at H&D Physical Therapy (http://www.hdphysicaltherapy.com/) and founded the LGBT bicycle club Fast and Fabulous (http://fastnfab.org/). He’ll be delivering a presentation on this topic at Bike Expo New York at Basketball City on the East River on May 3, 4 and 5. (http://www.bikenewyork.org/bike-expo-new-york/expo-programing/).
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