The exercise-anxiety link

Life is full of paradox. For instance, if everything is possible that means nothing is impossible, so the impossible is not possible meaning that not everything is possible. On a more mundane level paradoxes also abound. We park in driveways and yet drive in parkways. We have bigger houses and smaller families. “Reality television” relies on producers putting people in unreal and contrived situations then filming them. People only begin a sentence by saying, “With all due respect…” when they are about to show you no respect at all. Yes, life is one big box of paradox but thankfully our paradox load had been reduced marginally by one new study which has solved the biological paradox of how exercise can reduce anxiety.

The previous paradox in this arena was that exercise is known to reduce levels of anxiety yet exercise is also known to promote the growth of new neurons in a part of your brain known as the ventral hippocampus. This is a paradox because this part of the brain governs anxiety and since young neurons are typically more excitable than their older equivalents, exercise should lead to greater anxiety.

To attempt to discover why this paradox might exist researchers studied two groups of mice. One group was “active” and had free access to a running wheel. The second group was “sedentary” and had no running wheel. Mice love running and if given a wheel will run about four kilometres every night. Six weeks later, the mice were exposed to brief periods of cold water as a way of introducing stress aimed at promoting anxiety.

When they were exposed to the cold water the brains of the sedentary and active mice behaved differently. In the brains of active mice inhibitory neurons, which are known to keep excitable neurons in check, became much more active. Also, the neurons in the active mice’s brains released more GABA (gamma-aminobutyric acid), a neurotransmitter that calms down neural excitement. There were higher levels of the protein that packages GABA into vesicles for release into the synapse in the active mice.

So, although exercise promotes neuronal growth in the parts of the brain regulating anxiety, it at the same time inhibits neuronal activity in that part of the brain and reduces anxiety in doing so. There you have it, one paradox resolved although why people will choose to wear the cooling footwear sandals and place the warming garment socks underneath them will remain forever a mystery.