While the science of it is of course totally correct, and fitness is a great term as Brad mentions, I am not sure if dopamine is not too technical to make it a high probability sale. It did sell in .net (just the word dopamine) but for low $$$ and a decade ago. That is the only comparator sale I could find.
Dopamine is registered in 86 TLDs, perhaps encouraging (did not check how many developed) but it is available in both .fit and .fitness as handreg which may be a negative depending on if the end user is willing to consider more than .com.
FitnessDopamine is available in all other extensions, so some of those may be chosen over yours at hand reg fee.
A sale is possible of your domain name, but I would peg the probability as, unfortunately, low. I see that you have BIN priced it really low, so it is possible a fitness expert might like it. I personally would not renew it if I held it.
Bob