I know Buddhism stresses the importance of being a content person, but I can't help thinking that any action such as walking or even shifting my foot is a form of dissatisfaction for current moment. Why would I change anything if I am content?
I would suggest that Buddhism does not promote the importance of being a contented person, especially by suppressing any feelings, perceptions or other parts of experience. Instead, by learning to know dissatisfaction (suffering, dukkha) very well, we notice that the discontentment is separate from the experience (i.e. pain is pain, sickness is sickness, it's our minds that adds dissatisfaction on top of that).
By practicing to recognize dissatisfaction, we can then learn to put that dissatisfaction aside, and simply experience each moment as it is (painful, pleasurable or neutral). Once we are able to put dissatisfaction aside, contentment naturally arises.
I would like to stress that Buddhism does not promote becoming a contented person - this holding on to "me as a person being contented" is also a cause for discontentment, since it is certain to change. Once the situation changes ("me" no longer being content), there's dissatisfaction - my view of myself being contented does not fit with the experience I am having.
Walking or shifting your foot is not inherently dissatisfactory. It is what it is, what you experience are the sensations of lifting the foot, changes in pressure on the footsole, and so on. The experience can be pleasurable, neutral or unpleasant, but that does not have to equal dissatisfaction in that moment. Our minds add that on to it. Once we're able to let go of the added layer of judging the experience as satisfactory or unsatisfactory (it shouldn't be this way or this is great), contentment is with us, here and now.
There is a nice Zen saying:
Before Enlightenment chop wood, carry water, after Enlightenment, chop wood, carry water.
Overall, the view and motivation is the key. We need to accept that we have a conditioned body and it is actually very wise to sometimes walk into the kitchen to eat or use the bathroom from time to time!
In Mahayana tradition, practitioners take the Bodhisattva Vow and they promise they will not reach enlightenment until they help to liberate all other sentient beings. With that motivation, they will view their actions as means to benefit others. They will nurture their bodies so they can have good health and long lives and will engage in various activities to bring people happiness. There is an infinite number of acts of kindness we can do to our relatives, friends, neighbours, colleagues or even strangers.
Intentional bodily movements could generate Karma for an unenlightened person. But not for Arahaths. Read about "Kiriya Citta".
The discontent goes the other way:
It is not how much you own and can still keep them in possession that makes one content.
It is not that you have a beautiful wife, who at that moment is not arguing with you on certain things, and the children that you have who are, at that moment, still obedient to you that make you happy / content.
It is not the car that you have and is still in very good condition that makes one content.
Because the above can be one day lost. Let say your wife decided to leave, your kids, who you love so much, decided to do something opposite what you expected them to, the car broke down.
Until then, you become discontent. So in the Buddhist view, it is about trying not to "acquire / own" so much, to which one eventually forms a attachment.
It is not about being able to own them and be content because they are still in your possession / returning you the amount of "love" you expect / and are still in good condition.
All of the above, except the car (but even still can be possible) are required that they "love" you back for the contentedness to take place.
The car can't speak or feel, but one would usually form this "imaginary" reciprocals for the car itself -
"Hey, washed you up nicely yesterday, in and out, spotless, oil changed, and you run like a champ. Good, I love you" as if the car returned your TLC by "running good" itself.
Back to the foot:
When one is discontent or irritated, it is normally shown in his actions, facial expressions and body movements. The eye twitches, a sudden fist pump, the foot moves, hugging the head etc.
But isn't doing all that a form of discontent?
How many times do we see others, who in a very uncomfortable situation, still cast a smile on his face, but when in fact he is affected by the situation and thus discontent? Yes, they are there everyday. And are they content, just because he still smiles when he normally shouldn't.
So, it is not about the fact that you decided to go for a walk or move a foot that shows that you are discontent - because they might be of another forms.
Some go play basketball, when he is discontent. Some go lift weights.
Some call up their girlfriends and after a couple rounds of drink, decided to fly to Vegas out of the blue.
Or, some just simply sit there and pretentiously smile and shred tears within.
Or, some start picking a fight with someone for no reason or try to find a reason to argue.
So, the signs / the reactions here is "detrimental" and secondary. It is rather about what being content is and otherwise.
Owning less. Acquire less. Require thusly less. The less the attachment.
Compassion is different. One doesn't attach to it, but is still doing things that is benefitting the other(s) and beings.
Being content in Buddhism is when you get some experience which you evaluate and pleasant, unpleasant or neutral you do not further react this. You maintain equanimity of your mind being aware of the arising and passing of sensations.
If you are mindful of your body you will see that there are various sensations. Some times movement is prompted to get rid of sensation which might be due to staying in one position, or get rid of itching sensation, etc. This is as you mentioned to get rid of unsatisfactory in many cases. Some actions are triggered by habits, hence not necessarily to get rid of the unsatisfactoryness.