Today I went to see a physiotherapist who also happens to be one of my aikido teachers. When I was watching last tuesday he said he may be able to speed up the healing process by therapy.
Before therapy he asked me a about this injury and other small aches and ailments I have. He thinks my connective tissues seem to be a bit prone to injury. He tested my mobility and everything seems ok. That did not hurt at all. Only activities that strain that rib hurt (besides a dull constant pain when my painkiller wears off).
He also noticed that two other ribs in my upper chest are thickened and asked me if I had ever had Tietze's syndrom (costochronditis)
. I vaguely remember that these thickenings originated long ago. It was painful and if I remember well it was triggered by overstraining myself (prolonged and vigorously raking fallen leaves from our lawn or something like that).
He did not state my current injury might also be costochronditis, but after therapy I looked it up. Putting everything together I think it's likely that I have acute costochronditis, triggered by a number of strikes on that spot.