So, I wound up with an injury which looks almost identical to this:
I first noticed discomfort in my inner-thigh on Sunday (today is Friday) while hiking the last five miles of a ten mile hike which involved a fair amount of steep up and down hill hiking. (I had done a very similar hike three days earlier.) The pain never got terribly intense, but it was noticeable. The next day (Monday) I did no workout other than to walk an easy mile after doing some yard work. The inner-thigh area was sore, but the pain was not too intense and I did not notice any bruising. On Tuesday I did an easy jog/hike kind of workout on mixed terrain. Again the inner-thigh was somewhat sore, but I noticed no bruising. On Wednesday I did a short hike on mixed terrain and same thing, some soreness, but no bruising. Then on Thursday I did an easy running workout and the inner-thigh did not bother me at all while running, but when I got out of the shower I noticed the bruising and was very surprised as there was only slight soreness. Again today I did an easy running workout with very little soreness, but the bruising is amazingly similar to what's in the picture.
Here's what the article says about this kind of thing:
Either a minor acute strain or this repetitive trauma can happen right under your nose, so to speak, without you ever noticing it. When we do notice these things, it’s when they go from minor and asymptomatic (at least so you’d notice) to major and symptomatic.
If you’ve sustained this minor damage to a muscle and then later go in to lift, the muscle could be further damaged and become a more serious strain. So a Grade I strain can become a Grade II strain because the tissue is further damaged through use. But if that happened, you’d have a good chance of noticing it when it occurred. Wouldn’t you?
You’d be surprised. Depending on the degree of damage, you might not feel it. Just like you can overuse muscle without feeling pain, you can use slightly damaged muscles without feeling pain.
The entire article is very interesting:
https://www.strengthminded.com/can-you-pull-a-muscle-without-knowing-it/