I have just read this article about why veins become prominent while exercising: Why do veins pop out when exercising, and is that good or bad?
I have some questions about this:
The article mentions that the veins are pressed out to the skin by muscle contraction.
This makes sense. But how does one explain that athletes have often more bulging veins even when not exercising? Is this only due lower body fat percentages? Or is there also another mechanism acting?
Consider the forehead or temple area. One sometimes notices also bulging veins while exercising. I don't see how this can be explained by muscle contraction since the muscles in the forehead and temple area are small and usually not (actively) contracted while exercising. So what is the relevant mechanism in this case? May it be indirectly caused by muscle contractions in the trapezius? But if so, how does it exactly work?
The article also mentions that the diastolic blood pressure raises while lifting weights. So contrary to the statement of the article that bulging veins are not due to higher blood pressure while exercising this effect is not ruled out in weightlifing since there the pressure is indeed raised. So how significant is this raise in blood pressure while lifting weights in explaining prominent veins (in comparison to the muscle contraction thesis)? This effect my be depend on the breathing technique (for example using valsalva maneauver or not).
If possible, please include references to books or peer reviewed articles into your answer.