Weight Training: Good for your blood pressure
This article from the Times notes that recent review studies indicate weight training can help lower resting blood pressure:
It’s well known that regular aerobic exercise can improve circulation and reduce blood pressure. But what about weight lifting?
For years, people with hypertension were warned against it, because doctors feared that spikes in blood pressure during strenuous lifting might cause dangerous problems and, in the long term, raise blood pressure. But studies had not provided much evidence. And in recent years, large studies have found the opposite: that ultimately weight lifting reduces resting blood pressure, because with stronger muscles, there is less demand on the heart during everyday activities.
See this note from Mary Conover of Cross Fit North Santa Cruz on the body's response to holding your breath while lifting heavy weights. She analyzes why the mantra for lifting heavy weights is "Big breath! Hold it! Exhale!". The reason, beyond the obvious stiffening of the core, "has to do with blood pressure, heart rate, cardiac contractility, and conduction velocity between atria and ventricles". In brief, the body compensates for the rise in blood pressure from muscular contraction by doing things to reduce blood pressure, like dilating blood vessels and slowing the heart rate.
It's likely that training your body to minimize blood pressure under heavy loads carries over into normal activities resulting in the lower at rest blood pressure noted in the studies above.
Also, Dr Helen (while recovering from a heart attack), has been reading the strength training advice of Mark Rippetoe, the undisputed guru of strength training. Rippetoe explains in detail the logic behind holding your breath while lifting.