In the gym where I have worked out for 27 years, I have often noticed young athletes ignoring the core areas of the lower back and abs. They will spend 45 minutes doing every kind of bench press and arm work, and then finish with 5 minutes of ab work. As you might expect, they wind up with big arms and a big gut.
Over the years I have become more and more convinced that every workout should
start with 20 to 30 minutes of intense core work. Then follow that with whatever upper and/or lower body workout you need, but do each set
to complete failure. An excellent resource for core training workouts can be found at the
Sport Fitness Hut Blog.