"Dead butt syndrome"
In a article published in the NY Times, a condition known as “dead butt syndrome” is discussed. While the title of the article is a catchy one, to be sure, the take-home point of the article is that long-distance runners are increasingly suffering from injuries to their gluteals, in particular the gluteus medius. In the most extreme cases, the muscles of the gluteus medius stop firing efficiently (or altogether in some cases), resulting in a slew of running-related injuries (hence the term dead butt syndrome).
So what does this have to do with you? A couple of things:
Running, in particular running the same distance (or very similar distances), will only pay off up to a certain point (whether we’re talking about performance or general health). As Louie Simmons of westside bar bell is fond of saying (I paraphrase), “doing only running to get better at running is like reading the same book over and over again and expecting to get smarter.” You need to mix up your training in order to break through plateaus (an oversimplification, but nonetheless true).
You need to do barbell training to keep the gluteals (and the rest of your lower body) strong, powerful, and efficient. Running isn’t enough. Enter squats, deadlifts, cleans, snatches, and the like (in other words, stuff you’re already doing at Crossfit Dublin).
So whether you’re after better run times, better general fitness, or just good ol’ health, cut back on the long-distance running ad nauseum and supplement it with some barbell training.