I'm a distance runner and over the decades have dealt with a variety of mild to moderate problems including plantar fasciitis, calf and hamstring strains, and achilles strains. When I look at the primary medical literature on these conditions, it's almost 100% negative evidence. Almost every intervention or preventative measure seems to be ineffective when tested in high-quality studies, and this includes even reduction of the volume of activity. For many of these same conditions, however, you can find all kinds of advice from physical therapists or people writing in popular publications like Runner's World claiming to provide insight into the causes and prevention of these same injuries.
One of the common analyses that a lot of physical therapists seem to believe in, and which gets echoed in the pop-sci articles, is that the original sin is an imbalance in strength between opposing muscle groups, and the way to prevent reoccurrence of injury is to do exercises to fix this imbalance.
For example, a hamstring strain would be analyzed as something that happens because the quadriceps is too strong compared to the hamstring, so hamstring strengthening exercises would be prescribed.
Question: Is there reliable scientific evidence for this general hypothesis, or is it just a folk belief among physical therapists?