Hamstring injuries tend to recur, and the recurrrence rate for hamstring strains is higher than almost any other soft tissue injury. Once you strain a hamstring, your chances of straining the same hamstring are higher than the odds were of straining it in the first place. And the more often they recur, the more often they're likely to keep recurring. In fact, a pre-existing hamstring injury is the most likely indicator of a future hamstring injury. Pre-existing hamstring, age of the athlete, and racial background are the only three non-modifiable risk factors for hamstring injury (athletes of Black African origin are more susceptible to hamstring injury because they have a disproportionately higher percentage of Type II "fast twitch" muscle fibers).

But there are also a number of contributing factors that are modifiable - for instance, detailed, targeted strength training that focuses not just on the hamstring itself but the quadriceps, pelvic, glutes, and trunk muscles to correct any imbalances between the muscle groups. Flexibility techniques are obviously important, and "gait training" - evaluating the athlete's stride and his footwork to isolate potential hitches or sloppy "bad habits" in his step that put an unhealthy load on the hamstring, especially at critical stages of his stride, and correcting that gait. Sometimes, something as simple as teaching the athlete to shorten his stride and take slightly shorter but more steps can make a significant difference.

Another factor that often contributes to hamstring reinjury is scar tissue - when the muscle fibers tear, scar tissue forms at the site of the injury, and this tissue is stiffer and less flexible than the original muscle fibers. This has the effect of stiffening that entore portiion of the hamstring, which is a significant risk factor for a recurring hamstring injury. One way to treat that is deep tissue massage, which is a really painful process where the hamstring is twisted and kneaded back and forth like you're making bread, to shear the scar tissue fibers. I had that done many years ago with a severe quad injury, and it's one of the most painful therapies I've ever had. In fact, it's often done with a nerve block or even under general anesthesia. This is one of the treatments Watson has been receiving.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4223289/

Here are a couple of really interesting podcasts, with Dr. Bryan Heiderscheit of UW Madison. He's the guy who's working with Watson and Stokes, and if you have a half hour to kill he'll explain a lot. The first link was from this past November, and the second one is 7 years old. Still interesting, but not as up to date as the first.

https://www.listennotes.com/podcasts...t-sIfT_N8L2DG/

https://www.youtube.com/watch?v=OCq8BoxqLOQ&t=22s