"Strong hamstrings" refers to having well-developed and powerful muscles at the back of your thighs.
Sentences with «strong hamstrings»
You have to have very strong hamstrings and glutes. (muscleandbrawn.com)
Strong hamstrings help balance the look, feel, and performance of your legs, especially if you're a runner and need to kick it to the finish line. (health.com)
Strong hamstrings also help keep your knees stable and less prone toward injury. (cathe.com)