More Than Just a Curl Often mistakenly associated with bicep work, the Jefferson curl is actually ... you'll be strengthening your lower back and core muscles, as well as stretching your hamstrings.

In fact, the Jefferson curl is more of a mobility exercise that strengthens the muscles of the lower back and core, as well as stretching the hamstrings, to help build a more resilient spine.

Tight hamstrings can be a common problem for runners and people who spend long hours sitting but strengthening and stretching ...