Which of the following muscle groups must be strengthened in order to maintain a healthy back?

Knee flexors (hamstrings acting at the knee) do not directly stabilize the lumbar spine, and hip flexors are already often overactive and shortened, making them a poor target for back health strengthening.

Abdominals provide anterior spinal stabilization, the erector spinae support posterior spinal extension, and hip extensors (primarily gluteus maximus and hamstrings) maintain proper pelvic tilt and reduce lumbar stress. Together these three groups create the muscular balance necessary to protect the lumbar spine under load and during daily movement.

Hip flexors, when strengthened without adequate opposing hip extensor strength, increase anterior pelvic tilt and lumbar lordosis, which can worsen back problems rather than prevent them.

While hamstrings contribute as hip extensors, pairing them with hip flexors (psoas/iliacus) creates muscular imbalance around the pelvis and does not include the erector spinae needed for direct spinal support.