Which of the following exercises is contraindicated by the American College of Sports Medicine?

Pelvic tilts are a core stabilization exercise actively recommended by ACSM for improving lumbar health and are not contraindicated.

Trunk extensions performed with proper form and within pain-free range are not classified as contraindicated by ACSM.

Seated hip/trunk flexion is generally acceptable because the seated position provides spinal support and limits the harmful shear forces present in the unsupported version.

Unsupported forward trunk flexion - such as standing toe touches - forces the lumbar erectors and posterior ligaments to resist high shear loads across the intervertebral discs at end range, significantly increasing injury risk. The ACSM lists this movement as contraindicated in its exercise guidelines because safer, supported alternatives exist for training hip flexor and hamstring flexibility.