Normative parameters and anthropometric variability of lumbar muscle stiffness using ultrasound shear-wave elastography.

•Shear modulus at rest is approximately 4 kPa for the erector spinae muscles.•Shear modulus at rest is approximately 6 kPa for the lumbar multifidus muscles.•Shear modulus of the lumbar multifidus substantially increases during contraction.•Shear modulus also varies by sex, BMI, and self-reported activity level.•Men and larger and more active individuals generally have stiffer lumbar muscles.