Table 1 Inclusion and exclusion criteria for the study

18 years of age or older

Average LBP characterized as severe in the month preceding the current episode/aggravation

At the time of randomization, the participant’s current episode/aggravation of LBP must be between 2 and 12 weeks in duration.

Specific non-mechanical causes of LBP

Participants less than severe LBP on average in the month prior to the current episode/aggravation are eligible.

Contraindications to SMT or SSM (e.g., spinal fracture, progressive neurological deficits, inflammatory arthropathies of the lower back, surgical fusion of lumbar spine).

Average LBP severity ≥ 3 on the 0–10 numerical rating scale over past 7 days

Active management of current episode of LBP by another healthcare provider. Participants must agree to stop management with their current provider to enroll in the study (e.g., SMT, PT, prescription medication, psychological counseling/therapy, a structured program led by a healthcare provider that may include pain education, mind-body practices, coping strategies) to be included. Participants who had been prescribed opioid medication for LBP are required to obtain a note from a prescribing/medical provider to confirm they have safely discontinued their use of opioid medication to be included in the trial.

Medium or High Risk for persistent disabling back pain according to the STarT Back screening tool

Serious comorbid health condition that either requires medical attention (e.g., severe hypertension, inadequately managed serious mental health conditions, substance abuse), or has a risk for general health decline over the next year (e.g., Parkinson’s disease, Multiple Sclerosis, organ failure, Dementia, Alzheimer’s disease).

Ability to read and write fluently in English

Pregnancy, current or planned, and nursing mothers during the study period.

Inability or unwillingness to give written informed consent.