Low back pain (LBP) is a severe epidemic in the world. Despite its high prevalence, 90% of the cases have no identifiable cause. Approximately 44% of them experience recurrent LBP within one year and 10% of them develop chronic LBP that lasts for three months or more.

Mechanically, the lumbar spine is unstable and requires spinal muscle to maintain spinal stability and to prevent injuries. Lumbar multifidus (LM) muscle is thought to be the major spinal stabilizer responsible for spinal stability and spinal proprioception. Prior studies have revealed that increased fat infiltration, atrophy or activation deficits of LM in patients with LBP as compared to asymptomatic individuals. Unfortunately, inconsistent findings have also been reported.

Although prior research attempted to determine if abnormal LM characteristics can inform clinical decision-making, their results are limited because they only investigated a single LM characteristic at a time, which might not reflect the actual LM condition. Further, many studies adopted cross-sectional design that could not reveal the casual relations between abnormal LM characteristics and LBP. As such, the current study aims to identify specific LM characteristics that can predict new episode of LBP in asymptomatic individuals, and recurrent/chronic LBP in individuals with LBP at baseline.

Low back pain (LBP) is a severe epidemic in the world. Despite its high prevalence, 90% of the cases have no identifiable cause. While most people with LBP recover shortly after onset, approximately 44% of them experience recurrent LBP within one year and 10% of them develop chronic LBP that lasts for three months or more.

Mechanically, the lumbar spine is unstable and requires spinal muscle to maintain spinal stability and to prevent injuries. Lumbar multifidus (LM) muscle is thought to be the major spinal stabilizer responsible for spinal stability and spinal proprioception. Different cross-sectional studies have revealed that increased fat infiltration, atrophy or activation deficits of LM in patients with LBP as compared to asymptomatic individuals. Research has shown that abnormal morphology or activation of LM is associated with LBP intensity/location, or LBP-related disability. Unfortunately, inconsistent findings have also been reported.

Although prior research attempted to determine if abnormal LM characteristics can inform clinical decision-making, their results are limited because they only investigated a single LM characteristic at a time, which might not reflect the actual LM condition. Further, many studies adopted cross-sectional design that could not reveal the casual relations between abnormal LM characteristics and LBP.

Given the above, the current study aims to identify specific LM characteristics that can predict new episode of LBP in asymptomatic individuals, and recurrent/chronic LBP in individuals with LBP at baseline.

Inclusion Criteria:

• aged 18 to 65 years
• Symptomatic participants should have LBP that requires medical consultation(s) in the last three months
• LBP intensity of at least 5 on the 11-point numeric pain rating scale at baseline (for symptomatic participants)
• Asymptomatic participants should be pain free at baseline, and should not have LBP in the last year nor LBP lasting more than a week in the last 3 years

Exclusion Criteria:

• a history of neurological disease or vestibular impairment
• systemic inflammatory disease
• prior spinal surgery
• acute/chronic neuropathy or radiculopathy
• spinal infections/fractures/tumors, metabolic disorders,
• medical 'red flags'

Symptomatic participants should have LBP that requires medical consultation(s) in the last three months, and have LBP intensity of at least 5 on the 11-point numeric pain rating scale at baseline.

Asymptomatic participants should be pain free at baseline, and should not have LBP in the last year nor LBP lasting more than a week in the last 3 years.