The Underlying Mechanism of Spinal Manipulative Therapy and the Effect of Pain on Physical Outcome Measures

• Change of Modified Oswestry Low Back Pain Disability Index [ Time Frame: baseline, Day 3, and 1 week ] [ Designated as safety issue: No ]
  It is a questionnaire to assess the participants' perceived low back pain related functional disability.
  
  
• Change of 11-point Numeric Pain Rating Scale [ Time Frame: baseline, Day 3, and 1 week ] [ Designated as safety issue: No ]
  It is a scale to measure the perceived pain intensity by the participants.
  
  
• Change in Body Pain diagram [ Time Frame: Baseline, Day 3, and 1 week ] [ Designated as safety issue: No ]
  The diagram will be used to demarcate the location and area of symptoms
  
  

• Change in measurement of lumbar multifidus muscle thickness by rehabilitative ultrasound imaging [ Time Frame: Baseline, Day 3, and 1 week ] [ Designated as safety issue: No ]
  Using the rehabilitative ultrasound imaging to measure lumbar multifidus muscle thickness at rest and during an automatic muscle contraction.
  
  
• Change of spinal stiffness testing by a mechanical indentation machine [ Time Frame: Baseline, Day 3, and 1 week ] [ Designated as safety issue: No ]
  The spinal stiffness of participants will be measured by a validated mechanical indentation machine. Briefly, a 60 N load will be applied to the third lumbar spinous process and the corresponding spinal tissue deformations will be measured. The spinal stiffness will be calculated from the force-displacement curve of each indentation.
  
  
• Electromyography of trunk muscles [ Time Frame: At the third visit (1 week from the baseline) ] [ Designated as safety issue: No ]
  Electromyography of abdominal and erector spinae muscles during spinal stiffness testing will be measured.
  
  
• Magnetic resonance imaging of lumbar region [ Time Frame: 1 month before or after the first visit ] [ Designated as safety issue: No ]
  
• Fear Avoidance Beliefs Questionnaire [ Time Frame: Baseline ] [ Designated as safety issue: No ]
  It assesses the fear avoidance behaviour of participants
  
  
• Change in Borg Category-Ratio Scale of Perceived Exertion [ Time Frame: Baseline, Day 3, and 1 week ] [ Designated as safety issue: No ]
  It measures the subjective perception of exertion during the spinal stiffness test and muscle testings
  
  
• Global Rating Of Change [ Time Frame: 1 week after baseline ] [ Designated as safety issue: No ]
  It measures the perceived change of body function from the first visit.
  
  

• Measurement of lumbar multifidus muscle thickness by rehabilitative ultrasound imaging in the pain induction experiment [ Time Frame: A single visit ] [ Designated as safety issue: No ]
  Using the rehabilitative ultrasound imaging to measure lumbar multifidus muscle thickness at rest and during an automatic muscle contraction.
  
  
• Spinal stiffness assessment by mechanical indentation machine in the pain induction experiment [ Time Frame: A single visit ] [ Designated as safety issue: No ]
  The spinal stiffness of participants will be measured by a validated mechanical indentation machine. Briefly, a 60 N load will be applied to the third lumbar spinous process and the corresponding spinal tissue deformations will be measured. The spinal stiffness will be calculated from the force-displacement curve of each indentation.
  
  
• Electromyography of trunk muscles in the pain induction experiment [ Time Frame: A single visit ] [ Designated as safety issue: No ]
  Electromyography of abdominal and erector spinae muscles during spinal stiffness testing will be measured.
  
  
• 11-point Numeric Pain Rating Scale in the pain induction experiment [ Time Frame: A single visit ] [ Designated as safety issue: No ]
  It is a scale to measure the perceived pain intensity by the participants.
  
  
• Body Pain diagram in the pain induction experiment [ Time Frame: A single visit ] [ Designated as safety issue: No ]
  The diagram will be used to demarcate the location and area of symptoms
  
  
• Modified Oswestry low back pain disability index in the pain induction experiment [ Time Frame: A single visit ] [ Designated as safety issue: No ]
  It is a questionnaire to assess the participants' perceived low back pain related functional disability.
  
  
• Fear of Pain Questionnaire - III in the pain induction experiment [ Time Frame: A single visit ] [ Designated as safety issue: No ]
  It measures the perceived fear of pain under different hypothetical painful experiences.
  
  
• Fear Avoidance Beliefs Questionnaire in the pain induction experiment [ Time Frame: A single visit ] [ Designated as safety issue: No ]
  It assesses the fear avoidance behaviour of participants
  
  
• Borg Category-Ratio Scale of Perceived Exertion in the pain induction experiment [ Time Frame: A single visit ] [ Designated as safety issue: No ]
  It measures the subjective perception of exertion during the spinal stiffness test and muscle testings
  
  

SMT is a common manual therapy for treating patients with mechanical low back pain (LBP). SMT is defined as a high velocity, low amplitude thrust technique. Specifically, the clinician stands beside a supine patient. The patient is passively side-bent towards the side to be manipulated. The clinician passively rotates the patient and then delivers a high velocity, low amplitude thrust to the anterior superior iliac spine in a posteroinferior direction. SMT is indicated for patients with LBP judged to have spinal hypomobility or malalignment. Recently, our collaborators have discovered that LBP subjects who benefit from SMT can be identified prior to treatment by a five-item clinical prediction rule. Compared to non-responders, those who respond to SMT have: 1) more than 30% decrease in the modified Oswestry Disability Index score, 2) a significant and immediate decrease in spinal stiffness, and 3) a concurrent change in lumbar multifidus muscle activity. Taken together, the physical changes experienced by SMT responders alone provide an unique opportunity to better understand the mechanisms underlying SMT.

Since spinal stiffness is an important physical indicator of SMT response, it is important to understand the causal relation between pain, paraspinal muscle activity and spinal stiffness. Although research has shown positive correlation between pain and muscle activity, and between paraspinal muscle activity and spinal stiffness, the causal relation between pain, paraspinal muscle activity and spinal stiffness remains unknown. Given this background, an induction of temporary benign experimental pain to asymptomatic individuals can help clarify such causal relation and improve our understanding of physical responses in responders following pain resolution by SMT.