The purpose of the current study is to determine the effect of myofascial release of plantar fascia on pain, back function, lumbar flexibility and pain pressure threshold for patients with CNSLBP.

Chronic low back pain (CLBP) is a major cause of disability and represent a burden on healthcare services worldwide (Hong et al., 2013; Hoy et al., 2014). The prevalence suggested that approximately 540 million people have experienced 'activity-limiting' low back pain (LBP) for at least once in their lifetime (Hartvigsen et al., 2018).

Previous evidence suggested that all of those who experience LBP, about 30%-40% will continue experiencing symptoms beyond 3 months and thus, become chronic (Henschke et al., 2008; Traeger et al., 2014). Around 85% of those who experience any form of LBP have no precise diagnosis, therefore they are categorized as 'non-specific' LBP (Chou, 2010). Efforts have been done by the healthcare research to understand the mechanisms underlying the persistence of pain in chronic non-specific LBP (CNSLBP).

There are many factors that can cause LBP, although it is very difficult to determine the exact cause (Alemo & Sayadipour, 2008). Those factors may include genetic factors, aging, obesity, smoking, work-related factors such as heavy manual work and the prolonged sitting hours required in most of the jobs. Also psychosocial factors (such as monotonous work and low job satisfaction) and Physiological factors (such as inadequate trunk strength and low physical fitness) can cause LBP (Kumar et al., 2014; Wai et al., 2010a; Wai et al., 2010b; Shiri et al., 2010a; Shiri et al., 2010b).

The concept of regional interdependence is well-recognized in the field of physical therapy. It is well recognized that when there is a dysfunction in one anatomical region, adjacent regions can be affected, causing the patient to complain from these adjacent areas. This concept is well recognized in the phenomenon of referred or radiating pain (Wainner et al., 2007).

Previous studies found the necessity to find the correlations between these anatomical regions which can help us understand more the main reasons for a certain dysfunction and thus, find more effective treatments (Wainner et al., 2007). For example, Berglund et al. (2008), found a potential relationship between the thoracic spine and elbow impairments.

Several studies applied on rats, showed that the force generated by muscle fiber contraction is transmitted both longitudinally and laterally, via the intramuscular fascia to the surrounding muscles, tendons and the bones. That's why when myofascial release was applied on certain areas, adjacent joint were effected as in previous studies (Huijing & Jaspers, 2005).

Moreover, the structure and orientation of fascial fibers determine how force is transmitted through connective tissues to the surrounding elements (Stecco et al., 2013; Wilke et al., 2018). Recent data showed that in humans, the length of muscle fascicles is affected by the coupling between muscle and fascia (Karakuzu et al., 2017; Pamuk et al., 2016).

These anatomical correlations were investigated by several studies, which found intimate connections between muscles and other elements in the body by connective tissues called fascia, Myers called them fascial chains (Myers, 2020).

Treatments of fascial tissues became very popular in the musculoskeletal disorders (Engel et al., 2014; De las Pen˜as et al., 2005; Ndetan et al., 2012; Ong et al., 2004; Wardle et al., 2013). This is due to recent histologic findings and the discovery of contractile cells, free nerve endings, and mechanoreceptors which suggest that fascia plays a proprioceptive and mechanically active role (Schleip et al., 2019).

It was found that plantar fascia is connected to adjacent muscles through a myofascial chain, Myers called this the superficial back line (SBL). It expands from the plantar fascia (PF), over the Achilles tendon, the gastrocnemii muscles, the hamstrings, the sacrotuberous ligament, erector spinae muscles and, eventually, the epicranial fascia (Myers, 2020; Stecco et al., 2019; Wilke et al., 2016).

Previous reviews have shown that myofascial release (MFR) immediately increased range of motion of nearby joint or even distant joint along the same myofascial chain (Cheatham et al., 2015; Hughes & Ramer, 2019; Wiewelhove et al., 2019; Wilke et al., 2020; Wilke et al., 2020). This has also been investigated along the superficial back line (SBL) (Wilke et al., 2020).

This was investigated by several studies which found the correlation between the plantar fascia and lumbar spine. There was an acute increase in the ROM of the lower back of healthy volunteers, when myofascial release (MFR) such as single foam rolling was applied on the plantar surface (Grieve et al., 2015; Kwangsun et al., 2018). This implicate that fascial chains might be able to change their properties or functional capacities in non-adjacent areas along their course (Krause et al., 2016).

Many studies have been performed on applying myofascial release (MFR) on the SBL in healthy individuals but, unfortunately, there is a lack of knowledge on their efficacy on LBP and several musculoskeletal disorders. Since CNSLBP is affecting a great population, more studies are required to investigate the effect of MFR on the SBL in patients with CNSLBP.

Inclusion Criteria:

• Both genders between the age of 20-45 years old.
• BMI less than 30 Kg/m2.
• Patients diagnosed as CNSLBP (pain > 3 months).
• Minimum pain level 2 out of 10 in NPRS.
• Psychologically and mentally stable.
• At least on trigger point in the lumbar paraspinals.
• Minimal level of disability in ODI.
• Reduced hamstring flexibility.

Exclusion Criteria:

• Red flags (eg. Spinal fractures, tumors, infection).
• Cauda equina syndrome that requires urgent surgery.
• Pregnant patients.
• Previous lumbar surgery.
• Fibromyalgia.
• Disc lesions and spinal degenerative disease such as lumbar spondylosis.

due to the nature of the study, neither the participants nor the investigator will be blinded.