This study investigates the association between the duration of smart phone use and back pain and proprioception deficits in patients with chronic mechanical low back pain (CLBP).

It is hypothesized that increased duration of smart phone use will be associated with

1. Increased back pain as measured by the Visual Analogue Scale (VAS)
2. Reduced proprioception acuity as indicated by increased angle of error of back repositioning as measured by isokinetic dynamometer.

After patient screening against inclusion and exclusion criteria, eligible patients will be informed about the aim of the study and all testing procedures. Then, they will be asked to participate in the study, if agreed an informed consent will be signed . Basic demographic information as well as questions regarding the average daily smart phone use will be collected .

Patient will be tested in two separate sessions. During each session, the participant will be given a standardized phone and will be asked to play a standardized game "subway surfers " from a standardized sitting position for 10 or 30 minutes.

Pain and back repositioning error will be measured before and after the smart phone use. Pain will be measured first, then repositioning error.

Pain measurement:

Each participant will be instructed to rate the current level of pain by placing a mark across the horizontal VAS line. The distance in millimeters from the lower limit will be measured using a ruler.

Proprioception acuity:

Biodex isokinetic system preparation:

First, the system will be calibrated according to the manufacturer guidelines. For initialization of the Biodex system, the device, computer and dynamometer power will be switched on and all device attachments will be removed. Then, the start key in the control panel will be pressed. Few seconds will be allowed for the dynamometer shaft to rotate freely until the system displays a message that it is initializing the dynamometer. Once the initialization procedure is completed, the start key will be pressed again as indicated by the system status window. The personal data of each subject will be entered into the computer.

Repositioning error measurement:

Each participant will then be seated on the Biodex chair with his or her low back fitted backwards against the lumbar pad. Both knees will be fixed in place using two anterior curved leg pads. Legs will be kept relaxed vertically with both feet off the ground. The upper trunk will be fastened to the back of the chair using a belt. Both thighs will be fastened to the chair using straps while forearms will be kept crossed over the chest. The seat will be adjusted to allow the axis of rotation of the dynamometer to be at the level of L5/S1 disc space. Participants will be instructed to close their eyes during test performance. The limits of available range of motion (ROM) will determined for each participant by starting at the 0° position (neutral sitting with hips flexed 90°) and then instructing the participant to flex his or her trunk as much as possible to determine the available ROM in flexion and examine his or her ability to reach the target position for the isokinetic test (30° of lumbar flexion). The dynamometer will be locked in the 0° position to provide a fixed starting position for all participants during all trials The chosen protocol allows the participants to perform 1 familiarization trial followed by 1 actual test; this step will be repeated 3 times so that there will be 3 familiarization trials and 3 actual testing procedures. The average of the 3 actual testing results will be retrieved from the isokinetic device software. During the familiarization trial and after covering the eyes, participant will be instructed to flex his or her trunk until it is stopped by the machine at 30° of flexion. This position will be held for 5 seconds. The patients will be instructed to remember this position in order to reproduce it as precisely as possible during the subsequent actual test procedure. During the actual test procedure, the tested participants will press a hold button when they assume the target position to allow the device to record and save the reached angle. During the data collection process, no visual (eyes will be closed) or verbal feedback will be provided for the participants.

The results of the test will be recorded and printed by the isokinetic machine. It will include the value of error of every trial and the average error of the 3 trials.

Inclusion Criteria:

• Egyptian adult patients with mechanical CLBP Back pain duration is greater than 3 months Age ranging from 18 years to 45

Exclusion Criteria:

• Patients with any systemic disease that may affect spine function.
• Patients with previous history of spine trauma or dysfunction other than mechanical LBP.
• Lumbosacral nerve root entrapment.
• Patients with memory loss or impaired cognitive function
• patients who report back pain associated with sitting position

Seventy male and female adults will be recruited from out patient clinic of the faculties of Physical therapy and medicine, Cairo University. Further, physical therapy students who are diagnosed with CLBP will be recruited via advertising on social media.