The purpose of this study is to investigate the effect of lumbopelvic stabilization on hamstrings muscle stretching in individuals with history of low back pain suspected to have a clinical lumbar instability.

The participants between the age of 20 and 40 years with history of low back pain will be recruited from Mahidol University using a poster posted at Faculty of Physical Therapy. All participants will be explained the purposes, advantages, disadvantages and procedures of the study by the researcher. The participant will be asked to sign an informed consent if the participants are willing to participate in this study.

After obtaining the written informed consent, the researcher, who works in musculoskeletal system including low back pain for 7 years and has received 3 training sessions on clinical observation of aberrant movement, will perform 2 clinical tests including clinical observation of aberrant movement patterns and passive straight leg raising test to identify clinical lumbar instability, and measure hamstrings muscle length using clinical motion analysis system. The researcher will also screen for exclusion criteria using a check list.

For those who are qualified for the study, the participants will be asked to fill out the demographic data and physical activity questionnaire. The researcher will perform additional clinical examination including modified Thomas test, back extensor muscle strength test assessed by a handheld dynamometer, Trendelenburg's test and lumbar stability test. After clinical tests, lumbopelvic, pelvic, and lumbar range of motions during an active forward bend task will be measured by using the clinical motion analysis system. These outcome measures will be assessed for baseline (Pre-1). After baseline data collection, the participants will be divided into 2 groups; lumbopelvic stiffening group (LS) or lumbopelvic relaxing group (LR) by randomly generated code in a concealed envelope.

The participants in LS group will stretch the hamstrings muscle in standing position with lumbopelvic stabilization. Fifteen percent of the body weight will be used to standardize stretching force. This force will be controlled by visual feedback from load cell. During stretching protocol, the participants will be instructed to face the hydraulic table with the hips square, maintain trunk straight up and look straight ahead. Researcher commands "during adjusting the bed up, please tense the lower back rigid". After that, hydraulic bed will be lifted up until force reaches 15 percent of the body weight. Participant will perform 30 seconds/repetition for 4 repetitions with 15 seconds rest between repetitions. To ensure that participant correctly performs lumbopelvic stabilization, the researcher will palpate at ASIS and iliac crest to check pelvic motion during hamstrings muscle stretching. Pelvic motion indicates loss of lumbopelvic stabilization. Participant will be asked to re-perform another repetition. Our protocol is based on a previous study by DePino et al., 2000. Participant will perform 30 seconds/repetition for 4 repetitions with 15 seconds rest between repetitions. The investigators use 30 seconds because a systematic review suggests that 30 seconds is the most effective dose for hamstrings muscle stretching.

For the participants in LR group, the participants will be instructed to face the hydraulic table with the hips square, maintain trunk straight up and look straight ahead. The researcher commands "During adjusting the bed up, please relax the lower back". The hydraulic bed will be lifted up until force reaches 15 percent of the body weight. Participant will perform 30 seconds/repetition for 4 repetitions with 15 seconds rest between repetitions.

After the intervention, the participants will be reassessed for hamstrings muscle length test, lumbar motion, pelvic motion and total lumbopelvic motion (Post-1). Because this study uses a cross-over study design, participants will be asked to maintain the usual physical activity for 2 days as a wash-out period. Then, the participants will be re-assessed for baseline data (Pre-2), and cross-over to another stretching group (LS changes to LR, while LR changes to LS). After completion of intervention, the participants will be re-assessed for post-intervention (Post-2). These to determine the effectiveness of lumbopelvic stabilization during hamstrings stretching in standing.

Inclusion Criteria:

1. Between the ages of 20 and 40
2. A recurrent pattern of LBP at least two episodes that interfered with activities of daily living and/or required treatment
3. Presenting aberrant movement pattern during active forward bend test
4. Passive straight leg raising test (SLR) greater than 91 degrees
5. Having hamstrings muscle tightness of both legs (passive knee extension in supine with 90° hip flexion position greater than 20 degrees)

Exclusion Criteria:

1. Having a history of abdominal, back surgery and/or fracture.
2. Having any red flags, such as infection, tumor, fracture, radicular syndrome, or inflammatory.
3. Pregnancy or having menstruation.
4. Having spinal deformities, such as scoliosis.
5. Having neurological, musculoskeletal or cardiopulmonary diseases.
6. Previously receiving physical therapy intervention involving in motor control training.
7. Taking muscle relaxant medication.
8. Having hip joint stiffness or pain
9. Having positive Trendelenburg's sign.
10. Currently having routine vigorous exercise.

The IPD of this study will be shared upon official request.

The supporting information will be sent upon official request.

Having an official written request.

The assessor and investigator will be blinded to the random order. This process will be handled by the research manager.