Purpose: To conduct a pilot study of the effect of Cranial Laser Reflex Technique (CLRT) compared with sham laser on hamstring muscle flexibility, strength, and pain pressure threshold.

Participants: Active, young adults ages 18 to 35.

Procedures: A two-visit, assessor and participant-blinded crossover study with 1-week washout. Subjects will complete three functional hamstring tests before and after CLRT and sham laser treatment. Subjects will also complete questionnaires to assess their expectations and perceptions of the interventions.

First Visit: Subjects who met the inclusion criteria and gave consent completed a brief questionnaire on their activity level, history of hamstring injuries, and perceived hamstring tightness and were randomized to one of the following for the first treatment period: 1) active CLRT; or 2) sham laser.

After randomization, subjects were asked to complete the three functional hamstring tests: 90-90 Knee Extension Angle (KEA) to assess flexibility, handheld dynamometry (HHD) for strength, and pain pressure threshold (PPT).

Assessments. KEA: The 90-90 Knee Extension Angle test is a functional assessment designed to assess lower extremity flexibility and is considered the gold standard for hamstring length. The participant began in the supine position on a treatment table. The tested extremity (the right leg in each subject) was placed in a 90° hip and 90° knee position with the contralateral lower extremity placed flat on the table. A digital inclinometer was consistently placed at the level of the medial malleoli and the superior pole of the patella. The examiner maintained 90° of hip flexion. Pelvic position was monitored by palpation of the anterior superior iliac spine and lumbar spinous processes to maintain a neutral pelvic position. The examiner passively extended the knee to the point of a ''strong, but tolerable stretch," as reported by the subject. The examiner read the angle of the inclinometer and recorded the mean value of three attempts. A greater angle indicates greater degree of flexibility.

Hand held Dynamometry (HHD) is currently considered a reliable and valid measurement of peak muscle contraction. The subject began prone on the table with right leg bent to 90°. The tester placed the dynamometer (microFET2; Hoggan Health Industries, Salt Lake City, UT) at the heel of the participant and applied force to the heel, gradually increasing in 3 to 5 seconds. Participants was instructed to resist the applied force and maximally contract the hamstring muscle against the HHD device. The test ended once they are no longer able to resist the force and the leg begins to move (break point). The investigator recorded the mean value of three attempts.

Pain Pressure Threshold (PPT) is a reliable, accurate and valid method for measuring muscle pain sensitivity and response to treatment. The digital algometer (FDX, Wagner Instruments, Greenwich, CT) is a hand-held muscle tester with a range of 0-100 lbf that consists of a padded disc with a diameter of 0.5" attached to a microprocessor-control unit that measures peak force (pounds or kilograms). The unit has a digital readout for peak-applied pressure and provides a built-in calibration routine that verifies a valid calibration. In order to determine PPT, the researcher applied the tip of the algometer to a tender spot in the participant's hamstrings and increased the amount of pressure until the participant verbally informed the researcher when the sensation of pressure became pain. At this point the algometer was removed and the peak force recorded. The mean of three repeated measures was reported.

Intervention: Cranial Laser Reflex Technique (CLRT) is a novel complementary and alternative (CAM) medicine intervention for musculoskeletal conditions that incorporates principles of laser acupuncture with chiropractic cranial reflexology. Subjects wore protective eyewear. The hamstring reflexes are two lines on the posterior portion of the top of the head, approximately 2 cm long and 2 cm apart, running parallel to the sagittal suture. The posterior end of the reflexes can be located by finding the vertex, or CZ point in the standardized 10-20 EEG system, and moving laterally approximately 1 cm.

The aperture of the laser probe was placed at the posterior end of the reflex (b), turned on and moved anteriorly to point (a) at a speed of approximately 2 cm/s. The laser was turned off and quickly returned to the starting point, turned on and moved again. This was repeated for a total of 30 times. The probe skimmed the surface of the scalp, moving aside as much hair as possible.

Device: The treatment device used in this study is a Class IIIB 810nm 200 milliwatts (mW) near-infrared diode laser (THOR Photomedicine Ltd, Great Britain) that is currently marketed in the US. The laser probe is FDA-cleared and classified as a non-significant risk device. The spot size is 0.0364 cm^2, and the treatment time is 30 seconds. Current best-practice recommendations for laser acupuncture recommend a dosage between 1-4 J/cm^2 per point. Since the CRP is a line of 2 cm, for the purposes of calculating dosage, it was treated as a series of 10 connected points each with a diameter of 2mm. With the scanning rate of 2cm/s, each "point" on the line received 1/10 of each pass, totaling 3s (out of 30s total) exposure time per point. The dose per point for this intervention is calculated to be approximately 1.65 J/cm^2.

There was a one-week washout and the subject will return for the second treatment period.

Primary Outcome: Hamstring flexibility (90-90 Knee Extension Angle, KEA) A clinically significant effect size is an increase of 5 degrees. The investigator recorded the mean value of three attempts. Hypothesis: CLRT will increase hamstring flexibility.

Secondary Outcomes:

1. Hamstring Strength as assessed by Handheld Dynamometry. HHD . The investigator recorded the mean value of three attempts. Hypothesis: CLRT will have a neutral to positive effect on hamstring strength.
2. Pain Pressure Threshold. The mean of three repeated measures was reported. An increase in PPT signifies an increase in pain tolerance. Hypothesis: CLRT will increase pain tolerance.
3. Age, gender, activity level, perceived hamstring tightness, perceived hamstring flexibility and perceived hamstring strength were assessed at baseline and subsequent follow up visit. Results were stratified by these variables to assess interaction with treatment.

Sample Size and Power: Based on previously published results, a mean increase of 5º on the KEA (e.g., from 135º to 140º) is considered to be clinically meaningful, assuming a common standard deviation of 15º. It is also assumed that correlation between repeated measurements from the same individual will be at least 0.75 (likely a conservative assumption). Under these assumptions, enrolling 38 participants would provide at least 80% power using a two-sided test at the 0.05 level.

Inclusion Criteria:

1. Between 18-35 years of age
2. All genders
3. Willing to complete two study visits over 2-3 weeks
4. Able to read and communicate in English

Exclusion Criteria:

1. Current lower back condition with pain, numbness or tingling that radiates down the legs
2. Active treatment for a major medical illness, such as heart disease, uncontrolled diabetes or hypertension, malignancy, autoimmune, or immune deficiency disorder
3. History of vasculitis, intracranial mass, clotting disorder (including medication-induced, e.g., warfarin)
4. Current skin malignancy on scalp
5. Cognitive dysfunction preventing informed consent
6. Pending or currently receiving benefits from personal injury litigation, including worker's compensation
7. Chronic long-term disability related to lumbosacral injury/symptoms
8. Epilepsy

Data was collected on two visits separated by at least 1 week washout period. On the second visit, participants were asked about any adverse events. A survey on adverse events was sent 2 weeks after second visit asking for any information on adverse everts as well.

The high baseline flexibility of the population may have a ceiling effect on the intervention. Further examination of the effects of CLRT in a clinical population is warranted.

Subjects and assessors were blinded to treatment allocation. The subject was face down, eyes closed, and wearing protective eyewear that blocks the specific wavelength of the laser light during the intervention.

After each treatment session, the participants completed a de-blinding questionnaire administrated by the assessor providing a dichotomous 'yes' or 'no' answer as to whether active treatment was received. This response was followed by a second question regarding how certain they were that active treatment was received on a 0-10 numeric rating scale (NRS), where 0 represents absolutely uncertain and 10 represents absolutely certain.