Rehabilitative Ultrasound Imaging (US) is a procedure used to evaluate skeletal muscle size and function to inform clinical practice. US has been shown to be a reliable and valid tool for measuring changes in trunk muscle (i.e. abdominal and back muscle) size and activity during sub-maximal contractions in younger populations. Younger adults with low back pain as compared with healthy adults without pain demonstrate smaller back muscle size, lower back muscle activity, and greater back muscle asymmetry (differences in right side compared with left side).

No trials are published evaluating muscle adaptations using US in response to clinical treatments for low back pain in the older adult population. Increased muscle size and improved muscle symmetry have been reported in younger adults with low back pain who participate in low back stabilization exercises. These exercises use voluntary contractions of the back muscles with prolonged hold times and low loads. Neuromuscular Electrical Stimulation (NMES) is a treatment modality that increases muscle activity when voluntary activity is impaired and increases muscle size. Most studies assessing muscle size and activity in response to NMES have been conducted in the knee muscles (i.e. the quadriceps), while the impact of NMES on the back muscles remains relatively unexplored. Given the potential to evaluate back muscle size and activity with US, this assessment tool may be used to document muscle adaptations to a clinical intervention in older adults with low back pain.

The purpose of this study is to conduct a 6-week clinical trial to determine if NMES plus lumbar stabilization exercises (i.e. NMES AND Stabilization Exercises) is superior to lumbar stabilization exercises (i.e. Moist Heat AND Stabilization Exercises) for improving back muscle size, activity, and side-to-side (i.e. right side versus left side) symmetry in older adults with chronic low back pain (i.e. low back pain of greater than 3 months). Muscle size, activity, and symmetry will be assessed using US before and after the treatments to determine if the treatments positively impact muscle. Secondary clinical measures of success will include improvements in physical, psychological, and social function pre- to post-treatment.

Inclusion Criteria: This study will use a sample consisting of 36, English-speaking and English-reading, older male and female adults (ages 60-85 years) with chronic low back pain, i.e. pain of greater than 3 months duration. During the examination, potential participants must have 2/4 of the following for inclusion, based on previous work by Hicks et al, which outlined clinical predictors of success with a trunk muscle stabilization exercise program:

1. Fear-Avoidance Beliefs Questionnaire (FABQ) Physical Activity Sub-Scale score ≥9: The FABQ is a measure of an individual's beliefs regarding the impact of physical activity and work on his/her low back pain. The FABQ is comprised of two sub-scales: physical activity and work. Higher FABQ scores have been shown to predict pain and disability in individuals with chronic low back pain.
2. Aberrant Movement: Aberrant movement may be classified as any one of the following: (1) an "instability catch", defined as deviation from the plane of movement during flexion or extension; (2) "thigh climbing", which is defined as using the hands and pushing on the thighs to assist in obtaining an upright trunk position; (3) a "painful arc of motion", when flexing or returning to upright from a flexed spinal position; or (4) "reversal of the lumbopelvic rhythm", where the trunk is first extended and then the hips and pelvis extend to bring the body upright from a flexed position.
3. Posterior-to-Anterior Segmental Hypermobility: The participant will lie on his/her stomach and the examiner will apply a posterior-to-anterior (back-to-front) force over the spinous processes from S1 to T12 (just below the belt-line to the rib cage). The available mobility will be graded hypermobile (too much motion), normal, or hypomobile (too little motion).
4. Positive Prone Instability Test: The participant will lie on his/her stomach with the legs off the edge of the table and the feet resting on the floor. The examiner will apply a posterior-to-anterior pressure at each spinous process (T12-S1). Any provocation of pain will require the participant to lift their legs off the floor while the pressure is reapplied to the painful level. If the pain subsides with elevation of the legs, this is considered a positive test.

Exclusion Criteria: Exclusion criteria for participants includes (1) history of low back surgery; (2) recent trauma (i.e. motor vehicle accident, fall, etc. ); (3) receipt of services for low back pain within the last 6 months; (4) non-ambulatory or severely impaired mobility (i.e. use of an assistive device greater than a cane); (5) severe hearing or visual impairment; (6) non-mechanical low back pain; (7) neurological disorder; (8) presence of an acute illness; (9) diagnosis of scoliosis; (10) symptoms related to the back below the knee; (11) presence of a pacemaker; (12) participation in R21 clinical trial ongoing at the University of Delaware Physical Therapy Clinic; or (13) the inability to participate in the study for the full six weeks for any known reason (i.e. moving away, extended vacation). Potential participants will also be excluded if during the evaluation any of the following are found:

1. score < 24 on the Folstein Mini-Mental State Examination (MMSE): As scores greater than or equal to 24 may identify individuals who are cognitively intact, this screening tool will exclude those older adults with questionable reliability (i.e. consistency) on the self-report questionnaires secondary to cognitive impairment.
2. Modified Oswestry Low Back Pain Questionnaire (mOSW) score < 14 percent: This questionnaire will exclude those individuals with chronic low back pain who demonstrate minimal low back pain-related disability. Individuals with minimal disability may not be representative of those seeking outpatient physical therapy services for their back pain.
3. Facial Pain Scale-Revised (FPS-R) "worst" low back pain rating in last 24 hours of < 3/10: Pain rating ≥ 3/10 is being used in the hopes of recruiting a group of individuals who may be representative of those likely to seek clinical services for their low back pain. Also, all FPS-Rs ("current", "best", and "worst") will be used to document the impact of treatment on self-reported pain.
4. Inability to tolerate lying on belly with legs straight: This is a requirement for our standardized position for ultrasound.

Baseline, 6 weeks of intervention, and 6-week follow-up.

Adverse events were reported by study personnel in accordance with the University of Delaware Institutional Review Board for Human Subjects Research. Adverse event definitions as described in the Common Terminology Criteria for Adverse Events (CTCAE) from the National Institutes of Health are used for reporting.

Lack of long-term follow-up; short-duration intervention may have been insufficient for muscle change