The employee appeals the compensation judge’s finding that she failed to establish by a preponderance of the evidence that her work duties were a substantial contributing cause of a disc herniation sustained at her home on March 19, 2012.  We affirm.

The employee began working as a registered nurse around 1985.  In 1990, she started working eight-hour shifts for the employer in its intensive care unit.  Among other duties, her work included turning and moving patients in bed, assisting patients with getting into and out of bed, and pushing beds to transfer patients.

By 2001, the employee was working twelve-hour-plus shifts as a critical care nurse, usually in the intensive care unit.  She also had assignments in the emergency room or as a surgical care nurse.  Her duties involved prolonged standing, walking, reaching, stooping, bending, kneeling, and lifting patients.  The employee testified that sometimes her back or legs would become tired and sore from lifting patients and pushing beds on carpeted floors, but her soreness would go away with rest after a shift.  She did not see a doctor about these symptoms.

On November 16, 2011, the employee was seen by Maria Barrell, an osteopath, at the Duluth Family Practice Clinic.  The employee was concerned about transient back and pelvic pain that she had been having “for some years, worse with mechanical or physical labor.”  Dr. Barrell diagnosed mechanical back pain.  She suggested core-strengthening exercises and recommended therapeutic massage as needed for up to four months.

The employee began treating at the Duluth Clinic Fitness and Therapy Center on November 17, 2011 for therapeutic massage.  The employee presented with pain in her lower back.  She reported that her job was physically demanding, but that after resting and when off work she was pain free.  The employee had tension in the musculature from the back of her neck down her back and hips to her buttocks.  She was noted to respond well to massage.  On February 21, 2012, the employee had a second session of massage therapy, again concentrating on her lower back.  Her condition was unchanged from the prior appointment.

The employee sought no further treatment until March 19, 2012.  On that date, the employee was resting at home after two days off work.  When she got out of bed, she felt a sudden onset of severe lower back and right leg pain.

On March 21, 2012, the employee began treatment at Lempi Chiropractic for lower back pain and right leg pain which she reported had started on March 19.  She was diagnosed with a lumbar subluxation at the L3-4 level, with right sciatic radiculitis.  The employee continued to treat chiropractically for her low back and leg pain for about the next year, in addition to seeking medical treatment.

The employee went on a medical leave of absence beginning on March 23, 2012, her next scheduled work day.  She did not report a work-related injury at that time.

The employee returned to Dr. Barrell at the Duluth Clinic on April 11, 2012 and reported “a new problem” with her lower back.  She stated that it started when she awakened on March 19, 2012 with pain in her right hip and gluteal muscle shooting down her right leg.  The employee reported that this had been preceded by low back pain, without trauma, for about a week.  She also noted that she had previously had some pain and swelling in the right calf after doing some aggressive stretching, but that this had resolved with chiropractic treatment and pool therapy.  Dr. Barrell referred the employee to physical therapy for an evaluation.

On April 12, 2012, the employee was seen at the physical therapy department at Essentia Health.  According to the history taken from the employee, her symptoms “came on 3 weeks and 3 days ago for no apparent reason.”  She had awakened feeling a little stiff, started to stretch, and then got progressively worse, with right lower back pain which radiated into her right buttock and hip and down her right leg to the knee and sometimes the ankle.

X-rays of the employee’s lumbar spine were performed on April 22, 2012 and were read as showing mild degenerative disc disease of the lumbar spine without evidence of subluxation or fracture.  An MRI of the lumbar spine done on May 3, 2012 showed a large caudally extruded right paracentral free fragment herniation at L5-S1, with displacement and impingement of the right S1 root.  Disc bulging was present at L4-5 and L2-3.  There was advanced disc degeneration at T11-12, moderate degeneration at T12-L1 and L2-3, mild to moderate degeneration at L5-S1 and mild degeneration at L4-5.  There was mild cystic facet arthropathy on the right at the L2-3 and L3-4 levels.  The MRI also showed lower thoracic Scheuermann’s sequelae.  No central or foraminal stenosis was noted at any level.

The employee began treating with Dr. Edward E. Martinson at St. Luke’s Physical Medicine & Rehabilitation on May 14, 2102 on referral by Dr. Lempi.  The employee again gave a history of the onset of her symptoms on March 19, 2012, when she had pain down the right leg after awakening from a nap and getting up from bed.  The employee now also recalled in retrospect that she had been having slowly increasing low back pain and intermittent right lower extremity pain and weakness for several months before the March 19 incident.  At times during the months preceding March 19, the pain was severe enough that she had to physically lift her right leg into her car when entering it to go home from work.  Dr. Martinson diagnosed lumbar radiculopathy, consistent with a right L5-S1 disc herniation affecting the right S1 nerve root.  He recommended continued physical therapy and a neurosurgical consultation.

On May 16, 2012, the employee was seen by Dr. Lynn E. Quenemoen, at Essentia Health Occupational Medicine.  She reported that she had pain in the right calf on March 19 after awakening from a nap, and that “she tried to stretch it out, which aggravated the pain.”  She also stated that “after thinking back she used to note some discomfort in the right lower extremity after her long 12-hour work shifts” prior to the March 19 incident.  She did not, however, recall any specific work incident that might have caused her recent symptoms.

The employee was evaluated by Dr. Klironomos at St. Luke's Neurosurgery Associates on May 17, 2012.  He recommended that the employee continue treating with exercise, but that if her symptoms escalated, she could contact him again to discuss surgery.  The employee was not comfortable with Dr. Klironomos, and on June 1, 2012, she saw Dr. Derek J. Orton at Orthopaedic Associates of Duluth.  She gave a history of mild sciatica-type symptoms prior to a sudden onset of severe pain involving her right leg in an S1 nerve root distribution on March 19, 2012.  Dr. Orton discussed treatment options and the possibility of full return of function over time.  He recommended that the employee weigh non-operative versus operative treatment options.  If she continued to have severe pain, persistent weakness, and functional incapacity, he suggested she could consider proceeding with surgical intervention with Dr. Klironomos.

The employee testified that after she was told that her MRI showed that she had a herniated disc, “the light went on” and she decided it had to be work-related.  On May 30, 2012, the employee contacted the employer and requested a first report of injury form, which she completed and returned on June 4, 2012.

The employee filed a claim petition on July 12, 2012 alleging a Gillette^[1] injury culminating on March 19, 2012.  The employer and insurer answered denying primary liability.

On June 18, 2012, the employee filled out a long term disability application.  On that form, the employee explained that she believed her lumbar disc herniation and radiculopathy were work-related because she “had been having subtle symptoms with physical labor at work and subsequently after working.”  Dr. Martinson signed a medical form accompanying the application.

On June 13, 2012, the employee was seen for low back pain and right-sided sciatica by Dr. Darcy A. Murphy at Duluth Family Practice.  The employee gave Dr. Murphy a history of a work-related repetitive motion injury related to her work as a nurse.

The employee was seen on October 25, 2012 by Dr. David Carlson, an orthopedic surgeon, for a medical examination on behalf of the employer and insurer.  Dr. Carlson attributed the employee’s disc herniation solely to a specific action or movement on March 19, 2012 which placed a stress on the disc.  He saw nothing in the employee’s 2012 MRI or in the medical and chiropractic records prior to March 19, 2012 to support the employee’s claim that her herniated disc was the result of the cumulative physical effects of her work duties.  In deposition testimony, Dr. Carlson acknowledged the concept of a Gillette or cumulative trauma injury, but explained that, in his view, such a cumulative trauma injury resulting in an acute herniation was inconsistent with the absence of advanced degenerative findings at other levels of the employee’s lumbar spine.  He noted that a disc herniation could result even from relatively minor activities, including twisting or stretching in bed.  He concluded that the employee had sustained an acute herniation on March 19, 2011 as the result of some physical motion or action she performed when she woke up from her nap.

The employee returned to Dr. Murphy on December 17, 2012 for a follow up of her lumbar radiculopathy.  The employee discussed with the doctor whether her symptoms were work-related.  She told Dr. Murphy that she had intermittent right leg pain and weakness for two years prior to her acute onset of pain on March 19, 2012, although at that time she had attributed these symptoms to fatigue rather than to a disk pathology.  Then on March 19, 2012 she took an afternoon nap, and when she sat up on the edge of the bed, she noted right leg symptoms which progressed over the next 24 hours until she was unable to function.

During a follow up appointment with Dr. Martinson on December 31, 2012, the employee again discussed causation for the disc herniation.  She stated that she had already been “limping at work” due to low back and right leg pain prior to March 19, 2012, but had deferred reporting an injury or getting treatment at that time.  Dr. Martinson agreed that her reported history of symptoms was consistent with a cumulative trauma injury from the heavy and repetitive movements required in her job as a critical resource nurse.

On January 10, 2013, the employee returned to see Dr. Murphy.  His chart notes state that the employee wanted “to discuss definition of her illness.”  Dr. Murphy recorded as history that she reported having had symptoms consistent with a lumbar radiculopathy for approximately two years.  He agreed that the symptoms the employee described would be consistent with a cumulative injury related to her work.

The employee was examined by Dr. Mark C. Gregerson on February 6, 2013 at the request of her attorney.  In his report dated February 7, 2013, and in deposition testimony, Dr. Gregerson also opined that the employee's work activities were a substantial cause of her condition after March 19, 2012.  He explained that ongoing stress on the employee’s disc from periods of repetitive heavy lifting, bending, and twisting caused gradually increasing symptoms which culminated in the herniation on March 19, 2012 when the employee got up from her nap.

Following the hearing below, the compensation judge accepted Dr. Carlson’s causation opinion over those of Dr. Martinson, Dr. Murphy and Dr. Gregerson.  The compensation judge found that the employee had not established by a preponderance of the evidence that her work duties up to and including March 16, 2012 were a substantial contributing cause of the disc herniation she sustained on March 19, 2012.  The employee appeals.

In reviewing cases on appeal, the Workers’ Compensation Court of Appeals must determine whether “the findings of fact and order [are] clearly erroneous and unsupported by substantial evidence in view of the entire record as submitted.”  Minn. Stat. § 176.421, subd. 1.  Substantial evidence supports the findings if, in the context of the entire record, “they are supported by evidence that a reasonable mind might accept as adequate.”  Hengemuhle v. Long Prairie Jaycees, 358 N.W.2d 54, 59, 37 W.C.D. 235, 239 (Minn. 1984).  Where evidence conflicts or more than one inference may reasonably be drawn from the evidence, the findings are to be affirmed.  Id. at 60, 37 W.C.D. at 240.  Similarly, “[f]actfindings are clearly erroneous only if the reviewing court on the entire evidence is left with a definite and firm conviction that a mistake has been committed.”  Northern States Power Co. v. Lyon Foods Prods., Inc., 304 Minn. 196, 201, 229 N.W.2d 521, 524 (1975).  Findings of fact should not be disturbed, even though the reviewing court might disagree with them, “unless they are clearly erroneous in the sense that they are manifestly contrary to the weight of the evidence or not reasonably supported by the evidence as a whole.”  Id.

A Gillette injury is a result of repeated trauma or aggravation of a pre-existing condition which results in a compensable injury when the cumulative effect is sufficiently serious to disable the employee from further work.  Gillette v. Harold, Inc., 257 Minn. 313, 321-22, 101 N.W.2d 200, 205-06, 21 W.C.D. 105 (1960).  In order to establish a Gillette injury, an employee must “prove a causal connection between her ordinary work and ensuing disability.”  Steffen v. Target Stores, 517 N.W.2d 579, 581, 50 W.C.D. 464, 467 (Minn. 1994).  The determination of a Gillette injury “primarily depends on medical evidence.  Id.  Here, the compensation judge expressly adopted Dr. Carlson’s expert medical opinion and found that the herniation on March 19, 2012 was an acute injury on that date, rather than the culmination of a work-related Gillette injury.

The employee disputes the judge’s finding, raising several arguments on appeal.  First, the employee contends that the compensation judge used a wrong legal standard in considering whether the employee had sustained a Gillette injury.

Specifically, the employee points to reasoning set forth in the compensation judge’s memorandum, pointing out that it focuses heavily on the employee’s claimed radicular symptoms prior to the March 19, 2012 herniation, and that the compensation judge there notes as a significant factor in his decision that he did not find the employee’s recollections about those symptoms convincing.  The employee further points out that Dr. Carlson’s medical opinion similarly failed to accept the employee’s recollections about her symptoms prior to March 19, 2012, and that Dr. Carlson’s opinion was predicated in part on that doctor’s view that there was no convincing indication of prior radicular complaints in the employee’s medical records.  She contends that in relying on Dr. Carlson’s opinion, the compensation judge’s underlying focus was again principally on the history of the employee’s symptoms prior to March 19, 2012.

The employee argues that by focusing on the lack of pre-existing radicular symptoms, the judge implicitly “required an increasing crescendo” of symptoms.  She argues that the judge thus effectively used a Gillette injury standard that has been subsequently overruled by the supreme court.  We disagree.

The employee’s arguments refer to a Gillette injury standard set forth in Reese v. North Star Concrete, 38 W.C.D. 63 (W.C.C.A. 1985).  That standard required a showing of specific work activity resulting in specific symptoms which lead cumulatively and ultimately to work-related disability.  In Steffen, 517 N.W.2d 579, 581, 50 W.C.D. 464, 467 (Minn. 1994), the supreme court reversed and remanded a compensation judge’s denial of a Gillette injury where there was medical opinion supporting such an injury and the denial was based solely on the absence of a history of specific work activity and resultant symptoms of the kind required by Reese.  The supreme court reiterated that while evidence of specific work activities causing specific symptoms leading to disability “may be helpful as a practical matter,” the determination of a Gillette injury primarily depends on medical evidence.  Id.

Reading the compensation judge’s memorandum as a whole and viewing the judge’s discussion of the employee’s prior history of symptoms in context, it is clear that the judge was not considering the employee’s symptoms as part of some implicit application of the Reese standard.  The compensation judge’s memorandum notes that the various expert medical evidence offered to support the claimed Gillette nature of the injury, i.e., those of Dr. Martinson, Dr. Gregerson, and Dr. Murphy, are all expressly predicated on a prior history of radicular symptoms.  The compensation judge explained that he had discounted the employee’s testimony about prior radicular symptoms for three reasons.  First, the compensation judge found it unlikely that the employee would have failed to seek medical attention for her alleged two years of radicular symptoms, which she testified included even the occasional inability to lift her right leg into an automobile due to intense back and leg pain.  Second, the compensation judge noted that the list and duration of prior symptoms that employee reported to her doctors continued to expand over time during the weeks and months after the date of injury.  In addition, the compensation judge noted that the records of employee’s medical treatment for low back pain before March 19 referred solely to muscular low back pain rather than any symptoms strongly suggestive of a disc herniation.

The judge’s consideration of the prior history of symptoms was, accordingly, another factor which the judge considered in weighing the expert medical opinions.  Under the circumstances where the employee’s medical experts relied on the employee’s reported but undocumented history of radicular symptoms as a part of the basis for their opinions, it was not inappropriate for the compensation judge to make factual findings about that history in order to assess whether the expert opinions relying on it were well-founded.  It appears to us that the practical utility of such evidence in this context renders it permissible under Steffen, so long as the judge’s determination in the matter is supported by the medical evidence.

The employee also contends that the judge’s finding that the employee’s herniation was an acute injury reflects an erroneous view that a Gillette injury may not culminate in an acute event.  The employee cites several cases in which this court has affirmed a finding of a Gillette process culminating in an acute injury.  While we do not take issue with the suggestion that a Gillette process may lead to an acute injury event, we find nothing in the compensation judge’s findings or memorandum to suggest that he decided the case on this basis.

The employee next contends that the act of “rolling over in bed” or of “stretching” was not the kind of act which constitutes an intervening, superseding cause of injury, so as to result in the denial of benefits.  However, nothing in the findings or memorandum suggests that the compensation judge denied liability on the basis that the employee’s activities on March 19, 2012 constituted an “intervening cause” of the employee’s disc herniation.  The concept of intervening cause is applicable where the effect of a condition with an established work-related cause is then superseded by the effects of a non-work cause^[2].  Here, the judge simply failed to find a causal link between the employee’s work activities and her disc herniation or right-sided radicular symptoms.  The concept of an “intervening” cause has no application in this case.

The employee next argues that the compensation judge erred as a matter of law in accepting the opinion of Dr. Carlson.  She offers two different grounds for this contention.  First, she contends that Dr. Carlson’s opinion was disqualified as a matter of law in that Dr. Carlson had an “incorrect understanding of what constitutes a Gillette injury.”  Second, she argues that Dr. Carlson’s opinion lacked foundation.

With respect to the first contention, the employee focuses on statements by Dr. Carlson in which he opines that, in his view, the concept of a Gillette injury has only a very limited applicability in a situation involving acute herniation.  The employee argues that Dr. Carlson does not accept the concept of a Gillette injury as defined by statute, and that his opinions denying a Gillette injury in this case must therefore be deemed to be legally inadmissible.  We do not find this argument persuasive.  The workers’ compensation act allows compensation for repetitive use, Gillette, injuries.  However, it does not supplant medical opinion as to whether a particular condition was caused by a Gillette injury process.  Dr. Carlson’s opinion was simply that the employee sustained an acute injury to which her work activities had not contributed, an opinion he was qualified to render, whether or not other medical experts might offer a different medical opinion.

The employee also contends that Dr. Carlson’s opinion lacked foundation.  The employee argues that Dr. Carlson failed to properly interpret the employee’s MRI scan and the pre-herniation medical records.  The record, however, shows that Dr. Carlson had reviewed the MRI and its findings and the pre-herniation records, but that he simply disagreed with the employee’s experts about the significance to be given to the MRI and the records.  This is a question of medical opinion and not one of insufficient foundation.  Similarly, the employee contends that Dr. Carlson’s opinion was ill-founded in that he was unfamiliar with certain medical journal articles about the risks of back injury among nurses.  There was no evidence that the discussed journal articles, while relevant, constituted the kind of information that the medical community would deem to be necessary to render a valid medical opinion in this case.  We see no basis to reverse the compensation judge’s reliance on Dr. Carlson’s opinion on this basis.

Finally, the employee alleges, generally, that substantial evidence fails to support the compensation judge’s findings.  However, she simply reiterates her prior arguments, and lists the evidence supporting her position and asserts that it merited a determination in her favor.  We note that the compensation judge’s determination here rested largely on both a credibility determination and the judge’s choice of expert testimony.  The decision was also substantially supported by the medical records.  As this is a case of credibility,^[3] of the choice of medical experts,^[4] and of substantial evidence,^[5] we affirm.