The employee appeals from the judge’s decision that he did not injure his low back as a result of his work activities.  We affirm.

The employee has an extensive history of low back symptoms and treatment dating back to the late 1970s.  He has treated for low back pain repeatedly over the years, sometimes connecting his condition to a specific incident, while at other times not being aware of a particular incident or cause for his symptoms.  Diagnoses included SI joint strain, musculoskeletal pain, strain/sprain, myofascial strain, sacroiliac dysfunction, and degenerative disc disease.  He received medical care, physical therapy, and chiropractic treatment for flare-ups and eventually began receiving what he described as maintenance chiropractic care from either Dr. Eric Zeiszler or Dr. Mike Ameli.

The employee’s work with Malt-O-Meal [the employer] began in 1995.  During his employment with the employer, the employee received treatment on numerous occasions for low back symptoms.

On June 20, 2011, the employee cleaned up a spill of twelve-ounce bags of cereal off of the floor at work, bending to pick up the bags and then discarding or placing them in boxes.  The employee testified that this activity involved at least five and possibly as long as ten minutes of repetitive bending.  He also testified that, as he straightened up, he noticed stiffness and tight muscles on the left side of his low back.  He reported the incident to the employer that day and treated with Dr. Ameli the next day.

In his June 21, 2011, office note, Dr. Ameli noted that “the employee stated . . . he injured his low back lifting sacs off the floor” and that the employee related to the doctor that “he had no recent injuries to this area.”  Dr. Ameli’s diagnosis was low back pain.  At hearing, the employee testified that, although he had experienced low back problems in the past, he had been pain free, with no symptoms and no treatment, from October 6, 2010, until June 20, 2011.

Dr. Ameli treated the employee several times a week for a month, and he released the employee to work without restrictions on August 1, 2011, but he nevertheless administered more chiropractic treatments through mid-September 2011.

The employee’s claim for expenses for treatment from June 21, 2011, to September 13, 2011, came on for hearing before a compensation judge.  In a decision issued on August 24, 2012, the judge found the care to be reasonable and necessary to treat the employee’s low back condition, but he denied the claim based on his conclusion that the employee did not sustain a work-related injury on June 20, 2011.  In deciding that the employee did not sustain a work injury, the judge applied an “increased risk test” to determine whether the injury arose out of the employment.  He also relied on the analysis of independent medical examiner Dr. Jeffrey Dick, who stated in part,

On remand, the compensation judge requested briefs from both parties and, on June 26, 2013, he issued his findings and order on remand, wherein he found that the employee did not sustain a work-related injury on June 20, 2011.  The employee appeals.

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 (2012).  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, 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 evidence or not reasonably supported by the evidence as a whole.”  Northern States Power Co. v. Lyon Food Prods., Inc., 304 Minn. 196, 201, 229 N.W.2d 521, 524 (1975).

The judge found that the employee did not present a formal narrative report or testimony from a physician addressing the issues, noting further in his memorandum that the employee “offered no expert opinion establishing to a reasonable degree of medical certainty that the employee sustained a work related injury on June 20, 2011.”  The employee claims that this court has already ruled “that Dr. Ameli’s records and letter to Travelers adequately expressed Dr. Ameli’s expert opinion” that the employee sustained a work-related injury.  However, in our prior decision, we stated only that it was “evident from [Dr. Ameli’s] records that he believed the employee’s low back symptoms after June 20, 2011, to be causally related to the employee’s work activities on that date.”  In fact, Dr. Ameli never gave a specific explanation as to how the employee’s work activities caused, aggravated, or accelerated his low back condition.  Instead, Dr. Ameli’s office note of June 21, 2011, indicated merely that “the employee stated . . . he injured his low back lifting sacs off the floor” on June 20, 2011.  The employee also apparently related to the doctor that “he had no recent injuries in this area,” but there was no evidence that Dr. Ameli was aware that the employee had treated with Dr. Zeiszler as recently as May 12, 2011.^[3]

On July 14, 2011, Dr. Ameli completed a Health Care Provider Certification form and checked “yes” that the employee’s condition was work related.  However, while the form further directed “if yes, please explain,” Dr. Ameli provided no explanation.  And on August 11, 2011, Dr. Ameli sent a letter to the insurer in which he stated, “it appears to me that your denial is in question,” but he did not explain why he questioned the denial.  No written narrative report from Dr. Ameli was offered at trial, and his office notes are difficult to read.  Given all these circumstances, we cannot conclude that the judge erred in his determination as to the adequacy of Dr. Ameli’s records on the issue of causation.

The employee also contends that, because the compensation judge on remand did not specifically find the employee’s testimony about experiencing pain at work on June 20, 2011, to be lacking in credibility, the only conclusion to be reached is that, “as a result [he] experienced an aggravation of his low back condition.”  We disagree.

As the judge pointed out in his decision on remand, “a judge may rely on an employee’s testimony regarding the absence of symptoms prior to a work injury and their emergence shortly thereafter in finding a causal nexus between the work injury and ongoing disability but a judge is not required to do so.”  See Barnes v. Hyatt Corp., slip op. (W.C.C.A. May 24, 2002).  The judge in the present case made numerous findings regarding the employee’s past low back pain and treatment, and he also made findings regarding subsequent treatment during which the employee denied any history of prior low back pain or treatment.  The employee testified at hearing that, from October 6, 2010 to June 20, 2011, he did not have any low back symptoms, that he was “fine,” and that he had no pain.  The judge found that this testimony was directly contrary to the records of Dr. Zeiszler, and the judge’s ultimate conclusion was that the employee’s testimony was not credible.  Assessment of a witness’s credibility is the unique function of the trier of fact.  Even v. Kraft, Inc., 445 N.W.2d 831, 42 W.C.D. 220 (Minn. 1989).  We find no basis to reverse the judge’s decision on this issue here.^[4]

Having found the employee’s testimony to be lacking in credibility and that the employee did not provide adequate expert opinion establishing that he sustained a work-related injury on June 20, 2011, the judge denied the employee’s claim.  Substantial evidence supports the judge’s findings, and we affirm.^[5]