The Workers’ Compensation Act of Oklahoma requires that reports of physicians used as evidence be made in accordance with the latest Guides to the Evaluation of Permanent Impairment issued by the American Medical Association.1 In this case the employer’s examining doctor departed from those Guides, with the explanation that he did so because the claimant did not cooperate fully in the testing process. The trial judge denied benefits based on that report. The Court of Appeals reversed, holding that the doctor’s reasons afforded an insufficient basis for departing from the Guides. Having granted certiora-ri, we now vacate the Court of Appeals opinion and remand to the Workers’ Compensation Court for further proceedings.

Petitioner Branstetter alleged pulmonary injury due to her work at the manufacturing plant of respondent TRW/Reda Pump. At trial TRW admitted that Branstetter was employed there, but denied that she had suffered injury, or if she was injured, disagreed that the injury arose out of her employment with TRW.

Branstetter testified that her duties at the plant included working with chemicals whose fumes caused her to be unable to breathe. She stated that she had never *1307smoked or had any respiratory trouble pri- or to her employment there. She also introduced the report of Dr. C, which stated that she suffered from respiratory impairment and damage to the lungs. In his opinion, she had partial permanent impairment to the body as a whole of thirty-five percent (35%).

The employer introduced a physician’s report from Dr. F, which stated that in his opinion Branstetter was not disabled. The pulmonary function testing performed under Dr. F’s direction was, in his judgment, inconclusive. The computer-generated report of the FEV-1 test indicated severe obstructive lung defect, but contained a handwritten note by Dr. S, the pulmonary specialist who interpreted the tests, that “Inconsistent data suggests suboptimal performance.” Dr. F’s lengthy report concluded as follows:

"I can find no evidence of lung disease on this woman at this time. It is noted that her chest x-ray is normal as it has been in the past. Her pulmonary function studies cannot be evaluated as this woman did not cooperate fully with this test and according to the test results and according to Dr. [S’s] written interpretation, this woman was not trying on this test for unknown reasons.... These test results are not reliable and cannot be used in evaluation of this patient.

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This report is in variance from the AMA Guides, as this woman did not cooperate with the pulmonary functions studies and therefore the guides cannot be applied to this particular test.”

The Workers’ Compensation Court found in favor of the employer, and Branstetter appealed. The Court of Appeals reversed the order of the Workers’ Compensation Court, holding that Dr. F’s report was not competent because it deviated from the A.M.A. Guides, and that the subjective assessment of the doctor that she “was not trying on the test” was an insufficient reason for deviating from the Guides. Thus, under the ruling of Perlinger v. J. C. Rogers Constr. Co., 753 P.2d 905 (Okla. 1988), the Workers’ Compensation Court was directed to enter judgment in favor of petitioner. We previously granted certiorari and hereby vacate the opinion of the Court of Appeals.

We must apply the laws that were in effect at the time of Branstetter’s injury. Lee Way Motor Freight v. Wilson, 609 P.2d 777, 779 (Okla. 1980). A workers' compensation claim is ruled by the “law in existence at the time of the injury and not by laws enacted thereafter.” Id., citing Caswell v. Bird, 160 Okl. 224, 16 P.2d 859 (1933). The last date of Branstetter’s employment with TRW was November 18, 1985. Because she alleges an ongoing injury due to exposure to harmful fumes, we shall consider that date to be controlling, as it was the date of her last possible exposure.

Title 85 O.S.Supp.1985, § 3(11) became effective November 1, 1985, and is thus the law applicable to this case:

... Except as otherwise provided herein, any examining physician shall only evaluate impairment in accordance with the latest “Guides to the Evaluation of Permanent Impairment” adopted and published by the American Medical Association. The examining physician shall not deviate from said guides except as may be specifically provided for in the guides. These officially adopted guides shall be the exclusive basis for testimony and conclusions with regard to permanent impairment.... (emphasis added)

Also in effect at the time was Rule 20(i), Rules of the Workers’ Compensation Court, which said:

.... Whenever the physician deviates from the “Guides”, the basis for his deviation shall be stated together with full medical explanation_ (emphasis added)

The Employer argues that in giving his medical explanation for deviating from *1308the Guides Dr. F complied with Rule 20(i). Branstetter argues that under Section 3(11) of the Statutes deviation may occur only as specifically allowed by the Guides. To the extent that the two conflict, the answer is simple; a court rule cannot contravene a constitutional statute. Ogle v. Ogle, 517 P.2d 797 (Okla. 1973). The statute allows deviation from the Guides only as may be expressly provided for in the Guides, and does conflict with the rule that would allow deviation upon mere explanation. The statute must prevail. Oklahoma County Sheriff v. Hunter, 615 P.2d 1007 (Okla. 1980); Matter of Milton H., 614 P.2d 72 (Okla. 1980); Transok Pipe Line Co. v. Darks, 515 P.2d 218 (Okla. 1973). Thus the doctor’s report can support a finding of no impairment only if the basis for deviation from the Guides appears specifically in the Guides.

We have just recently looked to the Guides for directions in such a case as this. York v. Burgess-Norton Mfg. Co., 803 P.2d 697 (Okl. 1990) involved a comparable pulmonary complaint, inconsistent spirome-try (or pulmonary function) tests, and the conclusion of the same Dr. F that the claimant “either was not cooperating with this test or intentionally attempted to change the results to imitate lung disease.” Id. at 701. Turning to the Guides, we concluded that in order to have rendered a report capable of supporting a finding of no impairment, the doctor stopped one test short. The Guides (2nd Edition at P. 97) clearly state that testing to measure estimated exercise capacity, known as the V02, should be done when:

“(4) the individual has not performed maximally or correctly in the spirometry or Deo tests.” York at 701.

York is dispositive of today’s case. Here again the doctor disregarded the inconsistent spirometry tests based upon his belief that the claimant wasn’t trying. Here again he failed to follow-up with the V02 estimated exercise capacity test required by the Guides when the “individual has not performed maximally or correctly in the spirometry....” As in York, we must here also find that the Employer’s medical report is insufficient under the A.M.A. Guides to support the lower court’s denial of benefits.

The opinion of the Court of Appeals is vacated. The case, having been tried prior to our ruling in Gaines v. Sun Refinery, 790 P.2d 1073 (Okl. 1990) (which modified the earlier rule of Perlinger, supra on which the Court of Appeals relied), is hereby remanded to the Workers’ Compensation Court for a new trial.

dissenting:

I respectfully dissent from the majority’s opinion for the reasons expressed in my dissenting opinions m Gaines v. Sun Refining & Marketing, 790 P.2d 1073, 1081 (Okla. 1990), and York v. Burgess-Norton Mfg., Co., 803 P.2d 697, 704 (Okla. 1990). I would vacate the opinion of the Court of Appeals and sustain the Order of the Workers’ Compensation Court.

concurring specially:

I write separately to emphasize that in those causes arising after the issuance of the mandate in Gaines v. Sun Refining & Marketing, 790 P.2d 1073, 1081 (Okla. 1990), May 4, 1990, there will be no more “overs.” This rule is necessary to preserve judicial economy, and to assure that there will be a meaningful end to litigation.

with whom KAUGER, Justice, joins, concurring in result.

The court holds that (a) the provisions of 85 O.S.Supp.1985 § 3(11)1 — referred to as a “constitutional statute” — control over *1309Rule 20(i), Workers’ Compensation Court Rules, which is no longer in force,2 and (b) the claim’s denial must be vacated because the employer’s physician, who had found the claimant to be free from respiratory impairment, failed to administer an additional test prescribed by the Guides3 for uncooperative patients.4 I accede to the latter part of today’s pronouncement for the following reasons: a) the employer’s physician-expert offered no legal, medical or any other scientific basis for deviating from the Guides, b) the unwarranted departure from Guide-prescribed standards saps the employer’s report of its probative value and c) the court wisely remands the case for reexamination of all issues.5

As for the first part of the court’s holding — that a constitutional statute supersedes a contrary court rule — I accept this norm as a correct exposition of the law only in the abstract. The terms of § 3(11) in force at the time critical to this cause provided that

“... any examining physician shall only evaluate impairment in accordance with the latest [Guides] ... adopted and published by the American Medical Association. The examining physician shall not deviate from said guides except as may be specifically provided for in the guides. * * * ” (Emphasis added.)6

The quoted version of § 3(11) bound the physician to the AMA’s standards unless a specific exception was found in the Guides. The operative terms of Rule 20(i),7 on the other hand, allowed deviations as long as the physician gave a “full medical explana*1310tion.” The real issue to be decided here is whether § 3(11) must in all cases override Rule 20(i).

I would give here a far more qualified affirmative answer by holding that in this case the court rule will have to yield to the contrary text of the statute whose constitutional validity has not been challenged. A statute that is free from fundamental-law infirmity prevails over the contrary content of a rule which is not rested upon the promulgating court’s constitutional authority.8 There is no suggestion in this case that under the doctrine of delegata potestas non potest delegari9 § 3(11) may in its present or former version constitute an unlawful delegation of the state’s legislative power to a private entity (the AMA),10 or that the AMA text’s binding force may be vulnerable to challenge as an impermissible legislative predetermination of an adjudicatory scientific fact.11 I would hence narrowly conclude that § 3(11) must control here over the contrary content of Rule 20(i) because the statute’s validity has not been drawn in question.