delivered the opinion of the Court.

In the early morning of November 20, 1975, respondent Ralph Riley awoke with severe pains in his neck, shoulders, and arms, which later were attributed by physicians to an exacerbation of an arthritic condition. The United States Court of Appeals for the District of Columbia Circuit held that this “injury” was sufficient to invoke the “statutory presumption of compensability,”1 § 20(a) of the Longshoremen’s and Harbor Workers’ Compensation Act, 44 Stat. (part 2) 1436, 33 U. S. C. § 920(a), and vacated the administrative denial of disability benefits. We granted certiorari, 450 U. S. 979, and we now reverse.

*610Contending that he was permanently and totally disabled by the arthritic condition,2 Riley’s retained counsel filed with the Deputy Commissioner a claim for compensation under the Act. See 33 U. S. C. § 913. On standard form LS-203, in response to the direction to “[djescribe in full how the accident occurred,”3 Riley wrote that on November 19, 1975, he was “[ljifting duct work with co-worker, weighing approximately 500 pounds, felt sharp pain in neck and sat down.” App. 111.

An evidentiary hearing was convened before an Administrative Law Judge. After construing the evidence in a light most favorable to Riley and resolving all doubts in his favor, the Administrative Law Judge found “that Claimant sustained no injury within the meaning of Sec. 2(2) of the Act on November 19, 1975, as alleged, and that Claimant and Sutherland [Riley’s co-workerj gave false testimony as to the happening of the accident.” App. to Pet. for Cert. 24A.

A divided panel of the Benefits Review Board affirmed the denial of disability benefits, holding that the Administrative Law Judge’s findings were supported by substantial evidence. In dissent, Member Miller stated:

“The Act does not require that claimant prove an accident in order to establish a claim. To the contrary, compensation is payable under the Act if claimant is disabled because of injury which is causally related to his employment. 33 U. S. C. §§902(10), 902(2).” 9 BRBS 936, 940 (1979) (emphasis in origina:!).

*611Member Miller defined an injury as “something go[ne] wrong within the human frame.” Ibid. Riley suffered such an injury when he awoke on November 20 with severe pain. Therefore, Member Miller would have remanded the case for a determination of “the real issue in this case,” which “is not whether claimant sustained an accident at work but whether claimant’s injury is causally related to his employment.” Ibid. That determination was to be made in light of the § 20(a) presumption, which “places the burden on employer to prove by substantial evidence that claimant’s injury did not arise out of or in the course of employment.” Ibid.

On Riley’s petition for review, the Court of Appeals vacated the decision of the Benefits Review Board, agreeing with Member Miller’s position. Riley v. U. S. Industries/Federal Sheet Metal, Inc., 200 U. S. App. D. C. 402, 627 F. 2d 455 (1980). The court stated that “it can hardly be disputed that petitioner suffered an ‘injury^ when he awakened in pain on November 20, 1975.” Id., at 405, 627 F. 2d, at 458. The court then turned its “attention to the statutory presumption and the range of situations to which this Court has applied it.” Ibid. It construed its earlier cases as holding “that an injury need not have occurred during working hours” and “need not be traceable to any particular work-related incident to be compensable.” Id., at 405-406, 627 F. 2d, at 458-459.4

“The foregoing cases make clear the pervasive scope of the statutory presumption of compensability. Indeed, no decision of this Court has ever failed to apply the pre*612sumption to any facet of any claim before it. We now hold expressly that where a claimant has been injured, the Act requires that, in the absence of substantial evidence to the contrary, a claimant be given the benefit of a rebuttable presumption that the injury arose out of and in the course of the claimant’s employment.” Id., at 406, 627 F. 2d, at 459.

The question for remand was not whether Riley’s “injury” stemmed from a “work-related incident,” but whether it was “ ‘employment-bred. ’ ” Ibid.

The Court of Appeals erred because it overlooked (1) the statutory language that relates the § 20(a) presumption to the employee’s claim, and (2) the statutory definition of the term “injury.”

I

The Court of Appeals’ first error was its invocation of the § 20(a) presumption in support of a claim that was not made by Riley. Riley claimed that he suffered an injury at work on November 19 when he was lifting duct work and felt a sharp pain in his neck. The Administrative Law Judge found as a matter of fact that the accident had not occurred; this finding is no longer challenged. The Court of Appeals’ theory of recovery was that Riley suffered an injury at home in bed on November 20 and that Riley was entitled to .a presumption that this injury was “employment-bred.”

Section 20(a), 44 Stat. (part 2) 1436, provides that “[i]n any proceeding for the enforcement of a claim for compensation under this Act it shall be presumed, in the absence of substantial evidence to the contrary . . . [t]hat the claim comes within the provisions of this Act.” The coverage of the presumption is debatable,5 but one thing is clear: the pre*613sumption applies to the claim. Even if a claimant has an unfettered right to amend his claim to conform to the proof, the presumption by its terms cannot apply to a claim that has never been made.

Section 13 of the Act, 33 U. S. C. § 913, provides that a claimant must timely file a claim with the Deputy Commissioner. The content of the claim is not specified in that section. But § 12(b), 33 U. S. C. § 912(b), requires that the claimant timely give the Deputy Commissioner and his employer notice of his injury, and provides further that “[s]uch notice . . . shall contain ... a statement of the time, place, nature, and cause of the injury.”6 The claim, like the notice required by § 12 and like the pleadings required in any type of litigation, serves the purposes of notifying the adverse party of the allegations and of confining the issues to be tried and adjudicated.7

*614In Riley’s claim, he alleged that he suffered an accidental injury in the course of his employment on November 19. No claim has ever been made that the “injury” occurred at home and that it was somehow “employment-bred.” Even if such a vague claim stated a prima facie case of compensability, the statutory presumption does not require the administrative law judge to address and the employer to rebut every conceivable theory of recovery. At least when the claimant is represented by counsel,8 as Riley was, there is no reason to depart from the specific statutory direction that a claim be *615made and that the presumption, however construed, attach to the claim.

II

The Court of Appeals’ second error was its incorrect use of the term “injury.” The court stated that Riley’s attack of pain in the early morning of November 20 was an “injury” compensable under the Act if the employer did not disprove by substantial evidence that the “injury” was “employment-bred.” The fact that “‘something unexpectedly goes wrong with the human frame,’” 200 U. S. App. D. C., at 405, 627 F. 2d, at 458 (quoting Wheatley v. Adler, 132 U. S. App. D. C. 177, 183, 407 F. 2d 307, 313 (1968)), however, does not establish an “injury” within the meaning of the Act. The mere existence of a physical impairment is plainly insufficient to shift the burden of proof to the employer.

Section 3(a) provides that “[c]ompensation shall be payable under this Act in respect of disability... of an employee, but only if the disability . . . results from an injury.” 44 Stat. (part 2) 1426, as amended, 33 U. S. C. § 903(a). Injury is defined as an “accidental injury . . . arising out of and in the course of employment.” 33 U. S. C. §902(2). Arising “out of” and “in the course of” employment are separate elements: the former refers to injury causation; the latter refers to the time, place, and circumstances of the injury.9 Not only must the injury have been caused by the employment, it also must have arisen during the employment.

A prima facie “claim for compensation,” to which the statutory presumption refers, must at least allege an injury that arose in the course of employment as well as out of employment.10 The “injury” noticed by the Court of Appeals, how*616ever, arose in bed, not in the course of employment. Even if the Court of Appeals simply mislabeled the early morning attack of pain as the “injury” itself rather than as a manifestation of an earlier injury, the claim envisioned by the Court of Appeals did not allege any facts that would establish that Riley suffered an injury that arose in the course of employment. The statutory presumption is no substitute for the allegations necessary to state a prima facie case.

Ill

Riley’s claim stated a prima facie case of compensability; if the Administrative Law Judge had believed Riley’s allegations, he would have found that Riley’s attack of pain in the early morning of November 20 was caused by an injury suffered when Riley was lifting duct work on the job on November 19. The judge, however, disbelieved Riley’s allegations and marshaled substantial evidence to support his findings. The statutory presumption did not require him to adjudicate any claim that was not made, and the Court of Appeals erred in remanding for that purpose. Nor could the statutory presumption have aided Riley had he made the claim envisioned by the Court of Appeals — that he suffered an “injury” at home — for such a claim omits the requirement that a compen-sable injury arise in the course of employment.

The judgment of the Court of Appeals is reversed.

It is so ordered.

dissenting.

I

Section 20(a) of the Longshoremen’s and Harbor Workers’ Compensation Act (LHWCA), 33 U. S. C. § 920(a), provides that “it shall be presumed, in the absence of substantial evidence to the contrary . . . [t]hat [a] claim [for compensation] comes within the provisions of this chapter.” The central issue before us is whether this provision requires the employer in a compensation hearing to offer “substantial evidence” refuting the existence of a causal relationship between a compensation claimant’s injury and his employment. The question has been fully briefed and argued, but the Court does not address it. For me, however, the answer is clear and controls the proper disposition of this case.

By its terms, and quite in contrast to the practice in judicial proceedings, § 20(a) requires the employer to take the initial steps to disprove his liability. This preliminary shifting of the burden to the employer exemplifies the “humanitarian nature of the Act,” O’Keeffe v. Smith Associates, 380 U. S. 359, 362 (1965) (per curiam), and the “strong legislative policy favoring awards in arguable cases;” Wheatley v. Adler, 132 U. S. App. D. C. 177, 183, 407 F. 2d 307, 313 (1968) (en banc). Section 20(a) is clearly broad enough to encompass the question of causation. “The statutory presumption applies as much to the nexus between an employee’s malady and his employment activities as it does to any other aspect of a claim. ” In re District of Columbia Workmen’s Compensation Act, 180 U. S. App. D. C. 216, 223, 554 F. 2d 1075, 1082 (1976). To defeat a claim for compensation, the employer must rebut the presumption of compensability by offering substantial evidence that the claim is not one “arising out of and in the course of employment.” 33 U. S. C. §§902(2), 903; see Marra Bros., Inc. v. Cardillo, 154 F. 2d 357 (CA3 1946). Only after the employer offers such substantial evi*618dence does the presumption fall “out of the case.” Del Vecchio v. Bowers, 296 U. S. 280, 286 (1935).

The statutory presumption thus defines the basic agenda for the hearing before the Office of Workers’ Compensation Programs (OWCP), and the factfinding required before the OWCP may deny a compensation claim. In this case, there is no serious dispute that respondent Riley suffered some disabling injury.1 See Riley v. U. S. Industries/Federal Sheet Metal, Inc., 200 U. S. App. D. C. 402, 406, n. 3, 627 F. 2d 455, 459, n. 3 (1980). Riley has an arthritic neck condition, and “the pain [he] suffered . . . was due to an exacerbation of his arthritic neck condition.” Id., at 405, 627 F. 2d, at 458. Given the existence of this condition, and the statutory presumption, the relevant inquiry was whether the employer had shown that the condition was not sufficiently work-related to render the employer accountable.2 No such finding was ever entered. Rather, the Administrative Law Judge and the Benefits Review Board focused exclusively on the testimony of Riley and his co-worker that something happened to Riley while lifting duct work on November 19,1975, causing an immediate pain in his neck. The Administrative *619Law Judge concluded only that no such incident occurred; the Benefits Review Board affirmed that finding.

Had the Administrative Law Judge credited the testimony of Riley with respect to the November 19 incident, it would surely have strengthened Riley’s position that the exacerbation of his arthritic neck condition was work-related. But the finding that this incident did not occur hardly demonstrates that Riley’s disability did not arise out of and in the course of employment. An injury need not be traceable to a single event at work in order to be compensable. “Even if the asserted work-related incident had never occurred, the injuries suffered by the claimant might nevertheless have been ‘employment bred.’”3 Id., at 406, 627 F. 2d, at 459. *620Absent a finding excluding this possibility, compensation could not be denied. In addition, the failure of the Administrative Law Judge to focus on the broader issue of the injury’s work-relatedness suggests that he may have failed to conduct the proceedings with proper attentiveness to the basic issue in a case such as this: namely, had the claimant been disabled as a result of his employment? Because the agency did not make the crucial finding, the Court of Appeals quite properly remanded this case so that the necessary determination could be made.

HH hH

Rather than allow a remand so that the normal process of administrative adjudication might run its course, the Court discerns a dispositive procedural requirement within the Act. The Court places its emphasis on the language of § 20(a):

“In any proceeding for the enforcement of a claim for compensation under this Act it shall be presumed, in the absence of substantial evidence to the contrary . . . [t]hat the claim comes within the provisions of this Act.” (Emphasis added.)

Unremarkably, the Court reads this language as applying the presumption to the “claim for compensation.” But quite remarkably, and without any support in precedent or the language of the Act, the Court construes the words “claim for compensation” to mean some sort of legal document, or at least some stated theory, setting forth a prima facie case for compensation, upon which all further proceedings must be based, and to which the presumption may attach.

The Court appears to glean its understanding of the word “claim” from the meaning assigned to the term “claim for relief” by Rule 8(a) of the Federal Rules of Civil Procedure. The Court concedes, as it must, that this understanding of the word “claim” finds no direct authority in the LHWCA itself. The Act does require the employee to file a timely “claim” with the Deputy Commissioner. 33 U. S. C. *621§ 913(a). See ante, at 613. But it is clear that the referred-to “claim” is nothing more than a simple request for payment,4 carrying with it the implicit assertion of an entitlement to compensation. To the extent an allegation of “time, place, nature, and cause of injury” is statutorily required, it is only in connection with the notice to the employer referred to by § 12.5 33 U. S. C. §912.

Moreover, the Court’s reliance on a written pleading requirement is wholly out of step with the sensible informality with which the Act is administered.6 Under the present regime of administrative enforcement, issues are not narrowed through pleadings, but rather through a mixture of formal *622and informal prehearing procedures. 20 CFR §§702.311-702.317 (1981). The regulations governing the administration of the Act reflect the method chosen by the agency charged with administering the Act for addressing the practical problems of issue narrowing that inevitably arise in the course of administrative proceedings. In addition to the prehearing conference report, which sets, forth the issues for the hearing, the parties are required to submit a prehear-ing statement defining the issues to be considered. See §702.317. Nevertheless, the employee’s failure to raise a particular issue at the prehearing conference, or in his prehearing statement, does not preclude him from raising that issue at the formal hearing. See § 702.336(a). In addition, “[a]t any time prior to the filing of the compensation order. . . the administrative law judge may in his discretion” reopen the hearing to consider a new issue. § 702.336(b).7

Apparently the Court is of the view that its imported definition of “claim” is necessary to protect employers from being called into a compensation hearing without any warning of the basis upon which compensation is sought; on this argument, the employer would otherwise be forced to offer evidence refuting every conceivable basis upon which an employee’s claim might be grounded. I do not share the Court’s fear. The Act already contains sufficient accommodation to such legitimate employer concerns: in the form of a statutory notice requirement, in the practical manner in which the presumption of compensability has historically *623been applied, and in the good-sense application of agency regulations and case management principles by the administrative officials charged with the execution of this Act’s provisions. In sum, I am confident, as the Court apparently is not, that any legitimate claim of surprise by the employer in this or in any other case may be fairly considered within the framework of the governing regulations, and resolved in a manner that effectuates the humanitarian purposes of this Act. Rather than rely on some Active legal analysis to dispose of the case “as a matter of law,” by intertwining the problem of notice with the § 20(a) presumption, I would leave all such questions of proof and notice for the agency on remand, as did the Court of Appeals.

r — i k-H u-4

As Justice Douglas once had occasion to remind us, “[tjhe problems under this Act should rest mainly with the Courts of Appeals.” O’Keeffe v. Smith Associates, 380 U. S., at 371 (dubitante). The Court’s treatment of the relatively simple issues raised by the present case underscores the wisdom of that counsel of deference. The Court of Appeals concluded below that the relevant issues were never resolved by the Administrative Law Judge. I can hardly disagree. Therefore, I dissent.