| Filed January 30, 2002
 UNITED STATES COURT OF APPEALS
 FOR THE THIRD CIRCUIT
 No. 01-1709
 DELAWARE RIVER STEVEDORES, INC.,
 Petitioner,
 v.
 DIRECTOR, OFFICE OF WORKERS' COMPENSATION
 PROGRAMS, UNITED STATES DEPARTMENT OF LABOR,
 AND SOUTHERN STEVEDORES, INC.,
 Respondents.
 On Petition for Review of Order and Opinion
of the
 Benefits Review Board dated March 12, 2001
 entered in Agency Nos. 00-691 and 00-691A
 Argued December 18, 2001
 Before: SLOVITER and McKEE, Circuit Judges,
and
 DEBEVOISE, District Judge.*
 (OPINION FILED: January 30, 2002)
 Stephen M. Calder, Esq. (Argued)
 Palmer Biezup & Henderson LLP
 620 Chestnut Street, Suite 956
 Philadelphia, PA 19106
 Attorneys for Petitioner
  
  
 _________________________________________________________________
 * Honorable Dickinson R. Debevoise, United
States Senior District Judge
 for the District of New Jersey, sitting by
designation.
  
 Eugene Mattioni, Esq. (Argued)
 Mattioni, Ltd.
 399 Market Street, 2nd Floor
 Philadelphia, PA 19106
 Attorneys for Respondents
 OPINION OF THE COURT
 DEBEVOISE, Senior District Judge:
 This is a petition for review of an order
and opinion of the
 Benefits Review Board (the "Board") which
reversed the
 finding of the Administrative Law Judge ("ALJ")
that
 Respondent, Southern Stevedores, Inc. ("SSI")
is the
 employer responsible for the benefits awarded
to claimant
 James Loftus for his back injuries. We conclude
that the
 findings of the ALJ were not supported by
substantial
 evidence and will deny the petition for review.
 I. The Facts
 Loftus had worked as a longshoreman since
1974.
 Although he suffered several workplace injuries
before he
 commenced working for SSI in 1996, none affected
his
 back. At SSI Loftus worked as a 40-foot trailer
mechanic
 and inspected, repaired and overhauled gensets.
Gensets
 were generators that were mounted under the
bellies of
 trailer chassis. Loftus described trailer
maintenance and
 repair as follows:
 A. Well, if the landing gear gets broken off,
you've got
 to cut it off and put a new set on, reweld
it and
 everything. If an air valve's broke, you
got to take it off,
 unhook all the hoses under the trailer to
get a new air
 -- to get the valve off and replace a new
valve and put
 the hoses back under the trailer. You also
pull the big
 black tires, two at a time, to do a brake
job. And the
 springs that hold those brakes on aren't
very lightly
 stretched.
 (App. at 99).
 2
  
 A substantial part of Loftus's work consisted
of repairing
 and maintaining gensets. Although management
expected
 that it would take seven and one half hours
to repair a
 genset, Loftus and his teammate developed
the ability to
 accomplish the task in four hours or less.
He described his
 work on the genset:
 Q. How did you have to either repair or maintain
a
 genset at Southern in the period between
January to
 September of 1996?
 A. Well, we had to sit on a stool, Your Honor,
it's a
 little mechanic's stool . . .
 Q. What's a mechanic's stool?
 A. . . . and it measures exactly one foot
off the floor.
 It's a little stool with four wheels on it
and you could
 roll around. Now where the genset was mounted
on the
 trailer is very low. I'm already down a foot
off the floor
 and I have to stick my head in that hole
to get to that
 engine and do what I had to do. And I would
be bent
 over constantly one foot from the floor.
 Q. How many men do this job?
 A. Basically, it was me and Kevin Doyle.
 Q. When you're doing this, my point, do you
get two
 men working on the same genset?
 A. Well, I would be on this side. I would
take the side
 where the starter and the alternator and
everything
 was and this would be the trailer. And Kevin
Doyle
 would be on that side where he would drain
the oil and
 change the oil filters and work on the control
panel,
 which was up a little higher than the side
that I
 worked on.
 (App. at 99-100).
 After performing this work for a number of
months Loftus
 began to have trouble with his lower back.
In September
 1996 he went to his family doctor who prescribed
pain
 relieving drugs and, because it was a work
related problem,
 advised him to seek medical care through
his employer. SSI
 referred Loftus to Michael J. Mandarino,
M.D., P.C. who
 3
  
 examined Loftus on or about October 11. Dr.
Mandarino
 reported that Loftus complained of discomfort
up and down
 the spine and across the low back but denied
arm or leg
 radiation of discomfort. He concluded that
the complaints
 were consistent with a sprain and strain
and advised Loftus
 to exercise, swim as much as possible during
an
 approaching Florida vacation, to continue
taking his oral
 medication and to return for reevaluation
in two weeks.
 On December 9 and 16 Loftus returned to Dr.
Mandarino
 for tests and reevaluation. Loftus had had
a CT scan, a
 bone scan and MRI scan, all of which were
normal. On
 December 16 Dr. Mandarino noted that "On
examination
 today the patient has full motion of the
lumbar spine.
 Straight leg raise is negative. No neurological
deficit are
 noted at this time nor has there ever been
any neurologic
 deficit. It has been explained to Mr. Loftus
that all of the
 diagnostic studies are normal. He feels that
he is capable of
 returning to work." (App. at 32).
 Dr. Mandarino stated that Loftus could return
to work
 full duty without restriction the following
day-- December
 17, 1996. Loftus did in fact return to work,
and SSI made
 substantial adjustments in its work practices
to relieve the
 pressures on Loftus's back. As Loftus described
it:
 A. Well, the trailer came up higher off the
floor and
 everything. And then the trailer came up,
the genset
 came up, everything was up high. We had -
- they
 bought a hydraulic jack, we put it in the
back. We
 raised the back. And they had two big twelve-by-twelve
 chocks that we would put under the landing
gear. And
 everything came from this high on the floor
to where,
 you know, where you could sit and work in
there. You
 didn't have to stick your head in, you know,
you
 weren't bent over like this anymore.
 Q. Did you still have to use that one footstool?
 A. No, they had chairs just as high as this
here. You
 could raise the chair and lower the chair.
It had a back
 on it.
 (App. at 109-110).
 4
  
 Loftus returned to Dr. Mandarino on April
25, 1997
 reporting that since the December visit "the
job itself and
 the overall conditions of his job have been
improved
 tremendously" but that "over the last few
weeks there has
 been a gradual recurrence of discomfort in
the spine." (App.
 at 32). On examination of the lumbar spine
Dr. Mandarino
 found discomfort on motion. Straight leg
raising was
 negative. No neurological deficits were noted
in the lower
 extremities. Loftus was started on Medrol-dospak
and
 advised to return in three days for reevaluation.
 Loftus returned to Dr. Mandarino for reevaluation
on
 April 28 and May 2, 1997. Dr. Mandarino found
that none
 of the tests nor his examination would explain
Loftus's
 disabling pain. After explaining this to
Loftus, Dr.
 Mandarino cleared him orthopedically to return
to full duty
 without restriction. Dr. Mandarino advised
him to have a
 physical with his family doctor to see if
there were any
 nonwork related etiology for his discomfort
and discharged
 him from his care.
 On May 14, 1997 Loftus went to Dr. Gad Guttman,
 senior orthopedic surgeon at the Department
of Orthopedic
 Surgery at Albert Einstein Medical Center,
for a second
 opinion. Dr. Guttman reviewed Dr. Mandarino's
records
 reflecting the absence of radiculopathy,
Loftus's return to
 work on December 17, 1966, the recurrence
of back pain in
 April, 1997 and Dr. Mandarino's conclusion
that from an
 orthopedic standpoint Loftus was cleared
to return to full
 duty. Dr. Guttman also reviewed the December
12, 1996
 report of the radiologist reflecting Loftus's
return to work on
 December 17, 1996, the recurrence of back
pain in April
 1997 and Dr. Mandarino's conclusion that
from an
 orthopedic standpoint Loftus was cleared
to return to full
 duty. Dr. Guttman also reviewed the December
12, 1996
 report of the radiologist reflecting that
an MRI showed mild
 degenerative changes of discs 3-4 and 4-5
and mild bulging
 without disc herniation or foraminal stenosis.
These
 findings, Dr. Guttman stated, were confirmed
by the
 December CAT scan and bone scan, all of which
"were
 consistent with the findings of degenerative
changes of the
 lumbar spine which one would expect in a
patient in this
 type of work, with this habitus and weight
and so on."
 (Supp. App. at 48).
 5
  
 Dr. Guttman took Loftus's history and performed
a
 physical examination. During his testimony
Dr. Guttman
 was asked whether he had an opinion as to
whether
 Loftus's complaints emanating from October
of 1996 had
 closed when he saw him in May of 1997. Dr.
Guttman
 responded:
 I felt that at the time that I examined him
the patient's
 complaints were related more to his overweight,
to his
 overexertion and to the underlying degenerative
 changes. He kept working all the time and
it was not
 unusual to have pain coming and going after
such
 heavy work and he was in pretty bad overall
condition
 anyway. When I saw him he was overweight
and he
 had degenerative changes.
 So as far as the specific question, in I believe
1996 his
 symptoms started acutely. Then they resolved
in
 December of `96 I believe according to Dr.
Mandarino's
 report. He returned back to work. Then he
kept on
 working and after four months or so he started
having
 pain again. I called it overexertion and
deconditioning
 and underlying degenerative changes.
 (Supp. App. at 54).
 Because his back was hurting Loftus had taken
time off
 from his work from April 25 to May 4, 1997.
He saw Dr.
 Guttman on May 14 and took time off from
work from May
 8 to May 18. On or about May 18 he returned
to work full
 time. His back still caused him discomfort
and to relieve
 the pain he commenced seeing a chiropractor,
Dr. Izzo on
 July 16, continuing with him until September
12, 1997
 when his insurance coverage expired. Dr.
Izzo provided
 relief through ultrasound, a TENS device,
heat packs and
 stretching.
 At the end of August 1997 petitioner, Delaware
River
 Stevedores, Inc. ("DRS") acquired SSI's interest
in the
 facility at which Loftus worked. DRS acquired
SSI's
 equipment including the special equipment
that had been
 designed for Loftus to relieve his back problems.
Operations
 at the facility continued as before and the
nature of Loftus's
 work did not change after August of 1997.
 6
  
 In the four month period January through April
1998
 Loftus worked an extraordinary number of
overtime hours,
 ranging on many days from ten to eleven hours
and on
 others from seventeen to eighteen hours.
On one day he
 worked twenty-one hours. The demands placed
upon the
 stevedoring company to move incoming cargoes
of fruit was
 the reason for DRS's heavy time demands imposed
on its
 mechanics.
 By April 1998 Loftus's back was again causing
him
 serious pain. He was referred to Roy T. Lefkoe,
M.D., P.C.
 The referral letter from Branch Manager,
presumably of
 DRS's claims adjuster, Neil J. Davis stated:
"We are
 particularly interested in having you take
a complete
 history from the claimant, to determine whether
or not his
 recent complaints are the result of a new
injury with his
 present employer, Delaware River Stevedores,
or if they are
 attributable to the old accident of September
30,[1996]":**
 Dr. Lefkoe saw Loftus for an orthopedic consultation
on
 May 20, 1998. He reviewed Loftus's medical
records and
 took a history from Loftus, who reported
that "[i]n 4/98 his
 pain worsened without additional injury"
(App. at 38).
 Loftus reported low-back pain radiating into
both legs.
 Dr. Lefkoe conducted a physical examination.
His
 diagnosis was acute and chronic lumbosocral
strain/sprain
 and lumbar degenerative disc disease at L3-4
and L4-5 with
 bulging discs. He found Loftus to be in acute
pain and
 unable to continue working. He prescribed
medication and
 physical therapy to include aquatherapy,
modalities and
 exercise. As to the question Davis addressed
to him, he
 stated, "Based on all information available
to me, the cause
 of his present back condition still is the
original work injury
 of 9/30/96." (App at 40).
 Loftus did not return to work; rather he continued
seeing
 Dr. Lefkoe and proceeded with physical therapy.
Dr. Lefkoe
 received a July 9, 1988 report of neurologist
Steven
 Mandel, M.D., who stated, ". . . this gentleman
appears to
 _________________________________________________________________
 ** The letter (App. at 36) referred to September
30, 1990, but
 undoubtedly the author intended to refer
to September 30, 1996, and
 Dr. Lefkoe so understood it.
 7
  
 have complaints consistent with a diagnosis
of lumbar
 radiculopathy. There is evidence of chronic
changes and the
 L5 and S1 distribution without evidence of
any significant
 acute changes noted. There are only mild
changes noted in
 his right lumbar paraspinal muscles at the
L4-5 and L5-S1
 area." (App. at 47). Dr. Lefkoe prescribed
medication and
 referred Loftus to Dr. Sandra Kahn for injections.
None of
 this provided relief, and Loftus was referred
to Dr. Rosen in
 November, 1998. Dr. Rosen administered a
series of six
 epidural injections which had a beneficial
effect. Loftus
 testified that Dr. Rosen's treatment "brought
me back" to
 the extent that "I never knew anything was
wrong with me.
 It was so good." (App. at 122).
 Loftus was able to return to work with DRS
in January
 1999 with restrictions. He was not called
upon to go
 underneath the trailers. He usually wore
a TENS unit and
 occasionally took pills to relieve pain.
He worked only eight
 hour shifts and performed no overtime.
 Dr. Guttman, who had reported on Loftus's
condition
 after his work cessation in April 1997 saw
him again in
 June of 1998, about five weeks after he had
ceased work
 because of increased pain and after Loftus
had come under
 the care of Dr. Lefkoe. He saw him again
in August 1998.
 Dr. Guttman testified that Loftus was in
greater pain than
 when he had seen him the previous year. Dr.
Guttman was
 referred to the records showing Loftus's
longer hours
 during the months preceding May of 1998.
He testified:
 Basically they showed that he did quite a
lot of
 overwork and in those months, I believe January
 through April, he did extremely heavy long-time
work,
 what I call overwork, and that in itself
I believe can
 explain why he had this onset of pain after
he was
 already working there, but during those four
months
 he really worked extremely heavy and I believe
that
 that could explain his pain when I saw him
again
 which was a little bit worse in intensity
than the one
 that he had before.
 (Supp. App. at 58).
 Dr. Guttman was directed to assume that Loftus
worked
 unusually long hours in January, February,
March and
 8
  
 April 1998 and was asked if he had an opinion
as to the
 cause of Loftus's back pain in April and
May of 1998
 through the time he saw him in August 1998.
Dr. Guttman
 responded:
 Well, the information you give me I was also
privy to
 review before. It just amplifies my impression
that
 there was an exertion of work. He worked
much more
 than the normal person would work in a day's
session,
 almost twice as much sometimes, and that
was
 certainly very stressful for his back. So
the symptoms
 that he reported to me and came to me was
of being
 similar were much worse and intense when
I saw him
 in June of `98 than compared to the ones
that I saw
 him in April of `97 at which time he had
hardly any
 symptoms and, in fact, I felt he could go
back to work
 without problems. I didn't feel so when I
saw him in`98
 and explanation for that, he over exerted
himself. He
 stressed his back at work over time and that
was the
 cause of his problems and it was ongoing.
 (Supp. App. at 65-66).
 As recited above, after Dr. Guttman's August
examination
 Loftus continued medical treatment and physical
therapy
 and was able to return to work on a restricted
basis in
 January 1999.***
 II. Administrative Proceedings
 In August 1999 the ALJ heard Loftus's claim
for workers
 compensation benefits under the Longshore
and Harbor
 Workers' Compensation Act, as amended 33
U.S.C.S 901,
 et seq. (the "Act"). The parties to the proceeding
were the
 claimant, Loftus; the earlier employer, SSI;
and the
 subsequent employer, DRS. Of the four issues
before the
 ALJ, only one is the subject of the present
appeal, i.e.,
 _________________________________________________________________
 *** The portion of the testimony of Dr. Bong
Lee included in the record
 contributes little to resolution of the principal
issue in this case. In Dr.
 Lee's opinion the cause of Loftus's disability
was not due to a work
 incident or symptoms in September 1996 but
is due to his pre-existing
 back condition. This pre-existing back condition
would also be the cause
 of each subsequent flare up. (Supp. App.
15-76).
 9
  
 "[w]hich of the named Employers is responsible
for any
 compensation benefits awarded."****
 SSI asserted that Loftus suffered no work
related
 disability as a result of work Loftus performed
for it but
 that Loftus suffered a naturally occurring
degenerative
 spinal condition pre-existent to the September
1996
 manifestation of low back pain therefrom.
Alternatively SSI
 asserted that if Loftus was rendered disabled
by work
 related causes, such disability arose as
the result of a
 separate and discrete event of work overexertion
while in
 the employ of DRS between January and April
1998, thus
 placing liability for compensation benefits
upon DRS as of
 the May 20, 1998 manifestation of low back
pain and
 thereafter.
 DRS adopted SSI's first contention and alternatively
 urged that if Loftus were disabled from work
activity, it was
 his work activity at SSI, first manifested
by pain in
 September 1996 which exclusively placed liability
for
 compensation benefits solely upon SSI.
 The ALJ rejected SSI's and DRS's first argument
and
 concluded that Loftus was entitled to compensation
for
 total temporary disability for the periods
sought. As
 between SSI and DRS he found that SSI was
the employer
 responsible for all benefits awarded, stating:
 I find that the record evidence establishes
that
 Southern is the employer responsible for
benefits
 awarded herein. First, there is no evidence
that
 Claimant suffered from a severe back injury
or
 impairment or from back pain prohibiting
his work
 prior to the September 30, 1996 manifestation
of low
 back pain (See Tr. 25, 62). Second, Claimant's
back
 problems and same complaints of back pain
persisted
 throughout the time period subsequent to
September
 _________________________________________________________________
 **** In addition the ALJ had to determine
i) whether Loftus was entitled
 to compensation for total temporary disability
for the intermittent
 periods he was out of work between September
30, 1996 and January
 21, 1999, ii) whether Loftus was entitled
to compensation for temporary
 partial disability (loss of wage earning
capacity) after January 21, 1999
 and iii) Loftus's average weekly wage underlying
any compensation
 benefits awarded.
 10
  
 30, 1996 up to the present (Tr. 46; 105-6;
112-13).
 And Claimant promptly reported this back
pain to his
 foreman at that time (Tr. 31). Finally, the
more
 probative medical and lay evidence otherwise
 establishes that Southern is the employer
responsible
 for benefits.
 (App. at 17).
 In half a page the ALJ marshaled the evidence
he
 believed supported his conclusion. He rejected
SSI's
 contention that but for the four month period
of intensive
 work Loftus would not have been disabled
after late April
 1998 on the ground that "but for the initial
(September 30,
 1996) manifestation of back symptoms, Claimant
would not
 have suspended his work activities after
the April-May,
 1998 symptom flare-up". (App. at 17).
 The ALJ attached the greatest weight to Dr.
Lefkoe's May
 20, 1998 opinion that Loftus's back condition
in April-May
 1998 was caused by the original work injury
of September
 30, 1996. The ALJ further stated that Dr.
Lefkoe's
 deposition testimony "repeats this conclusion
even more
 firmly." (Id.)
 The ALJ acknowledged that "the episode of
extra heavy
 work exertion while Claimant was employed
at DRS in
 January through April 1998 may well have
furthered his
 low back pain," but he went on to state that"the
initial
 precipitant event of symptom manifestation
on September
 30, 1996 was the discrete event which ultimately
 eventuated and progressed to the final debilitating
event of
 late April - May, 1998 requiring the suspension
of work
 activity (and later necessitating the January,
1999 return to
 work at only a light daily job)." (Id.)
 SSI appealed to the Board the Decision and
Order of the
 ALJ finding it to be the responsible employer
for the period
 of temporary total disability from April
21, 1998 to January
 20, 1999. The Board concluded that the ALJ
applied
 erroneous legal principles and held that
as a matter of law
 DRS is liable for Loftus's temporary total
disability benefits
 for the period from May 1998 to January 20,
1999.
 The Board held that "[a]lthough the employer
at the time
 of an initial traumatic injury remains liable
for the full
 11
  
 disability resulting from the natural progression
of that
 injury, if claimant's subsequent employment
aggravates or
 accelerates claimant's condition resulting
in disability, the
 subsequent employer is fully liable." (App.
at 4). Phrased
 somewhat differently the Board also held
the law to be that
 "where claimant's work results in a temporary
exacerbation
 of symptoms, the employer at the time of
the work events
 leading to this exacerbation is responsible
for the resulting
 temporary total disability." (App. at 4).
 The Board found that the undisputed evidence
 established that Loftus's employment with
DRS, which
 included the four months of lengthy overtime,
aggravated
 Loftus's symptoms, resulting in increased
pain. This
 evidence included Dr. Guttman's, Dr. Lefkoe's
and Dr. Lee's
 opinions to that effect.
 The Board held that the ALJ misapplied the
law in that
 the test was not, as the ALJ ruled, that
Loftus"sustained
 a work-related injury on September 30, 1996,
and/or that
 his continued work activity aggravated his
low back
 impairment." (App. at 5).
 The Board further held that the ALJ misapplied
the law
 in holding that it was determinative that
"the initial
 precipitant event of symptom manifestation
on September
 30, 1996 was the discrete event which ultimately
 eventuated and progressed to the final debilitating
event of
 late April-May 1998 requiring the suspension
of work
 activity." (App. at 5).
 Based on what it found to be errors of law
the Board
 reversed the ALJ's finding that SSI is liable
for Loftus's
 period of temporary total disability benefits
from May 1998
 to January 20, 1999, holding that DRS is
the responsible
 employer for this period of disability as
a matter of law.
 III. Discussion
 We have jurisdiction of the petition to review
the Board's
 final order by virtue of Section 21(c) of
the Act, 33 U.S.C.
 S 921(c).
 Under the Act the Board is obligated to treat
the ALJ's
 findings of fact as "conclusive if supported
by substantial
 12
  
 evidence in the record considered as whole."
33 U.S.C.
 S 921(b)(3). Substantial evidence is "more
than a mere
 scintilla. It means such relevant evidence
as a reasonable
 mind might accept as adequate to support
a conclusion."
 Universal Camera Corporation v. NLRB, 340
U.S. 474, 477,
 71 S.Ct. 456, 459, 95 L.Ed. 456(1951).
 In reviewing the Board's decision this court
must
 ascertain i) whether the Board adhered to
the applicable
 scope of review, ii) whether the Board committed
any errors
 of law, and iii) whether the ALJ's findings
are supported by
 substantial evidence on the record as a whole.
Crum v.
 General Adjustment Bureau, 738 F.2d 474,
477 (D.C. Cir.
 1984).
 Both SSI and DRS agree that the law governing
the
 responsible employer in the case of multiple
traumatic
 injuries is set forth in Buchanan v. International
 Transportation Services, 33 BRBS 32 (1999),
aff 'd mem.,
 No. 99-70631 (9th Cir., Feb. 26, 2001). There
the Board
 stated:
 In determining the responsible employer in
the case of
 multiple traumatic injuries, if the disability
results
 from the natural progression of an initial
injury and
 would have occurred notwithstanding a subsequent
 injury, then the initial injury is the compensable
injury
 and accordingly the employer at the time
of that injury
 is responsible for the payment of benefits.
If, on the
 other hand, the subsequent injury aggravates,
 accelerates, or combines with claimant's
prior injury,
 thus resulting in claimant's disability,
then the
 subsequent injury is the compensable injury
and the
 subsequent employer is fully liable.
 Id. at 35.
 This is the law that the Board applied. It
noted, correctly,
 that "[i]f the conditions of a claimant's
employment cause
 him to become symptomatic, even if no permanent
harm
 results, the claimant has sustained an injury
within the
 meaning of the Act." The Board further noted,
correctly,
 that "where claimant's work results in a
temporary
 exacerbation of symptoms, the employer at
the time of the
 13
  
 work events leading to this exacerbation is
responsible for
 the resulting temporary total disability."
(App. at 3).
 Kelaita v. Director, OWCP, 799 F.2d 1308 (9th
Cir. 1986)
 is illustrative of the application of these
principles and
 bears a close parallel to the present case.
The claimant in
 that case suffered from a continuing shoulder
rotator cuff
 tear. He suffered a flare-up of pain which
interrupted his
 work while employed at Triple A. He voluntarily
quit Triple
 A in December 1974 and commenced work as
a machinist
 at General Engineering. There he suffered
another work
 interrupting flare-up of his arm. He filed
two claims for
 compensation. In the first he alleged cumulative
trauma
 injury to his right shoulder during employment
at Triple A.
 In the second he alleged an identical injury
during his
 employment at General.
 The ALJ found that the claimant's disability
resulted
 from continued use of his arm and that each
flare-up of
 pain represented cumulative trauma and aggravated
the
 underlying injury, resulting in each case
in a compensable
 injury.
 The Court of Appeals sustained the ALJ's conclusion
that
 because General was the employer during the
most recent
 aggravation, it should be held liable for
the disability
 stating:
 The last responsible employer rule is applied
to two-
 injury cases as follows:
 If, on the other hand, the [subsequent] injury
 aggravated, accelerated or combined with
claimant's
 prior injury, thus resulting in claimant's
disability,
 then the [subsequent] injury is the compensable
injury,
 and [the subsequent employer] is . . . responsible
. . .
 700 F.2d at 1311 (quoting Crawford v. Equitable
Shipyards,
 Inc., 11 BRBS 646, 649-50 (1979), aff 'd
sub nom.
 Employers National Ins. Co. v. Equitable
Shipyards, 640
 F.2d 383 (5th Cir. 1981)).
 The facts in the present case are almost identical
to those
 dealt with in Kelaita except that the underlying
injury
 resulting in periodic flare-ups involved
Loftus's continuing
 back condition rather than a continuing shoulder
 14
  
 condition. All the medical evidence confirmed
that Loftus
 suffered from chronic lumbar degenerative
disc disease.
 This resulted in two distinct flare-ups or
injuries. The first
 culminated in late September 1996 when the
back pain
 became so intractable that Loftus had to
stop work and
 undergo diagnosis and treatment. He recovered
sufficiently
 to return to work in December 1996. The underlying
 lumbar degenerative disc disease persisted
as was to be
 expected, requiring Loftus to resort to various
remedies
 from time to time to alleviate pain. However,
he was able to
 continue work, with occasional absences,
through all of
 1997 and on until May 1998 when he suffered
another
 flare-up, more serious than the first. The
flare-up required
 extensive treatment and Loftus was unable
to return to
 work until January 1999.
 It is DRS's contention that this was merely
a natural
 progression of the original injury rather
than the result of
 employment that aggravated or accelerated
Loftus's
 condition resulting in disability. The ALJ,
as the Board
 pointed out, did not address head-on the
critical issue
 whether the May 1998 episode aggravated or
accelerated
 claimant's condition. Rather his general
findings suggested
 that he was relying on erroneous legal principles
and his
 finding that Loftus's May 20, 1998 back condition
was
 caused by the original work injury of September
30, 1996
 was unsupported by any evidence.
 The ALJ gave a number of reasons for finding
that SSI is
 the employer responsible for benefits. He
stated that there
 is no evidence that Loftus suffered from
a severe back
 injury or impairment or from back pain prohibiting
his
 work prior to the September 30, 1996 manifestation
of low
 back pain and that "the initial precipitant
event of symptom
 manifestation on September 30, 1996 was the
discrete
 event which ultimately eventuated and progressed
to the
 final debilitating event of late April-May
1998." (App. at 17).
 As the Board pointed out in its decision,
however,"[t]he
 fact that the earlier injury was the `precipitant
event' is not
 determinative." (App. at 5). The determinative
question is
 whether Loftus's subsequent work aggravated
or
 exacerbated Loftus's condition first manifested
in
 September 1996.
 15
  
 Even the ALJ's own opinion concedes there
was an
 aggravation of the September 1996 injury.
In the section in
 which he awarded Loftus temporary total disability
he
 found a work-related injury on September
30, 1996"and/or
 that Loftus's continued work activity aggravated
his low
 back impairment" and that this conclusion
was"amply and
 preponderantly medically demonstrated in
this record."
 (App. at 16) (emphasis added). Further, the
ALJ refers to
 the April-May "flare-up" and concedes that"the
episode of
 extra heavy work exertion while claimant
was employed at
 DRS in January through April 1998 may well
have
 furthered his low back pain, the initial
precipitant event,
 etc. . . ." (App. at 17).
 The only medical evidence that might support
an
 inference that the May 1998 flare-up was
a continuation of
 the September 1996 flare-up is an opinion
stated in Dr.
 Lefkoe's May 20, 1998 report after he had
first examined
 Loftus in connection with the May 1998 flare-up.
He opined
 "[b]ased on all information available to
me, the cause of his
 present back condition still is the original
work injury of
 9/30/96." (App. at 40).
 The ALJ said that Dr. Lefkoe's opinion is
"the medical
 evidence to which I attach the greatest weight."
(App. at 6).
 In Dr. Lefkoe's deposition testimony, however,
he
 conceded that Loftus had not informed him
of the
 extraordinary number of hours he had worked
during the
 January through April 1998 period.
 Q. Did he advise you that he was working a
great deal
 of overtime sometimes 15, 16, 18 hour days?
 A. No, I was not aware of that . . . He just
told me
 that in April of 1998, his pain worsened
without any
 specific identifiable injury. . . That could
have
 aggravated his condition.
 Q. That would be aggravating his condition?
 A. That's correct.
 (Supp. App. at 16-17).
 After being referred to Loftus's testimony
concerning his
 long hours during the fruit season, Dr. Lefkoe
testified:
 16
  
 Q. If that's true, can we agree that that
heavy work
 aggravated his preexisting back problem?
 A. I think that that certainly could have
aggravated
 his preexisting back problem. (emphasis added)
 (Supp. App. at 36).
 Thus, given full information, Dr. Lefkoe discarded
the
 May 20, 1998 opinion upon which the ALJ relied
and
 revised it to express the view that Loftus's
January - April
 1998 working conditions "certainly could
have aggravated
 his preexisting back problem." His opinion
in this respect
 was consistent with the opinions of the other
medical
 experts, Dr. Guttman and Dr. Lee.
 IV. Conclusion
 The ALJ applied incorrect principles of law,
and his
 finding that the May 1998 flare-up was simply
a
 continuation of the September 1996 flare-up
was not
 supported by substantial evidence.
 We will deny the petition to review the Board's
reversal of
 the ALJ's finding that SSI is liable for
the May 1998 to
 January 20, 1999 period of benefits and to
review the
 Board's holding that DRS is the responsible
employer for
 this period of disability as a matter of
law.
 A True Copy:
 Teste:
 Clerk of the United States Court of Appeals
 for the Third Circuit
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