RESEARCH ARTICLE
Space Adaptation Back Pain: A Retrospective Study
Eric L. Kerstman, Richard A. Scheuring,
Matt G. Barnes, Tyson B. DeKorse, and Lynn G. Saile
KERSTMAN EL, SCHEURING RA, BARNES MG, DEKORSE TB, SAILE
LG. Space adaptation back pain: a retrospective study. Aviat Space
Environ Med 2012; 83:2–7.
Introduction: Back pain is frequently reported by astronauts during
the early phase of spaceflight as they adapt to microgravity. The epidemiology of space adaptation back pain has not been well defined. This
study aims to develop a case definition of space adaptation back pain,
determine its incidence, and assess the effectiveness of available treatments. Methods: Medical records from the Mercury, Apollo, ApolloSoyuz Test Project (ASTP), Skylab, Mir, International Space Station (ISS),
and Shuttle programs were reviewed. All episodes of in-flight back pain
that met the criteria for space adaptation back pain were recorded. Pain
characteristics, including intensity, location, and duration of the pain,
were noted. The effectiveness of specific treatments was also recorded.
Results: The incidence of space adaptation back pain among astronauts
was determined to be 52% (382/728). Most of the affected astronauts
reported mild pain (86%). Moderate pain was reported by 11% of the
affected astronauts and severe pain was reported by 3% of the affected
astronauts. The most effective treatments were fetal positioning (91%)
and the use of analgesic medications and exercise (primarily treadmill
and cycle ergometer), which were both 85% effective. Discussion: This
retrospective study examines the epidemiology of space adaptation back
pain. Space adaptation back pain is usually mild and self-limited. However, there is a risk of functional impairment and mission impact in cases
of moderate or severe pain that do not respond to currently available
treatments. Therefore, the development of preventive measures and
more effective treatments should be pursued.
Keywords: crewmembers, NASA, zero gravity environment, spine,
spinal lengthening, lumbar.
down tilt) with the same parameters during actual microgravity (4). The researchers concluded that back pain
in actual and simulated microgravity may result from
stretching of the spinal and/or paraspinal tissues until a
new spinal length is reached. In 2009, a retrospective
study evaluated in-flight musculoskeletal injuries
occurring throughout the U.S. space program (9).
However, cases of in-flight back pain related to space
adaptation were excluded from that study.
The main objective of this study was to determine the
incidence of SABP among astronauts in the U.S space
program. A case definition of SABP was developed to
facilitate the determination of this incidence. Additional
objectives of this study were to delineate the nature and
pattern of SABP, its treatment, and its operational impact. To accomplish these objectives, a comprehensive
analysis of astronaut mission medical records was
performed.
METHODS
All available mission records of astronauts in the U.S.
space program from the NASA Johnson Space Center
Flight Medicine Clinic were reviewed by the authors.
These records included mission summaries, flight surDelivered by Ingenta
to: ? preflight medical exams, postflight medical
geon logs,
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exams, and
postflight medical debriefs. All missions of
ACK PAIN IS frequently reported
by astronauts
in
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Aerospace
Medical
Association
the Mercury, Gemini, Apollo, Apollo-Soyuz Test Project
the early phase of spaceflight as they adapt to the
(ASTP), and Mir programs were included in the analymicrogravity environment (13,16). However, the epidesis. International Space Station (ISS) missions from
miology of space adaptation back pain (SABP) has not
Expedition 1 through Expedition 15 were included in
been well established. There have been few studies rethe analysis. All Shuttle missions from STS-1 through
garding SABP and the studies that have been performed
STS-122 were reviewed, with the exception of STS-51L
are of limited scope (14). The exact incidence of SABP
(Challenger) and STS-107 (Columbia). For most Shuttle
among astronauts is unknown. The pathophysiology and
missions, the postflight medical debriefs included a
operational impacts of SABP also are largely unknown.
standardized back pain questionnaire. If available,
In 1991, a retrospective review of the medical records
Shuttle medical debriefs were reviewed via electronic
of 58 Shuttle crewmembers was conducted by the Flight
data query. If electronic data were not available, paper
Medicine Clinic at NASA Johnson Space Center to determine the incidence of back pain during spaceflight
(16). Of the crewmembers, 68% had reported in-flight
From The University of Texas Medical Branch, Galveston, TX; NASA
back pain. To obtain additional information regarding
Johnson Space Center, Houston, TX; Dewitt Army Community Hospital/Wyle, Houston, TX; MSU/Wyle, Houston, TX; and Wyle Intethe nature of the reported in-flight back pain, pain quesgrated Science & Engineering, Houston, TX.
tionnaires were completed by 19 Shuttle payload speThis manuscript was received for review in July 2010. It was
cialists, a subset of the original 58 Shuttle crewmembers.
accepted for publication in September 2011.
Of the 19 payload specialists, 14 (74%) reported in-flight
Address correspondence and reprint requests to: Eric L. Kerstman,
M.D., Wyle Integrated Science & Engineering, 1290 Hercules, Housback pain.
ton, TX 77058; [email protected].
In 1994, a prospective bed rest study was performed
Reprint & Copyright © by the Aerospace Medical Association,
on eight subjects to compare back pain and spinal
Alexandria, VA.
lengthening during simulated microgravity (6° headDOI: 10.3357/ASEM.2876.2012
B
2
Aviation, Space, and Environmental Medicine x Vol. 83, No. 1 x January 2012
SPACE ADAPTATION BACK PAIN—KERSTMAN ET AL.
records were reviewed. All data for ISS missions were
obtained via the Private Medical Conference Tool, an
electronic method for documenting in-flight private
medical conferences between crewmembers and flight
surgeons.
A case definition was developed to determine the episodes of in-flight back pain that would be considered
SABP. The following criteria were used to define cases of
SABP:
relation structure. Associations with a P-value , 0.05
were considered significant. Odds ratios (OR) with 95%
confidence intervals (CI) are presented. The statistical
analysis for this paper was generated using SAS 9.1 software (SAS Institute Inc., Cary, NC).
RESULTS
A total of 772 astronaut flights were reviewed.
Depending on the SABP attribute considered, the number of respondents varied. Within these 772 astronaut
1. symptoms develop within the first 5 d of spaceflight;
flights, 382 cases of SABP were noted. In 346 of the astro2. symptoms are not precipitated by an injury; and
3. symptoms are not attributed to prolonged sitting on the launch
naut flights, a response of no back pain was noted, and
pad.
no response was noted in 44 of the astronaut flights. Of
those 44 no responses, 30 were from STS missions.
Only episodes of in-flight back pain that met all three of
Therefore, 382 positive responses of SABP were noted
the above criteria were considered cases of SABP.
among a total of 728 responders. Based on the above
Based on our review of the mission records, the foldata, the incidence of SABP among astronauts in the
lowing additional characteristics were determined to
U.S. space program was determined to be 52% (382/728).
further delineate SABP:
The incidence of SABP among male astronauts was de1. symptoms are usually mild or moderate;
termined to be 52% (323/627) and the incidence of SABP
2. symptoms are usually localized to the lumbar region;
among female astronauts was determined to be 58%
3. symptoms are usually described as an ache or stiffness;
(59/101). The incidence of SABP was determined to be
4. symptoms typically occur during the sleep period;
54% (126/233) among astronauts under the age of 40
5. neurological symptoms (radicular pain, numbness, tingling) are
absent; and
and 52% (256/495) among astronauts age 40 and above.
6. symptoms tend to improve or resolve with the use of one or more
In terms of the location of pain, of those astronauts who
of the following interventions: nonopioid analgesics, nonsteroireported location, 86% (277) reported lumbar pain, 12%
dal anti-inflammatories, loading of the spine, or bending the
knees to the chest.
(40) reported thoracic pain, and 2% (6) reported cervical
pain.
All reported in-flight back pain that developed within
Table I provides a summary of the incidence of SABP.
the first 5 d of spaceflight and that was not associated
The percent of responders and the availability of a back
with an injury was considered to be SABP. A report of
pain questionnaire for each spaceflight program are also
back awareness or discomfort was considered to be a
summarized in the table. Of those astronauts who remild form of back pain. Back pain attributed to proported the intensity of their back pain, 86% (247) relonged sitting in a recumbent position on the launch pad
ported mild pain, 11% (32) reported moderate pain, and
that resolved in microgravity was not considered to be
3% (10) reported severe pain. Table II provides a sumSABP.
mary of
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Ingenta
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? reported intensity of SABP. The percent of
Since an astronaut had the potential to develop SABP
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on each flight, multiple cases of SABP
were possible
for Medical
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naire are
also summarized in this table.
astronauts who flew more than one mission. However,
Fig. 1 depicts the flight day prevalence of SABP. SABP
there was a maximum of one case of SABP per flight for
was present in the early phase of spaceflight, with peak
each astronaut since multiple days of in-flight back pain
prevalence on flight day 2. None of the astronauts rewere considered as one case. To delineate the nature and
ported SABP after flight day 12 and only two astronauts
pattern of SABP, multiple descriptive factors regarding
reported SABP after flight day 10. Fig. 2 displays the
in-flight back pain symptoms were noted. These factors
flight day on which the onset of SABP occurred. In most
included the pain intensity, quality, location, and tempoSABP cases, the initial onset of symptoms was within
ral component. Additional data collected included the
in-flight treatments attempted and the effectiveness of
these treatments. Demographic data consisted of crewTABLE I. SABP INCIDENCE SUMMARY.
member role (commander/pilot, mission specialist/
Spaceflight
SABP
Percent
Back Pain
payload specialist/flight engineer), gender, age, spaceProgram
Incidence (%)
Responding
Questionnaire
flight vehicle, and spaceflight experience (number of
previous flights). Other factors considered included preMercury
0
95
No
Gemini
0
186
No
flight history of back pain and previous episodes of
ASTP
0
100
No
SABP.
Skylab
0
100
No
Generalized estimating equation (GEE) logistic reApollo
9
97
No
gression models were used to identify risk factors for
Mir
31
65
No
ISS
39
50
No
SAPB and determinants of missing data. GEEs were
STS
58
95
Yes
used to account for correlation between responses from
the same astronaut. It was assumed that the correlation
ASTP 5 Apollo-Soyuz Test Project; ISS 5 International Space Station;
STS 5 Space Shuttle.
within astronaut clusters followed an exchangeable corAviation, Space, and Environmental Medicine x Vol. 83, No. 1 x January 2012
3
SPACE ADAPTATION BACK PAIN—KERSTMAN ET AL.
TABLE II. SABP INTENSITY SUMMARY.
SABP Intensity
Spaceflight Program
Apollo
Mir
ISS
STS
Mild (%)
Moderate (%)
Severe (%)
Percent Responding
Back Pain Questionnaire
100
100
100
85
0
0
0
11
0
0
0
4
33%
25%
26%
74%
No
No
No
Yes
ISS 5 International Space Station; STS 5 Space Shuttle.
the first 2 d of spaceflight. Of those astronauts who retime flyers had greater odds of reporting SABP than asported the initial day of their symptoms, 126 astronauts
tronauts on subsequent flights (OR 1.6, 95% CI 1.2–2.1).
reported onset of symptoms within the first 2 d. Only 12
Among astronauts who flew more than one mission, the
astronauts reported onset of symptoms after flight day
odds of SABP on the first mission was higher than on
2. Of those astronauts who reported the time of day that
subsequent missions (OR 1.7, 95% CI 1.3–2.4).
their back pain was present, 75% reported symptoms
Fig. 4 shows the incidence of SABP related to the
only at night or during the sleep period. There were 10%
number of missions flown. Of the 772 astronauts, data
who reported symptoms only during the day and 15%
on history of lower back pain and SABP was available
reported symptoms during both the day and night.
for 441 (data not shown). Of this subset of astronauts,
In terms of the treatment of SABP, the most effective
the odds of SABP among astronauts who reported a histreatments were bending the knees to the chest (91% eftory of preflight back pain was marginally higher than
fective) or stretching the lumbar spine (90% effective). It
among astronauts who reported no history of preflight
should be noted that crewmembers who reported that
back pain (OR 1.4, 95% CI 1.0–2.0).
stretching of the spine was an effective treatment deOf the 772 charts, 44 had no response for back pain.
scribed the stretching as bringing their knees to their
Significant predictors of missing data were vehicle type
chest (fetal positioning). The next most effective treatand crew role (data not shown). The percent of missing
ments, not exclusive of each other, were the use of analdata was greatest for Capsules (19.35%) followed by Stagesic medication (ibuprofen or acetaminophen) and
tion (5.71%) and Shuttle (4.44%) (P , 0.001). The comexercise (primarily treadmill and cycle ergometer). Both
mander or pilot role had 8.95% missing data compared
were 85% effective. Spinal loading (e.g., standing on the
to 3.49% in other roles (P 5 0.0017). Table III provides a
treadmill with the harness attached) also was reported
summary of the above statistical analysis.
by several astronauts as effective in relieving SABP.
Although there were no findings that crewmembers’
None of the affected astronauts required the use of opiability to perform mission tasks were impacted from
oid analgesics or muscle relaxants.
SABP, there were multiple reports of associated sleep
Fig. 3 demonstrates SABP occurrence by vehicle.
Sky-by Ingenta
disturbance.
Delivered
to: ? Since sleep disturbance may result in faIP: 5.10.31.210
On:re-Mon,tigue
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lab, ASTP, Gemini, and Mercury astronauts
had no
impaired
cognition (15), SABP has the potenMedical
Association
ports of SABP. The incidence of SABPCopyright:
varied in Aerospace
relation
tial to indirectly
impact spaceflight operations.
to the spaceflight vehicle, crew role, and first flight staDISCUSSION
tus. When compared to astronauts in capsules (Apollo,
Gemini, Mercury, and ASTP), Shuttle (STS) and station
The results of this study confirmed many of the find(ISS, Skylab, ASTP, and Mir) astronauts had increased
ings of previous studies of SABP. SABP was found to be
odds of reporting SABP (Shuttle OR 24.5, 95% CI 6.8–
a frequent complaint of astronauts during the early
87.9; Station OR 5.2, 95% CI 1.2–21.6).
Mission specialists, payload specialists, and flight engineers had increased odds of reporting SABP compared
to commanders and pilots (OR 1.7, 95% CI 1.2–2.5). First
Fig. 1. Distribution of flight days that SABP was reported.
4
Fig. 2. The distribution of the initial day that SABP was reported.
Aviation, Space, and Environmental Medicine x Vol. 83, No. 1 x January 2012
SPACE ADAPTATION BACK PAIN—KERSTMAN ET AL.
reported the maximum discomfort on flight day 1
through flight day 6 (16).
Flight data from Apollo and Skylab indicated that the
spine lengthens 4 to 7 cm in microgravity (1,12). Bed rest
studies have confirmed a similar but smaller increase in
spinal lengthening during 6° head-down tilt (4). Bed rest
subjects have exhibited a peak increase of 2.1 6 0.5 cm in
height by day 3 of head-down tilt (4). Average back pain
intensity among these same subjects increased from zero
during the baseline control period to 2.3 6 0.4 (0-5 scale)
on days 1 through 3 of head down tilt. Only two subjects
reported any pain after day 9 of bed rest and during recovery. These findings appear very similar to the pattern
of SABP found in our study. This further supports the
Fig. 3. Incidence of SABP broken down by vehicle.
hypothesis that SABP is related to spinal lengthening
during exposure to microgravity (3,4,6,8). However, the
specific mechanism and spinal structures responsible
phase of spaceflight with an incidence of 52%. Previous
for SABP require further investigation.
studies limited to Shuttle astronauts reported incidences
Most astronauts with SABP reported symptoms durof in-flight back pain of 68% and 74% (16). The lower
ing the sleep period (85%). This apparently was due to
incidence of 52% determined by our study may be due
the fact that many astronauts reported that they were
to our case definition of SABP. For the purpose of this
unable to bring their knees to their chest in the sleep
study we did not consider back pain symptoms that
compartment, which was the most effective treatment of
were precipitated by injury or prolonged sitting on the
SABP. This finding supports a design requirement in fulaunch pad, or that developed after flight day 5 as SABP.
ture space vehicles for a sleep compartment that accomAnother factor contributing to the lower incidence of
modates a sleep position of knees bent to the chest.
SABP found in our study may be that the incidence of
Neither the current Human Integration Design Hand52% was not limited to Shuttle astronauts. When limitbook (HIDH) nor the Man System Integration Standards
ing our findings to Shuttle astronauts, the incidence of
address this requirement.
SABP was 58%. An additional factor explaining the difShuttle astronauts had the highest incidence of SABP.
ference between our incidence and other studies may be
This may have been due to the fact that Shuttle crewrelated to our larger sample size compared to previous
members often reported that they were unable to obtain
studies.
a comfortable position (knees bent to chest) within their
Most astronauts (85%) affected by SABP reported
sleep compartments. The use of a standardized postmild symptoms. This finding was consistent with the
flight questionnaire addressing in-flight back pain also
findings of previous studies (16). Most of the affected
may have contributed to the higher incidence of SABP
Delivered
to: ?
astronauts (86%) reported symptoms localized
to theby Ingenta
Shuttle
astronauts.
IP: 5.10.31.210 On: Mon, among
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lower back. This finding also was consistent
with
previ- Medical
The incidence
of SABP was 49% among commanders
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ous studies (16).
and pilots. The incidence of SABP was 55% among misSABP was found to be present in the early phase of
sion specialists, payload specialists, and flight engineers.
spaceflight (flight day 1 to flight day 12), with a peak
The lower incidence of SABP among commanders and
prevalence on flight day 2. Most SABP cases had an
pilots may be due to the fact that they were more likely
initial onset within the first 2 d of spaceflight. These
to be repeat fliers. Of commander/pilot flights, 63%
findings were consistent with previous studies, which
were repeat flights, whereas 52% of mission specialist
flights were repeat flyers. As noted below, the incidence
of SABP was lower among repeat fliers.
First time flyers had a 58% incidence of SABP, whereas
repeat flyers had a 48% incidence of SABP. This difference was statistically significant. This finding was consistent with a previous study of space motion sickness
(SMS) among Space Shuttle astronauts (2). The incidence
of SMS among astronauts on their first Shuttle flight was
reported as 67%, while the incidence of SMS among astronauts on their second flight decreased to 46%. Although this difference was not statistically significant,
the sample size of this study was relatively small.
Although the incidence of SABP among female astronauts (58%) was greater than the incidence of SABP
among male astronauts (52%), most of the female astroFig. 4. Percentage of flyers reporting SABP based on the number of
nauts flew Shuttle missions only. As noted above, the
missions flown.
Aviation, Space, and Environmental Medicine x Vol. 83, No. 1 x January 2012
5
SPACE ADAPTATION BACK PAIN—KERSTMAN ET AL.
TABLE III. ANALYSIS OF EXPLANATORY FACTORS FOR SABP.
95% Confidence Interval
Variable
Age Category
40 or over
, 40
First Flight
Yes
No
Sex
Male
Female
Position
FE/MS/PS*
Commander/Pilot
Vehicle Type
Shuttle
Station
Capsule
Percent with SABP (N 5 728)
Odds Ratio
Lower Bound
Upper Bound
P-Value
54.1
51.7
0.8
0.6
1.1
0.15
58.1
48.3
1.6
1.2
2.1
0.0016
51.5
58.4
0.7
0.4
1.2
0.16
54.6
49.1
1.7
1.2
2.5
0.0042
57.7
24.2
4.0
24.5
5.2
6.8
1.2
87.9
21.6
, 0.0001
0.025
* Flight engineers, mission specialists, and payload specialists.
incidence of SABP among astronauts on the Shuttle was
disturbance. These cases of SABP may cause indirect
mission impact by resulting in a decrement in astronaut
found to be higher (58%) than the incidence of SABP
performance due to potential daytime somnolence or
among astronauts on all vehicles (52%). The incidence of
SABP among male and female astronauts on Shuttle
fatigue. Since astronauts are required to perform complex
tasks requiring high levels of cognitive function, even
missions was 57% and 59%, respectively. Therefore, the
mild cognitive impairment could result in the inability
higher incidence of SABP among female astronauts
to successfully complete these tasks (15). In addition,
compared to male astronauts may have been because
the potential adverse side effects of anti-inflammatory
most female astronauts flew on Shuttle missions only.
medications, such as gastrointestinal bleeding, could reTwo other parameters that were considered were assult in severe illness and subsequent mission impact.
tronaut age and history of preflight back pain. Astronaut
Several limitations of this study deserve note. A major
age did not appear to affect the incidence of SABP, as the
limitation is its retrospective nature. Since all data were
incidence of SABP was noted to be similar among astroobtained from past mission records, there is missing
nauts under age 40 (54%) and above age 40 (52%). Astrodata, as well as the potential for misinterpretation of
nauts who reported a history of preflight back pain had
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data.
To minimize data misinterpretation, a
a greater incidence of SABP (65%)IP:than
those
who
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case defiAssociation
nition of SABP was developed. In addition, all
ported no history of preflight back pain
(52%). Since
the
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raw data were reviewed by clinicians familiar with the
mechanism of SABP has not been clearly delineated, it is
diagnosis and treatment of back pain. However, the podifficult to determine if there is any correlation between
preflight back pain and SABP. A recent study found an
tential to underestimate the true incidence of SABP exincreased incidence of herniated disc among astronauts
ists for two reasons. First, the Shuttle Program was the
only one to use a postflight questionnaire to address inpostflight (5). Preliminary analysis revealed no correflight back pain. Second, since many astronauts may
lation between SABP and these postflight herniated
have had concerns regarding future flight assignments
discs.
if they reported any medical problems, they may have
Analgesic medications were frequently used by astronauts to treat SABP. This finding was consistent with
been reluctant to report in-flight symptoms such as back
previous studies (7,15). The use of analgesic medications
pain. For example, based on our review of available
Apollo mission records, a 9% incidence of SABP was
(primarily ibuprofen) was effective in the treatment of
noted among Apollo astronauts. However, the Apollo
SABP. Fetal positioning, exercise, and spinal loading
Medical Operations Summit held in 2006 noted that
were also noted as effective treatments for SABP. Degreater than 70% of the Apollo crewmembers had increased spinal lengthening may be a common mechaflight back pain (10).
nism of these treatments.
Most SAPB cases were mild, self-limited, or responIn conclusion, in-flight back pain has been reported
by astronauts since the Apollo missions, but no extensive to available treatments. There were no reports of
sive epidemiological studies of this condition have been
operational impact or inability to perform assigned misperformed. This study was a comprehensive retrospecsion tasks related to SABP. However, severe cases of
tive analysis of in-flight back pain related to adaptation
SABP have the potential to cause direct operational imto the microgravity environment of spaceflight. To compact. Since most SABP cases occurred during the sleep
plete this study, a case definition of SABP was developed.
period, there were many reports of associated sleep
6
Aviation, Space, and Environmental Medicine x Vol. 83, No. 1 x January 2012
SPACE ADAPTATION BACK PAIN—KERSTMAN ET AL.
Tyson B. DeKorse, M.D., MSU/Wyle, Houston, TX; and Lynn G. Saile,
The incidence of SABP among astronauts in the U.S.
M.S., Wyle Integrated Science and Engineering, Houston, TX.
space program was determined for missions dating back
to the initial Mercury missions. The nature and pattern
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Copyright: Aerospace Medicaland
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ACKNOWLEDGMENT
The authors would like to thank Dr. Mary Freire De Carvalho for her
contribution to the statistical analysis of this study.
Authors and affiliations: Eric L. Kerstman, M.D., M.P.H., The
University of Texas Medical Branch, Galveston, TX; Richard A.
Scheuring, D.O., NASA Johnson Space Center, Houston, TX; Matt G.
Barnes, M.D., Dewitt Army Community Hospital/Wyle, Houston, TX;
Aviation, Space, and Environmental Medicine x Vol. 83, No. 1 x January 2012
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