04Wfggg A RS TEST T0 EVALUATE THE PHYSICAL CAPACrTY N OF PERORMING L-1 ANTI-G STRAINING MANEUVERS WEN-WCWHOU, M.D. WRGHSMUNYMTYDTIC DATR)N, 01NO045435 ELECTE S FEB 0 7.18311 SEPTEMBER 1988 FINA REP ORTFOR PER 100 AUGUST 1987 -A UGUST1988 Approved for public release; dstrbution is unlimited. HARRY G. ARMVSTRONG AEROSPA CE MEDICAL RESEARCH LABORA WRY Wr"MA SYSTEMS DIVSION AIR FORCE SYSEMS COMMAND WRJGH1:PATERSON AIR FORCE BASE, OHIO 45433-6573 89 2 6073
Transcript
04Wfggg
A RS TEST T0 EVALUATE THE PHYSICAL CAPACrTYN OF PERORMING L-1 ANTI-G STRAINING MANEUVERS
WEN-WCWHOU, M.D.
WRGHSMUNYMTYDTICDATR)N, 01NO045435 ELECTE
S FEB 0 7.18311
SEPTEMBER 1988
FINA REP ORTFOR PER 100 AUGUST 1987 -A UGUST1988
Approved for public release; dstrbution is unlimited.
HARRY G. ARMVSTRONG AEROSPA CE MEDICAL RESEARCH LABORA WRYWr"MA SYSTEMS DIVSION
AIR FORCE SYSEMS COMMANDWRJGH1:PATERSON AIR FORCE BASE, OHIO 45433-6573
89 2 6073
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TECHNICAL REVIEW AND APPROVAL
AAMRL-TR-88-047
The experiments reported herein were conducted according to the "Guide for the Care and Use ofLaboratory Animals," Institute of Laboratory Animal Resources, National Research Council.
The voluntary informed consent of the subjects used in this research was obtained as required by AirForce Regulation 169-3.
This report has been reviewed by the Office of Public Affairs (PA) and is releasable to the NationalTechnical Information Service (NTIS). At NTIS, it will be available to the general public, includingloreign nations.
This technical report has been reviewed and is approved for publication.
FOR THE COMMANDER
4 ESW BRINKLEYActing DirectorBiodynamics and Bioengineerlng DivisionArmstrong Aerospace Medical Research Laboratory
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A Stress Test to Evaluate the Physical Capacity of Performing L-1 Anti-G Straining Maneuvers,12. PERSONAL AUTHOR(S)
WEN-YAW CHIOU, M.D.
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0; Duty Cycle Anti-G Straining Maneuvers_ fO/419. ABSTRACT (Continue on reverse if necessary and identify by block number)To evaluate the physical capacity of performing L-1 anti-G straining maneuvers (AGSM), 9subjects participated in stress test protocols which were designed to use repetitive AGSM (exercise on the ground. Physiological responses of oxygen uptake (VO3, minute pulmonaryventilation (VE), respiratory exchange ratio (RER) and heart rate (HR were determined forsteady state exercise at AGSM duty cyclEs cf 2,, 215%, 33% and 50%. Thesc exercise loadsconsisted of repeated 5-second L-1 AGSM maneuvers and were each followed by a 20, 15, 10,5-second rest period, respectively. A total of 36 min progressive intensity (with respectto duty cycle), discontinuous protocols were used where exercise at each duty cycle was 4min in duration followed by a 5 min rest interval. Physiological responses were found tobe fairly linear in relationship to duty cycles.- Another total 8 min progressive inten-sity, continuous protocol with 2 min exercise at each duty cycle, but no rest interval, wasalso tested. Since the continuous protocol takes less time and the results from bothprotocols show no significant difference (p n1.05), it is reascnable to choose a continuous
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protocol instead of a discontinuous one. All nine subjects repeated the continuous proto-col and no significant differences (p10.05) were found between the test and retest for anypeak values of the monitored physiological variables at 50% duty cycle. This AGSM contin-uous protocol was found to be reliable. Individual's endurance time of AGSM performancewas defined by the self-exerted exercise duration at 50% duty cycle of continuous protocoluntil the VO dropped 40% of his peak value. The individual's physical capacity forperforming AGSM can be objectively evaluated by the strength (peak output) and endurance(time to 40% fatigue) aspects of this continuous stress test. The higher peak VO achieved,the greater was considered the aerobic energy output for AGSM performance. This is depend-ent upon the muscle mass available, the condition of the muscles, as well as cardiopul-monary fitness of the individual. The longer endurance time for the ground test, thelonger tolerance duration will most likely be obtained during actual centrifuge G-forcetesting. Therefore, the described AGSM stress test on the ground may be a convenient,inexpensive and useful tool to objectively evaluate the physical capacity of individualsfor performing AGSM. Such a test may be used for pilot candidate screening prior tocentrifuge and aircraft G-tolerance testing. Future studies need to correlate results ofthis ground test with centrifuge G-force tolerance.
ii
PREFACE
This study was supported by the Laboratory Director's Fund of the
Armstrong Aerospace Medical Research Laboratory, Wright-Patterson Air
Force Base, Ohio 45433-6573. The utilization of humans for this
project was authorized by the Air Force Human Use Committee (AAMRL
Protocol 88-03 ), and by the Institutional Review Board Committee
at Wright State University (Protocol HSP#704). This report is a
dissertation submitted to Wright State University in partial
fulfillment of the requirements for the degree of Master of Science
in Aerospace Medicine.
ACKNOWLEDGEMENTS
There are many people that the author wishes to thank for making
this project a successful experience. They include: Dr. Robert
Van Patten for providing me invaluable guidance for this study
opportunity, Dr. Satya Sangal for his advice in analyzing the
statistics, and Dr. Stanley Mohler for his encouragement and support.
I especially would like to express my appreciation to my major advisor,
Dr. Roger Glaser, who provided me with the facilities, instrumentation,
as well as his knowledge, expertise and advice. I am also grateful to
TSgt. Lloyd Tripp and those subjects who contributed their time and
effort to make this study possible. I would also like to express my
appreciation to Steve Collins, M.S. and Debbie Hendershot, M.S. for
their help in teaching me to operate the scientific instrumentation
used for this study, to Dr. Steve Figoni who contributed his research
expertise in exercise physiology, to Janet Ponichtera who helped me to
produce the graphs, and to Michelle Hackett for her excellent typing.
; ["!+
I . .. .
. i. m HIIlKli H i Imm|I IN[] Iil
TABLE OF CONTENTS
CHAPTER PAGE
I. INTRODUCTION.....................................................I
II. METHODS......................................................... 3
12. A Comparison of Pre- and Post-Exercise Mean Blood Lactate
Between the Protocols ......................................... 16
13. A Comparison of Mean Endurance Time at 50% Duty Cycle Between
Trial I and 2 Continuous AGSM Stress Test ..................... 17
LIST OF APPENDICES
APPENDIX PAGE
A. Subject Descriptive Data ..................................... 24
B. Discontinuous AGSM Stress Test Data .......................... 25
C. Data of Peak Values for Various Physiological Variablesat 50% Duty Cycle in the AGSM Stress Tests ................... 28
V
I. INTRODUCTION
Today's high performance aircraft with high thrust-to-weight
ratios and low wing loading are more maneuverable than ever before.They are capable of maintaining +Gz acceleration longer and at higherlevels (1,2,7). Under this condition, physiological tolerances ofhumans to acceleration can be easily exceeded, resulting in G-inducedloss of consciousness due to insufficient cerebral blood flow(13,14,15). In order to protect the pilot against the effects of +Gzacceleration, several protective techniques and devices have beendeveloped. These include L-I/M-I anti-G straining maneuver (AGSM),
positive pressure breathing, anti-G suit, reclined seat, etc. The L-1AGSM is one of the major protective techniques which, when properly
performed, provides approximately 2 +Gz additional physiologicalprotection as compared to the relaxed condition with or without ananti-G suit (8). The L-1 AGSM consists of coordinated vigorousmuscular tension of the abdomen and the extremities combined with
simultaneously applied forced expiratory thrust upon the completelyclosed glottis. It is believed that maximized isometric contractionand intrathoracic pressure during the straining maneuver directlycontribute to its greatest G-protection (26,27). However, frequentrepetition of the AGSM, as required during actual aerial combatmaneuvers (ACMs), can lead to a pilot's exhaustion and limit his AGSM
performance (5,6). Thus, both strength and endurance for performing
this maneuver are crucial for a pilot's suc-ess in operational ACMs.
There is much evidence to indicate a regime of weight trainingwill lead to an increase in G-tolerance as determined by centrifugetesting (17-24). The assumption of these studies is that resistance-type exercise training can enhance the strength and endurance ofmuscular contraction in performing AGSM, which thus increases theG-tolerance level and duration. However, no published study actually
uses direct measurement to assess the effects of physical training onthe capacity for performing AGSM at I +Gz. Also, there is no publishedstudy estimating the direct effect of AGSM performance at 1 +Gz on
actual G-tolerance. In order to quantify these effects, a laboratorytest that can objectively evaluate the physical capacity for performingAGSM is necessary. It would also be desirable to evaluate ifimprovements in AGSM performance actually increase +Gz tolerance on the
centrifuge.
It has also been suggested that measurement of variousphysiological indices of exercise in order to evaluate an individual's
capacity for executing the fatiguing straining maneuvers be used as aselection procedure for high-performance aircraft pilots (23).Therefore, it would be very useful to develop a simple exercise stresstest to predict +Gz tolerance of pilots based upon their physicalcapacity for performing the AGSM. Although there are many widelyaccepted protocols for physical evaluation using treadmill, bicycleergometer, arm crank, rowing, swimming, and other exercise tasks, thereis no available protocol that can be used for AGSM exercise testing.
1
In order to apply the concepL of exercise specificity (21), a gradedexercise stress test using the actual AGSM i.,2ds to be designed andvalidated for pilot evaluation.
The purpose of this study was to develop a valid and reliableexercise stress test protocol using the L-1 AGSM in order toobjectively evaluate and classify individuals' capability forperforming the AGSM. Th.e results of such a test may be applicable forthe selection of high-performance aircraft pilots who can tolerate highoperational G-force.
2
IT. METHODS
1. Subjects
Nine healthy subjects (eight males and one female) from the
sustained acceleration stress panel at Wright-Patterson Air Force Basevolunteered to participate in this study. All of the them have
experience performing L-1 maneuvers. The physical characteristics(X+SD) of the subjects were: age, 27.7+3.4 years; height, 172.o+
9.2 cm; and weight, 72.4+16.0 kg (Table 1; raw data in Appendix A).
Each subject was informed as to the purpose of the study, their extentof involvement, any known risks, and their right to terminateparticipation at will. Each expressed understanding by signing a
statement of informed consent. The protocols and procedures used forthis study have been approved by the Institutional Review Board (IRB)
of Wright State University, and the Human Use Review Committee ofArmstrong Aerospace Medical Research Laboratory.
TABLE I
ANTHROPOMETRIC CHARACTERISTICS OF THE SUBJECT POPULATION (n=9)
A "pilot's seat" used in another experiment (23) was adjusted to a
seat back angle of 30 degrees, spine-to-thigh angle of 105 degrees andthigh-to-calf angle of 105 degrees in order to simulate the F-16 seat
(Figure 1). Subjects were seated in the chair with their backs againstthe seatback and restrained in this fixed position by a lap belt. They
were also instructed not to generate any external net force with theirlegs during the L-l maneuver.
AGSM stress testing, hereafter also called exercise, consisted
of repetitive performance of the L-1 maneuvers with pt-og r- ss ive I yincreasing duty cycle (ratio of the duration of L-l maneuver to L-1
3
B.
Figure 1. A: Experimental set-up of "Pilot's Seat"
and metabolic cart.
B: Scene of AGSM stress test.
maneuver plus rest) to increase exercise intensity. Four differentduty cycles, analogous to incremental exercise load levels, wereestablished as: 20%, 25%, 33% and 50%. Thus, to perform these dutycycles, a 5-second maximal effort L-I maneuver was followed by restperiods of either 20, 15, 10, 5 seconds, respectively.
There were two stress test protocols in this study: i) Theprogressive intensity, discontinuous protocol (Figure 2) included 5minutes of rest before exercise, 4 minutes of exercise at each dutycycle of 20%, 25%, 33% and 50% with 5 minutes rest intervals betweensubsequent intensity levels, and another 5 minutes of rest afterexercise terminated to evaluate recovery patterns. 2) The progressiveintensity, continuous protocol (Figure 3) included 5 minutes of restbefore exercise, 2 minutes of exercise at each duty cycle of 20%, 25%,33% and 50% without rest interval (the final 50% duty cycle lasteduntil subject fatigued or when V02 dropped 40% below its peak value at50% of duty cycle), and another 5 minutes of rest after exercise toevaluate recovery patterns. The exercise duration spent above 60% ofone's peak oxygen uptake at 50% duty cycle of continuous protocols wascounted as his endurance time.
50 -
40
30300
20
o 10
Rest
I I I I I I I I
0 5 10 15 20 25 30 35
t Time (min)Start
exercise
Figure 2. Discontinuous AGSM stress test protocol5
50 -
40
8 30
5, 2000
Rest
0 5 10 15
1 Time (min)Start
exercise
Figure 3. Continuous AGSM stress test protocol
3. Physiological Monitoring
Peak values of oxygen uptake (V02, ml/kg/min), minute pulmonaryventilation (VE, I/min) and respiratory exchange ratio (RER, VCO 2/VO2)at each duty cycle of discontinuous AGSM stress test and at 50% dutycycle of continuous AGSM stress test were calculated by automatedopen-circuit spirometry (Metabolic Cart, System 2001, Medical GraphicsCorp., St. Paul, MN) during the stress tests. Pulmonary functiontesting (Table 1), including slow vital capacity (SVC), inspiratorycapacity (IC), forced vital capacity (FVC), forced expiratory volume inthe first second (FEVI), maximal voluntary ventilation (MVV), wasperformcd with System 1070 of the same instrument. Lactateconcentration in capillary blood (LA, mmol/l) was determined at restand three minutes following maximal exercise from a fingertip bloodsample (model 23L lactate analyzer, Yellow Springs Instrument Co. Inc.,Yellow Springs, OH). Bipolar surface electrodes were attached on thesternum area and the left 5th intercostal space for monitoring theheart rate.
6
4. Experimental Procedures
On a separate day prior to experimental testing, all subjects were
familiarized with the testing procedures and the instrumentation forphysiological determinations. Pulmonary function and general resting
data were obtained. Each subject was observed by the investigator forcorrect performance of the L-1 maneuvers before actual testing was
conducted. All subjects were instructed not to engage in strenuousphysical activity before each testing day. On the morning of testing
days, resting cardiopulmonary data were obtained after each subjectremained seated quietly in the "pilot's seat" for 5 minutes. Thesedeterminations were continuously monitored during the entire stresstest with the subjects breathing through a mouthpiece and a breathingvalve which directed expired gases to the metabolic cart. EKG
electrodes were placed on the chest for heart rate determination. Theinvestigator always encouraged the subject to exert maximal effort
during the L-1 maneuvers. Exercise was terminated by either fatigue orany condition which indicated high risk to the subject. Blood lactateconcentration was determined at 1 minute before the start of exerciseand 3 minutes after the end of 50% duty cycle exercise in bothprotocols. The discontinuous and continuous excrcise protocols were
performed on separate days. The continuous exercise stress testprotocol was repeated at least 3 days after the previous continuoustest to determine test-retest reliability.
5. Statistical Analysis
Standard statistical analyses including means, standard
deviations, paired t tests and correlation coefficients were calculated
using a programmable calculator (Texas Instruments TI-55 III).
Statistical significance was chosen at 5% level.
7
III. RESULTS
All subjects completed the AGSM stress tests without any
particular discomfort other than sweating, exhaustion and fatigue.There were no adverse effects following any of these AGSM stresstests. Subjects indicated that they preferred the continuous protocolto the discontinuous one because of the shorter exercise duration.
Figures 4-7 respectively present the steady-state V02 , VE, RER
and HR resporses at rest and during the discontinuous AGSM stre6s
test at 20%, 25%, 33% and 50% duty cycles (raw data in Appendix B).
All of these physiological variables were found to increase in an
approximately linear fashion with respect to duty cycle which simulates
increased exercise loads. The responses at 50% duty cycle was
considered the peak that the subjects could achieve.
25
+1 200I--
S 15
] 10C\J
0.>
CU 5a)
0 LRest 10 20 30 40 50
Duty Cycle (%)
Figure 4. Relationship between the mean peak V0 2 and duty
cycle (n=9).
8
70-
o 60I)
+150 50
I--
M 40
3o-
> 20
10 1020
0 I I I I I
Rest 10 20 30 40 50
Duty Cycle (%)
Figure 5. Relationship between the mean peak 'E and dutycycle (n = 9).
9
1.3 -0U) 1.2 "+1
o 1.1G>
N01.
m.9W• F
0Q.8
Rest 10 20 30 40 50
Duty Cycle (%)
Figure 6. Relationship between the mean peak RER and dutycycle (n = 9).
10
170
150
+1 130 -
9C Lm110
I 701"
T--- I I I IRest 10 20 30 40 50
Duty cycle (%)
Figure 7. Relationship between the mean peak HR and dutycycle (n = 9).
Figures 8-13 present the comparison of the mean peak V02 , yE,RER, HR, LA and endurance time at the 50% duty cycle level betweenthe discontinuous and continuous (trials I & 2) stress testprotocols. The means and standard deviations of those abovephysiological variables were shown in Table 2 (raw data in AppendixC). Table 3 presents the results of paired t tests between themeans for each variable. It indicated that none of them wassignificantly different at the p < 0.05 level. Table 4 presents thecorrelation coefficients (r) for each physiological variable betweenthe discontinuous and continuous (trials I & 2) AGSM stress testprotocols. These correlation coefficients were significant at the p< 0.05 level.
II
30
25
+1-
o. 20
- 15
o 10•>
a)CL 5
01 1Discon Con T1 Con T2
Protocols
Figure 8. A comparison of mean peak VO2 at 50% dutycycle between the Discontinuous (Discon) andContinuous (Con, Trials 1 & 2) AGSM stresstest protocols (n = 9).
12
80
60
C,)+1
a.c" 40
_J
w0>
0
20
0"
Discon Con T1 Con T2
Protocols
Figure 9. A comparison of mean peak yE at 50% duty cyclebetween the Discontinous (Discon) and Continuous(Con, Trials 1 & 2) AGSM stress test protocols (n --= 9).
13
1.5
+1.0
00>
0
c0.5
0-Discon Con T1 Con T2
Protocols
Figure 10. A comparison of mean peak RER at 50%duty cycle between the Discontinuous(Discon) and Continuous (Con, Trials 1 & 2)AGSM stress test protocols (n = 9).
14
200
150-
+1
m 100
"I
a. 50
0-Discon Con T1 Con T2
Protocols
Figure 11. A comparison of mean peak HR at 50% dutycycle between the Discontinuous (Discon)and Continuous (Con,Trials 1 & 2) AGSMstress test protocols (n = 9).
15
4 40
I 3. 3o
3 -.0-o+1 E
4.-
0I
S2 20v0
CD 0
0 J0 10
Pre Post Pre Post Pre Post
Discon Con T1 Con T2
Protocols
Figure 12. A comparison of Pre- and Post- exercise meanblood lactate levels between the Discontinuous(Discon) and Continuous (Con, Trials 1 & 2)AGSM stress test protocols. (n = 9).
I
25
20
+-1
0 0C
15
E
5-
0
Con T1 Con T2
Protocol
Figure 13. A comparison of mean endurance timeat 50% duty cycle between ContinuousAGSM stress test protocol Trial 1 andTrial 2 (n - 9).
,117
iC
V~ u liam m llllin mI
CL
z 1+1 +1
--4 z
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V) N N4 Nl
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< Q 0 +1 +1 +1 +1
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TABLE 4
Correlation coefficients (r) for each physiological variable at 50% duty
cycle between the discontinuous (DISCON) and continuous (CON, Trials I
& 2) AGSM stress tests.
COMPARISON V0 2 yE RER HR LA ENDURANCE
DISCON vs CON TI 0.92 0.70 0.66 0.80 0.87
DISCON vs CON T2 0.73 0.77 0.81 0.82 0.75
CON TI vs CON T2 0.97 0.66 0.73 0.86 0.77 0.94
Note: All values are significant at 5% level.
20
IV. DISCUSSION
The AGSM stress test protocols devised in this study provided anexercise load that is similar to that which is actually encountered byfighter pilots both in centrifuge training and in-flight ACMs.Therefore, it appears that these tests can be used for objectiveevaluation of one's fitness and capacity of performing AGSMs. There isstill a need to correlate the capability of performing AGSMs and actualG-tolerance. The duty cycles selected for this study were 20%, 25%,
33% and 50% which are repeated 5-second AGSM exercise bouts interruptedby 20, 15, 10 and 5 seconds rest period, respectively. It isuniversally agreed that the optimal L-I AGSM duration is 3-5 secondsincluding an expiratory thrust upon closed glottis and a quickrespiration (2). However, a previous study showed that three AGSMs insuccession, without interruption for a ground test, can produce peakmean arterial blood pressure averaging 195 mmHg (23). For safetyreasons, it was decided not to use continuous AGSMs but to interruptthem with rest periods. For the discontinuous protocol, physiologicaldata were collected during the fourth minute of each AGSM exercise dutycycle to obtain steady state values. The 5-min rest periods thatfollowed bouts of exercise were used to allow time for recovery of thesubjects. The physiological responses elicited by the various dutycycles indicated the ability to gradually increase the stress effects.This is analogous to the progressive increase in exercise intensitythat is used for treadmill and bicycle ergometer stress testing. Thus,the described AGSM stress tests may be useful for objectivelyevaluating one's fitness for performing this activity.
Energy for most endurance exercise (more than a few minutes induration) is derived from aerobic metabolism. Oxygen uptake reflectsthis energy utilization. The peak oxygen uptake indicates the peakrate that energy can be derived by aerobic metabolism. It is dependentupon the fitness of the active muscles and the capacities of thecardiovascular and pulmonary systems. In comparing individuals'physical capacity, absolute peak V02 (1/min) is often expressed inrelative terms (ml/kg/min) by dividing the absolute value by bodyweight. The higher the relative peak V0 2 value, the greater is the
quality of the person's body weight. Since AGSM is a kind of staticexercise with isometric contractions, one may expect to obtain lowerpeak oxygen uptake value than can be obtained from treadmill or cycleergometer stress testing. However, the peak oxygen uptake during theAGSM tests is still a good indicator of individual's physicalcapability for performing this activity.
It is difficult to precisely measure the subject's musclecontraction strength during AGSM performance. Fortunately, all ourvolunteer subjects came from the Air Force Acceleration Panel. Thus,they have had extensive experience for performing AGSMs. Since they
are regularly performing these maneuvers, it was assumed that they wereexerting their maximal effort for each maneuver as was directed by theinvestigator.
As indicated, the AGSM tests consisted of intermittent isometric
exercise with alternating 5 seconds muscular contractions and 5 to 20
21
seconds of relaxation. In such a short duration, high intensity
exercise, it is expected that there would be a substantial anaerobicenergy component with a concommitant accumulation of lactate in the
blood. Indeed, blood lactate cor.centration increased 2-2.5 times abovethe rest level after completion of the 50% AGSM duty cycle. Burton et
al. (7) pointed out that the AGSMs performed during high-G centrifugetesting elicited blood lactate levels that were 200% higher than theAGSMs performed at I-G control. This suggests that there may beconsiderably more anaerobic activity, independent of the AGSM,
occurring during actual G loading.
Cote et al. (11) did a study analyzing the relationship betweeninspiratory volume and G-tolerance. He concluded that the inspiratory
volume during performing of AGSMs positively relates to G-tolerancelevel. Rapid, small breaths similar to hyperventilation can producerespiratory alkalosis. Therefore, lowered G-tolerance may result from
decreased cerebral blood flow. Another factor is that a largeinspiratory volume can contribute to increasing the intrathoracic
pressure which can help build up cerebral blood pressure. Finally, hesuggested pilots take large breaths (about 85% maximal inspiratoryvolume) without excessively exerting themselves in order to achieve
better G-tolerance. In the present study, subjects were instructed totake relatively large breaths.
None of the monitored physiological variables were significantly
different between the discontinuous test and continuous test trial 1 orbetween the discontinuous test and continuous test trial 2. Thisindicates that it is possible to use the continuous test protocolinstead of the discontinuous test protocol and elicit the same peak
responses in a shorter time period. The test results from thecontinuous test protocol trial I and 2 were very consistent, althoughthese tests were performed at least 3 days apart. This indicates thatthere is high test-retest reliability for the continuous AGSM stress
test protocol.
Peak V0 2 and endurance time attained during the continuous AGSMprotocol provides information on the strength and endurance componentsof an individual's AGSM performance capability. These data can beclassified and correlated to actual G-tolerance on the centrifuge in
further studies. Based on the inter-individual variability of peak V0 2
and endurance time during the AGSM test, these subjects exhibited awide range of AGSM performance capability (Table 2). Since this is a
voluntary exertion exercise, the consistency of maximal effort of every
AGSM bout can be influenced by the individual's motivation, will to
compete and stamina. Therefore, the magnitude of the peak V0 2 and
endurance time may not fully reflect the individual's capability forAGSM performance. However, fighter pilots, in general, may exhibitmore stamina, they are highly competitive, and they may be more
motivated for AGSM exercise tests. Therefore, when using actual
pilots, results may be more valid.
Further study will incur the results of this experiment tovalidate the correlation between capability of AGSM performed at I +Gz
and actual G-tolerance on centrifuge.
22
V. CONCLUSION
1. The proportional magnituds of the physiological responseselicited at the various duty cycles indicated the ability to graduallyincrease the stress effects. Thus, the described AGSM stress tests maybe useful for objectively evaluating the maximal energy citput(including endurance) by individual for performing this activity.
2. No significant difference for any or the monitored physiologicalvariables was found between the discontinuous AGSM stress test and the
continuous AGSM stress test (trials 1 & 2). Therefore, the continuousAGSM stress test protoco1. which is a substantially shorter test can beused instead of the longer duration discontinuous AGSM stress test, and
it can be expected that similar peak magnitudes of physiologicalresponses dill be obtained.
3. The high correlations for oxygen uptake and endurance value
between trial I and trial 2 indicated high test-retest reliability formeasuring physical capacity of performing AGSM.
4. The described AGSM stress test on the ground may be a convenient,
inexpensive and useful tool for objectively evaluating the physical
capacity of individuals for performing AGSM. Future studies need tocorrelate results of this ground test with centrifuge G-force toleranceto substantiate the validity of the AGSM stress test, and to better
understand the limiting factors for G-force tolerance.
23
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HqmN Mc , I '
H) OCa
~2
APPENDIX B
DISCONTINUOUS AGSM STRESS TEST DATA
REST
SUBJECT V02 yE RER(ml/kg/min) (1/min) (VCO 2 /V02 ) (bpm)
6. Burton, R.R.: Simulated aerial combat maneuvering tolerance andphysical conditioning: current status. Aviat. Space Environ.Med. 57(7):712-714. 1986.
7. Burton, R.R.: Anaerobic energetics of the Simulated Aerial CombatManeuver. Aviat. Space Environ. Med. 58:761-767. 1987.
8. Bulbulian, R.: Physical training and +Gz tolerance reevaluated.Aviat. Space Environ. Med. 57(7):709-711. 1986.
9. Clark, N.P.: The pathophysiology of high sustained ,-Gzacceleration, limitations to air combat maneuvering and the use ofcentrifuges in performance training. AGARD conf. proc. No. 169London: Harford House. 1976.
10. Comens, P., Reed, D., Mette, M.: Physiologic responses of pilotsflying high-performance aircraft. Aviat. Space Environ. Med.58(3):205-210. 1987.
11. Cote, R., Tripp, L., Jennings, T., Kark, A., Goodyear, C. Wiley,R.: Effect of inspiratory volume on intrathoracic pressuregenerated by an L-1 Maneuver. Aviation Space Environ. Med.57(11):1035-1038. 1986.
12. Epperson, W.L., Burton, R.R., Bernauer, E.M.: The influence ofdifferential physical conditioning regimens on simulated aerialcombat maneuvering tolerance. Aviat. Space Environ. Med.53(11):1091-1097. 1982.
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13. Epperson, W.L., Burton, R.R., Bernauer, E.M.: The effectiveness
of specific weight training regimens on simulated aerial combatmaneuvering G tolerance. Aviat. Space Environ. Med.56(6):534-539. 1985.
14. Houghton, J.O., McBride, D.K., Hannah, K.: Performance andphysiological effects of acceleration induced (+Gz) less of
consciousness. Aviat. Space Environ. Med. 56(10):899-904. 1985.
15. Jacobs, I.: Effects of hydraulic resistance circuit training onphysical fitness components of potential relevance to +Gz
tolerance. Aviat. Space Environ. Med. 58:754-760. 1987.
16. Leverett, S.D., Jr.: Physiologic responses to high sustained +Gz
acceleration. San Antonio, TX: School of Aerospace Medicine,Dec. 1973. SAM-TR-73-21. NTIS AD-777 604.
17. McCafferty, W.R.: Specificity of exercise and specificity oftraining: a subcellular response. Res. Q. Am. Assoc. HealthPhys. Educ. 48:358-371. 1973.
18. New fighters' high G loads draw increased USAF focus. AW&ST
June 17, 1985.
19. Parkhurst, M.J.: Human tolerance to high, sustained +Gz
acceleration. Aerospace Med. 43(7):708-712, 1972.
20. Rayman, R.B.: In-flight loss of consciousness. Aerospace Med.
44(5):506-509. 1973.
21. Tesch, P.A., Hjort, H., Balldin, U.I.: Effects of strengthtraining on G tolerance. Aviat. Space Environ. Med.
54(8):691-695. 1983.
22. Whinnery, J.E., Parnell, M.J.: The effects of long-term aerobic
conditioning on +Gz tolerance. Aviat. Space Environ. Med.58(3):199-204. 1987.
23. Williams, C.A., Douglas, J.E., Miller, G.: The relationship
between changes in arterial pressure, esophageal pressure and theEMG of various muscle groups during the L-1 straining maneuver at
different spine-to-thigh angles: A final report.
AAYMRL-TR-87-049. June 1987.
24. Wood, E.H.: The hydro- and resulting bio-dynamics of +Gz induced
losses of consciousness and its history. IEEE. 988-995. 1987.
