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Work and fatigue characteristics of unsuited and suited humans during isolated isokinetic joint motions
L. JAVIER GONZALEZ†, J. C. MAIDA§∗, E.H. MILES‡
S.L. RAJULU†† and A.K. PANDYA‡
†SPACEHAB, Houston, Texas
§ (P.I.) NASA Johnson Space Center, Houston, Texas
‡Lockheed Martin Space Operations, Houston, Texas
††NSBRI, Houston, Texas
Keywords: Joint fatigue; Joint strength; Task planning; Extra-Vehicular Activity (EVA);
Extra-vehicular Mobility Unit (EMU)
The effects of a pressurized suit on human performance were investigated. The suit is
known as an Extra-vehicular Mobility Unit (EMU) and is worn by astronauts while
working outside of their space craft in low earth orbit. Isolated isokinetic joint torques of
three female and three male subjects (all experienced users of the suit in 1G) were
measured while working at 100% and 80% of their maximum voluntary torque (MVT),
(here MVT is synonymous with maximum voluntary contraction (MVC)). It was found
that the average decrease in the total amount of work done when the subjects were
wearing the EMU was 48% and 41% while working at 100% and 80% MVT,
respectively. There is a clear relationship between the MVT and the time and amount of
∗ Author for correspondence. E-mail: jim.maida@jsc.nasa.gov
1
work done until fatigue. In general the stronger joints took longer to fatigue and did
more work than the weaker joints. It was found that the EMU decreases the work output
at the wrist and shoulder joints the most. This is due to the EMU joint geometry. The
average total amount of work done by the test subjects increased by 5.2% (20.4%) for the
unsuited (suited) case, when the test subjects decreased the level of effort from 100% to
80% MVT. Also, the average time to fatigue increased by 9.2% (25.6%) for the unsuited
(suited) case, when the test subjects decreased the level of effort from 100% to 80%
MVT. The EMU also decreased the joint range of motion. It was also found that the
experimentally measured torque decay could be predicted by a logarithmic equation. The
absolute average error in the predictions was found to be 18.3% and 18.9% for the
unsuited and suited subject, respectively, working at 100% MVT, and 22.5% and 18.8%
for the unsuited and suited subject, respectively, working at 80% MVT. These results
could be very useful in the design of future EMU suits, and planning of Extra-Vehicular
Activity (EVA) for the upcoming International Space Station assembly operations.
1. Introduction
With the upcoming International Space Station assembly missions, EVA will increase
dramatically. Approximately 900 EVA hours will be required to assemble the Space
Station with an additional 200 hours per year for maintenance requirements. Task
planning could increase the efficiency of the suited astronaut while performing Extra-
Vehicular Activities (EVAs). Efficient task planning could be facilitated by a simulation
using a three-dimensional human model with proper range of motion (ROM), strength,
and fatigue characteristics for all the major joints of the body.
2
While no comprehensive database exists which contains strength and fatigue
measurements for all the isolated joints of an unsuited and suited astronaut, much
research has been done to investigate the ergonomic characteristics of unsuited and suited
astronauts (O’Hara 1989; Shafer et al. 1992; Bishu and Klute 1993; Poliner et al. 1993,
1994; Rajulu and Klute 1993; Rajulu et al. 1993; Bishu et al. 1994; Wilmington et al.
1994; Morgan et al. 1996, Rajulu et al. 1998). One objective of this study was to acquire
and analyze experimental data for unsuited and suited humans while performing isolated
joint motions for all the major joints of the upper body (the upper body joints are the ones
most commonly used to perform EVAs). It is desirable, in particular, to study the
differences in the time to fatigue and total work done on a joint-by-joint basis, for suited
and unsuited humans, in order to compare and evaluate suit designs. An additional long-
term objective is to develop a predictive model for work and fatigue (Pandya et al.
1992a). This requires identifying and quantifying a trend in the torque decay over time
for each joint axis direction. Quantifying this torque decay is an objective of the present
research. The torque decay trend in conjunction with a maximum available torque model
(Pandya et al. 1992b) can be used to predict work and fatigue. This model could then be
integrated into a model for simulation and optimization of tasks in suited and unsuited
conditions.
2. Experiments
2.1 Subjects
Three female and three male subjects were used in the experiments. The low subject
count was due to time constraints. First, the availability of a suit and a qualified subject
3
at the same point in time was limited. Second, time spent wearing the suit was a
constraint, being generally two to three hours for one session, thus creating the need for
many sessions per subject with the additional session set up time. Third, because we
were measuring fatigue, additional time per subject was required in order to reach the
50% MVT threshold and to allow for subject recovery. Finally, the subjects participating
in the experiments were required to have a current Air Force Class 3 physical. In order to
minimize learning effects, only subjects with considerable experience in the use of the
EMU were allowed to participate in the experiments. The experience in the EMU for all
subjects is 41 hours. Table 1 gives a description of the test subjects.
[Insert table 1 about here]
2.2 Test facility and equipment
The experiments were conducted in the Precision Air Bearing Facility (PABF) at Johnson
Space Center. This facility allowed for multiple test configurations through the use of its
floor sled, smooth floor area, and air bearings. Extremely heavy objects mounted on top
of air bearings can easily be moved around the PABF floor once the air supply to the
bearings has been activated. This aided in positioning the test hardware and subjects in
proper alignment for conducting the strength and fatigue tests.
Joint strength and fatigue measurements were made using a LIDO Multi-Joint II
testing unit (Loredan Biomedical, Inc., West Sacramento, CA). The LIDO Multi-Joint II
is an integrated system consisting of a dynamometer connected to a personal computer.
The system has a series of attachments that enable strength measurements of the various
joints of the human body. The system also allows setting of experimentally defined
4
exercise parameters such as: velocity, ROM, and torque limits. A unique feature of the
LIDO is that it incorporates a gravity compensation feature that takes into account the
one-gravity artifact throughout the ROM. This capability is used to remove the effect of
the weight of the LIDO attachment, EMU suit segment, and the subject’s limbs from the
measured torques and forces, providing the subject’s actual effort. The gravity
compensation routine works as follows: the subject passively grasps the attachment as it
travels through the ROM, during which the LIDO computer calculates the torque
generated by the weight of the attachment, body segment, plus suit segment (when
applicable) in order to subtract these artifacts from subsequent measurements.
Standard Shuttle EMU suits with external air supplies were used for these
experiments. This suit is known to restrict the motion at the shoulder and wrist joints.
The scye opening, which is the opening through which the arm exits, is much larger than
the shoulder circumference, while the suit wrist joint is located two to three inches above
the actual wrist joint. An environmental control system was also used to maintain the suit
pressurization at 29.6 kPa. During testing, a floor sled was used to relieve the test subject
of the mass of the suit (approximately 118 to 123 kg). Figure 1 shows a suited subject
during one of the tests. The unsuited tests were also done using the floor sled in the
PABF.
[insert figure 1 about here]
2.3 Procedure
Since upper-body movements (e.g., locomotion using hand rails, using tools to repair
objects, and moving large masses) are integral to most EVA operations, emphasis was
5
placed on testing strength and fatigue for the major joints of the upper body. The five
isolated isokinetic joint motions that were included were: (1) shoulder flexion/extension,
(2) shoulder abduction/adduction, (3) shoulder internal/external rotation, (4) elbow
flexion/extension, and (5) wrist flexion/extension. All of the testing was performed on
the subject’s right side with the subject secured in an upright (standing) posture.
The procedure to find the MVT is now described. The subject drove the LIDO
attachment back and forth using maximum exertion at a prescribed angular velocity of
1.05 rad/s throughout the ROM for three non-stop repetitions. Because of time
constraints only one angular velocity was used. The angular velocity of 1.05 rad/s was
selected as the benchmark based on previous work done by Pandya et al. 1992b. The
variation between the three torque curves was then computed using the LIDO computer.
A variation of more than ten percent was used as a measure to indicate that the subject
was not using maximal exertion during the strength test. If the variation was less than ten
percent, the subject’s MVT for both directions of motion was computed by averaging the
three peak torque values for each direction.
For the fatigue tests the subject drove the LIDO attachment repeatedly at the
prescribed angular velocity of 1.05 rad/s throughout the entire ROM using the target level
of exertion (100% or 80% of the MVT) without stopping. During the submaximal
fatigue tests (80% of the MVT), the subject received real-time visual feedback of her/his
performance plotted against the target submaximal force level on the data acquisition
computer display. For the first repetition, the subject was given a window of ± 3% of the
target level. The subject was allowed to continue the test until the torque output in both
directions dropped below the defined fatigue index value (50% of the MVT) for three
6
consecutive repetitions. If the subject did not reach fatigue after five minutes, the test
was stopped. A five-minute rest period was allowed between joint measurements. This
procedure was used for both the unsuited and suited tests. The 80% level of exertion was
determined from pilot testing, since it provided the best range of data before reaching the
50% of the MVT mark.
The use of 50% of the MVT as the fatigue index requires some explanation. This
number came from the work of Patton et al. 1978, which found that the use of 50% MVT
as a fatigue index ensures a significant decline in function. Others have also used this
protocol to denote fatigue, such as Schwendner et al. 1995 who concluded that an
isokinetic fatigue test to 50% MVT, repeated three times, was an appropriate fatigue
generating protocol for most active males.
3. Results
3.1 Unsuited versus suited performance
The time to fatigue presented here was computed in a manner different than the protocol
used in the experiments. Here, the time to fatigue is defined as the ending time of the
repetition for which the computed work done during that repetition dropped below 50%
of the work done during the first repetition. This method was used because it was desired
to quantify fatigue as a function of the decline in energy output, and we believe that this
is a more overall measure of fatigue. The time to fatigue was then used as the ending
time for computing the number of repetitions, and work to fatigue. Figure 2 illustrates
how the time to fatigue was computed as just described for subject 5 during elbow
7
flexion while working at 100% of the MVT. For the case shown in figure 2, subject 5
fatigued at 73 seconds for the unsuited test, and at 53 seconds for the suited test. Figure 3
shows the mean torque per repetition, for subject 5 during elbow flexion while working at
100% of the MVT, while figure 4 shows polar plots of the torque measurements, also for
subject 5 during elbow flexion while working at 100% of the MVT.
[insert figures 2, 3 and 4 about here]
Tables 2 and 3 show the MVT, number of repetitions, time, and work to fatigue
(for each joint motion averaged across all subjects) for the unsuited and suited subject
working at 100% and 80% of their MVT, respectively. Table 4 shows the percent
decrease in work done by the test subjects from unsuited to suited for each joint motion.
Figures 5 and 6 show bar plots of the work done to fatigue for each joint motion averaged
across all subjects working at 100% and 80% MVT, respectively.
[insert tables 2, 3, and 4 about here]
[insert figures 5 and 6 around here]
3.2 Prediction of torque decay as a function of time
The procedure to obtain equations to predict the torque decay as a function of time for a
specific joint motion is now described. First, the mean torque for each repetition and
corresponding mean time was computed for the fatigue task. The data for all the subjects
was then grouped and smoothed before it was normalized. A moving average of ten
consecutive data points was visually found to provide sufficient smoothing of the data
while keeping the characteristics of the torque decay. The data was normalized using the
8
maximum torque value of the grouped smoothed data. It was then found, by trial and
error (with the use of the solver function in Microsoft Excel), that an equation of the
form:
| , (1) ct|ln ba norm ++=τ
where τnorm is the normalized torque, t is time, and a, b and c are coefficients, represents
the torque decay quite well. Figure 7 shows the actual normalized data and curve fits for
shoulder flexion for the unsuited and suited subjects working at 100% of their MVT.
Table 5 gives the coefficients for equation (1) for unsuited and suited subjects working at
100% of their MVT, while table 6 gives the coefficients for equation (1) for unsuited and
suited subjects working at 80% of their MVT. Given equation (1) and the maximum
torque (τmax) for the first repetition of a repetitive task, the torque decay (τ) as a function
of time can then be predicted by:
|]ct|ln b[a max ++=ττ . (2)
Using equation (2) the predictions were computed for subjects 1-6. The average absolute
error in the predictions for all subjects was 18.3% for the unsuited case and 18.9% for the
suited case at 100% MVT, and 22.5% for the unsuited case and 18.8% for the suited case
at 80% MVT. Table 7 gives the absolute average error in the predictions for each joint
averaged across the six subjects. Figure 8 shows the actual and predicted torque for
subject 2 during wrist extension at 100% MVT, while figure 9 shows the actual and
predicted torque for subject 3 during shoulder internal rotation at 80% MVT.
[insert figure 7 about here]
[insert tables 5 and 6 about here]
[insert figures 8 and 9 about here]
9
4. Discussion
One objective of this study was to quantify the effects of an EMU suit on the human
performance. Another objective was to develop equations that can be used to predict the
torque decay for each joint motion tested. In this section, a brief discussion of the
justification of the experimental and modeling procedures is provided. This is followed
by a discussion of the results pertaining to the two objectives mentioned above.
4.1 Justification of assumptions
For the data analysis, the female and male data were grouped. In light of the fact that
individuals use the same muscle groups, and that these muscle groups basically have the
same shape, orientation, and points of attachment, but differ in magnitude of force
exerted (Pandya et al. 1992b), it is felt that grouping of the data is justified since it was
normalized. For this reason, the low number of test subjects used is also thought to be
sufficient to give the trends of the work and fatigue characteristics of unsuited and suited
humans during isolated isokinetic joint motions.
4.2 Unsuited versus suited performance
The effect of the suit on performance is clearly evident. In general, the work and mean
torque per repetition decreased when the subject was suited (figures 2 and 3,
respectively). The joint range of motion also decreased in general for the suited subject
(figure 4). The average decrease in the total amount of work done when the subjects
were wearing a suit was 48% and 41% while working at 100% and 80% MVT,
10
respectively. There is a clear relationship between the MVT and the amount of work
done until fatigue. In general, the larger the MVT the more work that was done (tables 2
and 3). Further, for the case with the test subjects working at 100% MVT, wrist
extension and shoulder flexion are affected the most, while at 80% MVT, wrist flexion
and shoulder external rotation are affected the most (table 4). As mentioned previously,
the EMU is known to restrict the motion at the shoulder and wrist joints; therefore, these
findings are in check with the known restrictions of the EMU.
The average total amount of work done by the test subjects increased by 5.2%
(20.4%) for the unsuited (suited) case, when the test subjects decreased the level of effort
from 100% to 80% MVT, this corresponds to an increase of work done by the test
subjects of 62 Joules (128 Joules) for the unsuited (suited). Also, the average time to
fatigue increased by 9.2% (25.6%) for the unsuited (suited) case, when the test subjects
decreased the level of effort from 100% to 80%MVT, this corresponds to an increase of
time to fatigue for the test subjects of 10 seconds (20 seconds) for the unsuited (suited).
These results require some explanation. While working at 80% of the MVT the suit
offers less resistance, therefore, the effort of the subjects is directed towards moving the
Lido attachment rather than working against the suit. It makes sense then, that the time to
fatigue when working at 80% MVT increases, and consequently so does the amount of
work done. The significance of these results is obvious, i.e., astronauts should be
instructed to work at an MVT less then 100% MVT if the time to complete the task is not
an issue. These results could be very useful in the planning of EVAs.
4.3 Prediction of torque decay as a function of time
11
It was found that the torque decay could be predicted by a logarithmic equation (equation
(2), figures 7, 8 and 9). The average correlation coefficient, R2, for the curve fit for all
the joint motions is 0.89 for both the unsuited and suited cases at 100% MVT, and 0.91
and 0.89 for the unsuited and suited cases, respectively, at 80 % MVT, which indicates a
good fit. The absolute average error in the predictions was found to be 18.3% and 18.9%
for the unsuited and suited subject, respectively, working at 100% MVT, and 22.5% and
18.8% for the unsuited and suited subject, respectively, working at 80% MVT. As
mentioned in the introduction, a torque decay trend, used in conjunction with a maximum
available torque model (Pandya et al. 1992b), can be used to predict work and fatigue.
This predictor can also be integrated into a three-dimensional dynamic model for
analyses of tasks in both suited and unsuited conditions.
4.4 General discussion
The main intent of this research was to quantify the fatigue effects of wearing a
pressurized suit and to develop predictor equations for the torque decay as a function of
time. Pandya et al. 1992b, developed relations to predict dynamic isolated joint torques
from an individual’s lean body mass, however, in the work presented here, the lean body
mass of the subjects was not recorded since the intent of this study was not to relate
fatigue to lean body mass. With this in mind, it should be noted that the subjects in these
experiments belong to a specific population, i.e., they are all healthy subjects and
regularly participate in fitness training programs, and therefore, findings from this
research study may not be generalizable. But, these findings could be generalized to
specific skill tasks that require fit individuals.
12
5. Summary and future work
The effects of an EMU on isolated joint torque were measured. Using six subjects, both
suited and unsuited, isolated isokinetic joint torques were measured with the subjects
working at 100% and 80% of their MVT, using 50% of the MVT as the fatigue index. It
was found, on average, that the EMU reduced total work by about 50%, and the larger the
MVT, the longer the time to fatigue and the greater amount of work done. It was found
that the EMU decreases the work output at the wrist and shoulder joints the most. This is
due to the EMU joint geometry as mentioned earlier. The amount of work and time to
fatigue improved the most for the suited case, when the subject started at 80% MVT. The
EMU also decreased the joint range of motion. It was also found that the experimentally
measured torque decay trend could be predicted by a logarithmic equation with an
average error of ± 9.3% and 10.3% for the 100% and 80% MVT cases, respectively.
These results could be very useful in the design of future EMU suits, and planning of
Extra-Vehicular Activity (EVA\) for International Space Station assembly missions.
Future work includes the incorporation of these results into a human three-dimensional
dynamic model.
±
6. Acknowledgements
This project was funded by NASA grant number 96-HEDS-05.
13
References
BISHU, R.R. and KLUTE, G. 1993, Investigation of the effects of extravehicular activity
(EVA) gloves on performance, NASA Technical Paper 3401.
BISHU, R.R., BRONKEMA, L.A., GARCIA, D., KLUTE, G. and RAJULU, S. 1994,
Tactility as a function of grasp force: Effects of glove, orientation, pressure, load,
and handle, NASA Technical Paper 3474.
MORGAN, D.A., WILMINGTON, R.P., PANDYA, A.K., MAIDA, J.C. and DEMEL,
K.J. 1996, Comparison of extravehicular mobility unit (EMU) suited and unsuited
isolated joint strength measurements, NASA Technical Report TP-3613.
O’HARA, J.M. 1989, The effect of pressure suit gloves on hand performance,
Proceedings of the Human Factors Society 33rd Annual Meeting, 139-142.
PANDYA, A.K., MAIDA, J.C., ALDRIDGE, A.M., HASSON, S.M. and WOOLFORD,
B.J. 1992a, The validation of a human force model to predict dynamic forces
resulting from multi-joint motions, NASA Technical Paper 3206.
14
PANDYA, A.K., HASSON, S.M., ALDRIDGE, A.M. and MAIDA, J.C. 1992b,
Correlation and prediction of dynamic human isolated joint strength from lean
body mass, NASA Technical Paper 3207.
PATTON, R.W., HINSON, M.M., ARNOLD, B.R. and LESSARD, B. 1978, Fatigue
curves of isokinetic contractions, Arch. Phys. Med. Rehabili., 59, 507-509.
POLINER, J., WILMINGTON, R.P., KLUTE, G.K. 1993, Strength capabilities and load
requirements while performing torquing tasks in zero gravity, NASA Technical
Paper 3433.
POLINER, J., WILMINGTON, R.P. and KLUTE, G.K. 1994, Geometry and gravity
influences on strength capability, NASA Technical Paper 3511.
RAJULU, S.L., KAKAVAND, A., MULANI, K. and MAIDA, J.C. 1998, Hand strength
in a simulated microgravity environment, 28th International Conference on
Environmental Systems, (Danvers, Massachusetts).
RAJULU, S.L. and KLUTE, G.K. 1993, A comparison of hand grasp breakaway
strengths and bare-handed grip strengths of the astronauts, SML III test subjects,
and the subjects from the general population, NASA Technical Paper 3286.
15
RAJULU, S.L., POLINER, J., KLUTE, G.K. 1993, Loads produced by a suited subject
performing tool tasks without the use of foot restraints, NASA Technical Paper
3424.
SCHAFER, L.E., RAJULU, S.L. and KLUTE, G.K. 1992, A comparison of two shuttle
launch and entry suits: reach envelope, isokinetic strength, and treadmill tests,
22nd International Conference on Environmental Systems, (Seattle, Washington).
SCHWENDNER, K.I., MIKESKY, A.E., WIGGLESWORTH, J.K. and BURR, D.B.
1995, Recovery of dynamic muscle function following isokinetic fatigue testing,
International Journal of Sports Medicine, 16(3), 185-189.
WILMINGTON, R.P., POLINER, J. and KLUTE, G.K. 1994, Use of a pitch adjustable
foot restraint system: Operator strength capability and load requirements, NASA
Technical Paper 3477.
16
Tables
Table 1. Description of test subjects.
Subject 1 Subject 2 Subject 3 Subject 4 Subject 5 Subject 6 Gender female male male male female female Mass (kg) 59 77 86 66 68 54 Height (cm) 165 172 181 170 165 168 Hand dominance right right left right right right EMU experience (hrs) 20 60 70 25 40 35
17
Tabl
e 2.
Rep
etiti
ons,
time
and
wor
k to
fatig
ue fo
r uns
uite
d an
d su
ited
subj
ects
wor
king
at 1
00%
of t
heir
MV
T (s
tand
ard
devi
atio
ns in
pare
nthe
sis)
.
U
NSU
ITE
D
SU
ITE
DJo
int m
otio
n |M
VT
| (N
⋅m)
Rep
etiti
ons
Tim
e (s
) W
ork
(J)
|MV
T| (
N⋅m
) R
epet
ition
s T
ime
(s)
Wor
k (J
) W
rist e
xten
sion
11
(4)
40 (1
7)
107
(47)
24
3 (7
3)
7 (2
) 25
(5)
59 (8
) 96
(35)
W
rist f
lexi
on
18 (7
) 22
(13)
61
(41)
23
6 (1
18)
11 (5
) 19
(7)
47 (1
8)
115
(93)
El
bow
ext
ensi
on
43 (1
5)
29 (9
) 11
0 (2
7)
1199
(613
) 34
(15)
30
(10)
83
(26)
76
9 (3
83)
Elbo
w fl
exio
n 39
(17)
18
(5)
69 (1
8)
711
(427
) 33
(16)
16
(5)
43 (9
) 37
7 (2
09)
Shou
lder
ext
ensi
on
63 (2
7)
23 (4
) 10
8 (1
8)
2017
(120
7)
67 (3
1)
27 (1
5)
91 (5
9)
1134
(597
) Sh
ould
er fl
exio
n 61
(16)
24
(6)
108
(26)
19
23 (4
32)
42 (1
2)
26 (8
) 87
(43)
66
8 (2
24)
Shou
lder
abd
uctio
n 50
(13)
45
(15)
20
2 (7
3)
2520
(729
) 34
(31)
56
(23)
15
2 (6
5)
1207
(185
) Sh
ould
er a
dduc
tion
54 (2
3)
28 (2
2)
125
(99)
16
60 (9
07)
41 (3
3)
41 (1
3)
112
(55)
11
07 (3
57)
Shou
lder
ext
erna
l 21
(8)
25 (8
) 89
(29)
43
6 (2
41)
19 (8
) 15
(7)
48 (1
8)
234
(205
) Sh
ould
er in
tern
al
39 (1
4)
30 (1
0)
108
(35)
10
49 (4
07)
37 (9
) 18
(3)
60 (1
2)
562
(103
) A
vera
ge
4028
109
1199
3327
7862
7
18
Tabl
e 3.
Rep
etiti
ons,
time
and
wor
k to
fatig
ue fo
r uns
uite
d an
d su
ited
subj
ects
wor
king
at 8
0% o
f the
ir M
VT
(sta
ndar
d de
viat
ions
in
pare
nthe
sis)
.
U
NSU
ITE
D
SU
ITE
DJo
int m
otio
n |M
VT
| (N
⋅m)
Rep
etiti
ons
Tim
e (s
) W
ork
(J)
|MV
T| (
N⋅m
) R
epet
ition
s T
ime
(s)
Wor
k (J
) W
rist e
xten
sion
11
(4)
34 (1
6)
95 (4
7)
228
(61)
7
(2)
41 (2
2)
105
(69)
14
0 (5
2)
Wris
t fle
xion
18
(7)
30 (1
0)
79 (2
8)
324
(104
) 11
(5)
26 (1
7)
63 (4
3)
99 (7
8)
Elbo
w e
xten
sion
43
(15)
34
(15)
14
9 (7
0)
1193
(502
) 34
(15)
37
(15)
95
(31)
10
05 (6
04)
Elbo
w fl
exio
n 39
(17)
27
(15)
11
1 (6
7)
890
(568
) 33
(16)
22
(10)
58
(23)
51
4 (2
76)
Shou
lder
ext
ensi
on
63 (2
7)
32 (1
0)
148
(47)
24
26 (9
38)
67 (3
1)
31 (1
2)
97 (3
9)
1257
(105
4)
Shou
lder
flex
ion
61 (1
6)
19 (4
) 84
(20)
14
47 (3
97)
42 (1
2)
28 (7
) 83
(17)
77
5 (2
04)
Shou
lder
abd
uctio
n 50
(13)
35
(4)
144
(19)
23
27 (8
8)
34 (3
1)
69 (3
7)
152
(57)
13
10 (6
10)
Shou
lder
add
uctio
n 54
(23)
39
(20)
17
3 (7
9)
2095
(105
6)
41 (3
3)
62 (4
4)
148
(96)
13
28 (9
57)
Shou
lder
ext
erna
l 21
(8)
32 (1
2)
114
(49)
45
3 (1
21)
19 (8
) 22
(14)
71
(36)
27
2 (1
98)
Shou
lder
inte
rnal
39
(14)
28
(1)
98 (1
) 12
24 (1
84)
37 (9
) 31
(16)
10
8 (4
2)
851
(352
) A
vera
ge
4031
119
1261
3337
9875
5
19
Table 4. Percent decrease in work done to fatigue from unsuited to suited case.
Joint motion 100% MVT 80% MVT Wrist extension 60 39 Wrist flexion 51 69
Elbow extension 36 16 Elbow flexion 47 42
Shoulder extension 44 48 Shoulder flexion 65 46
Shoulder abduction 52 44 Shoulder adduction 33 37
Shoulder external rotation 46 40 Shoulder internal rotation 46 30
Average 48 41
20
Tabl
e 5.
Coe
ffic
ient
s for
equ
atio
n (1
) and
cor
rela
tion
coef
ficie
nt R
2 for 1
00%
MV
T.
U
nsui
ted
Su
ited
Join
t mot
ion
a b
c R
2
a
b c
R2
Wris
t ext
ensi
on
1.46
1-0
.192
11.0
610.
900.
917
-0.0
86-0
.385
0.77
Wris
t fle
xion
1.
268
-0.1
864.
211
0.96
1.34
5-0
.206
5.32
50.
95El
bow
ext
ensi
on
1.20
8-0
.122
5.50
20.
761.
568
-0.2
3311
.416
0.90
Elbo
w fl
exio
n
1.
350
-0.1
707.
815
0.81
1.13
2-0
.156
2.33
20.
81Sh
ould
er e
xten
sion
1.
486
-0.2
0011
.378
0.91
1.28
1-0
.154
6.22
20.
86Sh
ould
er fl
exio
n
1.
468
-0.1
8113
.367
0.93
1.34
5-0
.177
7.01
70.
94Sh
ould
er a
bduc
tion
1.85
8-0
.239
36.1
190.
891.
407
-0.1
7110
.742
0.94
Shou
lder
add
uctio
n
2.
257
-0.3
2249
.292
0.90
1.29
1-0
.164
5.92
40.
90Sh
ould
er e
xter
nal r
otat
ion
2.13
9 -0
.334
30
.202
0.
92
1.60
0 -0
.238
12
.412
0.
89
Shou
lder
inte
rnal
rota
tion
1.44
9 -0
.187
11
.006
0.
94
1.34
4 -0
.195
5.
813
0.94
21
Tabl
e 6.
Coe
ffic
ient
s for
equ
atio
n (1
) and
cor
rela
tion
coef
ficie
nt R
2 for 8
0% M
VT.
U
nsui
ted
Su
ited
Join
t mot
ion
a b
c R
2
a
b c
R2
Wris
t ext
ensi
on
1.37
4-0
.181
7.86
30.
870.
941
-0.0
67-0
.410
0.78
Wris
t fle
xion
2.
189
-0.3
0350
.797
0.80
1.33
2-0
.148
9.36
70.
80El
bow
ext
ensi
on
1.66
2-0
.223
19.5
340.
933.
061
-0.4
7278
.713
0.88
Elbo
w fl
exio
n
1.
663
-0.2
4914
.358
0.93
1.71
8-0
.281
12.9
290.
92Sh
ould
er e
xten
sion
1.
615
-0.2
1417
.757
0.93
2.34
9-0
.347
49.1
340.
94Sh
ould
er fl
exio
n
1.
427
-0.1
7511
.424
0.90
1.13
2-0
.115
3.14
30.
87Sh
ould
er a
bduc
tion
2.70
6-0
.372
98.3
010.
911.
231
-0.1
157.
454
0.90
Shou
lder
add
uctio
n
1.
534
-0.1
8318
.503
0.91
1.14
5-0
.116
3.50
00.
91Sh
ould
er e
xter
nal r
otat
ion
1.91
1 -0
.280
25
.835
0.
96
2.07
6 -0
.327
26
.807
0.
95
Shou
lder
inte
rnal
rota
tion
1.85
4 -0
.250
30
.285
0.
95
1.75
2 -0
.251
20
.007
0.
96
22
Tabl
e 7.
Abs
olut
e av
erag
e pe
rcen
t erro
r in
torq
ue p
redi
ctio
n fo
r eac
h jo
int.
Uns
uite
dSu
ited
Join
t mot
ion
100%
MV
T
80%
MV
T
100%
MV
T
80%
MV
T
Wris
t ext
ensi
on
18.2
23.0
15.1
25.5
Wris
t fle
xion
29
.730
.715
.419
.3El
bow
ext
ensi
on
12.6
22.3
17.2
19.0
Elbo
w fl
exio
n
14
.623
.924
.219
.4Sh
ould
er e
xten
sion
16
.416
.317
.316
.3Sh
ould
er fl
exio
n
15
.231
.123
.217
.6Sh
ould
er a
bduc
tion
11.6
18.9
16.4
17.2
Shou
lder
add
uctio
n
26
.324
.418
.218
.8Sh
ould
er e
xter
nal r
otat
ion
18.3
17
.8
25.7
21
.7
Shou
lder
inte
rnal
rota
tion
20.6
16
.2
16.4
13
.3
Ave
rage
18
.322
.518
.918
.8
23
FIGURE CAPTIONS
Figure 1. Suited subject with LIDO Multi-Joint II testing unit while being supported by air bearing floor sled.
Figure 2. Work per repetition for subject 5 during elbow flexion at 100% MVT. Figure 3. Mean torque per repetition for subject 5 during elbow flexion at 100% MVT. Figure 4. Polar plots of torque measurements for subject 5 during elbow flexion at 100%
MVT (angles in degrees). Figures 4c and 4d are close up views of 4a and 4b, respectively.
Figure 5. Work to fatigue for test subjects working at 100% MVT. Figure 6. Work to fatigue for test subjects working at 80% MVT. Figure 7. Normalized actual data and logarithmic curve fit for shoulder flexion at 100%
MVT. Figure 8. Actual and predicted torque for subject 2 during wrist extension at 100% MVT. Figure 9. Actual and predicted torque for subject 3 during shoulder internal rotation at
80% MVT.
24
25
0 50 100 150 200 250 3005
10
15
20
25
30
35
40
45
50 W
ork
Per R
ep (J
)
Time (s)
Unsuited Suited 50% of Work Done in 1st Rep (Unsuited) 50% of Work Done in 1st Rep (Suited)
26
0 50 100 150 200 250 3000
5
10
15
20
25
30
Mea
n To
rque
Per
Rep
(New
ton
met
ers)
Time (s)
Unsuited Suited
27
Unsuited Suited (a) (b)
(c) (d)
20
40
30
210
60
240
90
270
120
300
150
330
180 0
Joint Torque (Newton meters)
20
40
30
210
60
240
90
270
120
300
150
330
180 0
Joint Torque (Newton meters)
0
180
start time fatigue time start time fatigue time
28
0
500
1000
1500
2000
2500
3000
wrist e
xt
wrist fl
ex
elbow
ext
elbow
flex
shou
lder e
xt
shou
lder fl
ex
shou
lder a
b
shou
lder a
d
shou
lder e
xt
shou
lder in
t
Wor
k (J
)
UnsuitedSuited
29
0
500
1000
1500
2000
2500
3000
wrist e
xt
wrist fl
ex
elbow
ext
elbow
flex
shou
lder e
xt
shou
lder fl
ex
shou
lder a
b
shou
lder a
d
shou
lder e
xt
shou
lder in
t
Wor
k (J
)
UnsuitedSuited
30
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 50 100 150 200 250 300
Time (s)
Nor
mal
ized
Mea
n To
rque
Per
Rep
Unsuited (actual)
Suited (actual)
Unsuited (log fit)
Suited (log fit)
31
0
2
4
6
8
10
12
0 20 40 60 80 100 120
Time (s)
Mea
n To
rque
Per
Rep
(New
ton
met
ers)
Actual (unsuited)
Predicted (unsuited)
Actual (suited)
Predicted (suited)
32
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
0 20 40 60 80 100 120
Time (s)
Mea
n To
rque
Per
Rep
(New
ton
met
ers)
Actual (unsuited)Predicted (unsuited)Actual (suited)Predicted (suited)
.
33
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