Caldwell, E. E.

De Witt, J. K.

Fincke, R. S.

Humphreys, B. T.

Lewandowski, B. E.

Mulugeta, L.

Myers, J. G.

Newby, N. J.

Pennline, J. A.

Peters, B. T.

Ploutz-Snyder, L.

Scott-Pandorf, M. M.

Thompson, W. K.

NASA Technical Reports Server

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COMPUTATIONAL BIOMECHANICAL MODELS OF SQUAT EXERCISE 
PERFORMED ON THE ADVANCED RESISTIVE EXERCISE DEVICE (ARED) 
W. K. Thompson1, B.T. Humphreys2, E.E. Caldwell3, N.J. Newby3, B.E. Lewandowski1, L. Ploutz-Snyder4, J.A. Pennline1, L. Mulugeta4 
1NASA Glenn Research Center, 21000 Brookpark Rd., Cleveland, OH 44135  
2ZIN Technologies, 6745 Engle Road, Airport Executive Park, Cleveland, OH 44130 
3Wyle Science, Technology & Engineering Group, 1290 Hercules Drive, Houston, TX 77058 
4Universities Space Research Assoc., Div. of Space Life Sciences, 3600 Bay Area Blvd., Houston, TX 77058 
 
This work is funded by the NASA Human Research Program, 
managed by the NASA Johnson Space Center. Specifically, this 
work is part of the Digital Astronaut Project (DAP), which  directly 
supports the Human Health and Countermeasures (HHC) 
Element.  The DAP project is managed out of NASA/Glenn 
Research Center (GRC) by DeVon W. Griffin, Ph.D., and  
Lealem Mulugeta of USRA Houston serves as the DAP Project 
Scientist. 
RESULTS: MUSCLE AND JOINT-ONLY MODULES 
ACKNOWLEDGEMENTS 
FUTURE WORK 
REFERENCES 
    
 
     
 
     
 
 
 
 
 
BACKGROUND 
METHODS: BIO-MECH., ARED & INTEGRATED MODULES 
METHODS: IMPLEMENTATION DETAILS 
Biomechanical Modules 
(GRC and Wyle S.T.&E.) 
 
• Derived from motion capture 
(MoCap) and ground reaction 
force (GRF) data acquired on the 
ARED ground unit using an 
exercise-experienced male 
subject 
• Constructed a forward 
dynamics module in LifeMOD®  
(a plug-in to AdamsTM) during the 
performance of a 1-repetition 
maximum squat exercise 
• Joint-only and joint/muscle 
configurations 
 
ARED Device Module2,7  
(ZIN Technologies) 
 
• ARED is a resistance-training 
exercise device for the crew of the 
International Space Station (ISS) 
• Rigid Body Dynamics module 
developed using Pro-E solid 
model files, engineering 
specifications, and engineering 
hardware verification data. 
• Constructed in MSC AdamsTM 
Integration in LifeMOD 
Modeling of Contacts Between Biomechanical Module and ARED 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
VERIFICATION AND VALIDATION (V&V)  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
DISCUSSION: ACCOMPLISHMENTS AND FINDINGS  
PARTNERS 
Feet in contact with 
simulated force platform 
Ellipsoid-Plane 
Contacts 
Hands and upper back 
in contact with the bar 
Hand grip 
contacts 
Grip contact with 
spinal marker on 
the upper torso. 
Contact plane 
simulates Kistler® 
force plate measuring 
ground reaction 
forces during motion 
capture 
 Verification: Is the model constructed correctly? 
• Compare joint angles and displacements between the forward dynamics 
(driven by the trained module) with inverse dynamics (driven by MoCap data) 
 
• Vary the load setting on the ARED module and examine the resulting forces, 
muscle tensions and joint torques 
 Validation: Are the model results meaningful? 
• Compare calculated forces, muscle tensions and  joint torques with reported 
measurements in the literature made under similar loading conditions. 
 
• Conform to NASA-STD-7009 standards for assessing the credibility of 
computational models in all V&V activities 
Joint  Data 
• Key joints of interest:, Hip, Knee, Thoracic Spine and Lumbar Spine 
Enhance ARED Squat Model 
 
• Obtain 0g motion capture data from ISS 
video to fully develop 0g ARED squat model 
• Quantify the effects of 0g and the VIS on 
exercise kinematics and dynamics  
• Analyze effects of posture, positioning and 
cadence on module outputs (kinematics, joint 
forces/torques and muscle tensions) 
• Overcome limitations in the 1g model such 
as small data set, artifacts and absence of 
upper body musculature 
Model Other Exercises on ARED 
  
ARED Module  
Adjustable 
bar position 
Vibration 
Isolation 
System 
(VIS) 
Adjustable 
load setting 
NASA’s Digital Astronaut Project (DAP) Vision 
 
The Digital Astronaut Project implements well-vetted 
computational models to predict and assess spaceflight 
health and performance risks, and enhance 
countermeasure development, by 
 
• Partnering with subject matter experts to inform HRP knowledge 
gaps and countermeasure development decisions;  
 
• Modeling and simulating the adverse physiologic responses to 
exposure to reduced gravity and analog environments; and  
 
• Ultimately providing timely input to mission architecture and 
operations decisions in areas where clinical data are lacking. 
HRP Risks/Gaps Addressed by This Effort 
Risk of Muscle Atrophy: impaired performance due to 
reduced muscle mass, strength and endurance  
•  Gap M7: Can the current in-flight performance be maintained with 
reduced exercise volume? 
•  Gap M8: What is the minimum exercise regimen needed to maintain 
fitness levels for tasks? 
•  Gap M9: What is the minimum set of exercise hardware needed to 
maintain those fitness levels? 
 
Risk of Loss of Bone Mineral Density: early onset of 
osteoporosis and bone fracture 
•   Osteo 7: We need to identify options for mitigating early onset 
osteoporosis before, during and after spaceflight.  (formerly Gap B15) 
•  Osteo 6: How do skeletal changes due to spaceflight modify the terrestrial 
risk of osteoporotic fractures?  (formerly Gap B1) 
National Aeronautics and 
Space Administration 
Validation by comparison with the literature 
Joint Torques 
• Calculated moments at key 
joints in primary planes of 
interest 
• Indicate the dynamics of the 
movement 
Inform Musculoskeletal Adaptation Models 
 
• DAP Bone Adaptation Model  
• Provide exercise-induced loading inputs  
• Key skeletal sites: hip, spine and femoral neck 
• DAP Muscle Adaptation Model12  
• Change LifeMOD muscle parameters to 
   reflect adaptations to spaceflight 
• Quantify effects of changes to cross-sectional area, 
maximum isometric force and pennation or individual 
muscles on overall performance 
 
Single-leg 
Squat 
Deadlift 
(muscle model) 
Accomplishments to date 
• Completed integrated modules for the 1g squat exercise in both 
joint-only (ASM-i) and muscle/joint (ASM-im) configurations. 
• Verified kinematics, joint forces/torques, muscle lengths and GRF 
• Validated model kinematics, dynamics and GRF’s versus 
literature on the squat exercise 
• Performed preliminary sensitivity analysis to quantify effects of 
perturbations to model parameters 
• NASA-STD-7009 credibility assessed for 1g, estimated for 0g 
 
 
Major Findings 
• Kinematic agreement is better during the ascent/descent 
phases than at the start/end of the movement 
• Joint forces are more accurately reproduced in the ASM-im 
model than the ASM-i 
• Relative muscle tensions among muscles mimic the 
activation patterns reported in the literature. 
• The 0g kinematics cannot be predicted by simply ignoring 
gravity and activating the VIS on the ARED. 
 
 
Heel Raise 
www.nasa.gov 
Ground Reaction Forces (GRF) - Verification 
• Compare model-predicted GRF data with measured GRF 
 
Joint Forces 
• Calculated forces at the 
body segment joints 
• Indicate loading on key 
skeletal segments 
• Inform bone adaptation 
models 
Muscle Lengths 
• Calculated  contractile length 
histories for select muscles 
• Indicate the muscle 
kinematic behaviors and range 
of motion 
• Right/Left agree within ±2% 
• Gray dashed lines indicate 
transition from descent/ascent 
 
Joint  Angle Errors 
• Differences in joint angles 
between forward and inverse 
dynamics 
• Indicate imperfections in the 
ability of the forward module to 
exactly duplicate the kinematics 
• <2 deg error during key phases 
of the squat movement 
Muscle Tensions 
• Calculated tensile forces in 
the primary muscle actuators 
• Indicate the contributions of 
specific muscle groups, but not 
necessarily individual muscles 
within groups 
• Inform the DAP muscle 
adaptation model 
Muscle Data 
• Key muscles of interest: Gluteals/Hips, Quads, Adductors, Hamstrings, Calves 
ARED Squat Module – Integrated 
(ASM-i, Trained joints only) 
ARED Squat Module – Integrated & 
with Muscles (ASM-im)  
Integrated ARED Squat Modules7,8,10,11  
(NASA GRC) 
Integration Process 
Normal Squat 
(NS) Module 
Muscles matched 
to MRI data for 
CSA and trained 
from inverse 
kinematics 
Trainable joints 
Scaled skeletal 
segments match 
the subject 
• Prior to model merge operation 
• Preset ARED exercise bar to 
squat configuration 
• Align reference frames of ARED 
and biomechanical modules   
• Balancing of GRF’s (vs. measured 
GRF data) iteratively determines 
proper co-alignment of the modules 
• Visual inspection of model posture 
used to verify results of equilibrium 
analysis 
• Motion capture marker weights are 
adjusted  to obtain proper posture 
• Physical contacts modeled as below 
 
Joint and Muscle Training 
• Adjustable parameters 
• Servo joints 
• Proportional gain 
• Derivative gain 
• Passive joints 
• Translational Stiffness/Damping 
• Rotational Stiffness/Damping 
• Muscles 
• Stiffness 
• Damping 
• Phys. Cross Sectional Area 
(matches MRI data) 
• Tone 
• PID gains 
• Insertion geometry 
 
Other Steps 
• Motion tracker agent 
• Residual forces applied at pelvis in 
transverse directions to keep the 
model stable during the exercise 
• Adjustable rotational and 
translational stiffness 
• GRF data and joint angle errors 
iteratively verify the forward dynamics 
simulations 
• With ARED 
• Without ARED – compare to 
existing biomechanical models 
• Adjust gain and stiffness /damping 
until model is verified 
 
ASM-im (muscles) ASM-i (joint only) 
GRF profile measured for 
fast-cadence squat3 
compares well with both 
measured and calculated 
GRF for this effort 
Tibiofemoral compressive 
force during a barbell squat4 
compares well with 
calculated Y axis knee 
forces (with sign inverted). 
Compare model-
calculated joint 
angles, torques 
and forces with 
reported data 
Compare model-
calculated 
muscle tension 
vs. reported 
relative muscle 
activation via 
EMG 
Compare 
measured and 
model-calculated 
GRF’s with 
reported GRF 
data 
Rectus femoris measured 
EMG during barbell squat5.  
Profile shape compares 
with calculated muscle 
tension profiles but the 
asymmetry between 
descent and ascent is not 
fully captured by the 
model. 
1. Caldwell EE, Newby NJ, Scott-Pandorf MM, Peters B, Fincke RS, De 
Witt JK, “Biomechanics Exercise Models”,    Development Report,   
Wyle Integrated Sci. & Engr., 2011. 
2. Humphreys BT, “ARED Adams® Model Description Document”, DA-
DOC-001, ZIN Technologies Contractor Report, 2011. 
3. Bentley JR, Amonette WE, De Witt JK, Hagan RD, “Effects of Different 
Lifting Cadences on the Ground Reaction Forces  during the Squat 
Exercise”, J Strength and Conditioning Res 24(5): p1414-20, 2010. 
4. Escamilla RF, et al., “Effect of technique variations on knee 
biomechanics during squat and leg press”, MedSci Sports Exerc., Vol. 
33, No. 9, pp. 1552-66, 2001. 
5. McCaw ST, Melrose DR., “Stance width and bar load effects on leg 
muscle activity during the parallel squat.”, Med Sci Sports Exerc. 1999 
Mar;31(3):428-36. 
 
 
 
6. Newby et al., Poster #4163, HRP IWS 2012, 14-16 Feb. 2012, Houston, 
TX.  
7. Humphreys et al., Poster #4104, HRP IWS 2012, 14-16 Feb. 2012, 
Houston, TX. 
8. Thompson et al., Poster #4111, HRP IWS 2012, 14-16 Feb. 2012, 
Houston, TX.  
9. NASA-STD-7009: Standard for Models and Simulations, 2008. NASA: 
Washington, DC. 
10. Thompson WK, et al., “ARED Squat Model – Integrated (ASM-i)”, 
Report, NASA GRC 2012. 
11. Thompson WK, et al., “ARED Squat Model – Integrated and with 
Muscles (ASM-im)”, Report, NASA GRC 2012. 
12. Lewandowski et al., Poster #4184, HRP IWS 2012, 14-16 Feb. 2012, 
Houston, TX. 
 
 
 Results of V&V of ASM-im in 1g per NASA-STD-70099 
• V&V Scores for 1g models  
• 1.8 for ASM-I   
• 1.5 for ASM-im  
• Preliminary 0g assessments  
• 1.4 for ASM-I  
• 1.1 for ASM-im,  
• Lower use history and robustness scores in 0g.  
1,6,10,11 
CAS Score
Overall 
Weight
Overall 
Credibility
Thresholds MAX
Verification 2 0.4 3 4
Validation 2 0.5 2 4
Input Pedigree 2 0.2 3 4
Results Uncertainty 1 0.1 1.8 2 4
Results Robustness 2 0.2 2 4
Use History 1 0.15 2 4
M&S Management 2 0.1 3 4
People Qualifications 3 0.15 3 4
https://ntrs.nasa.gov/search.jsp?R=20150010330 2019-08-31T08:05:44+00:00Z


Computational Biomechanical Models of Squat Exercise Performed on the Advanced Resistive Exercise Device (ARED)

Computational Biomechanical Models of Squat Exercise Performed on the Advanced Resistive Exercise Device (ARED)

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