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An evaluation of inertial motion capture technology for use in the optimization of road cycling kinematics John Cockcroft University of Stellenbosch

John Cockcroft University of Stellenbosch

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An evaluation of inertial motion capture technology for use in the optimization of road cycling kinematics. John Cockcroft University of Stellenbosch. Overview of Presentation. Background to inertial motion capture and road cycling Research motication objectives Experimental work - PowerPoint PPT Presentation

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Page 1: John Cockcroft University of Stellenbosch

An evaluation of inertial motion capture technology for use in the optimization of road cycling kinematics

John CockcroftUniversity of Stellenbosch

Page 2: John Cockcroft University of Stellenbosch

Overview of Presentation

• Background to inertial motion capture and road cycling

• Research motication objectives

• Experimental work

• Analysis of magnetic interference

• Analysis of cycling kinematics

• Conclusions

Page 3: John Cockcroft University of Stellenbosch

Inertial motion capture technology

• The MVN BIOMECH system

• Produced by Dutch company Xsens B.V • One of the fastest growing European technology companies• Track motion with accelerometers and gyroscopes attached to

the body with a body fitting Lycra suit

Page 4: John Cockcroft University of Stellenbosch

Portable storage

Wireless data transmission

Kinematic Analysis

Body-fit Lycra suit Digital model

Sensor to segmentcalculations

Page 5: John Cockcroft University of Stellenbosch

Sternum

Head

Forearm Hand

Upper leg

Lower leg

Upper arm

L3L5

Foot

T8T12

NeckShoulder

Toe

FULL BODY KINEMATICS:BIOMECHANICAL MODEL

23 Segments, 22 joints Anthropometrical scaling

Page 6: John Cockcroft University of Stellenbosch

INERTIAL MEASUREMENT UNITS

• Inertial navigation system

• Gyroscope provide angular data• Accelerometer provide linear data• Magnetometer provide heading in the global frame

• Errors in sensor kinematics

• Integration error in gyroscope and accelerometer data• Magnetic disturbances

Page 7: John Cockcroft University of Stellenbosch

ELIMINATING GYROSCOPE INTEGRATION ERROR

• Sensor drift

• Gyroscope offset errors are cumulative over time• Orientation error can become very large in just a few seconds

• Sensor fusion

• Accelerometer is used as an inclinometer to stabilize gyroscope data in the vertical plane

• Magnetometer data is used to stabilize gyroscope data in the horizontal plane

Page 8: John Cockcroft University of Stellenbosch

REDUCING ACCELEROMETER DRIFT ERROR

• Joint Updates

• Joint constraints reduce error in joint centre estimation

• Estimation of contact points

• Decreased drift of biomechanical model in global frame

Page 9: John Cockcroft University of Stellenbosch

REDUCING MAGNETIC INTERFERENCE

• Permanent constant interference

• E.g. prostheses, orthotics• Characterized as a priori by Kalman filter and removed

• Temporary constant/varying interference

• E.g. walking past a speaker or metal structure• Rejected by advanced Kalman filtering

• Permanent varying interference (>30s)

• E.g. metal beams in the floor• Kinetic Coupling algorithm for lower leg joint flexion

Page 10: John Cockcroft University of Stellenbosch

Road Cycling

• Goals of technique enhancement

• Minimize power demand by increasing aerodynamic efficiency• Maximize power production by increasing biomechanical

efficiency• Decreased risk of overuse injuries by improving technique• i.e. Optimize bike fit

Page 11: John Cockcroft University of Stellenbosch

Fore-aft position Handlebar adjustment

Saddle-heightadjustment

Down tube

Top tube

Seat tube

Seat tube angle

Page 12: John Cockcroft University of Stellenbosch

Objectives

• Objectives

• Perform measurements of outdoor cycling kinematics• Investigate level of magnetic interference from road bikes• Compare indoor and outdoor results• Investigate the link between rider kinematics and optimal bike fit

• Motivation

• Sports science research has been slow to adopt motion capture• There is very little sports related work being done with the MVN• Outdoor measurements of cycling kinematics not yet been

conducted

Page 13: John Cockcroft University of Stellenbosch

Test Protocol

• General suit setup

• 10 male sub-elite cyclists using own bicycles

• Two tests on separate days

• Indoor on stationary trainer• Outdoor followed by pursuit vehicle

• Three sessions per test

• Low, medium and high intensity (2, 3.5 and 5.5 W.kg-1)• 1min long steady-state recordings using the MVN suit

Page 14: John Cockcroft University of Stellenbosch

Test Protocol

Page 15: John Cockcroft University of Stellenbosch

Test Protocol

Page 16: John Cockcroft University of Stellenbosch

Test Protocol

Page 17: John Cockcroft University of Stellenbosch

Magnetic Measurement Results

• Test environments

• The indoor results show significant disturbances• Outdoor tests were undisturbed

• Road bicycles

• Hand sensors experienced worst interference• Chains, sprockets and pedals disturbed foot sensors

• Sensor fusion settings

• Kinematic Coupling algorithm is immune to interference• Can only be used for lower body when moving

Page 18: John Cockcroft University of Stellenbosch

0

20

40

60

80

1 2 3 4 5 6 7 8 9 10

MAg

netic

fiel

d in

tens

ity

Cyclists

Magnetic readings around left upper arm

Indoor

Outdoor

Undisturbed

Page 19: John Cockcroft University of Stellenbosch

0

20

40

60

80

1 2 3 4 5 6 7 8 9 10

MAg

netic

fiel

d in

tens

ity

Cyclists

Magnetic readings around left forearm

Indoor

Outdoor

Undisturbed

Page 20: John Cockcroft University of Stellenbosch

0

20

40

60

80

1 2 3 4 5 6 7 8 9 10

MAg

netic

fiel

d st

reng

th

Cyclists

Magnetic readings around left hand

Indoor

Outdoor

Undisturbed

Page 21: John Cockcroft University of Stellenbosch

ΘK

ΘH

Ankle

Knee

Hip

ΘA

Hip, knee and ankle flexion definitions

Page 22: John Cockcroft University of Stellenbosch
Page 23: John Cockcroft University of Stellenbosch

Overview of outdoor kinematics

• Flexion measurements are valid

• Joint excursions correlate well with past studies• Significant variability in flexion between cyclists

Maximum Minimum Range

Hip 75.5 ± 9.7(~90**)

23.5 ± 8.5(~45**)

52 ± 4.6(54 ± 4*) (~45**)

Knee 117 ± 7.7(~110**)

31.5 ± 7.7(30-60**)

85.5 ± 6.5(69 ± 4*) (~75**)

Ankle 12.1 ± 8.9(plantarflexion)

-9.8 ± 8.8(dorsiflexion)

21.9 ± 6.8(19 ± 4*)(~20**)

* (Bini RR, 2008)

** (R.J Gregor, 2000)

Page 24: John Cockcroft University of Stellenbosch

Comparison of indoor/outdoor tests

• Ecological validity of indoor testing

• Is laboratory testing on a trainer realistic?• No wind resistance, rigid wheel fixtures etc.

• Comparison of laboratory and road tests

• Hip and knee values in outdoor tests higher on average• Ankle values in outdoor tests lower on average• However, no clear trend between indoor and outdoor tests

Δ Maximum Δ Minimum Δ Range

Hip -4.7° -6.0° 1.3°

Knee -1.8° -3.9° 2.1°

Ankle 3.9° 4.0° -0.1°

Page 25: John Cockcroft University of Stellenbosch

1 2 3 4 5 6 7 8 9 100

20

40

60

80

100

120

140

Left Knee Maximum Flexion

Cyclists

Flex

ion

Angl

e[de

g]

Page 26: John Cockcroft University of Stellenbosch

Conclusions

• Can the MVN system measure accurate outdoor cycling kinematics?

• No. Road bikes cause unacceptable magnetic interference• Only lower body joint angles in the sagittal plane• Flexion values correlate well with other studies

• What was learned from the kinematic data?

• No clear difference between indoor and outdoor kinematics• High variability in hip, knee and ankle flexion suggest that

bicycle fit should not be based on anthropometrical data

Page 27: John Cockcroft University of Stellenbosch

THANK YOU

Page 28: John Cockcroft University of Stellenbosch

Motion Capture

• What is motion capture technology?

• Converting analogue marker tracking to a digital model• Applications in entertainment (e.g. movies and games)• Used in movement science (e.g. medical research of gait)

M

M

M

M

M

M

M

M

M

M

M

M

PHYSICAL SETUP MARKER TRACKING DIGITAL MODEL

Page 29: John Cockcroft University of Stellenbosch

OVERVIEW OF MOTION CAPTURE PROCESS:MVN SENSOR FUSION SCHEME

Page 30: John Cockcroft University of Stellenbosch

Orientation error θε

Gyroscope offset error bε

Magnetic disturbance error dε

QHM, Qd

QZM

QZG, QHG, Qb, Qθ

Accelerometer model

Gyroscope model

Magnetometer model

Kalman filter

Magnetometer signal

Gyroscope signal

Accelerometer signal +

+

_

_

VA

VG

HG

HM

GYROSCOPE SENSOR FUSION:ERROR-STATE KALMAN FILTER

Page 31: John Cockcroft University of Stellenbosch

SEGMENT KINEMATICS:CALIBRATIONS

N-pose T-pose Squat Hand-touch

Page 32: John Cockcroft University of Stellenbosch

ESTIMATING SEGMENT KINEMATICS

Page 33: John Cockcroft University of Stellenbosch

Effect of workload on kinematics

• Relationship between cycling power and rider kinematics

• Negligible change between low, medium and high power• Confirms the claims of current published literature

Δ Maximum Δ Minimum Δ Range

Hip 2.2 2.2 1.5

Knee 1.0 2.0 1.0

Ankle 2.9 4.1 3.6

Page 34: John Cockcroft University of Stellenbosch

Bilateral Asymmetry

• What is bilateral asymmetry?

• Difference between left and right sides of the body• Can be a difference in kinetics or kinematics• Can be caused by limb dominance, differences in joint

characteristics, anatomical differences, lateral pelvic tilt etc.

• Results

• Over 30% of the cyclists displayed significant asymmetry• Greatest asymmetry in hip and knee during downstroke• Greatest asymmetry for the ankles during the upstroke

Page 35: John Cockcroft University of Stellenbosch

-20

-15

-10

-5

0

5

10

15

20

1 2 3 4 5 6 7 8 9 10

Asym

met

ry in

flex

ion

[deg

rees

]

Cyclists

High Power

Medium Power

Low Power

Right more flexed

Left more flexed

Bilateral asymmetry of the knee joint at minimum flexion

Page 36: John Cockcroft University of Stellenbosch

Knee overuse injuries

• Knee overuse injuries very common in cycling

• Over 33% of knee injuries are to the patellofemoral joint (PFJ)

• Second most common is iliotibial band friction syndrome (ITBFS)

• Results from analysis

• 50% of the cyclists had knee flexion of over 120° and are at risk of PFJ pain

• 30% of the cyclists went under 25° flexion and are at high risk of ITBFS

Page 37: John Cockcroft University of Stellenbosch

Future Work

• Improvements to test protocol

• Design of ferromagnetic-free road bicycle• Protocol for clinical anthropometrical measurements

• Avenues for future studies

• Integration of MVN data with measurements of kinetic, neuromuscular and metabolic variables

• Analysis of biomechanical efficiency using 3D joint angles• Study of fatigue effects on upper body kinematics• Dynamic bicycle fit interventions for prevention of injury