Ground Reaction Forces in Ground Reaction Forces in Distance RunningDistance Running

Peter Cavanagh Peter Cavanagh

Mario LafortuneMario Lafortune

IntroductionIntroduction

High incidence of lower extremity injuries High incidence of lower extremity injuries in runners due to overusein runners due to overuse

The design of footwear should depend The design of footwear should depend upon knowledge of the force and pressure upon knowledge of the force and pressure environment during runningenvironment during running

Development of a shoe testing laboratoryDevelopment of a shoe testing laboratory

Purpose of the StudyPurpose of the Study

Document the ground reaction forces in Document the ground reaction forces in runningrunning

Examine the center of pressure Examine the center of pressure distrubutiondistrubution

Gain insight into the changes in velocity of Gain insight into the changes in velocity of the body center of massthe body center of mass

Methods - SubjectsMethods - Subjects

17 runners (10 males & 7 females)17 runners (10 males & 7 females)

Weekly running distances of 10-160 kmWeekly running distances of 10-160 km

Data CollectionData Collection

Kristal type force plate located in the Kristal type force plate located in the middle of a 40 m runwaymiddle of a 40 m runway

Photocells at hip height situated 5 m from Photocells at hip height situated 5 m from the center of the force platethe center of the force plate

Subjects were given practice trials to get Subjects were given practice trials to get accustomed to hitting the force plate with accustomed to hitting the force plate with their right foot while running at 4.5 m/s (6 their right foot while running at 4.5 m/s (6 min/mile pace)min/mile pace)

Data CollectionData Collection

If the running speed was outside of the If the running speed was outside of the desired range (4.12 – 4.87 m/s) the trials desired range (4.12 – 4.87 m/s) the trials were discardedwere discarded

The subjects were required to run in a The subjects were required to run in a smooth fashion and hit the center of the smooth fashion and hit the center of the force plateforce plate

Determination of Foot PlacementDetermination of Foot Placement

All subjects wore All subjects wore Etonic Km 505 running Etonic Km 505 running shoesshoesThe surface of the The surface of the force plate was force plate was covered with tapecovered with tapeThe subjects ran The subjects ran through chalk prior to through chalk prior to contacting the force contacting the force plateplateThe position of the The position of the shoe on the plate was shoe on the plate was determined from the determined from the chalk imprintchalk imprint

Data ProcessingData Processing

Data from 5 right foot Data from 5 right foot contacts were contacts were recordedrecordedFx, Fy, Fz, Mx and Fx, Fy, Fz, Mx and My were sampled at My were sampled at 500 Hz with a PDP 500 Hz with a PDP 11/34 computer11/34 computerAnalog comparator Analog comparator with Fz = 50 N was with Fz = 50 N was used to identify GRF used to identify GRF curvescurves

Average CurvesAverage Curves

Averaging curves with Averaging curves with different durations different durations and asynchronous and asynchronous peaks tends to peaks tends to attenuate peak valuesattenuate peak values

Velocity Changes of CMVelocity Changes of CM

Fxdtm

VxiVxf1

Fydtm

VyiVyf1

dtmgFzm

VziVzf )(1

Center of PressureCenter of Pressure

Fz

Myx

Fz

Mxy

Results: Center of Pressure Results: Center of Pressure

Rearfoot strikers had a foot placement Rearfoot strikers had a foot placement angle of 10.4angle of 10.4

By 42 ms into contact the COP had moved By 42 ms into contact the COP had moved anteriorly to 50% of shoe lengthanteriorly to 50% of shoe length

It remained within 50-80% until the end of It remained within 50-80% until the end of support, 146 ms latersupport, 146 ms later

Results: Center of PressureResults: Center of Pressure

Midfoot Strikers:Midfoot Strikers:

First contact was made at 50% of shoe First contact was made at 50% of shoe lengthlength

Following a brief anterior movement the Following a brief anterior movement the COP migrates posteriorly and medially, COP migrates posteriorly and medially, reaching most posterior point at 20 msreaching most posterior point at 20 ms

Followed by a rapid anterior movement Followed by a rapid anterior movement reaching 65% of shoe length in 40 msreaching 65% of shoe length in 40 ms

.12 BW range .35 BW range

.43 BW at 46 ms .45 BW at 11 ms

.45 BW at 38 ms

2.2 BW at 23 ms2.7 BW at 75 ms

Shoe DesignShoe Design

Prior to this paper, track authorities stated that heel-toe patterns should be Prior to this paper, track authorities stated that heel-toe patterns should be used in long distance running and mid-foot patterns should be used in middle used in long distance running and mid-foot patterns should be used in middle distance.distance.Protection from impact forces should extend from the heel to 60% of shoe Protection from impact forces should extend from the heel to 60% of shoe length.length.The mid-foot group requires additional mid-foot impact protection.The mid-foot group requires additional mid-foot impact protection.The backward slope of the force vectors indicates that braking occurs while The backward slope of the force vectors indicates that braking occurs while the cop is as much as 70% of shoe length from the heel. As a result the the cop is as much as 70% of shoe length from the heel. As a result the outer sole should provide friction for braking throughout this region of the outer sole should provide friction for braking throughout this region of the shoe.shoe.