KIN 100 1st Edition Lecture 17Gait Biomechanics and Footwear- Lecture by Carl● Running walking goals■ rotational->linear motion(move forward)■ Speed■ Efficiency● how economical is movement○ Stride cycle-Walking■ right foot strike to next right foot strike● or left foot■ stance phase● foot in contact with ground■ swing phase● foot off of ground■ Single support● only one leg on ground■ double support● both legs on ground● only in walking○ Stride cycle- running■ stance phase● much shorter● one foot only■ swing phase■ flight phase● no feet in contact with ground● only running○ Stride= stance + swing■ as speed increases, stance and flight times change● stance time decreases○ Quantifying stride cycle■ stride rate(frequency)-# of strides/sec■ stride length- distance covered by one stride● distance between one right foot touch and the next■ stride rate x stride length = speed● Efficiency Increased via○ minimize Vertical COM displacement■ dont want to waste energy moving up and down■ economical running-com stays at a constant height● Relationship bewtween force and velocity○ 2nd law of motion■ force = m x a○ early in stance, runners foot is exerting a forward directed force on ground■ ground pushes back with equal force-ground reaction force■ breaking stage● posterior acceleration● force from ground is opposite of direction○ late stance- propulsive force■ anterior acceleration■ increase speed-force in direction of motion○ horizontal forces- constant speed■ breaking forces=propulsive forces■ slowing down- breaking force> propulsive force■ accelerating- breaking force< propulsive force○ horizontal forces and efficiency■ always include breaking and accelerating■ try and minimize force producing equal breaking and propulsive forces● minimize breaking force● Quantifying motion during gait○ pronation angle (rearfoot angle-tibial angle)■ pronation- ankle rolls inward■ supination- ankle rolls outward○ pronation and supination pattern- normal■ supination-> neutral->pronation->neutral->supination● Footwear-Shoe Type○ 1960s running shoes all similar■ rubber outsole■ cushioned midsole- EVA foam■ nylon upper material○ fitness boom of 1970s brought more runners○ 1980 companies surveyed more when making shoes○ majority of injury● “training error”● excessive foot motion (over pronation)● poor body alignment■ injury prevention● valgus=inward bending of knees(distal segment)-knock knees● varus=bow-legged outward bending of distal segment● patellofemoral pain○ pain originating from posterior surface of the patella and the femur bone● achilles tendonitis-overuse injury straining tendon● plantar fasciitis- inflammation of the tendon tissue- tissue on bottom of foot● tibial stress syndrome- shin splints, ■ injury interventions● orthotics○ put something into shoe to change how foot interacts with the ground● gait retraining○ teach body how to move in more economical way● shoe design○ change stiffness of materials○ change geometry of the cushioning○ brooks introduced varus wedge■ controls foot motion○ 3 types of shoes (also used for foot classification)■ motion control■ stability■ cushioned/neutral■ minimalist shoes● level platform-zero lift○ shoe/foot classification■ using pronation to assign shoes has limited scope■ now looking at coupling at knee ankle hip■ whole foot motion, not just pronation● foot strike patterns○ rearfoot runners■ land with heal- transition to midfoot and push off○ midfoot strikers■ land flat transition to toe■ land on toe but heel touches○ forefoot strikers■ land on the ball of the foot■ no heel touch○ Forefoot(ff) vs rearfoot(rf)■ impact peak- occurs early in stance phase■ active peak- occurs in middle■ not studies have supported that rearfoot is running is bad for you● doesn’t decrease risk of injury just location of injury● drastic change can cause injury■ elite distance runners change foot strike pattern over course of race● increase speed= greater tendency to land on balls of feet● Barefoot/minimalist running○ advocates believe it allows body to move more naturally○ not end all cure all■ environment- tarahumara don’t run on cement■ gradual and smooth transition works- don’t do it all at once■ might be more useful as a tool in training to strengthen muscles instead of complete
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