Biomechanics of Running

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Biomechanics of Running Powered By Docstoc
					                 Walking Gait Cycle
   Walking Gait Cycle - 60:40 stance to swing phase

    Stance Phase: (IC) LR – MS – TST – PSW
    LR – beginning of 1st double support phase
    MS – foot is in full contact – adapting to env’t,
       beginning of single support, which is of equal
       duration of contralateral swing phase
    TST – foot is preparing to toe off (TO)
    PSW – 2nd double support phase

    Swing Phase: begins with TO and ends w/ IC
       ISW – MSW - TSW
      Running vs. Walking Gait Cycles
   The Running Gait Cycle has a temporal reversal of
    Stance:Swing phases (40:60) as compared to
    Walking Gait Cycle (60:40); the stance phase during
    sprinting may be as low as 22% of cycle

    Stance Phase: Absorption – (Mid stance) – Propulsion
    Swing Phase: ISW (75%) – (MSW) - TSW (25%)

Running Gait – two periods of double float in swing;
  refers to when neither foot is in contact w/ the
  ground; at the beginning and at the end of each
  running swing phase

Walking Gait – two double support periods in stance
Float vs. Support
                Running Gait Cycle
   Step length – IC of one foot to IC of the 2nd foot
   Stride length – IC of 1st foot to IC of the same foot
   Cadence – number of steps in a given time; on
    average about 100-122 steps/min with females
    averaging about 6-9 s/m higher

   As running Velocity increases, there is an initial
    increase in step length, followed by increased cadence
   Stride length is limited by runner’s leg length, height,
    and ability; generally the longer the stride, the higher
    the velocity
   When optimum stride length is attained; further
    velocity increases will come from increased cadence
   Kinematics of Walking and Running are much
   There is an increase in joint ROM with increasing
   Virtually no difference is found in the transverse
    and frontal plane kinematics; with most of the
    difference occurring in the sagittal plane
     • Lower C of G
     • Increased speed due to increased flexion of
       hips and knees; and increased dorsiflexion of
       the ankle
          Knee Kinematics of Running
   The knee demonstrates increased flexion with increasing
    velocity, but as seen with the hip, extension decreases
   Absorption phase of the stance phase sees knee flexion to
    accommodate ground reactive forces; walking only requires
    about 10 deg of flexion vs.35 during running
   Max knee flexion occurs at MS, after IC, during the absorption
    phase; this is followed sequentially by knee ext; max knee
    flexion during walking occurs just after TO
   Avg. Knee ROM is 63 deg during Running and 60 deg during
    walking; the major difference is that max flexion during walking
    only reaches an avg. of 64 deg, whereas during running it
    reaches an avg. of 79 deg.; conversely, knee extension is on
    average, 10 degrees less during running than during walking
    (-16 deg. vs -6 deg).
        Hip Kinematics of Running
   Flexion of the hip increases, as extension of the
    hip actually decreases with increasing velocity

    • One study of walking found overall ROM of 43
      deg, with 37 deg of flexion and 6 deg of ext;
      this study also found an increased ROM during
      running, with overall ROM averaging 46 deg,
      all of which was hip flexion with the hip never
      reaching neutral (negative extension)

    • Max hip ext occurs at TO; Max hip flex occurs
      at TSW
          Ankle and Foot Kinematics
   Ankle joint – primary plantar/dorsiflexor

   Foot joints – including subtalar, oblique midtarsal,
    longitudinal midtarsal and 5th ray; provide for tri-
    planar pronation/supination
     • Pronation – dorsiflexion/eversion/abduction
     • Supination – plantarflexion/inversion/adduction

   Metatarsalphalangeal joints (MTP) are biplanar –
    mostly dorsiflexion/plantarflexion w/ some abd/add
Foot Osteology
          Ankle and Foot Kinematics cont.
   Walking: ankle plantarflexes after IC and during LR,
    followed by dorsiflexion at MS; overall ROM is approx. 30
    deg (18 plantarflex/12dorsiflex)

   Running: overall ankle ROM of 50 deg;
     • At IC (rearfoot in most), ankle undergoes rapid
       dorsiflexion during absorption (pronation)
     • Supination is limited due to diminished time of
       plantarflexion, and pronation is increased
     • May lead to excessive pronation injuries
     • Running shoes or orthotics may limit this excessive
       pronation, and allow for more supination, and thus a
       more rigid foot for propulsion
     • A pronated subtalar joint allows the foot to become the
       “mobile adapter”; whereas a supinated subtalar joint
       serves to lock the midtarsal joints, creating a rigid lever
       to better serve propulsion
Windlass Mechanism
              The plantar fascia
              and the intrinsic
              foot muscles
              increase the
              efficiency of
              propulsion by
              providing “spring-
              like” support to the
              medial arch of the
              foot, helping to
              deliver the foot
              into supination,
              and contributing an
              elastic tension.
Windlass Mechanism (cont.)
Lower Extremity Kinematics of Running
   At IC, the pelvis, femur and tibia begin to
    internally rotate; int. rotation lasts through LR
    until MS; this everts and unlocks the subtalar
    joint, oblique and longitudinal midtarsal joints
    and in turn absorbs shock (pronation)
   External Rotation of the pelvis, femur and tibia
    begin following MS, causing inversion and
    subtalar and mid foot locking, creating the rigid
    lever for propulsion
   All lower extremity joints work together during
    walking/running to provide a biomechanically
    efficient means of locomotion
   These joints depend on each other and upon
    muscular action to carry out walking or running
Lower Extremity Kinematics of Running (cont.)

Metatarsal Break-
  the oblique line
  drawn across the
  metatarsal heads.
  This oblique axis
  promotes hind foot
  inversion during toe
  off, which
  contributes to
  external rotation of
  the entire stance
Lower Extremity Kinematics
           Lower Extremity Kinetics
   Kinetics – the study of forces that cause movement,
    both internally (muscular) and externally (ground
    reactive forces)
   As compared to walking, running increases muscle
    activity in all muscles
   Ground reactive forces – measured with a force
    plate system – demonstrates that vertical reactive
    forces are the most significant in running
   In rearfoot or heel strikers (80% of runners), there
    is a “two-bump” force plate appearance with one
    occurring in the rearfoot during loading response
    and one in the forefoot during propulsion
   Walking produces GRF of 1.3-1.5x body weight
   Running produces GRF of 3-4x body weight
                       Clinical Note
   Running injuries typically occur as a result of volume training
   With 3-4x body weight with each impact, 50-70 steps per foot
    per minute, 300-900 times per mile, the cumulative load can
    be measured in tons
   Stress fractures occur as a result of high volume training,
    combined with inadequate rest and recovery and/or
    biomechanical flaws
   Observed running injuries often occur at sites that mirror areas
    of peak force plate measures
   Placing a runner in a cushioning shoe may minimize peak
    force; however, the extra shock absorbing materials built into
    the midsole may result in excessive pronation in some runners,
    both due to less restriction of pronation and possibly due to
    increased moment arm on which GRFs act
Stress Fractures
              Running Economy
   Measured in terms of Submaximal Metabolic
    Energy Expenditure (VO2submax), running
    economy is a method by which running
    biomechanics are studied to determine their
    affect on running performance
   It is hypothesized that some variations in
    economy might be due to differences in genetic
    factors that cannot be changed through
    technique adjustments or training
   Other factors that are thought to contribute
    include motor unit recruitment, anatomical
    mechanical advantage and movement skill
         Factors and their Positive Effect
              on Running Economy
Vertical oscillation
Trunk lean
A-P Impulse
Knee Extension                       VO2
Plantarflexion velocity
Arm motions
Vertical Force
Hip Extension
Stride Length
Stride Index
          Running Economy (cont.)
   It is likely that Running Economy is directly effected by
    running mechanics
   However, it is not known how much running performance
    can be enhanced by altering a runner’s technique or style
   Many running related movement patterns that may seem
    uneconomical or sub-optimal may be as a result of an
    adaptation to a structural or functional anomaly; where
    alteration of that pattern may diminish economy and/or
    increase risk of injury
   External factors that can influence economy include shoe
    weight, midsole composition, wind velocity, materials and
    slope of running surface. These have been identified and
    are relatively easy to measure.
   Identifying running styles or techniques that can
    predictably result in economy changes is very difficult
   O’Connor, F and Wilder, R (2001). Textbook of
    Running Medicine, McGraw Hill.
   Neumann, D.A. (2002). Kinesiology of the
    Musculoskeletal System. St. Louis, Missouri.
   McGinnis, P.M. (2005). Biomechanics of Sport
    and Exercise 2nd ed. Champaign, IL. Human
   Cavanagh, P.R. (1990). Biomechanics of Distance
    Running. Champaign, IL. Human Kinetics