5/14/2012
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Run Smart not Hard:
The Effect of Stride Cadence on
Impact Variables
Caitlin Pearl, MSClinical Biomechanist
National Institute for Athletic Health & Performance
Sanford Health: Sioux Falls, SD
Outline
BACKGROUND
• Injury Mechanisms
• Impact Force
– Injured vs. Uninjured
– Controlling Impact Force
• Manipulating Step Rate
– Joint mechanics
– Injury rate (?)
APPLICATIONS
FDM-T
– Sanford Services
– Research Opportunities
Running…
• Running is comprised of a series of repetitive
single-limb impacts which requires:
– Sufficient impact force attenuation
– Limb/trunk stability
Powers, 2012
…Is All About Balance
Passive Shock Absorption
Active Shock Absorption
Bone and Cartilage
Eccentric Muscle
Contraction
…Is All About Balance
Passive Shock Absorption
Active Shock Absorption
…Is All About Balance
Passive Shock Absorption
Active Shock Absorption
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Numbers Game
• According to the 2009 National
Runner Demographics, there are
37 million runners in the US
– 11 million run ≥100 times per
year
• About 56% of recreational
runners, and as many as 90% of
runners training for a marathon
will experience some type of
running-related injury each year
http://www.trackshack.com/services/sponsor-demographics.shtml
Running Performance Services:
Sanford Health
• Team of sport rehabilitation
specialists & clinical biomechanist
• Evaluate injured and healthy
runners
• 90-minute evaluation:
– Functional movement screen
with PT: lower extremity
strength, flexibility, posture
– Treadmill running and video
analysis in frontal + sagittal
planes
– Recommendations and
treatment options
Assessing Runners with h/p/cosmos and FDM-T
Image copyright: zebris Medical GmbH, Germany
• Excessive and repetitive impacts (Heiderschiet et al., 2011)
– First 10% of stance phase
• Can reach magnitudes from 1.5 to 5x body weight within 10-30 ms (Hreljac et al. 2004)
– Too much energy for the body to safely absorb
Mechanisms of Injury
Mechanisms of Injury
• Impact forces are associated with overuse running
injuries (Cavanagh et al., 1980, Clement et al., 1980, James et al., 1978, Nigg 1986)
• Overuse injuries, such as stress fractures, are
dependent on both loading magnitude and loading
exposure (Edwards et al., 2009)
– Muscles failing to adequately absorb the energy from impact may
lead to “over-reliance” of passive structures, causing injury (Derrick et al., 1998)
What Determines Impact Force?
• The magnitude of impact force during running is
dependent on: (Heidershchiet et al., 2011)
o Landing mechanics
o Running speed, foot & COM velocity at contact
o Body mass
o Shoe properties
o Surface properties
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vGRF- A Closer Look
Pete Larson, http://www.runblogger.com/2011/02/vertical-impact-loading-rate-in-running.html
vGRF- A Closer Look
Pete Larson, http://www.runblogger.com/2011/02/vertical-impact-loading-rate-in-running.html
vGRF- A Closer Look
Pete Larson, http://www.runblogger.com/2011/02/vertical-impact-loading-rate-in-running.html
vGRF and Footstrike
• Approximately 80% of shod
runners are heelstrikers
• RFS experience higher impact
peaks and loading rates than MFS
and FFS
– -More vulnerable to injuries?
Davis et al., 2010
FDM-T: Heel strike FDM-T: Midfoot Strike
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FDM-T: Forefoot Strike Do Impacts Cause Injury?
• No published data comparing footstrike and injury
• Davis et al. (2010) initiated first prospective study
– Compared the impact loads of rearfoot strike runners who go on to
develop a running injury to their uninjured counterparts.
Comparison of impacts between injured
and non-injured runners
• 57% experienced a prospective injury
• Injured runners had significantly
higher impact loading variables, with
the exception of VILR, than the
uninjured runners
• Peak vertical force was identical
between groups
- Need for further research
Davis et al., 2010
Impact Peak & Loading Rate in Injured vs.
Non-Injured Runners
*
Previously injured runners exhibited a higher impact peak and loading rate than injury-free
runners
Hreljac et al., 2000
*
Kinetic Variables in Subjects with Previous
Lower-Extremity Stress Fractures
PPA (g) vGRF (BW) ILR (BW/s) ALR (BW/s)
Stress Fracture 9.24 3.87 158.61 117.93
Uninjured 7.16 2.48 108.89 77.52
Ferber et al., 2002
22% 36% 32% 34% DIFFERENCE:
Injury Frequency, Impact Peak and Loading Rate
Runners displaying a high impact peak and loading rate did not show an increased number
of running-related injuries over a 6 month monitoring period
Nigg et al., 2001
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How can we control impact?
• Increase step-rate (cadence)
– Decrease step length
• Improve mechanics at initial contact (extended knee, dorsiflexed
ankle)
– Decrease IC COM-heel distance
• Farther the foot strikes the ground in front of COM, greater the
braking impulse
• Most injuries occur during contact. By reducing
contact time, can we reduce the risk of injury?
Manipulating Cadence
Before After
Landing Mechanics
159 steps/min 175 steps/min
Step Frequency and Lower Extremity Loading
VIP= Vertical Impact Peak
VILR= Vertical Instantaneous Loading Rate
VALR= Vertical Average Loading Rate
Lower extremity loading
variables minimized at around
+15% of preferred step
frequency
Hobara et al., 2011
Effects of Step Rate Manipulation on Joint
Mechanics During Running
• Increasing one’s step rate by 10% of greater will result in a reduced
impact load on the body, due to less vertical COM velocity at
landing (Derrick et al. 1998, Hamill et al. 1995)
– As a result, less energy absorption is required by the lower extremity, specifically the
knee
• Can reduce the risk of developing a running-related injury or
facilitating recovery from an existing injury (Heiderscheit 2011)
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Increasing Step Rate Decreases Step Length
* ** *
Heiderscheit et al., 2011
Step Rate and COM Heel Distance
As step rate increased:
• Step length was shorter
• Less COM vertical displacement
• Heel was placed horizontally
closer to COM at touchdown
Heiderscheit et al., 2011
Increasing Step Rate Decreases Heel-COM
Distance at Contact
**
**
Heiderscheit et al., 2011
Increasing Step Rate Decreases Braking Impulse
**
* *
Heiderscheit et al., 2011
Peak vGRF was significantly reduced at +10% preferred step rate
and significantly increased at -10% (±±±± .6 N/kg)
FDM-T: Force Reduction
Peak vGRF 159 steps/min= 1304.2 N
= 18.55 N/kg
Peak vGRF 175 steps/min= 1205.7 N
= 17.15 N/kg
-1.4 N/kg
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Step Rate and Mechanical Energy
Step rate above preferred:
Decrease energy absorption (negative
work) at the knee and hip
Proportional decrease in energy
generation across all joints
Heiderscheit et al., 2011
Clinical Applications: Increased Cadence
Despite a greater number of loading cycles, running with an increased cadence has
been suggested to reduce the risk of tibial stress fractures. (Edwards et al., 2009)
Clinical Applications: Increased Cadence
• The reduced energy absorption at the hip in knee
when running with an increased cadence may prove
useful in rehabilitation (Heiderscheit, 2011)
– Can injured runners continue to run without aggravating
symptoms?
– Can we facilitate a progressive return to running?
Bottom Line
• It is unclear if, how or why impacts cause injury.
• Discover new meaning for “take a load off”:
increasing cadence may offer an easy, quick solution
for improving large, detrimental forces seen at
impact.
• HOWEVER, it is also important to explore alternative
methods for improving shock/impact absorption,
such as developing hip strength and control, and this
opportunity should be seriously considered for long-
term benefits.
FDM-T: Opportunities for Research?
• Observe the cumulative effect of loading
– Prospective study following loading patterns and injury
occurrence
• Continue seeking cause and effect relationship: impacts vs. injury
rate
– Footstrike patterns and injury occurrence
• MFS/FFS: 1st or 2nd metatarsal stress fracture?
• RFS- Tibial stress fractures, plantar fascitis?
• ITBS, PTF pain?
• Are the biomechanical changes seen with increased
step rate observed beyond short term?
Think about this:
It is estimated a runner sustains 1200-1500 impacts per
mile (each contact= ~1.5-5x BW).
FDM-T provides the opportunity to
look at each one of them.
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Questions?