Editing Running (section)

==Description==
[[File:Muybridge runner.jpg|thumb|[[Eadweard Muybridge]] photo sequence]]

Running gait can be divided into two phases regarding the lower [[Limb (anatomy)|extremity]]: stance and swing.<ref name="Anderson 1996 76–89">{{cite journal|last=Anderson|first=T|title=Biomechanics and Running Economy|journal=Sports Medicine|year=1996|volume=22|issue=2|pages=76–89|doi=10.2165/00007256-199622020-00003|pmid=8857704|s2cid=22159220}}</ref><ref name="Nicola 2012 187–201">{{cite journal |last1=Nicola |first1=T. L. |last2=Jewison |first2=D. J. |title=The Anatomy and Biomechanics of Running|journal=Clinical Journal of Sport Medicine|year=2012|volume=31|issue=2 |pages=187–201|doi=10.1016/j.csm.2011.10.001|pmid=22341011 }}</ref><ref name="Novacheck 1998 77–95">{{cite journal|last=Novacheck|first=T.F.|title=The biomechanics of running|journal=Gait & Posture|year=1998|volume=7|issue=1|pages=77–95|doi=10.1016/s0966-6362(97)00038-6|pmid=10200378|s2cid=2057865 }}</ref><ref name="Schache 1999 30–47">{{cite journal|last=Schache|first=A.G.|title=The coordinated movement of the lumbo-pelvic-hip complex during running: a literature review|journal=Gait & Posture|year=1999|volume=10|issue=1|pages=30–47|doi=10.1016/s0966-6362(99)00025-9|pmid=10469939}}</ref> These can be further divided into absorption, propulsion, initial swing, and terminal swing.  Due to the continuous nature of running gait, no certain point is assumed to be the beginning.  However, for simplicity, it will be assumed that absorption and footstrike mark the beginning of the running cycle in a body already in motion.

===Footstrike===
Footstrike occurs when a plantar portion of the foot makes initial contact with the ground.  Common footstrike types include forefoot, midfoot, and heel strike types.<ref name="Daoud 2012 1325–34">{{cite journal|last=Daoud|first=A.I.|title=Foot Strike and Injury Rates in Endurance Runners: a retrospective study|journal= Medicine and Science in Sports and Exercise|year=2012|volume=44|issue=7|pages=1325–1334|doi=10.1249/mss.0b013e3182465115|pmid=22217561|s2cid=14642908|doi-access=free}}</ref><ref>{{cite journal|last=Larson|first=P|title=Foot strike patterns of recreational and sub-elite runners in a long-distance road race|journal=Journal of Sports Sciences|year=2011|volume=29|issue=15|pages=1665–1673|doi=10.1080/02640414.2011.610347|pmid=22092253|s2cid=12239202}}</ref><ref>{{cite journal|last=Smeathers|first=J.E.|title=Transient Vibrations Caused by Heel Strike|journal= Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine|year=1989|volume=203|issue=4|pages=181–186|doi=10.1243/PIME_PROC_1989_203_036_01|pmid=2701953|s2cid=36483935}}</ref> These are characterized by initial contact of the ball of the foot, ball and heel of the foot simultaneously and heel of the foot respectively.  During this time, the [[hip joint]] is undergoing extension from being in maximal flexion from the previous swing phase.  For proper force absorption, the knee joint should be flexed upon the footstrike, and the ankle should be slightly in front of the body.<ref name="Davis 1980 1590–95">{{cite journal|last=Davis|first=G.J.|title=Mechanisms of Selected Knee Injuries|journal=Journal of the American Physical Therapy Association|year=1980|volume=60|pages=1590–1595}}</ref> Footstrike begins the absorption phase as forces from initial contact are attenuated throughout the lower extremity. Absorption of forces continues as the body moves from footstrike to midstance due to vertical propulsion from the toe-off during a previous gait cycle.

===Midstance===
Midstance is when the lower extremity limb of focus is in knee flexion directly underneath the trunk, pelvis, and hips.  At this point, propulsion begins to occur as the hips undergo hip extension, the knee joint undergoes extension, and the ankle undergoes plantar flexion.  Propulsion continues until the leg is extended behind the body and toe-off occurs.  This involves a maximal hip extension, knee extension, and plantar flexion for the subject, resulting in the body being pushed forward from this motion, and the ankle/foot leaves the ground as the initial swing begins.

===Propulsion phase===
Research, especially in the footstrike debate, has primarily focused on identifying and preventing injuries during the absorption phases of running. The propulsion phase, which occurs from midstance to toe-off, is crucial for understanding how the body moves forward.<ref name="Nicola 2012 187–201" /><ref name="Novacheck 1998 77–95" /><ref name="Hammer 2010 2709–16">{{cite journal |last=Hammer |first=S.R. |year=2010 |title=Muscle contributions to propulsion and support during running |journal=Journal of Biomechanics |volume=43 |issue=14 |pages=2709–2716 |doi=10.1016/j.jbiomech.2010.06.025 |pmc=2973845 |pmid=20691972}}</ref> 

In a full stride length model, elements of both the terminal swing and footstrike contribute to propulsion.<ref name="Schache 1999 30–47" /><ref name="Ardigo 2008 17–22">{{cite journal |last=Ardigo |first=L.P. |year=2008 |title=Metabolic and mechanical aspects of foot landing type, forefoot, and rearfoot strike, in human running |journal=Acta Physiologica Scandinavica |volume=155 |issue=1 |pages=17–22 |doi=10.1111/j.1748-1716.1995.tb09943.x |pmid=8553873}}</ref> 
The setup for propulsion begins at the end of the terminal swing when the hip joint flexes, allowing the hip extensors to generate force as they accelerate through the maximal range of motion.

As the hip extensors transition from inhibitory to primary muscle movers, the lower extremity moves back towards the ground, aided by the [[stretch reflex]] and gravity.<ref name="Schache 1999 30–47" /> The footstrike and absorption phases follow, leading to two possible outcomes.

With a heel strike, this phase may be just a continuation of momentum from the stretch reflex, gravity, and light hip extension, offering little force absorption through the ankle joint.<ref name="Hammer 2010 2709–16" /><ref name="Bergmann 2000 817–827">{{cite journal |last=Bergmann |first=G. |year=2000 |title=Influence of shoes and heel strike on the loading of the hip joint |journal=Journal of Biomechanics |volume=28 |issue=7 |pages=817–827 |doi=10.1016/0021-9290(94)00129-r |pmid=7657680}}</ref><ref name="Lieberman 2010 531–535">{{cite journal |last=Lieberman |first=D. |year=2010 |title=Foot strike patterns and collision forces in habitually barefoot versus shod runners |journal=Nature |volume=463 |issue=7280 |pages=531–535 |bibcode=2010Natur.463..531L |doi=10.1038/nature08723 |pmid=20111000 |s2cid=216420}}</ref> On the other hand, a mid/forefoot strike helps in shock absorption, supporting plantar flexion from midstance to toe-off.<ref name="Lieberman 2010 531–535" /><ref name="Williams 2000 210–218">{{cite journal |last=Williams |first=D.S. |year=2000 |title=Lower Extremity Mechanics in Runners with a Converted Forefoot Strike Pattern |journal=Journal of Applied Biomechanics |volume=16 |issue=2 |pages=210–218 |doi=10.1123/jab.16.2.210}}</ref>

The actual propulsion begins when the lower extremity enters midstance.<ref name="Hammer 2010 2709–16" /> The hip extensors continue contracting, assisted by gravity and the stretch reflex from maximal hip flexion during the terminal swing. Hip extension pulls the ground underneath the body, propelling the runner forward.

During midstance, the knee should be slightly flexed due to elastic loading from the absorption and footstrike phases, preserving forward momentum.<ref name="Kubo 2000 181–187">{{cite journal |last=Kubo |first=K. |year=2000 |title=Elastic properties of muscle-tendon complex in long-distance runners |journal=European Journal of Applied Physiology |volume=81 |issue=3 |pages=181–187 |doi=10.1007/s004210050028 |pmid=10638375 |s2cid=10044650}}</ref><ref name="Magness">{{cite web |last=Magness |first=S. |date=4 August 2010 |title=How to Run: Running with proper biomechanics |url=http://www.scienceofrunning.com/2010/08/how-to-run-running-with-proper.html |access-date=3 October 2012}}</ref><ref name="Thys 1975 281–286">{{cite journal |last=Thys |first=H. |year=1975 |title=The role played by elasticity in an exercise involving movements of small amplitude |journal=European Journal of Physiology |volume=354 |issue=3 |pages=281–286 |doi=10.1007/bf00584651 |pmid=1167681 |s2cid=21309186}}</ref> The ankle joint is in [[dorsiflexion]] at this point, either elastically loaded from a mid/forefoot strike or preparing for stand-alone concentric plantar flexion.

The final propulsive movements during toe-off involve all three joints: ankle, knee, and hip.<ref name="Hammer 2010 2709–16" /><ref name="Bergmann 2000 817–827" /><ref name="Lieberman 2010 531–535" /><ref name="Williams 2000 210–218" /> The plantar flexors push off from the ground, returning from dorsiflexion in midstance. This can occur either by releasing the elastic load from an earlier mid/forefoot strike or through concentric contraction from a heel strike.

With a forefoot strike, the ankle and knee joints release their stored elastic energy from the footstrike/absorption phase.<ref name="Kubo 2000 181–187" /><ref name="Magness" /><ref name="Thys 1975 281–286" /> The quadriceps group/knee extensors fully extend the knee, pushing the body off the ground. Simultaneously, the knee flexors and stretch reflex pull the knee back into flexion, initiating the initial swing phase. The hip extensors extend to the maximum, contributing to forces pulling and pushing off the ground, as well as initiating knee flexion and the initial swing phase.

===Swing phase===
Initial swing is the response of both stretch reflexes and concentric movements to the propulsion movements of the body.  Hip flexion and knee flexion occur, beginning the return of the limb to the starting position and setting up for another foot strike.  The initial swing ends at midswing when the limb is again directly underneath the trunk, pelvis, and hip with the knee joint flexed and hip flexion continuing.  Terminal swing then begins as hip flexion continues to the point of activation of the stretch reflex of the hip extensors.  The knee begins to extend slightly as it swings to the anterior portion of the body.  The foot then makes contact with the ground with a foot strike, completing the running cycle of one side of the lower extremity.
Each limb of the lower extremity works opposite to the other.  When one side is in toe-off/propulsion, the other hand is in the swing/recovery phase preparing for footstrike.<ref name="Anderson 1996 76–89"/><ref name="Nicola 2012 187–201"/><ref name="Novacheck 1998 77–95"/><ref name="Schache 1999 30–47"/> Following toe-off and the beginning of the initial swing of one side, there is a flight phase where neither extremity is in contact with the ground due to the opposite side finishing terminal swing.  As the footstrike of the one hand occurs, the initial swing continues.  The opposing limbs meet with one in midstance and midswing, beginning the propulsion and terminal swing phases.

===Upper extremity function===
[[file:Police running in North Point lockdown area 20210128.gif|thumb|upright=1.1|Video of man running]]
The upper extremity function serves mainly in providing balance in conjunction with the opposing side of the lower extremity.<ref name="Nicola 2012 187–201"/> The movement of each leg is paired with the opposite arm, which serves to counterbalance the body, particularly during the stance phase.<ref name="Hammer 2010 2709–16"/> The arms move most effectively (as seen in elite athletes) with the elbow joint at approximately 90 degrees or less, the hands swinging from the hips up to mid-chest level with the opposite leg, the Humerus moving from being parallel with the trunk to approximately 45 degrees shoulder extension (never passing the trunk in flexion) and with as little movement in the transverse plane as possible.<ref name="Cavanagh 1990">{{cite book|last=Cavanagh|first=P.R.|title=Biomechanics of Distance Running|year=1990|publisher=Human Kinetics Books|location=Champaign, I.L}}</ref> The trunk also rotates in conjunction with arm swing. It mainly serves as a balance point from which the limbs are anchored.  Thus trunk motion should remain mostly stable with little motion except for slight rotation, as excessive movement would contribute to transverse motion and wasted energy.

===Footstrike debate===
Recent research into various forms of running has focused on the differences in the potential [[injury]] risks and shock absorption capabilities between heel and mid/forefoot footstrikes.  It has been shown that heel striking is generally associated with higher rates of injury and impact due to inefficient shock absorption and inefficient biomechanical compensations for these forces.<ref name="Daoud 2012 1325–34"/> This is due to pressures from a heel strike traveling through bones for shock absorption rather than being absorbed by muscles.  Since bones cannot disperse forces easily, the forces are transmitted to other parts of the body, including ligaments, joints, and bones in the rest of the lower extremities up to the lower back.<ref>{{cite journal|last=Verdini|first=F.|title=Identification and characterization of heel strike transient|journal=Gait & Posture|year=2005|volume=24|issue=1|pages=77–84|doi=10.1016/j.gaitpost.2005.07.008|pmid=16263287|hdl=11566/25362 }}</ref> This causes the body to use abnormal compensatory motions in an attempt to avoid serious bone injuries.<ref>{{cite journal|last=Walter|first=N.E.|title=Stress fractures in young athletes|journal=The American Journal of Sports Medicine|year=1977|volume=5|issue=4|pages=165–170|doi=10.1177/036354657700500405|pmid=883588|s2cid=39643507}}</ref> These compensations include internal rotation of the tibia, knee, and hip joints.  Excessive compensation over time has been linked to a higher risk of injuries in those joints and the muscles involved in those motions.<ref name="Bergmann 2000 817–827"/> Conversely, a mid/forefoot strike has been associated with greater efficiency and lower injury risk due to the [[Triceps surae muscle|triceps surae]] being used as a lever system to absorb forces with the muscles eccentrically rather than through the bone.<ref name="Daoud 2012 1325–34"/> Landing with a mid/forefoot strike has also been shown to properly attenuate shock and allow the triceps surae to aid in propulsion via reflexive plantarflexion after stretching to absorb ground contact forces.<ref name="Ardigo 2008 17–22"/><ref>{{cite journal|last=Perl|first=D.P|title=Effects of Footwear and Strike Type of Running Economy|journal= Medicine & Science in Sports & Exercise|year=2012|volume=44|issue=7|pages=1335–1343|doi=10.1249/mss.0b013e318247989e|pmid=22217565|s2cid=449934|doi-access=free}}</ref> Thus a mid/forefoot strike may aid in propulsion.
However, even among elite athletes, there are variations in self-selected footstrike types.<ref>{{cite journal|last=Hasegawa|first=H.|title=Foot Strike Patterns of Runners at the 15-km Point During Elite-Level Half Marathon|journal=Journal of Strength and Conditioning Research|year=2007|volume=21|issue=3|pages=888–893|doi=10.1519/00124278-200708000-00040|pmid=17685722}}</ref> This is especially true in longer distance events, where there is a prevalence of heel strikers.<ref>{{cite journal|last=Larson|first=P.|title=Foot strike patterns of recreational and sub-elite runners in a long-distance road race|journal=Journal of Sports Sciences|year=2011|volume=29|issue=15|pages=1665–1673|doi=10.1080/02640414.2011.610347|pmid=22092253|s2cid=12239202}}</ref> There does tend however to be a greater percentage of mid/forefoot striking runners in the elite fields, particularly in the faster racers and the winning individuals or groups.<ref name="Cavanagh 1990"/> While one could attribute the faster speeds of elite runners compared to recreational runners with similar footstrikes to physiological differences, the hip, and joints have been left out of the equation for proper propulsion.  This raises the question of how heel-striking elite distance runners can keep up such high paces with a supposedly inefficient and injurious foot strike technique.

===Stride length, hip and knee function===
Biomechanical factors associated with elite runners include increased hip function, use, and stride length over recreational runners.<ref name="Cavanagh 1990"/><ref name="Pink 1994 541–549">{{cite journal|last=Pink|first=M.|title=Lower Extremity Range of Motion in the Recreational Sport Runner|journal=American Journal of Sports Medicine|year=1994|volume=22|issue=4|pages=541–549|doi=10.1177/036354659402200418|pmid=7943522|s2cid=1744981}}</ref> An increase in running speeds causes increased ground reaction forces, and elite distance runners must compensate for this to maintain their pace over long distances.<ref name="Weyand 2010 1991–1999">{{cite journal|last=Weyand|first=P.G.|title=Faster top running speeds are achieved with greater ground forces not more rapid leg movements|journal=Journal of Applied Physiology|year=2010|volume=89|issue=5|pages=1991–1999|doi=10.1152/jappl.2000.89.5.1991|pmid=11053354|s2cid=2448066|doi-access=free}}</ref>
These forces are attenuated through increased stride length via increased hip flexion and extension through decreased ground contact time and more energy being used in propulsion.<ref name="Weyand 2010 1991–1999"/><ref>{{cite journal|last=Mercer|first=J.A.|title=Individual Effects of Stride Length and Frequency on Shock Attenuation during Running|journal= Medicine & Science in Sports & Exercise|year=2003|volume=35|issue=2|pages=307–313|doi=10.1249/01.mss.0000048837.81430.e7|pmid=12569221|s2cid=23896334 |doi-access=free}}</ref><ref>{{cite journal|last=Stergiou|first=N.|title=Subtalara and knee joint interaction during running at various stride lengths|journal=Journal of Sports Medicine and Physical Fitness|year=2003|volume=43|issue=3|pages=319–326|pmid=14625513 }}</ref> With increased propulsion in the horizontal plane, less impact occurs from the decreased force in the vertical plane.<ref>{{cite journal|last=Mercer|first=J.A.|title=Relationship between shock attenuation and stride length during running at different velocities|journal=European Journal of Applied Physiology|year=2002|volume=87|issue=4–5|pages=403–408|doi=10.1007/s00421-002-0646-9|pmid=12172880|s2cid=26016865}}</ref> Increased hip flexion allows for increased use of the hip extensors through midstance and toe-off, allowing for more force production.<ref name="Hammer 2010 2709–16"/>
The difference even between world-class and national-level 1500-m runners has been associated with more efficient hip joint function.<ref name="Leskinen 2009 1–9">{{cite journal|last=Leskinen|first=A.|title=Comparison of running kinematics between elite and national-standard 1500-m runners|journal=Sports Biomechanics|year=2009|volume=8|issue=1|pages=1–9|doi=10.1080/14763140802632382|pmid=19391490|s2cid=25422801}}</ref> The increase in velocity likely comes from the increased range of motion in hip flexion and extension, allowing for greater acceleration and speed.  The hip extensors and extension have been linked to more powerful knee extension during toe-off, contributing to propulsion.<ref name="Cavanagh 1990"/>
Stride length must be appropriately increased with some degree of knee flexion maintained through the terminal swing phases, as excessive knee extension during this phase along with footstrike has been associated with higher impact forces due to braking and an increased prevalence of heel striking.<ref>{{cite journal|last=Lafortune|first=M.A.|title=Dominant role of interface over knee angle for cushioning impact loading and regulating initial leg stiffness|journal=Journal of Biomechanics|year=2006|volume=29|issue=12|pages=1523–1529|doi=10.1016/s0021-9290(96)80003-0|pmid=8945650}}</ref> Elite runners tend to exhibit some degree of knee flexion at footstrike and midstance, which first serves to eccentrically absorb impact forces in the quadriceps muscle group.<ref name="Leskinen 2009 1–9"/><ref>{{cite journal|last=Skoff|first=B.|title=Kinematic analysis of Jolanda Ceplak's running technique|journal=New Studies in Athletics|year=2004|volume=19|issue=1|pages=23–31}}</ref><ref>{{cite journal|last=Skoff|first=B|title=Kinematic analysis of Jolanda Ceplak's running technique|journal=New Studies in Athletics|year=2004|volume=19|issue=1|pages=23–31}}</ref> Secondly it allows for the knee joint to contract concentrically and provides significant aid in propulsion during toe-off as the quadriceps group is capable of producing large amounts of force.<ref name="Hammer 2010 2709–16"/>
Recreational runners have been shown to increase stride length through increased knee extension rather than increased hip flexion, as exhibited by elite runners, which provides an intense braking motion with each step and decreases the rate and efficiency of knee extension during toe-off, slowing down speed.<ref name="Pink 1994 541–549"/> Knee extension, however, contributes to additional stride length and propulsion during toe-off and is seen more frequently in elite runners as well.<ref name="Cavanagh 1990"/>