Creative Running: Racing Towards Creativity

All About Running

(From Wikipedia, the free encyclopedia.)

Running is a means of terrestrial locomotion allowing humans and other animals to move rapidly on foot. It is simply defined in athletics terms as a gait in which at regular points during the running cycle both feet are off the ground. This is in contrast to walking, where one foot is always in contact with the ground, the legs are kept mostly straight and the center of gravity vaults over the stance leg or legs in an inverted pendulum fashion.^[1] A characteristic feature of a running body from the viewpoint of spring-mass mechanics is that changes in kinetic and potential energy within a stride occur simultaneously, with energy storage accomplished by springy tendons and passive muscle elasticity.^[2] The term running can refer to any of a variety of speeds ranging from jogging to sprinting.

The ancestors of mankind developed the ability to run for long distances about four and a half million years ago,^{[citation needed]} probably in order to hunt animals. Competitive running grew out of religious festivals in various areas. Records of competitive racing date back to the Tailteann Games in Ireland in 1829 BCE,^{[citation needed]} while the first recorded Olympic Games took place in 776 BCE.

History

It is thought that human running evolved at least four and a half million years ago out of the ability of the ape-like Australopithecus, an early ancestor of humans, to walk upright on two legs.^[3]

The theory proposed considered to be the most likely evolution of running is of early humans' developing as endurance runners from the practice of persistence hunting of animals, the activity of following and chasing until a prey is too exhausted to flee, succumbing to "chase myopathy" (Sears 2001), and that human features such as the nuchal ligament, abundant sweat glands, the Achilles tendons, big knee joints and muscular glutei maximi, were changes caused by this type of activity (Bramble & Lieberman 2004, et al.).^[4][5][6] The theory as first proposed used comparitative physiological evidence and the natural habits of animals when running, indicating the likelihood of this activity as a successful hunting method. Further evidence from observation of modern day hunting practice also indicated this likelihood (Carrier et al. 1984). ^[6][7] According to Sears (p. 12) scientific investigation (Walker & Leakey 1993) of the Nariokotome Skeleton provided further evidence for the Carrier theory.^[8]

Competitive running grew out of religious festivals in various areas such as Greece, Egypt, Asia, and the East African Rift in Africa. The Tailteann Games, an Irish sporting festival in honour of the goddess Tailtiu, dates back to 1829 BCE, and is one of the earliest records of competitive running.^[9] The origins of the Olympics and Marathon running are shrouded by myth and legend, though the first recorded game took place in 776 BCE.^[10]

Running kinematic description

Running gait can be divided into two phases in regard to the lower extremity: stance and swing.^{[11][12][13][14]} 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.^[15][16][17] 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 footstrike and the ankle should be slightly in front of the body.^[18] 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 defined as the time at which the lower extremity limb of focus is in knee flexion directly underneath the trunk, pelvis and hips. It is at this point that 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 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 initial swing begins.

Propulsion phase

Most recent research, particularly regarding the footstrike debate, has focused solely on the absorption phases for injury identification and prevention purposes. The propulsion phase of running involves the movement beginning at midstance until toe off.^[12][13][19] From a full stride length model however, components of the terminal swing and footstrike can aid in propulsion.^[14][20] Set up for propulsion begins at the end of terminal swing as the hip joint flexes, creating the maximal range of motion for the hip extensors to accelerate through and produce force. As the hip extensors change from reciporatory inhibitors to primary muscle movers, the lower extremity is brought back toward the ground, although aided greatly by the stretch reflex and gravity.^[14] Footstrike and absorption phases occur next with two types of outcomes. This phase can be only a continuation of momentum from the stretch reflex reaction to hip flexion, gravity and light hip extension with a heel strike, which does little to provide force absorption through the ankle joint.^[19][21][22] With a mid/forefoot strike, loading of the gastro-soleus complex from shock absorption will serve to aid in plantar flexion from midstance to toe-off.^[22][23] As the lower extremity enters midstance, true propulsion begins.^[19] The hip extensors continue contracting along with help from the acceleration of gravity and the stretch reflex left over from maximal hip flexion during the terminal swing phase. Hip extension pulls the ground underneath the body, thereby pulling the runner forward. During midstance, the knee should be in some degree of knee flexion due to elastic loading from the absorption and footstrike phases to preserve forward momentum.^[24][25][26] The ankle joint is in dorsiflexion at this point underneath the body, either elastically loaded from a mid/forefoot strike or preparing for stand-alone concentric plantar flexion. All three joints perform the final propulsive movements during toe-off.^{[19][21][22][23]} The plantar flexors plantar flex, pushing off from the ground and returning from dorsiflexion in midstance. This can either occur by releasing the elastic load from an earlier mid/forefoot strike or concentrically contracting from a heel strike. With a forefoot strike, both the ankle and knee joints will release their stored elastic energy from the footstrike/absorption phase.^[24][25][26] The quadriceps group/knee extensors go into full knee extension, pushing the body off of the ground. At the same time, the knee flexors and stretch reflex pull the knee back into flexion, adding to a pulling motion on the ground and beginning the initial swing phase. The hip extensors extend to maximum, adding the forces pulling and pushing off of the ground. The movement and momentum generated by the hip extensors also contributes to knee flexion and the beginning of 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 footstrike. 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 footstrike, 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 side is in the swing/recovery phase preparing for footstrike.^{[11][12][13][14]} 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 one side occurs, initial swing continues. The opposing limbs meet with one in midstance and midswing, beginning the propulsion and terminal swing phases.

Upper extremity function

Upper extremity function serves mainly in providing balance in conjunction with the opposing side of the lower extremity.^[12] The movement of each leg is paired with the opposite arm which serves to counterbalance the body, particularly during the stance phase.^[19] The arms move most effectively (as seen in elite athletes) with the elbow joint at an 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.^[27] 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. Mechanics of Propulsion

Footstrike debate

Recent research into running form 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.^[15] This is due to forces from a heel strike traveling through bones for shock absorption rather than being absorbed by muscles. Since bones cannot disperse forces easily, the forces transmitted to other parts of the body, including ligaments, joints and bones in the rest of the lower extremity all the way up to the lower back.^[28] This causes the body to use abnormal compensatory motions in an attempt to avoid serious bone injuries.^[29] These compensations include internal rotation of the tibia, knee and hip joints. Excessive amounts of compensation over time have been linked to higher risk of injuries in those joints as well as the muscles involved in those motions.^[21] Conversely, a mid/forefoot strike has been associated with greater efficiency and lower injury risk due to the grasctro-soleus complex being used as a lever system to absorb forces with the muscles eccentrically rather than through the bone.^[15] Landing with a mid/forefoot strike has also been shown to not only properly attenuate shock but allows the grastro-soleus complex to aid in propulsion via reflexive plantarflexion after stretching to absorb ground contact forces.^[20][30] Thus a mid/forefoot strike may aid in propulsion. However, even among elite athletes there are variations in self selected footstrike types.^[31] This is especially true in longer distance events, where there is a prevalence of heel strikers.^[32] 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.^[27] While one could attribute the faster speeds of elite runners compared to recreational runners with similar foostrikes to physiological differences, the hip and joints have been left out of the equation for proper propulsion. This brings up the question as to how heel striking elite distance runners are able to keep up such high paces with a supposedly inefficient and injurious footstrike technique.

Stride length, hip and knee function

Biomechanical factors associated with elite runners include increased hip function, use and stride length over recreational runners.^[27][33] 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.^[34] These forces are attenuated through increased stride length via increased hip flexion and extension through decreased ground contact time and more force being used in propulsion.^[34][35][36] With increased propulsion in the horizontal plane, less impact occurs from decreased force in the vertical plane.^[37] Increased hip flexion allows for increased use of the hip extensors through midstance and toe-off, allowing for more force production.^[19] The difference even between world class and national level distance runners has been associated with more efficient hip joint function.^[38] The increase in velocity likely comes from the increased range of motion in hip flexion and extension, allowing for greater acceleration and velocity. The hip extensors and hip extension have been linked to more powerful knee extension during toe-off, which contributes to propulsion.^[27] Stride length must be properly 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.^[39] 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.^[38][40][41] Secondly it allows for the knee joint to concentrically contract and provides major aid in propulsion during toe-off as the quadriceps group is capable of produce large amounts of force.^[19] Recreational runners have been shown to increase stride length through increased knee extension rather than increased hip flexion as exhibited by elite runners, which serves instead to provide an intense breaking motion with each step and decrease the rate and efficiency of knee extension during toe-off, slowing down speed.^[42] Knee extension however contributes to additional stride length and propulsion during toe-off and is seen more frequently in elite runners as well.^[27]