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. Early humans most likely developed into 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.). The theory as first proposed used comparative 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 practices also indicated this likelihood (Carrier et al. 1984).
According to Sears (p. 12) scientific investigation (Walker & Leakey 1993) of the Nariokotome skeleton provided further evidence for the Carrier theory. 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 honor of the goddess Tailtiu, dates back to 1829 BCE and is one of the earliest records of competitive running. The origins of the Olympics and Marathon running are shrouded by myth and legend, though the first recorded games took place in 776 BCE.
Running in Ancient Greece can be traced back to these games of 776 BCE. Running gait can be divided into two phases regarding the lower extremity: stance and swing.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 occurs when a plantar portion of the foot makes initial contact with the ground. Common footstrike types include forefoot, midfoot, and heel strike types. 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. 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 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.
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. In a full stride length model, elements of both the terminal swing and footstrike contribute to propulsion. 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. 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.
On the other hand, a mid/forefoot strike helps in shock absorption, supporting plantar flexion from midstance to toe-off. Actual propulsion begins as the lower extremity enters midstance.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. 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. 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. 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. 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. 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. The upper extremity function serves mainly in providing balance in conjunction with the opposing side of the lower extremity. The movement of each leg is paired with the opposite arm, which serves to counterbalance the body, particularly during the stance phase.
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. 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. 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.
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. This causes the body to use abnormal compensatory motions in an attempt to avoid serious bone injuries. 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.
Conversely, a mid/forefoot strike has been associated with greater efficiency and lower injury risk due to the triceps surae being used as a lever system to absorb forces with the muscles eccentrically rather than through the bone. 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. Thus a mid/forefoot strike may aid in propulsion.
However, even among elite athletes, there are variations in self-selected footstrike types. This is especially true in longer distance events, where there is a prevalence of heel strikers. 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. 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.Biomechanical factors associated with elite runners include increased hip function, use, and stride length over recreational runners. 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.
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. With increased propulsion in the horizontal plane, less impact occurs from the decreased force in the vertical plane. Increased hip flexion allows for increased use of the hip extensors through midstance and toe-off, allowing for more force production. The difference even between world-class and national-level 1500-m runners has been associated with more efficient hip joint function.
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. 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.
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. 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.
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. Knee extension, however, contributes to additional stride length and propulsion during toe-off and is seen more frequently in elite runners as well.
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