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«A Thesis Submitted to the Graduate Faculty of the Louisiana State University and Agricultural Mechanical College in partial fulfillment of the ...»

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2.1. Common Running Injuries McGrath and Finch‟s (1996) report features a cause-and-effect analysis of common injuries among track runners. The document provides detailed descriptions of what causes the problems faced when runners wear track spikes. This research showed the following related

injuries that can occur when the spike shoes do not fit the athlete:

 Plantar fasciitis: an inflammation of the thick band of tissue from the heel to the base of the toes in the bottom of the foot. When placed under stress, the plantar fascia stretches and tears, leading to inflammation.

 Shin splint, also called tibial stress syndrome: the inflammation of the tendons on the inside of the front of the lower leg, i.e. the shins.

 Achilles tendinitis: occurs when the Achilles tendon, a large tendon connecting the two major calf muscles (gastronemius and soleus), is placed under too much stress causing inflammation. If the inflamed Achilles continues to be stressed, it can tear or rupture.

 Chondromalacia: a cracking or wearing away of the cartilage under the kneecap, resulting in pain and inflammation.

 Iliotibial band syndrome: inflammation and pain on the outside of the thigh, where the iliotibial band rubs against the femur.

Such findings are comparable to the previously mentioned observations of the Louisiana State University track-and-field team. They also coincide with statements from the track-and-field team staff.

In a personal interview (2007), Assistant Coach Mark Elliott, who coaches distance and mid-distance at Louisiana State University, stated that track athletes wear spikes on a minimum basis of four days per week and three hours per day. Elliott added that from two months to one year, the amount of time spent wearing spikes accumulates, and athletes tend to develop problems in their legs, lower back, tibia, metatarsals, and patella, as illustrated in Figure 2.1.

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The research of Myburgh et al. (1988) indicated that 84% of injuries among runners occur on the tibia (shin) area, and 13% are linked to the Achilles tendon. This project thus focuses on these two areas and the related muscles.

2.2. Running and Walking Techniques and the Common Track Spike Shoe 2.2.1. Running and Walking Biomechanics Au et al. (2006) provided a model for the ankle-foot walking process, in which the study described each phase and its corresponding foot angle. The walking process is divided into two major stages: stance and swing. Stance, which constitutes the majority of the walking process (about 60%), is made up of three phases or moments:

Controlled plantarflexion: begins at heel-strike and ends at foot-flat. During this

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Controlled dorsiflexion: begins at foot-flat and continues until the ankle reaches a state of maximum dorsiflexion. The main function of the human ankle during controlled dorsiflexion is to store the elastic energy needed to propel the body

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Powered plantarflexion: begins at maximum dorsiflexion and ends at toe-off.

During this phase, additional energy is supplied, along with the spring energy stored during the previous phase to achieve the high plantarflexion power during

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Swing is thus the phase that separates each stance, starting at toe-off and ending at heelstrike. During swing, the foot is lifted, proceeding to actual geographic locomotion. The

following figure illustrates the biomechanics of walking and its distinct phases:

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Figure 2.3 graphs the ankle angle change in combination with the torque, that is, the rotary moment during walking.

Segments 1-2, 2-3, and 3-4 represent the ankle torque-angle behaviors during Controlled Plantarflexion, Controlled Dorsiflexion, and Powered Plantarflexion phases of gait, respectively. One must note, however, that the foot does not touch the ground during the swing phase and therefore little pressure is exerted upon the heel, the Achilles tendon, or the tibialis anterior. The research concerning this project is more centered on the stance phase.

Furthermore, one may notice on Figures 2.2 and 2.3 that the swing phase of one leg corresponds to the stance phase of the other.

Given the fact that each athlete has a unique running technique (gait), a shoe should be adjustable to facilitate and support his/her motion. Raptopoulos et al. (2006) conducted a gait analysis of gait modes among men and women. Their results showed stronger hip movements among women. However, women‟s walking and running pattern indicate use of extrinsic foot muscles similar to that of men. When combined with observations from the Louisiana State University track team and testimonials from the team staff regarding female injuries, Raptopoulos et al.‟s (2006) gait analysis indicate that female runners could benefit from the removable heel as much as men could.

In Principles of Human Anatomy, Tortora (2002) defines the movements that characterize

different walking and running techniques:

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The classic spikes are designed for plantarflexion, that is, for short and mid-distance runners. Yet, these athletes walk in dorsiflexion mode (flat-footed), while common spikes are generally designed for athletes to run on the toes. Thus, those who walk on their heels after extreme physical activity have minimal stability and cushion and therefore, can easily hurt their Achilles‟ tendons, as much pressure is exerted onto their tibia and gastrocnemius.





In addition, Donley and Leyes (2001) wrote that extreme or repetitive dorsiflexion can lead to direct trauma, along with anterior bony ankle impingement, that is, the formation of osteophytes (bone spurs) on the anterior edge of the distal tibia. This is, according to the article, a common problem among runners. Injuries related to extreme dorsiflexion are limiting the athlete not only in terms of painful symptoms, but also because they eventually prevent the runners from performing to the best of their abilities: “patients will complain of painful limitation of dorsiflexion, catching, and swelling of the ankle. These symptoms can be debilitating and considerably limit their athletic performance.” Such injuries would increase in intensity and gravity were dorsiflexion to be practiced in shoes designed for plantar flexion. For instance, the non-operative treatments Donley and Leyes (2001) proposed in a successfully experiment included rest, rubber-sole wedge shoes, and, interestingly, an internal or external heel lift.

Saunders et al. (1953) established a list of gait determinants that differentiate normal and pathological walking. According to their research, an inefficient, pathological gait pattern is characterized by numerous lateral and vertical excursions in the body‟s center of gravity. Thus, using the argument that “locomotion is the translation of the center of gravity through space along a pathway requiring the least expenditure of energy supplies” (Saunders et al., 1953), minimizing these excursions improves the quality of the gait. The article states that gait assessment is accomplished upon observation of these six major factors, also called major

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The determinant of interest in this thesis is the knee and ankle interaction. In effect, Thompson‟s (2002) study of Saunders et al. (1953) designated this determinant as one of the limitations to the troughs (or low points) in the sinusoidal pathway that occur during the gait cycle. An analysis of the biomechanics of walking (see Figure 2.3) finds that walking in spike shoes without a heel challenges the ankle in maintaining balance in the body, creating a vertical excursion in the center of gravity as pressure is exerted on the tibialis anterior and the Achilles tendon. Thus, when compared to the normal human gait pattern, walking in spike shoes with no heels qualifies as a pathological gait, and therefore requires correction. This project presents a removable heel as a potential correction to such a pathological gait.

Wakeling et al. (2001) conducted a study of the muscle activity as a response to ground reaction forces. Their project began from the starting point in which the human body reacts to the impact forces that occur at heel strike. Their study thus tests the level of muscle activity in the lower extremity muscles (among which are the gastrocnemius and the tibialis anterior) as they respond to the rate of impact forces, using a pendulum to deliver impacts to the heel repetitively, using various materials in the subjects‟ shoes, as seen in Figure 2.4. The pendulum apparatus, as set in the illustration, was pulled back to a reference stop. It swung for the subject to impact the wall with his right heel.

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The results of this study showed that there is a ratio of 96% in the tibialis anterior and 48% in the gastrocnemius between the pre-activation intensity and the muscle activity intensity. Therefore, conditions in which the impact to the ground is increased, such as when walking in heelless spike shoes, implicate a more intense muscle activity in the gastrocnemius and tibialis anterior, eventually or occasionally resulting in stress or fatigue. Inversely, a feature that would absorb some of the intensity of the impact, such as a removable heel, should reduce the intensity of muscle activity and thereby reduce risks of injuries related to stress and fatigue in the lower extremities.

2.2.2. Muscles Involved: The Extrinsic Foot Muscles Extrinsic foot muscles can be defined as the “muscles that insert on the foot but originate proximal to the foot” (O‟Connor et al., 2004). This group is constituted by the following muscles (Smith et al., 1996):

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extensor hallucis longus extensor digitorum longus Because of their impact on foot motion, this specific group of muscles is related to numerous running injuries among track-and-field athletes. O‟Connor et al. (2004, 2006) studied the role of extrinsic foot muscles during running using mfMRI technology and, more extensively, electromyography. According to the authors, these muscles act as “invertor muscles of the foot and are attributed the primary role in resisting foot pronation during the first stance” (O‟Connor et al., 2006). Pronation being the act of turning one‟s feet downward – as opposed to supination – extrinsic foot muscles are responsible for maintaining balance and channeling energy toward the purpose of geographic motion (walking or running). Figure 2.5 provides a labeled visual representation of the extrinsic foot muscles.

Due to the importance of their role during the walking and running stance and to the preponderance of tibial stress syndrome and Achilles tendinitis injuries among track-and-field runners, two extrinsic foot muscles, the tibialis anterior and the gastrocnemius, were selected to provide insight into the quality of walking after running, thus evaluating biomechanically modified track-and-field spike shoes. These two muscles were targeted in the study as their muscular reaction to the removable heel provides valuable information as to any reduction in the risk of exercise-induced injury.

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2.2.2.1. The Tibialis Anterior Muscle This muscle is an invertor of the foot. Reber et al. (1993) and Hunt et al.‟s (2001) measurements of extrinsic foot muscles‟ impact indicate some degree of tibialis “overuse” among track-and-field athletes during running, but a failure to relieve and rest this muscle after exercise, as walking demands effort from this muscle as well if the foot does not have the support needed such as that provided by a heel. In effect, “tibialis anterior fires above the fatigue threshold for 85% of the time. This may account for the high number of fatigue-related injuries to the tibialis anterior muscle seen in runners” (Reber et al., 1993). This statement is particularly relevant in light of the tibialis anterior‟s controlling role on heel stress. Indeed, during walking, this muscle “restrains rearfoot plantarflexion from heel contact to 10% stance (see Figure 2.3) and eversion between 10% stance and footflat” (Hunt et al., 2001). Thus, literature suggests that if extreme stress is inflicted to the tibialis anterior during running, an athlete must have extra heel support to make up for a fatigued foot-invertor muscle.

2.2.2.2. The Gastrocnemius Muscle This muscle is responsible for controlling foot motion, exerting much force during walking and running for plantar flexion and foot pronation resistance (O‟Connor et al., 2004, 2006). Thompson (2002) provides a visual of the role of this muscle during a normal walking gait, as depicted in Figure 2.6 that illustrates the gastrocnemius activity during stance, illustrating the intensity of the pressure exerted on the ankle and the gastrocnemius during walking.

Regarding Achilles tendinitis, the second most common injury among track athletes, it is important to understand to impact of the gastrocnemius muscle activity. Effectively, this injury is an inflammation of the Achilles tendon, which is constituted of tendons of the gastrocnemius and soleus muscles (see Figure 2.5). Roy (1988), who studied and experienced running injuries, explains that running shoes are supposed to possess a heel wedge to reduce Achilles tendon stretch. Similarly, Reilly‟s (2009) historic of the ergonomics of running shoes explains that shock absorption properties such as outer and midsole with a wedge in between at the shoe‟s back, air bubbles, or heel counters aids in stabilizing the rearfoot and decreasing the risk of Achilles tendinitis. Nevertheless, such features apply to shoes designed for long distance runners, since their stance is longer than that of sprinters and mid-distance runners; this stance increases the need for heel support during running. Yet, heelless sprint and mid-distance spike shoes are elevated at the toes to aid in speeding up the stance during running. In addition, they provide no heel wedge during the longer walking stance, which means that the Achilles tendon of a walking athlete is stretched more intensely – due to the shape of the shoe – and for a longer amount of time –walking taking longer than running – if the athlete does so in his / her spike shoes.



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