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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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Figure 2.6: and muscle activity during normal walking gait cycle Source: Thompson (2002) In regard to another common injury among track-and-field runners that involves the gastrocnemius, namely plantar fasciitis, the main cause is an inflammation of the plantar fascia due to abnormal pronation (Roy, 1988), that is, a failure of the gastrocnemius to properly resist pronation.

2.3. Transition between Running and Walking The biomechanical modification hereby tested enables runners to rest their heels as well as reduce gastrocnemius and tibialis fatigue after or before exercise or competition. Indeed, the study of O‟Connor et al. (2006), examining the role of extrinsic muscles through mfMRI and EMG measurements, indicates that these muscles control rearfoot motion to alter the activation in order to maintain a preferred movement pattern. Thus, transition from one gait to another (from running to walking), is a naturally challenging phenomenon for the runner‟s extrinsic foot muscles. This suggests that a runner‟s extrinsic foot muscles could benefit from assistance or intervention in altering foot motion, especially after an intensive race.

Measurements of muscle fatigue during transition from running to walking and viceversa have been performed and reported in a published study from the Department of Movement and Sport Sciences at Ghent University (Segers et al., 2006). The study mostly consisted of EMG measurements on a group of subjects‟ tibialis anterior. According to Segers et al. (2006), tibialis anterior fatigue is attributable to more than just the metabolic change or cost, which is to say, the “change to another type of locomotion reduces oxygen consumption.” In effect, differences of foot angle when switching from plantarflexion (running) to walking tends to affect the intensity of tibialis anterior activity. EMG of the tibialis anterior during walking and running has a typical pattern with a burst during the eccentric foot plantar flexion movement following heel contact.

Such eccentric activity tends to increase exertion, which might serve as protective mechanism to prevent further damage. Walking and running, when performed at speeds in proximity of the transition-speed, differed in the fact that the touch-down angle of the foot is smaller during running. Another possible explanation could be the greater instability of the foot after TA fatigue. During the heel strike stage of walking stance (see Figure 2.3), the eversion load is maximized. If the TA fails to sufficiently counteract foot eversion, with secondary function preventing eversion, this would cause a medial shift of the center of pressure and a lateral shift of the center of mass.

This report thus indicates not only that the foot tends to be more instable when walking after running, but also that a reduction in heel pressure would certainly reduce fatigue of the tibialis anterior as well.

Similarly, Nigg et al. (2003) examined the influence of shoe soles on muscle activation and energy through EMG measurements. Their research indicated a change in oxygen consumption and a change in lower extremities muscle activation (including tibialis anterior and medial gastrocnemius), as the subjects ran in shoes with different heel materials. During running, track athletes experience forces of impact that range between 1.0 and 2.5 times their body weight. Running thus constitutes a great effort on muscles in the lower extremities, which could benefit from after-running support to absorb and provide relief them from some of the shock due to heel impact when walking away from the track after competition or exercise. In addition, the authors use the expression “muscle tuning” to refer to the muscles‟ tendency to adopt an activation pattern. This complements the conclusions of O‟Connor et al. (2006). Nigg et al.

explained that muscles become conditioned to acting a certain way during a specific activity, thereby making a transition to another activity increase muscle effort and sometimes trigger fatigue. In the case of the transition from running to walking, Nigg et al. suggested that “a reduction of muscle activity before heel strike is associated with fatigue.” Since walking implies a reduction of muscle activity from running, it can be deducted that a decrease in locomotion speed (transitioning from running to walking) can also trigger fatigue due to the effort of pulling away from the previous “muscle tuning” experienced during running.

Thus, in light of Segers et al. (2006), it may be concluded that the heel material directly influences muscle activation and the subsequent oxygen consumption. One can therefore expect a significant change in muscle activity during the experiment performed in this thesis. However, one major difference from the studies of Nigg et al. (2003) and Segers et al. (2006) is that the task assigned to the subjects was to run in various heel and sole conditions, whereas in this thesis, participants were asked to walk at different speeds and in different heel conditions.

Nevertheless, Nigg et al. stated that the phenomena studied and reported should provide insight into understanding “many aspects of human locomotion, including work, performance, fatigue, and possible injuries,” thus making their research and the corresponding results relevant for studying the locomotion mode of walking in various heel conditions.

2.4. Consequences of Inappropriate Equipment Research regarding the ergonomics of sports shoes is a relatively new phenomenon. Reilly (2009) wrote a historical analysis of the running shoes market, whereupon sports shoes companies became attentive to safety issues in the 1970s-1980s explosion in the popularity of track-and-field events. Before that, runners carried lightweight spike shoes for the track, as well as heavier shoes to exercise outside the track. Manufacturers then introduced new materials based on “ergonomics criteria that prioritized comfort, safety, and performance” (Reilly, 2009), designed by Dr. Peter Cavanagh.

A personal interview with Kaitlin Smith (2007), an athletic trainer at Louisiana State University, was conducted on relative subject matters. Smith stated that among LSU track and field athletes, the most common injuries that resulted from wearing cleats, under normal circumstances (properly worn and fitted, and used only during the event), were turf toe, a sprain of the ligaments in the big toe, and plantar fasciitis, the inflammation of the interface between the fascia and the first layer of intrinsic muscles. After returning from a period that excluded training in their spikes, Smith notes that the athletes complained a lot about overall soreness.

Some examples were blisters, metatarsal bruising, and a tight Achilles or calf muscle. She further commented that the worst danger in over-use of cleats would be chronic Achilles tightness, shortening of the calf muscles, tight hamstring muscles, low back pain, associated foot soreness, and an altered running stride.

A level spike shoe to reduce some, if not all, of these risks was suggested. Smith replied:

“A leveling of the heel increases heel striking, therefore making the runners slower. However, during times where the athletes do not need to be in spikes, the level cleat would benefit them. In conjunction with the level cleat, communication with the coaching staff of any problems is key, especially with the dangers of over-use of spikes.” According to Smith, the athletes would be interested in the use of a level cleat with a removable heel. This would not only cause an easy switch from walking footwear to competition footwear, but this would also reduce the number of various types of footwear that the athletes carry.

2.5. Electromyography (EMG) 2.5.1. Definition and Explanation EMG is the use of various electronic devices that use volts to measure muscle activity in the body. It aims at measuring a specific muscle‟s activity by interpreting electrophysiological signals. EMG is used in various industries, such as a) medicine, b) sports medicine and kinesiology, c) work physiology, and d) biomechanics, to provide “objective evaluation of the musculoskeletal stress” (Lee et al., 1986). Further, EMG monitors physiological parameters for the generation of ergonomic or medical solutions to problems related to muscle pain, fatigue, and abnormal / inappropriate activity (Solomonow et al., 2003).

There are several types of EMG systems, depending on the user‟s needs in regard to area / discipline. One of he most commonly used in biomechanics is surface EMG. Surface EMG is characterized by the use of adhesive electrodes (called non-invasive) that are placed on the skin that covers the muscle of interest. Other types of equipment include wire and needle electrodes that are inserted through the skin to the muscle of interest (Nimbarte, 2009).

For this study, surface EMG was employed (see Figure 5.7). A wireless, battery-operated device was used to provide the flexibility and freedom of movement needed for the participants to complete the walking drills (lightweight and transmission up to 250 m). Participants were tested with a Myomonitor IV Wireless Transmission and Datalogging system by Delsys.

Results of EMG testing are displayed in a graph called an electromyogram, sometimes

called an EMG graph. Figure 2.7 provide examples of typical electromyograms:

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Using a software such as Excel, an electromyogram‟s appearance can be modified by adding comments, legends, or titles. To compile the data, to average it, or to compare different subjects‟ information, EMG data must be normalized. Sommerich et al. (2000) provide an analytical review of the use of surface EMG. They present normalization as the process used “to address variation introduced in the measurement process by differences in electrode spacing, natomical factors, and variation in electrode placement in order to facilitate comparisons between differenct muscles and individual subjects.” Failure to proceed to normalization can affect the reliability of the results because the amplitude‟s percentage will include exertion movement that are irrelevant to the study.

Weimer (2009) explained EMG waveform interpretation, stating that a solitary graph does not mean much. However, when compared to another one, a standard case or a different condition undergone by the same subject / patient / participant, an electromyogram reveals “which case represents the greatest amount of work done by the muscle”.

2.5.2. EMG Applications in Biomechanics, Work Physiology, and Kinesiology Nigg et al. (2003) provided an example of EMG application for ergonomic purposes. The study used electromyography to identify muscle activity for selected muscles, including medial gastrocnemius and tibialis anterior, with 20 participants performing drills in two differentlyheeled running shoes. Similar to the experiment conducted in this thesis, the data collected “were compared for the different conditions using an ANOVA (α = 0.05).” The same testing procedure was used in this study, within a similar controlled environment, with the exception of the

following major elements:

Rather than changing shoes, the participants kept the same shoes, yet exchanged

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Body maps were also used to complement the objective scientific EMG data with the subjective ratings, to indicate how the subject experienced the heel/without

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The concept of a shoe with a removable heel is not a new invention per se. Several inventors have examined this option and even submitted patents in the past, as early as the 1880s.

The earliest patents promoted removable heels, because heels historically represent the fastest worn part of a shoe. Replacing a heel is thus less expensive than buying a whole new pair of shoes. Later on, the literature indicates a certain diversity in the design and use of removable heels, and the concept has been adapted and adopted in various areas, including the arena of sports.

2.6.1. Orthopedics Orthopedic heel elevations are common practice. They usually consist in adding a prosthesis inside the shoe. People with pathologically asymmetrical leg length use the prosthesis to even leg length and restore balance in their hips and back. The device is usually small enough to fit inside the shoe in a virtually invisible manner.

Orchard et al. (1996) used a similar device with long-distance track athletes who suffer from iliotibial band friction syndrome (ITBFS) (see Figure 2.1). This type of injury is common among distance runners (McGrath and Finch, 1996), because of their recurrent knee flexion to the angular zone in which friction occurs, that is, 30˚ (whereas not only do sprinters flex their knees beyond the impingement zone, but the flexion moment spent in the friction zone is much shorter, since they run faster than distance runners do). The study consisted in a cadaveric anatomical examination of 11 normal knees and a video analysis of 9 distance runners suffering from ITBFS who ran on a treadmill for 2 minutes twice. For this dynamic section of the study, the subjects ran once with normal running shoes, and then ran for a second time with a 50 mm heel raise.

Despite the methodological resemblance between the biomechanical model proposed in Orchard et al.‟s (1996) study and the removable heel proposed in this thesis, the purposes differ in that the 50 mm heel elevation device was designed for etiological evaluation and assessment of ITBFS. Indeed, the model aimed at identifying angular patterns in the gait of distance runners with ITBFS, not at correcting these patterns, whereas the removable heel evaluated in this thesis is proposed as a solution to prevent running injuries among sprint runners.

2.6.2. Bowling Famolare (1994) designed a bowling shoe, in which the removable heel functions to “vary the friction of the bowling shoe sole on the bowling surface.” This shoe is characterized by a hook and pile fastener that makes a sliding pad.

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