**1. Introduction**

Computational Intelligence in Electromyography Analysis – 64 A Perspective on Current Applications and Future Challenges

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Footwear is the "interface" between the locomotive system and the athlete's physical environment through which all the forces that act and react between the legs and the ground are transmitted.

According to Nigg (1986), the choice of footwear is based on the price, durability, comfort, colour, safety, weight, and performance; but, how footwear affects the human-ground interaction?

During jogging, running shoes have to reduce foot shock impact with the ground, to hold the foot, to control the pronation-supination, to direct the force at the time of propulsion for takeoff (Luethi & Stacoff 1987), and to increase efficiency.

Nowadays, more and more people practice sport, being jogging an activity common to many sports, besides being a sport specialty itself. Jogging is a complex activity requiring an exact timing of muscle activation and a precise control of movement. Many injuries occurred during jogging affect the musculoskeletal system: (1) tendonitis of: tibialis anterior, peroneus brevis, tibialis posterior, quadriceps, and Achilles tendon; (2) calcaneal apophysitis; (3) chronic syndromes: anterior and posterior compartments; (4) stress fractures; (5) plantar fasciitis; and (6) rupture of the hamstrings (Reber et al. 1993). Certain types of contractions may predispose the runner to a particular injury (Vaughan 1984).

The displacement speed is determined by the frequency and length of the stride. These variables are the result of the successful integration of many mechanical and neuromuscular processes.

The human body is a biological system that has many possibilities of action and reaction to external environmental influences. During the movement, the neuromuscular system is

© 2012 Garcia et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Garcia et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

involved not only in the production of force to move the segments, but through different mechanisms sensory feedback is capable of reacting to small changes. Facilitation or reduction of these feedback mechanisms enable the human motor system for a wide variety of functions, such as: (1) control of the position and stiffness of joints, (2) shock absorption, (3) dynamic stability during the support, and (4) propulsion, facilitating that the involved muscles perform with suitable elastic and contractile characteristics (Gollhofer and Komi 1987).

Comparison by EMG of Running Barefoot and Running Shod 67

1. Sagittal plane: the axis of rotation is medial-lateral and the movements are of flexion-

1.a. In the ankle: *support phase* –dorsiflexion (10°), plantar flexion (45°); phase of non

1.b. In the knee: *support phase* –flexion (20°), extension (18°); *phase of non support* – flexion

1.c. In the hip: *support phase* –extension (35°); *phase of non support* – flexion (40°),

1.d. The pelvis has a rocking motion, respect to the anterior-superior iliac spine: forward or down and back or up. In the stance phase there are up and down

2. Transverse plane: the lower limb segments rotate around a vertical axis, the direction of rotation is outward or inward and its development is the same in the components of the lower extremity: pelvis, thigh, and leg, but their magnitudes vary. The swing phase is characterized by the internal rotation of each segment; the more distal segments rotate faster and in a greater degree than the proximal ones. The average rotation of the pelvis is 5° and that of the tibia and femur 9°, summing up a total of 23°. In support phase the

3. Coronal or frontal plane: the axis of rotation is anterior-posterior and the movements are of ab-adduction. The displacements of the pelvis and lower extremity in the frontal plane are not large but are very important to maintain balance. In the knee and ankle the movements are ab-adduction and are limited by the characteristics of the joints and the presence of lateral ligaments. During jogging, the hip is adduced during the support phase until half of it. In the swing phase occurs continuous abduction of the supporting

4. The movements of the ankle with the tibiofibular and subtalar joints produce the

From a biomechanical perspective, the factors that dictate the movement are our inherent structure and alignment, the joint range of motion, and the muscle strength available. The joint range is partly defined by the anatomical structure. In the following, the peculiarities of the joints of the legs and their angular displacements during locomotion are described

Each of the lower extremities is a system of articulated segments, with its own mechanical characteristics. The different joints involved are: (1) lumbosacral, (2) the two hips, (3) the two knees, (4) the two ankles, (5) the subtalar joints, and (6) the midtarsal joints. In studies on locomotion the foot is considered as a rigid segment (although it is formed by 26 bones) serving for the transmission of force between the body and the ground. During the

According to Arsenault et al. (1987) it seems clear that the kinematics of locomotion does not show high variability. From the data found in the literature, we describe the angular

extension (10°) (Milliron & Cavanagh, 1990; Mann et al. 1986).

movements; and in the no-support phase, down, up, and down.

external rotation continues and then, halfway, its direction changes.

leg and at half of the way, it changes its direction to adduction.

extension.

support –dorsiflexion (45°).

movement of supination-pronation.

(Testut 1971, Inman 1981, Perry 1992, Behnke 2001).

movement, the body segments serve as levers (Perry 1992).

**1.2. Anatomy of the joints** 

(90°), extension (90°).

During one cycle of jogging, lower extremities undergoes a phase of unipodal support (in which only of the feet is in contact with the ground), one of swinging, and two phases of flight (in which none of the feet are in contact with the ground): the first takes place before the swing phase and the second, after it. Support phase lasts less than 50% of the stride. Slocum & James (1968) divided the jogging stride in the following phases:


Another way of dividing the non-phase support is as follows: period of follow-through (after leg takeoff, the hip stretches); forward period (the ipsilateral leg moves forward while the hip is flexed); and period of descend of the foot.

### **1.1. Movement of the joints**

The displacement of the centre of gravity is due to the angular movement of the joints caused by the resultant of different forces: muscular force (caused by the neuromuscular system), ground reaction force, weight of the segments, misalignment of body weight, and the inertia of the moving segments. During jogging, the path of body's centre of gravity is sinusoidal, moving twice in the vertical direction, so there are two peaks for each stride. At the same time, when the centre of gravity loses height, it loses also horizontal speed, and the kinetic and potential energies are in phase, so large changes occur in the resultant of both forms of energy at each step. However, a significant amount of mechanical energy is conserved stored as potential elastic energy in the tissues. Another mechanism to save energy is its transferring between segments by two-joint muscles.

In jogging, the movements of the joints are larger in the sagittal (or anteroposterior) plane, even though the movements in the coronal and transverse planes facilitate the stability and progress in the sagittal plane, respectively. The movements are as follows:

	- 1.a. In the ankle: *support phase* –dorsiflexion (10°), plantar flexion (45°); phase of non support –dorsiflexion (45°).
	- 1.b. In the knee: *support phase* –flexion (20°), extension (18°); *phase of non support*  flexion (90°), extension (90°).
	- 1.c. In the hip: *support phase* –extension (35°); *phase of non support*  flexion (40°), extension (10°) (Milliron & Cavanagh, 1990; Mann et al. 1986).
	- 1.d. The pelvis has a rocking motion, respect to the anterior-superior iliac spine: forward or down and back or up. In the stance phase there are up and down movements; and in the no-support phase, down, up, and down.
