**1.2. Anatomy of the joints**

Computational Intelligence in Electromyography Analysis – 66 A Perspective on Current Applications and Future Challenges

leave the ground.

**1.1. Movement of the joints** 

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

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.

1. Support (or stand) phase: begins when one foot contacts the ground and ends when the first finger of the same foot is no longer in contact with the ground. This phase can be subdivided into three: (1.a) impact phase; (1.b) phase of medium support or of absorption: time when the whole foot is resting on the ground; and (1.c) propulsion or push phase, which begins when the foot is lifted off the ground and ends when the toes

2. Phase of no support or of recovery, which comprising three phases: (2.a) initial flight phase: begins when the first toe of the support foot is no longer in contact with the ground and ends when the heel of the contralateral foot (opposite one) touches the ground; (2.b) half swing phase: begins when the heel of the contralateral foot contacts the ground and ends when its first finger is no longer in contact with the ground; and (2.c) final flight phase: begins when the first finger of the opposite foot is no longer in contact with the

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 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

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

ground and ends when the heel of the ipsilateral foot rests again on the floor.

the hip is flexed); and period of descend of the foot.

energy is its transferring between segments by two-joint muscles.

progress in the sagittal plane, respectively. The movements are as follows:

with suitable elastic and contractile characteristics (Gollhofer and Komi 1987).

Slocum & James (1968) divided the jogging stride in the following phases:

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

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

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 movements of different segments: pelvis, thigh, leg, and foot of the lower extremity in three planes: sagittal, coronal, and transverse during the different phases of the cycle locomotion.

Comparison by EMG of Running Barefoot and Running Shod 69

The movement in the coronal plane facilitates vertical balance on the leg, particularly during leg stance. In each cycle the knee moves into abduction and adduction. In support phase, the movement is of abduction. During oscillation, the knee returns to a more neutral position in adduction. In the transverse plane of a position of maximum external rotation at the end of the stance phase, the lower limb starts an internal rotation in the take-off of the leg and continues during the oscillation and the load response (initial part of the support phase).

The hip function differs from the other two joints in the following respects: (1) represents the junction between the passenger and the motor system, (2) allows movements in three planes of space with a specific control in each plane, although in the coronal plane movement is

In the sagittal plane hip extends in the phase of support and flexes in the non-support one. The hip has small arcs of motion in adduction and in abduction. At the initial contact of the heel with the ground, the hip is in adduced position. At the beginning of the swing phase, the hip is in a relative abduction of 5°. In the transverse plane, the internal rotation peak occurs at the end of the loading phase and maximum external rotation occurs at the end of

During the stride, the pelvis moves in three directions asynchronously. The point of support is the hip of the leg that is in support. All its ranges of motion are small: in the sagittal plane

De Wit et al. (2000) describe different angular displacements of the knee and ankle when subjects ran barefoot and when running shod. During running, the body reacts to the external environment which produces the ground reaction force (GRF) that occurs in response to the force action transmitted by the leg in contact with the ground. The GRF reflects the net effect of the muscle action and the accelerations of the segments while the foot is in contact with the ground (Martin & Morgan 1992). All segments contribute to the total acceleration of the body

The three components of the GRF (vertical, anterior-posterior, and medial-lateral) change their size when using footwear (Nigg 1983). The GRF reflects the acceleration and deceleration of

During movement, the GRFv varies above and below the body weight due to the positive and negative accelerations undergone by the body. The difference between the vertical

it is a rocking motion of 4°; in the frontal plane, 7°; and in the transverse plane, 10°.

in proportion to the acceleration of its centre of gravity and its relative mass.

the centre of gravity. The gravity eases the contact of the foot with the ground.

limited, but the mechanical demands are substantial.

**1.3. Differences in locomotion due to shoes** 

*1.3.1. Vertical component (GRFv)* 

*1.2.3. Hip* 

the pre-swing phase.

*1.2.4. Pelvis* 

In the sagittal plane, the movements are wider. In the other two planes the movements are small but are involved in the magnitude of the displacement of the center of gravity in the sagittal plane and also provide stability.
