Radiographic images of her lumbar spine, hips and pelvis, and knees were all normal. Scanogram of her pelvis to ankles demonstrated no anatomic leg length discrepancy. An electrodiagnostic study (EDX) of her right lower extremity and lumbar spine was normal.

Individual anthropometric differences, turn over speeds, stride lengths, arm swing, and endurance, all contribute to the overall performance and success of the athlete. Correct treatment of the athlete with a lower extremity or spine injury begins with an assessment of his/her gait. Walking and running are two of the most obvious and fundamental actions of life. It is important for the sports medicine clinician to appreciate the complexities of gait, the determinates of an efficient gait, the differences in gait relative to age and gender, the importance of symmetry in gait, and the identification of impairments and their functional impact on athletic performance [1]. The ability of the sports practitioner to visualize and discern different gait patterns is key to understanding the complexities of gait, can give insight into possible injury mechanisms, and provides possible rehabilitative avenues for a successful return to sport [2].

An analysis of gait begins with understanding the components of the gait cycle. A single gait cycle has been defined as the period from initial heel contact until the initial heel contact on the ipsilateral leg [3]. Walking is the act of falling forward and catching oneself [4]. The tasks of walking and running involve forward propulsion , which is accomplished by an inverted pendulum gait. This is accomplished when the body is vaulted over a stationary limb with each step, moving continuously in the direction of travel. This involves each limb in turn either advancing forward or providing support to the contralateral advancing limb. The assessment of these activities takes time, practice, and technical skill [4]. It begins with an understanding of the definitions, phases, and determinants of gait.

Each foot has two main phases during the gait cycle : a stance phase where the foot is in contact with the ground and swing phase where the foot is off the ground [5]. When allowed to walk at a self-selected walking speed, stance phase is around 60 % of the gait cycle, while swing phase accounts for approximately 40 % [5]. During walking, one foot is always in contact with the ground. It involves periods of single limb support (SLS) and double limb support (DLS). Running, on the other hand, involves periods of flight in which neither foot is in contact with a surface, called flight phase (Fig. 4.3 ). Walking and running demonstrate a reversal of the percentage of stance and swing phase. It is therefore intuitive that the slower the walking speed, the longer the time spent in DLS. Conversely, faster walking speeds result in less time spent in DLS and running involves no DLS phase and includes a flight phase.

The basic unit of walking and running is the gait cycle ; also known as stride . The gait cycle involves a pattern of acceleration and deceleration which is controlled by contraction of muscles. It is important to remember that the entire body is involved in the gait cycle, with movements occurring in the cardinal planes simultaneously (Fig. 4.1) It also involves functional and temporal variables [2]. The functional aspects of the gait cycle are weight acceptance and support during the stance and swing phases [2]. There are eight phases of the gait cycle beginning with the initial contact of the loading response and ending with terminal swing before the next initial contact (Table 4.2 and Fig. 4.4a–h) [3]. It is important to understand the temporal–spatial gait parameters including the difference between stride time and step time. Stride time is defined as initial contact on one limb to initial contact on ipsilateral limb and step time is defined as initial contact on one limb to initial contact on the contralateral limb. The stride length is the distance covered during one stride and gait velocity is determined by dividing the stride distance by the time taken. Walking speed is the distance travelled per unit of time. Cadence is the number of steps taken in a decided timeframe [1–3, 6].

In order to analyze gait, it is important to have a good understanding of the kinematics of gait. Kinematics is the science of motion. In athletic movement, it is the study of positions, angles, velocities, and accelerations of individual body segments and joints during movement. The kinematics of gait of the individual during walking or running is evaluated by observing the body as composed of body segments (links) and joints (connections) between segments. Body segments, for the purposes of describing human motion, are considered to be rigid bodies. These include the foot, leg (shank), thigh, pelvis, thorax, hand, forearm, upper arm, and head. Joints or links between segments include the ankle (both talocrural and subtalar joints), knee, hip, wrist, elbow, and shoulder. The kinematics of the individual or system is determined by taking into account the orientation and position of each segment. Position describes the relative location of the body segment or joint space. Each body segment has a center of mass (COM) or center of gravity (COG). Furthermore, the whole system, the body, also has a COM or COG. As segments move, their positions in time and space affect the balance and energy use of the system as the whole body COM distribution changes [7]. Kinematics is best evaluated through quantitative and not qualitative means. Three-dimensional (3D) gait analysis provides information relative to degrees of movement of the joint and relationships to the body segments in terms of frontal, sagittal, and transverse arrangements. The flexion–extension, abduction–adduction, and internal–external rotation relationship of the segments and joints are evaluated, as well as the side to side, front to back symmetry within an individual. The COM for the segments and the COM of the body are expressed in terms of vertical, anterior to posterior, and medial to lateral relationships [8, 9]. The body’s COM reaches its highest point in stance when the speed is minimal [10]. During normal walking , for example, the maximums of COM and height are during double stance phase. ⁸ During running, however, the maximums of COM and height are during flight at maximum velocity [10].

The muscles play a pivotal role in energy conservation and joint movement in normal gait. Electromyographic studies have demonstrated that during running and walking most muscle activity occurs at the start and end of swing phase [11]. This would suggest that the main function of the muscles during gait is to accelerate and decelerate the body. The remainder of the energy expenditure is contributed by passive forces through the limbs and joints [12].

During running, the amount of time in stance and swing phase is inverted compared to walking, with approximately 40 % of time spent in stance phase. Furthermore, it includes a flight phase in which both feet are airborne twice in each gait cycle [23]. While runners may run at different rates, running consists of periods of acceleration and deceleration similar to walking gait. During late flight, the quadriceps and hip flexors contract eccentrically to prepare the limb for ground contact and shock absorption during heel strike [11, 23]. This helps stabilize the knee by restraining the posterior movement of the tibia during knee flexion. The hamstrings and hip extensors contract concentrically to extend the hip during the lateral half of swing phase and the first half of stance phase [23]. The hamstrings also contract eccentrically to slow the limb down just prior to heel strike and initial contact [12]. Acute hamstring strains are most likely to occur when the hamstring is lengthened, during eccentric contraction, in the terminal swing phase of the gait cycle [24–27]. The gastrosoleus complex and hamstrings have important concentric and eccentric functions, while the knee extensors function concentrically during running. Similar to walking gait, the ankle dorsiflexors concentrically contract during swing to provide clearance for the foot and contract eccentrically during initial contact to control lowering of the forefoot [8, 11, 23].

In order to completely understand and analyze gait the practitioner must have an understanding of the kinetics of gait [ 2]. Kinetics is the study of forces acting on bodies to cause motion [3]. In order to understand kinetics, one must understand Newton’s three lows of motion; a body will change velocity only if a force is applied to it; the change in velocity is proportional to the force; and a force applied to an object will result in an equal and opposite reaction. This means that for every force there is a reaction force that is equal in size, but opposite in direction [2]. In the context of gait analysis, the expression of the forces exerted on the foot during contact with the ground called the ground reaction force (GRF). While the body is exerting a force on the ground via gravity and body weight, the ground is exacting an equal and opposite force against the body.