and moving towards the leg that is in the swing phase. skip skipping is a gait children display when they are about four to five years old. while a jog is similar to a horse's trot, the skip is closer to the bipedal equivalent of a horse's canter. in order to investigate the gait strategies likely to be favored at low gravity, a study by ackermann and van den bogert ran a series of predictive, computational simulations of gait using a physiological model of the musculoskeletal system, without assuming any particular type of gait. they used a computationally efficient optimization strategy, allowing for multiple simulations. their results reveal skipping as more efficient and less fatiguing than walking or running and suggest the existence of a walk-skip rather than a walk-run transition at low gravity. gait patterns in children time and distance parameters of gait patterns are dependent on a child's age. different age leads to different step speed and timing. arm swinging slows when the speed of walking is increased. height of a child plays a significant role in stride distance and speed. the taller the child is the longer the stride will be and the further the step will be. gait patterns are velocity and age dependent. for example, as age increased so did velocity. meanwhile, as age increases, cadence (rate at which someone walks that is measured in steps per minute) of the gait pattern decreased. physical attributes such as height, weight, and even head circumference can also play a role in gait patterns in children. environmental and emotional status also play a role in with speed, velocity, and gait patterns that a child uses. besides, children of different genders will have different rates of gait development. significant developmental changes in gait parameters such as stride time, swing time, and cadence occur in a child's gait two months after the onset of independent walking, possibly due to an increase in postural control at this point of development. by the age of three, most children have mastered the basic principles of walking, consistent with that of adults. age is not the only deciding factor in gait development. gender differences have been seen in young children as early as three years old. girls tend to have a more stable gait than boys between the ages of 3–6 years old. another difference includes the plantar contact area. girls showed a smaller contact area in plantar loading patterns than boys in children with healthy feet. sex differences there are sex differences in human gait patterns: females tend to walk with smaller step width and more pelvic movement. gait analysis generally takes biological sex into consideration. sex differences in human gait can be explored using a demonstration created by the biomotion laboratory at york university in toronto. efficiency and evolutionary implications even though plantigrade locomotion usually distributes more weight toward the end of the limb than digitigrade locomotion, which increases energy expenditure in most systems, studies have shown that humans are economical walkers, but not economical runners, which is said to be consistent with evolutionary specialization for both economical walking and endurance running. for the same distance, walking with a natural heel-first gait burns roughly 70% less energy than running. differences of this magnitude are unusual in mammals. kathyrn knight of the journal of experimental biology summarizes the findings of one study: "landing heel first also allows us to transfer more energy from one step to the next to improve our efficiency, while placing the foot flat on the ground reduces the forces around the ankle (generated by the ground pushing against us), which our muscles have to counteract." according to david carrier of the university of utah, who helped perform the study, "given the great distances hunter-gatherers travel, it is not surprising that humans are economical walkers." key determinants of gait a normal gait pattern depends on a range of biomechanical features, controlled by the nervous system for increased energy conservation and balance. these biomechanical features of normal gait have been defined as key determinants of gait. it is therefore necessary for the refined neurological control and integration of these gait features for accuracy and precision with less energy expenditure. as a result, any abnormality of the neuro-musculo-skeletal system may lead to abnormality in gait and increased energy expenditure. the six kinematics or determinants of gait, described below, were introduced by saunders et al. in 1953, and have been widely embraced with various refinements. recent studies have suggested that the first three determinants might contribute less to reducing the vertical displacement of the center of mass (com). these determinants of gait are known to ensure economical locomotion, by the reduction in vertical center of mass (com) excursion leading to reduction in metabolic energy. it is therefore suggested that the precise control of these determinants of gait leads to increased energy conservation. these kinematic features of gait are integrated or coordinated in order to ensure a circular arc trajectory of the com, as theory proposed as the 'compass gait (straight knee)'. the theory underlying the determinants run contrary to that of the 'inverted pendulum' theory with a static stance leg acting as a pendulum that prescribes an arc. the six determinants of gaits and their effects on com displacement and energy conservation are described below in chronological order: pelvic rotation: this kinematic feature of gait operates under the theory of compass gait model. in this model, the pelvis rotates side to side during normal gait. in effect, it aids in the progression of the contralateral side through reduced hip flexion and extension. its effect on the reduction of metabolic energy and the increased energy conservation is through the reduction of vertical com displacement. this notion of reduction of metabolic cost may be disputed by a study done by gard and childress (1997), who stated that there may be minimal effect of pelvic rotation on vertical com displacement. furthermore, other studies have found pelvic rotation to have little effect on the smoothing of com trajectory. pelvic rotation has been shown to account for about 12% reduction in the total com vertical displacement. pelvic tilt/obliquity: normal gait results in tilting of the swing phase side, in relation to the control by the stance side hip abductors. as a consequence, there is the neutralization of raising of com during the transition from hip flexion to extension. its effect on the reduction of metabolic energy and the increased energy conservation is via the reduction of vertical com trajectory or peak form compass gait model. pelvic obliquity's effects on reduction of vertical displacement of com has been examined and been shown to only reduce vertical displacement of com by at most, only 2–4 mm. knee flexion at stance phase: the knee usually supports the body weight in flexed position during walking. the knee is usually fully extended at heel strike and then begins to flex (average magnitude of 15 degrees) when foot is completely flat on the ground. the effects of the stance-phase knee flexion is to lower the apex of vertical trajectory of the com via shortening of the leg resulting in some energy conservation. but recent studies testing this third determinant of gait have reported varied results. it was found out that stance-phase knee flexion did not contribute to the reduction in vertical trajectory of com. furthermore, gard and childress (1997) indicated that maximum com is reached at mid-stance when knee is slightly flexed, depicting minor reduction of the maximum height of the com by a few millimeters. foot and ankle motions: saunders et al. showed relationship between angular displacement and motions of foot, ankle and knee. this results in two intersecting arcs of rotation at the foot during stance phase at heel contact and heel rise. at heel contact the com reaches its lowest point of downward displacement when the foot is dorsiflexed and the knee joint fully extended in order for the extremity to be at its maximum length. the ankle rockers at heel strike and mid-stance leads to decrease com displacement through the shortening of the leg. studies by kerrigan et al. (2001) and gard & childress (1997) have showed the major role played by heel rise in reducing the com vertical displacement. knee motion: the motion of the knee are related to those of the ankle and foot motions and results in the reduction of com vertical displacement. therefore, an immobile knee or ankle could lead to increases in com displacement and energy cost. lateral pelvic displacement: in this key gait feature, the displacement of the com is realized by the lateral shift of the pelvis or by relative adduction of the hip. correction of disproportionate lateral displacement of the pelvis is mediated by the effect of tibiofemoral angle, and relative adduction of the hip, which results in reduction in vertical com displacement. it is clear that these kinematic features play a critical role in ensuring efficiency in normal gait. but there may be the need for further extensive testing or validation of each of the key determinants of gait. abnormal gaits abnormal gait is a result of one or more of these tracts being disturbed. this can happen developmentally or as the result of neurodegeneration. the most prominent example of gait irregularities due to developmental problems comes from studies of children on the autism spectrum. they have decreased muscle coordination, thus resulting in abnormalities in gait. some of this is associated with decreased muscle tone, also known as hypotonia, which is also common in asd. the most prominent example of abnormal gait as a result of neurodegeneration is parkinson's. although these are the best understood examples of abnormal gait, there are other phenomena that are described in the medical field. antalgic gait: limping caused by pain that appears or worsens when bearing weight on one limb, due to injury, disease, or other painful conditions charlie chaplin gait: occurs in tibial torsion. circumduction gait: occurs in hemiplegia waddling gait: occurs in bilateral congenital hip dislocation high stepping gait: occurs in foot drop scissor gait: occurs in cerebral palsy stiff hip gait: occurs in ankylosis of the hip trendelenburg gait: occurs in unstable hip due to congenital dislocation of hip, gluteus medius muscle weakness abnormal gait can also be a result of a stroke. however, by using treadmill therapy to activate the cerebellum, abnormalities in gait can be improved.