n. The movement of your foot away from the midline of your body during pronation.
Achilles’ tendon n.The major tendon at the back of your ankle that connects the major muscles of your calf (gastrocnemius and soleus) to your heel bone (calcaneus). When you contract (shorten) your calf muscles, your Achilles’ Tendon extends your foot. (note - your Achilles tendon can become inflamed through improper support or improper foot alignment.)
adduction n. The movement of your foot toward the midline of your body during supination.
anatomical position n. Standing upright, with your feet together, arms by your sides and palms forward.
ankylosis n. Destruction of a joint, resulting in a total loss of movement.
anteriorn. To the front of the body (in the anatomical position.)
ASTM n.
American Society of Testing and Materials. A group that standardizes the testing and measurements used in science.
arch n. The bow-like upward curve on the bottom of your midfoot.
atrophy
n. Loss of bulk, especially of a muscle.
biofeedback n. Allowing a person to see how well they are performing a task, so that they can make immediate improvements.
biomechanics n.
The mechanics of body function. The investigation of biological systems through the application of mechanical laws and principles. The investigative study of motion and the effects of both internal and external forces that occur during the actions performed by living organisms. The study of external forces acting upon the mechanical and biological components of an organism as they relate to some life function. For example, studying how the bones, muscles, tendons, and ligaments in your foot interact when you run.
bunion n. A deformity affecting the big toe that forces the joint to point away from the midline of the body.
butterfly diagram n. A graph displaying ground reaction forces during the gait cycle.
cadence n. The number of steps (not strides) in a given time.
calcaneus n. Your heel bone.
calf size n. The size of your calf muscle. Two things determine how a boot will fit your
lower leg: the size of your calf muscle, and the point where your calf muscle attaches to your leg. If your calf muscle is lower than most people, you will be most comfortable in a boot that fits a larger calf.
calibration angle n. The measurement of a reference angle. Calibration angles for supination and pronation are taken while you are standing still. The most common condition is a slightly positive angle
(supination. )
callus n. An area where the skin has thickened and become hard. Usually caused by friction against your footwear. Calluses are a good indication of too much pressure on an area.
cant n. A slanting or tilted lateral position. The side to side angle of your ski on the snow or your foot on the ground; “Canting” or “adjusting the cant” allows your skis or your feet to rest perfectly
flat on the ground when you’re in your normal stance. Without canting most skiers’ and golfers’ weight is incorrectly balanced over either the outside or inside edges of their skis or shoes.
cartilage n.
Gristle; White elastic tissue found around your joints.
center of gravity (CG) n. The point within an object at which the mass of the object is concentrated. The point in your body through which gravitational
forces pass. Your center of weight. Your sway. The net location of your body’s weight in a vertical direction. The weighted average of the center of gravity of each of your body segments. The terms center of gravity (CG) and
center of pressure (CP) are often confused or incorrectly interchanged. Your center of gravity is totally independent of your body’s velocity and acceleration. Your center of pressure includes your body’s velocity and acceleration.
center of pressure (CP) n.
The weighted average and location of your body’s downward forces, such as during heel strike. Your neuromuscular response to imbalances in your center of gravity. The location of the vertical ground reaction force vector, as recorded by a force platform. The point beneath your foot through which the ground reaction force is passing.
cinematographics n. Filming an event or process that occurs very fast, then slowing it down and analyzing it. (usually with 16 mm film at a rate greater than 200 frames per second)
concentric contraction n.
Muscle contraction in which the muscle gets shorter as it develops tension.
contracture n. A reduction in the range of motion of a joint, due to restriction by inelastic connective tissue.
corn n.
1. An area of thickened skin on the toes. Usually caused by pressure points in footwear.
corn n. 2. Spring snow.
counter n.
The sculpted-out area at the base of the back of the orthotic surrounding your heel. The orthotic’s well defined, rigid heel pocket provides a secure fit, keeping your foot from sliding front to back. The heel counter provides rear stability and shock absorption, significantly reducing muscle load during heel strike. Additionally, it decreases your levels of excess pronation, resulting in much greater stability and stronger push-off. The sculpted-out area at the base of the back of the footwear; The better defined the heel pocket, the more secure the fit. A snug fit at the instep and heel pocket helps keep your foot from sliding front to back.
couple n. Two parallel forces acting in opposite directions, which combine to produce a turning effect or rotation.
coupling n.
Due to the alignment of a joint, movement in one direction automatically produces movement in another direction, known as coupling.
coxa vara n.
Abnormal angulation of the upper end of the femur, making the femoral neck too horizontal.
cuff n. The Part of the shell that surrounds your ankle and lower leg.
cut v.
Quickly changing your lateral direction. Cutting causes tremendous friction against the surface on which the cut takes place, and generates forces that are several times your body weight.
cycle time n.
The time taken to complete a single gait cycle.
deep n. Far from the surface.
determinants of gait n.
The 6 strategies used to minimize energy consumption in normal gait. 6 optimizations used to minimize the excursions of the center of gravity in normal gait: pelvic rotation, pelvic obliquity, knee flexion, ankle mechanism, foot mechanism, and lateral displacement of the body.
digitize n.
To store information in a format that a computer can understand. To translate a photographic or video image into a computerized format. To capture the coordinates of markers placed on your body for motion analysis.
distal n. Situated away from the point of origin. Directed away from the midpoint of the body.
dorsal n. Pertaining to or situated on the back.
dorsiflexion n.
To bend backward. Movement of the foot towards the knee.
dorsiflexor n. A muscle that bends a body part backward at the joint.
dorsum n. The upper surface of the foot.
double support n.
The period in the walking gait cycle in which both feet are on the ground, one in loading response, and one in pre-swing.
eccentric contraction n.
Muscle contraction in which the external force overpowers the muscle so that it gets longer.
electrogoniometer n.
A device that is positioned across a joint and puts out a continuous electrical signal describing the angle of the joint.
electromyogram (EMG) n. Recording of the electrical activity of a muscle.
etiology n.
The study of the causes of ailments. The cause of origin of a disease.
EVA n.
Ethyline Vinyl Acetate; A dense, industrial grade, durable, flexible, shock absorbing, nontoxic copolymer that is used extensively in the manufacture of medical devices and sporting equipment, such as wheels, exercise mats, and insoles. EVA is the most common material used to make the mid-soles of athletic shoes. Copolymers of the polyolefins (polypropylene) family derived from random copolymerization of acetate and ethylene.
eversion n. The turning out of the sole of your foot during pronation. The internal roation about the long axis of the foot.
extend v. To stretch out or hold out a part of the body.
extensor
n. A muscle that straightens a part of your body. Extensor movements most commonly push your body away from the ground.
feet adjacent n.
Event in the swing phase of the gait cycle when the foot of the swinging leg passes the supporting foot.
fibula n. The outer, thinner bone that runs alongside your shin bone from your knee to your ankle.
flat foot
n. A foot with a sunken/ fallen arch.
flex v. To Bend a part of your body at a joint. When you bend your arm or knee at the joint, you flex it.
flex n.
The stiffness of footwear. The footwear’s resistance to bending. Stiffer footwear responds faster to your movements, but is less tolerant of imperfect technique.
flexion contracture n.
Condition in which contraction of soft tissues prevent a joint from fully extending.
flexor n. A muscle that causes bending at a joint. Flexor moments most commonly bring your body toward the ground.
float phase n. – The non-contact phase of the running gait cycle when neither foot is in contact with the ground.
foot flat n.
Point in the stance phase of the gait cycle at which the forefoot contacts the ground, when initial contact has been made by the heel.
foot slap n.
Abrupt and audible lowering of the foot following initial heel strike.
footstrike n. Also known as heel impact, heel strike or initial contact. The first major motion in the gait cycle. When your heel
first contacts the ground. Marks the transition from swing phase to stance phase.
force platform n.
A surface consisting of force transducers, amplifiers, and recording devices that measure the forces of human movement. The most commonly measured components include not only vertical forces, but also anterior-posterior and medial-lateral forces. Used to measure gound reaction forces.
force transducer n. A device that measures forces during human movement. Types of force transducers include include strain gauge, piezoelectric, piezoresistive, and capacitive
forefoot n. The front part of your foot; The ball of your foot; The widest part of your foot. The foot’s five metatarsal bones and toes.
forgiveness n.
The extent to which footwear allows you to make technical mistakes without penalizing you for it (transmitting the inappropriate maneuvers to the ground or skis.)
free body diagram (FBD) n. A sketch or diagram
illustrating all of the forces and moments acting on a system or subsystem.
gait n. Your manner or style of walking, stepping or running.
gait cycle n. The time interval between two successive
occurrences of one of the repetitive events of walking (usually initial contact on one side.)
ground reaction force n. The upward force applied by the ground to the foot, in response to the downward force applied by the
foot to the ground. A common measurement taken by a force platform.
hallux n. Your big toe.
heel pocket or heel counter n.
The sculpted-out area at the base of the back of the orthotic surrounding your heel. The orthotic’s well defined, rigid heel pocket provides a secure fit, keeping your foot from sliding front to back. The heel counter provides rear stability and shock absorption, significantly reducing muscle load during heel strike. Additionally, it decreases your levels of excess pronation, resulting in much greater stability and stronger push-off. The sculpted-out area at the base of the back of the footwear; The better defined the heel pocket, the more secure the fit. A snug fit at the instep and heel pocket helps keep your foot from sliding front to back.
heel rise n. Event in the stance phase of the gait cycle at which the heel lifts away from the supporting surface.
heelstrike n. Also known as heel impact or foot strike. The first major motion in
the gait cycle. When your heel first touches the ground. Marks the transition from swing phase to stance phase. When your foot is absorbing shock and adapting to the angle and friction of the ground surface. The first sub-phase
of the gait cycle’s stance phase.
high speed video n.
Filming an event or process that occurs very fast, then slowing it down and analyzing it. (usually at a rate between 30 and 10,000 images per second. Many of today’s high speed video cameras can automatically digitize the data.
hindfoot n. The two bones in the heel of your foot: the talus and calcaneus.
idiopathic n. Of unknown origin.
infarct n.
Tissue that has broken down due to obstruction of blood supply to the area.
inferior n. Lower down the body (in the anatomical position.)
initial swing n.
The period in the swing phase of the gait cycle between toe off and feet adjacent.
instep n. The top of your midfoot; The part of your foot above your arch.
inter n. Between.
internal moment n. A turning or rotating movement generated by the muscles and/or ligaments in the vicinity of a joint.
inversion n. The turning inward of the sole of your foot during supination.
isometric contraction n. A muscle contraction in which a muscle develops tension but remains the same length.
joint n. A connection of two bones.
jump v.
Leaping to vertically displace the body. Jumping generates landing forces greater than seven times your body weight.
kinematics n. Studying your body in motion.
last n.
1. The template or model upon which footwear is built.
last n. 2. The interior shape of either the shell or the liner of a ski boot.
latent n. Hidden.
lateral n.
Away from the midline of the body.
lateral support n.
The degree to which footwear resists bending side to side. Also called “lateral flex.” Lateral support provides stability during aggressive maneuvers, cutting, pivoting, and high speed skiing.
ligament
n. A tough band of relatively inelastic fibrous tissue that connects bones or supports organs.
line of gravity n. A vertical line downwards from your center of gravity.
line of progression n. The straight line corresponding to the average path taken by the body in walking.
liner n. The cushioned inner boot.
loading response n.
The period in the stance phase of the gait cycle between initial contact and opposite toe off.
locomotion n. Movement. How you move.
lordosis n.
A forward curvature of the spine that causes concavity of the lumbar region of the back.
lower motor neuron n. Nerve fiber producing muscular contraction, running from the spinal cord to the muscle.
malleolus n. The round protruding bone on either side of your ankle.
marker n. A visible coordinate placed on your body in a predetermined, consistent manner that is used to derive
position and measure attributes, such as pronation and supination. Typically a small sphere covered in reflective tape.
materials testing n.
Processes used to determine a material’s mechanical properties under highly constrained experimental circumstances. A material’s response to test conditions is measured during either single-trial or cyclical tests.
medial
n. Middle. Towards the midline of your body.
metatarsal n. Of or pertaining to the bony structure in your foot just in back of your toes.
metatarsalgia n.
One of the most commonly reported conditions in the foot. Severe pain in the forefoot beneath the back of your toes caused by nerve compression. Abnormal pronation is the most common biomechanical problem that can cause metatarsalgia. A forefoot varus prolongs the time your subtalar joint is pronating, thus causing your foot to be hypermobile during push-off.
metatarsus n. The bony structure in your foot just in back of your toes.
midfoot n. The 5 tarsal bones: the navicular, cuboid, and medial, intermediate and lateral cuneiforms.
midsole n.
The part of your shoe between its outsole and upper. This part of your shoe plays a critical role in both shock absorption and stability.
mid-stance n.
The second motion (or sub-phase) in the gait cycle’s stance phase. When your foot is relatively flat on the ground, and ready to accept your body weight.
moments of force n.
Torque. The force resulting from all muscular, ligament and frictional influences acting on a joint. An applied force that typically causes a rotation or turning effect.
motor control n. The biomechanical and
neurophysiological mechanisms that control your posture, voluntary movement and skill acquisition.
neuralgia n.
Short, stabbing pain in a nerve or along the course of a nerve. Neuralgias commonly last only a short time but recur suddenly.
neuritis n. Inflammation of a nerve.
neuroma n.
– An inflammation or thickening of a nerve. Neuromas of the foot occur most frequently near the toes. Over-pronation (rolling your foot too far to the inside) or tight fitting toe boxes are common causes of neuromas. Over-pronation compresses your metatarsal bones.
neutral position n. See
.noise
n. Random errors which affect any form of measurement.
occlusion n. The act of closing.
optoelectronic video n.
A type of analysis system that utilizes infrared sensing cameras and infrared light emitting diodes for markers. The markers are tracked and digitized in real time to provide coordinates.
orthotic or orthoses
n.
A foot bed that improves your foot’s function by supporting the ligaments and osseous (bony) structures of your foot, and aligning your ankle in its strongest range of motion. An external support for any part of the body.
outer-sole n. The outermost part of your shoe’s sole, that is treaded. The tread on your running shoes should enhance moving in a straight line. The tread on your cross trainers should enhance lateral stability.
over-pronation n. When your foot flattens too much.
peripheral nerves n. Nerves that originate in the spinal cord, as opposed to cranial nerves, that originate in the brain.
physiology of exercise
. n. The scientific investigation of human adaptations to acute or chronic exercise. The biological and chemical investigation into neural control of the cardiovascular system and muscle fatigue.
pivot v.
Quickly swiveling or rotating. Pivoting generates significant friction against the surface on which the pivot takes place.
plane of progression n.
The flat, vertical plane that follows the average path taken by your body in walking or running.
plantar n. Pertaining to the sole of the foot.
plantar fascia n.
the tough fibrous tissues that run from your calcaneus (heel) to your proximal phalanges (just before your toes.) The plantar fascia supports your arch. Your arch is like a bow, and the plantar fascia is like the bow string.
plantar fasciitis n.
An inflammation, strain or tearing of the plantar fascia. Plantar fasciitis is commonly caused by improper foot alignment, improper foot support or over-pronation. Frequently seen in long distance runners. A common symptom is initial pain after arising from bed in the morning.
plantarflexion n. Movement of your foot away from your knee.
posterior n. To the back of the body in the anatomical position.
pre-swing n.
The period in the stance phase of the gait cycle between opposite initial contact and toe off.
pressure sore n.
An ulcer. A blister that forms over an area of skin exposed to pressure sufficient enough to cut off your blood supply to that area.
pronate v.
Roll downward. Rotate downward. To roll the inner edge of your foot downward so that it’s lower than the outer edge of your foot. You naturally and normally do this before pushing off the ground.
pronation n.
Also known as dorsiflexion of the ankle joint. Pronation is the natural and necessary movement of your foot and ankle from the outside of your body to the inside. It describes how the front of your foot rolls inward just before
pushing off. Pronation describes the position of your foot when it is pointed down. The inner side is lower than the outer side. You change this angle between the outer edge of your foot, the inner edge of your foot and the
ground as you walk or run.
The process of pronation is best described with an example. As your heel strikes the ground your weight is placed mostly on the outside (outer side) of your foot. As you roll your foot from your heel
to your toe, you gradually shift your weight from the outer side of your foot to the inner side. When your foot leaves the ground your weight is mostly on your big toe. In between you’ve moved your weight over not just the
length of your foot, but also over the width.
When you over pronate (roll your foot too far inward) or under pronate (fail to roll your foot far enough inward) you push off and propel yourself with a lot less power than you could
have. Excessive pronation (too much roll or foot mobility) makes your foot unstable. Your other muscles, tendons, ligaments and joints must compensate for this instability. This causes sub-optimal performance and needless
fatigue. It also places a great deal of stress on the surrounding ligaments and bones, as well as on your lower leg, knee, and hips. Injuries such as tendinitis and knee sprain are often the result.
The more precisely you pronate,
the better you perform athletically, and the more you avoid injury. Your levels of under and over pronation can be precisely measured by drawing a line between your leg, ankle, and the heel of your foot, and measuring the angle. This
angle is then compared to the "natural" or calibration angle of your normal standing state. Pronation is usually expressed as a negative angle relative to the calibration angle. Custom computer milled foot
orthotics specific to your feet can be made to correct for your improper levels of pronation, putting you into the ideal range for pronation (outer to inner foot rotation
propulsion n.
Also known as push-off. The third (and final) major motion in the gait cycle. When your foot pushes off the ground to propel you forward.
proximal n.
Situated toward the point of attachment. Towards the rest of the body.
rearfoot motion n.
Also known as pronation and supination. The motion that is visible when observing your foot from the back when you are running or walking or swinging a club. Both excessive and inadequate rearfoot motion decrease athletic performance and contribute to injuries such as Achilles tendonitis, plantar fasciitis, and patella-femoral pain.
responsiveness n. Quickness; The speed with which footwear translates your movements to the ground or to your ski.
rockers n.
The three mechanisms used to move the tibia forward while the foot is on the ground.
run v.
Moving in an essentially straight line. Running shoe designs should emphasize cushioning and ankle stability. Most other sports’ shoe designs should focus on lateral support for cutting, pivoting, and jumping.
sagittal
n. From front to back.
sagittal plane n. A line that divides a body part into the right and left portions.
shell n. A boot’s rigid plastic outside casting.
shuffle
v. Laterally moving side-to-side. This movement generates forces several times your body weight.
single support n.
Period during the gait cycle in which only one foot is in contact with the ground; corresponds to swing phase on the other side.
sockliner n.
The liner inside footwear that usually provides some minimal arch support and shock absorption.
soft tissue n. – Muscles, tendons and ligaments.
spasticity n.
The involuntary resistance of muscles to being stretched.
sports medicine. The investigation of habitual exercise’s effects on health and disease. The study of musculoskeletal tolerance to exercise.
stability n. 1. The degree to which your foot can maintain balance, particularly during excessive supination and excessive pronation.
stability n.
2.The ability of footwear to maintain stableness relative to forces and loads. The ability of a boot to maintain control of the ski, relative to higher speeds, turns, and skiing in difficult snow.
stance n.
The position of your body while standing. The relative position of your feet. When skiing this is your position in the boot with your knees comfortably bent and your weight distributed evenly over the balls and heels of your feet.
stance phase n. –The second major phase of the gait cycle. The contact phase of the gait cycle. The phase in the gait cycle when your foot is in contact with the ground.
step n.
The advancement of a single foot.
step length n. The distance one foot moves ahead of the other foot during the gait cycle.
stride n. The advancement of both feet (one step by each side of your body.)
stride cycle n. Your complete range of motion during walking or running. Your stride begins when your heel first touches the ground. Your stride continues through liftoff, and ends when your foot contacts the
ground again.
stride length n. The distance either foot moves forward during the gait cycle.
subcutaneous n. Beneath the skin.
subject testing n. Processes used to determine a device’s
or material’s effect upon your performance. Processes used to determine an element’s interaction with your body.
sublaxation n.
Partial dislocation of a joint. The action where a joint’s surfaces move in and out of correct alignment.
subtalar joint (talocalcaneal joint) n.
The joint that lies just below your ankle joint. The joint that lies between the talus above and and calcaneus (heel bone) below. The subtalar joint permits abduction and adduction (valgus/ varus motion) of the hindfoot. At the subtalar joint large numbers of ligaments join the talus and the calcaneous to each other and to all the adjacent bones.
subtalar neutral joint position n.
The optimally aligned position of your foot and ankle when the bones of your lower extremity, as opposed to your ligaments and tendons, are fully supporting your weight. The most efficient position of your foot and ankle in your body’s most perfectly aligned stance. The position of your foot in the midstance of the gait cycle (when your foot is relatively flat on the ground and ready to accept your full weight.) The position of your foot when it is neither pronated nor supinated, and therefore causes no compensatory movements in your lower kinetic chain. The position of your foot where the talus is congruent with the navicular. The position of your foot where fully rotating (supinating) your foot out angles (inverts) your heel bone (calcaneus) twice as many degrees as fully rotating (pronating) your foot in (eversion.)
superficial n. Close to the surface.
superiorn. Higher up the body (in the anatomical position.)
supinate v.
Roll upward. Rotate upward. To roll the inner edge of your foot upward so that it is higher than the outer edge of your foot. You naturally do this before your heel strikes the ground.
supination n. The
opposite of Pronation. Supination describes the position of your foot when it’s pointed up. The inner side is higher than the outer side. The turning inward of the sole of your foot (inversion) and movement of your foot toward
the midline of your body (adduction.) Supination is the process of rolling your foot from the inner side to the outer side.
Supination is best explained with an example. Your foot just left the ground on its way up. Before your foot
comes down again you’re going to change the side to side angle of your foot so that the mid to outer part of your heel can absorb your step.
When you under supinate (fail to roll your foot far enough outward), you land on the inside
of your foot (flat-footed.) This provides inadequate stability and causes your ensuing push-off to be weak because the foot is not rigid enough. When you over supinate (roll your foot too far outward), you land too far to
the outside of your heel. This provides inadequate shock absorption.
The more precisely you supinate, the better you perform athletically, and the more you avoid injury. Your levels of under and over supination can be
precisely measured by drawing a line between your leg, ankle, and the heel of your foot. This angle is then compared to your "natural" or calibration angle at normal standing state. Supination is usually expressed as a
positive angle relative to your calibration angle. Custom computer milled foot orthotics specific to your feet can be made to correct for your improper levels of supination, putting you into the ideal range for supination (inner to
outer foot rotation.)
supine n. Lying on the back.
support moment n. A representation of the total limb pattern used to push away from the ground. An integrated view of your pattern of
movement that sums the movements of your ankle, knee, and hip.
swing phase n.
– The non-contact phase of the gait cycle after your foot has pushed off. The phase in the gait cycle when your foot is swinging through the air.
swing time n.
The duration of the swing phase, between toe off and initial contact.
tarsus n. The collection of bones in your foot that enter into your ankle joint.
tendon n.
A white fibrous cord that connects muscle to bone.
terminal stance n. The period in the stance phase of the gait cycle between heel rise and opposite heel strike.
terminal swing n.
The period in the swing phase of the gait cycle between when your shin bone is vertical and your heel strikes the ground.
three dimensional analysis n.
The recording and analysis of motion in three dimensions through the use of two or more cameras or sensors that measure three perpendicular axes.
tibia n.
Your shin bone. The main bone that runs between your knee and ankle.
tibia vertical n.
An event in the swing phase of the gait cycle in which your shin bone passes through the vertical in moving from behind the body to in front of the body.
toe box n.
The very front of a shoe, boot liner, or boot shell.
toe drag n. Failure to clear the ground with the toes during the swing phase of the gait cycle.
toe in n.
The angle measured between your foot and your line of progression, where your toes are inclined towards your body.
toe off n.
An event in the gait cycle when the foot (normally the toe) leaves the ground. Marks the transition from the stance phase to the swing phase.
toe out n.
The angle measured between your foot and your line of progression, where your toes are inclined away from your body.
toestrike n.
Making initial contact with the toes, rather than the heel or flat foot (normally seen during sprinting.)
tone n. The degree to which a muscle resists attempts to stretch it. High tone is present in spasticity.
torque n. Moments of force resulting from all muscular, ligament and frictional influences acting on a joint.
transverse plane n. The plane that divides a body part into upper and lower portions.
ulcer
n. A loss of covering skin or epithelium.
upper n. The uppermost part of the footwear that encompasses the laces.
upper motor neuron n.
Nerve fiber producing muscular contraction, running from the brain to the spinal cord, where it connects with lower motor neurons.
valgus n.
Joint angulation with the further part sloping away from your body’s midline.
varus n. Joint angulation with the further part sloping towards your body’s midline.
ventral n.
Pertaining to the front of the body, or the front surface.
video analysis n.
Digitizing then analyzing selected relevant points from a film or video. In analyzing pronation or supination the points that make up the angle between your leg, ankle and foot are measured and selectively analyzed.
walking base n. The side-to-side distance between the paths taken by your two feet.
