Running

Running Overview

• Running involves two "flight" periods, where both feet are off the ground, replacing the double-limb support seen in walking
• Compared to walking, running has a shorter stance phase, which is about 40% of the cycle, whereas walking is roughly 60%
• As speed increases, the stride duration decreases, and the percentage of the stance phase in the total running cycle also diminishes

The Running (Stride) Cycle

• Initial Contact is the moment the foot strikes the ground
• Loading Response is the period between initial contact and maximum knee flexion, where significant shock absorption occurs
• Mid Stance is the point when the body's center of mass is directly over the support limb
• Pre Swing is the period from heel off to toe off
• Early Swing is the first half of the swing phase, from toe off to mid swing
• Mid Swing is the point when the knee of the swinging limb passes the knee of the contralateral stance limb
• Late Swing is the remainder of the swing phase, from mid swing to the subsequent initial contact

Variability in Running Cycle

• Greater variability at initial contact (foot strike) during running compared to walking
• Initial contact can occur as a rearfoot, midfoot or forefoot strike
• The type of foot strike influences lower extremity kinematics and the amount of stress put on structures, potentially predisposing runners to injury

Sagittal Plane Kinematics: Pelvis

• Total motion amplitude of the pelvis is around 5° during running
• The pelvis has an average anterior tilt position of 15 - 20° through the running cycle
• The pelvis tilts posteriorly during the loading response after initial contact, then tilts anteriorly
• The greatest amount of anterior tilt occurs at toe off
• The cycle repeats during the swing phase due to demands from the contralateral limb during its stance phase

Sagittal Plane Kinematics: Hip

• The hip is flexed around 35° at initial contact
• The hip angle is maintained or slightly increased during the loading response
• The hip extends throughout the remainder of the stance, reaching 0 - 5° of hip extension near toe off
• The hip flexes during the early swing to advance the limb forward, then reverses towards extension for the next initial contact
• Simultaneous pelvic tilt impacts the true angle at the hip join

Sagittal Plane Kinematics: Knee

• The knee is flexed 10 - 20° at initial contact, reaching maximum flexion of 45 - 50° near midstance
• Flexion during loading response provides shock absorption and decelerates the descent of the center of mass
• The knee extends throughout the second half of stance, reaching 20° flexion just before toe off
• In the swing phase, the knee flexes up to 100 - 120° near midswing
• The knee extends in the second half of the swing phase in preparation for initial contact, at 10 - 20°

Sagittal Plane Kinematics: Ankle

• The ankle is at 0 - 5° of dorsiflexion at initial contact
• As the tibia advances over the foot, the ankle approaches ~30° of dorsiflexion near midstance
• During the pre swing, the ankle plantarflexes to generate power for propulsion, at ~10 - 20° of plantarflexion just after toe off
• The ankle dorsiflexes during the early swing, followed by plantarflexion to return to slight dorsiflexion at initial contact

Frontal Plane Kinematics: Pelvis

• The iliac crest on the stance limb is slightly elevated relative to the contralateral side at initial contact
• Contralateral drop increases in loading response, peaking just before midstance
• After midstance, the direction of tilt reverses
• The pelvis laterally tilts toward the stance limb, reaching a maximum position at toe off
• In the swing phase, the motion cycle repeats, which depends on demands on contralateral pelvis during its stance phase

Frontal Plane Kinematics: Hip

• The hip is slightly adducted at initial contact
• The hip continues to adduct to 8 - 10° just before midstance
• The hip abducts during the remainder of the stance phase and through the early swing
• The hip returns to an adducted position during the late swing in preparation for initial contact
• Pelvis position influences hip motion in the frontal plane during running
• Peak hip adduction and contralateral drop of the pelvis occur synchronously near midstance
• Peak hip abduction coincides with peak elevation of the contralateral pelvis

Frontal Plane Kinematics: Subtalar Joint

• There is significant variability among individuals regarding subtalar joint position at initial contact, ranging from 5° of inversion to 10° of eversion
• Throughout the stance phase the joint everts during initial stance, reaching peak eversion around midstance. The range is from 5 - 20°, and it relates to subtalar joint position at initial contact
• The total excursion from initial contact to peak eversion is roughly 10°
• In the 2nd half of the stance phase, the subtalar joint inverts
• The position at toe off is close to the position at initial contact

Transverse Plane Kinematics: Pelvis

• The pelvis rotates 10 – 15° in the transverse plane, with equal amounts of internal and external rotation
• From initial contact to loading response, the pelvis rotates backward
• The pelvis then rotates forward through the remainder of the stance phase
• The pelvis is neutral in the transverse plane at toe off
• There is maximum forward rotation near mid swing, which corresponds to mid stance on the contralateral limb

Transverse Plane Kinematics: Hip

• The total amplitude of hip motion across the stride cycle is approximately 10° in the transverse plane
• Several small direction changes occur during the swing phase
• The average hip rotation angle across the entire stride cycle is near 0° or neutral
• Transverse plane rotation of the hip during the loading response is most variable

Trunk Kinematics

• The trunk flexes and extends 5 - 10° throughout the stride cycle
• On average, it remains within 2 - 15° of flexion
• Trunk flexion is least at initial contact and peaks just after midstance
• With increased speed, trunk flexion at initial contact also increases
• While the total flexion and extension excursion throughout the cycle doesn’t increase
• The total amplitude of lateral flexion is approximately 10° (5° in each direction)
• The maximum lateral flexion coincides with ipsilateral initial contact
• Greater transverse plane trunk motion occurs in the upper trunk compared to the lower trunk
• Lower trunk - maximum rotation is just before initial contact of the ipsilateral side
• Upper trunk follows the same pattern, but with approximately 3x more total amplitude of motion

Upper Extremities

• The arm swings opposite of the lower extremity
• At initial contact, the shoulder is extended ~ 40° and progressively flexes during the stance phase to ~ 10° of flexion near toe off
• The shoulder returns to 40° of extension during the swing phase
• Shoulder motion varies among individuals and is influenced by running stride length
  • Longer stride length results in greater shoulder motion
• Elbows are held near 90° of flexion throughout the running cycle
• Motion at elbow is generally less than 30°

Muscle Activity with Running

• Muscles often become active well before their primary intended function
• Anticipatory muscle activity allows muscles to be more responsive to impending demands

Muscle Activity: Erector Spinae

• Bursts of simultaneous, bilateral muscle activity at initial contact
• Increased muscle activity controls forward momentum of the trunk relative to the pelvis as the foot contacts the ground

Muscle Activity: Rectus Abdominis

• Displays two periods of increased activity, though at relatively low levels
• The 1st period precedes initial contact, lasting until 20% of the stride cycle
• The 2nd period occurs from 40% to 70% of the stride cycle, corresponding with the initial half of the stance phase of the contralateral limb
• Rectus Abdominis activity is synergistic with deep abdominals to control and stabilize trunk motion and provide support for the abdominal viscera

Muscle Activity: Hip Extensors

• The Gluteus maximus is active before initial contact for hip extension and preparing for loading response
• Activity peaks early in the loading response
• Acts briefly eccentrically following initial contact to decelerate the downward velocity of the body
• Then becomes concentrically active until midstance
• Relatively inactive throughout the remainder of the stance and early swing
• Becomes eccentrically active in late swing to decelerate hip flexion before initiating hip extension
• Substantial increase in Gluteus maximus activity with increased running speeds
• The Adductor magnus shows a peak activity near midstance
• Hamstrings are active prior to initial contact and remain active until about 30% of the stride cycle, contributing about 1½ as much as the Gluteus maximus to hip extension during this portion
• Hamstrings activity peaks at 85% to 90% of stride cycle
• Hamstrings act eccentrically to decelerate hip flexion before initiating hip extension prior to subsequent initial contact

Muscle Activity: Hip Flexors

• The Iliopsoas acts primarily before and after toe off
• Through toe off, the Iliopsoas is eccentrically active, followed by concentric activity just after toe off into early swing
• Peak activity of the Iliopsoas occurs only after toe off
  • Initiates hip flexion and forward acceleration of the limb
  • Magnitude of activity and force increases with increased speed
• The Rectus femoris and Sartorius assist with hip flexion during early swing

Muscle Activity: Hip Abductors

• The Gluteus medius is active prior to initial contact in preparation for loading response, remaining active through most of the stance phase
• Acts eccentrically in loading response to control hip adduction
• After loading response, the Gluteus medius acts concentrically to produce hip abduction during the remainder of its active period in stance
• Relatively inactive in the last part of stance phase through swing
  • In late swing, activity gradually increases in preparation for foot contact

Muscle Activity: Hip Adductors and Rotators

• Adductor magnus and longus have generally low-level activity through most of the stride cycle
• Adductor magnus activity peaks near midstance, assisting with hip extension
• Adductor longus peak activity is during early swing, assisting with initiating hip flexion
• Quadratus femoris is generally active through the stride cycle
  • Two bursts of activity occur during the stance phase and late swing
  • Likely acts eccentrically to control hip internal rotation during loading response
  • During late swing, it functions to provide joint stability during a period of large extensor torque

Muscle Activity: Knee Extensors

• Quads have a burst of activity prior to initial contact, lasting until midstance
• Most active at loading response to eccentrically control knee flexion and support the center of mass
• The Rectus femoris has a burst of activity from 40% to 60% of stride cycle to assist in hip flexion
• Quads become active in preparation for foot contact around late swing

Muscle Activity: Knee Flexors

• Hamstrings display a low-to-moderate level of activity throughout the stance phase, contributing to hip extension
• Relatively inactive during the early swing
• Hamstrings show a burst of activity around 70% and peaks near 90% of the stride cycle
  • Related to deceleration of knee extension to properly position the lower extremity for foot contact

Muscle Activity: Tibialis Anterior

• Low-level activity is present immediately after initial contact to control the lowering of the forefoot to the ground, with a greater magnitude in runners using a rearfoot strike
• Most active during the swing phase, where a small burst of concentric activity occurs during early swing to initiate ankle dorsiflexion after toe off, to enable the foot to clear the ground as the limb swings forward
• Peak activity is present during the late swing, which occurs in coordination with activation of plantarflexors to stabilize the ankle for initial contact

Muscle Activity: Gastrocnemius & Soleus

• Active before initial contact and peak near midstance
• Function eccentrically to control ankle dorsiflexion as the tibia rotates over the foot on the ground
• Act concentrically from midstance until toe off to rapidly plantar flex the ankle during pre swing and propel the body forward
• Relatively inactive throughout the swing phase, until just before the subsequent foot contact
• With a forefoot strike, the force of the ground causes the ankle to rapidly dorsiflex, and plantar flexors act eccentrically at initial contact, resulting in greater total load incurred by these muscles during each stride

Muscle Activity: Tibialis Posterior

• Remains active throughout the entire stance phase
• Becomes active just before initial contact and reaches peak activity by 10% to 20% of the stride cycle
  • Coincides with subtalar joint eversion, so the Tibialis posterior is active eccentrically during the initial half of the stance phase to control foot eversion
• From midstance through toe off, it acts concentrically to initiate subtalar joint
• Relatively inactive during the swing phase

Muscle Activity: Fibularis Muscles

• The Fibularis longus & brevis are active throughout late swing and the entire stance phase
• Peak activity occurs near 15% of the stride cycle, coinciding with peak subtalar joint eversion
• Most likely working synergistically with the Tibialis posterior to stabilize the subtalar joint

Factors Affecting Running Mechanics

• Age
• Gender
• Speed
• Surface incline
• Surface stiffness

Factors Affecting Running Mechanics: Age

• When running at the same speed, older runners (>60) tend to take shorter steps and have a higher step rate
  • Older runners tend to have reduced float times and decreased vertical displacement of the center of mass
  • Older runners demonstrate higher vertical GRF impact peak & loading rate, and greater active peak in GRF, suggesting a loss of shock-absorbing capacity
  • Older runners have reduced peak ankle plantar flexion torque and power generation at the ankle

Factors Affecting Running Mechanics: Gender

• Females demonstrate greater frontal and transverse plane motions during running
  • Greater peak hip internal rotation and adduction, as well as greater peak knee abduction motion
  • Greater power absorption at the hip in the frontal and horizontal planes
• Gluteus maximus EMG signal intensity in females roughly 2x greater of males running at the same speed
  • Also a larger increase in gluteus medius and vastus lateralis activity with either running speed or surface incline increases

Factors Affecting Running Mechanics: Speed

• As running speed increases:
  • Stride length increases, particularly with speeds characteristic of distance
  • Stride frequency increases, particularly with high-speed running and sprinting
  • Stance time decreases
  • GRF increases with speed, which is most pronounced at sub-maximum speeds

Factors Affecting Running Mechanics: Surface Incline

• Increased vertical GRF impact peak and loading rate when running downhill
• Decreased vertical GRF impact peak and loading rate when running uphill
• Propulsive impulse increases with uphill running
• Braking impulse increases with downhill running, which is more pronounced than the increased propulsive increase of uphill running

Factors Affecting Running Mechanics: Surface Stiffness

• Impact peaks are generally similar when running on different surfaces
  • Attributed to corresponding adjustments in joint mechanics to compensate for the surface stiffness
  • Examples of adjustments are greater knee flexion at initial contact when running on harder surfaces, or transitioning to midfoot or forefoot strike rather than a rearfoot strike
• There is significant individual variability in how joint angles and torques are adjusted for surface stiffness
• Movement of the center of mass and ground contact time are not affected by surface stiffness
• The ability to quickly adapt the stiffness of the lower extremity allows runners to run similarly on various surfaces