Running Gait

Introduction to Running Gait and Biomechanics

Running shoe companies, recognizing a growing market, invested in research to better understand chronic running injuries. These injuries typically arise from repetitive application of small loads over many cycles, unlike acute traumatic events such as ACL ruptures. The tissues respond differently to these repetitive loads, leading to various intrinsic and extrinsic factors contributing to injury development. Notably, almost 75% of running injuries fall into six specific categories, as observed by James and Jones [8].

Understanding Injury Patterns

While it might seem intuitive that specific anatomical abnormalities lead to particular injury patterns (e.g., hyperpronation predisposing to posterior tibial syndrome), few such direct relationships have been established. The challenge has been to understand the biomechanical causes of these injuries to improve diagnosis and counseling.

Biomechanics and Running Gait

This article focuses on the biomechanics of running gait and its application to injury prevention. Clinical information is reviewed to highlight key issues, but the primary focus is on biomechanical insights. For a comprehensive review of clinical and pathophysiological issues, readers are referred to articles and chapters dedicated to these topics [3–7,9–14].

Essential References

• Running Injuries by Gary N. Guten, MD [15]
• The Biomechanics of Distance Running edited by Peter R. Cavanagh [22]

The Gap Between Biomechanics and Clinical Practice

There is a significant gap between the world of biomechanists and clinicians. While some clinicians, such as Dr. Stan James, have demonstrated a deep understanding of running gait biomechanics [23], the broader application of biomechanical insights to clinical practice remains limited. Shoe manufacturers have led some areas of biomechanics research, but maintaining a broad focus is crucial.

Key Coaching Points

• Repetitive Loads: Chronic running injuries are often due to repetitive application of small loads over many cycles.
• Injury Patterns: Most injuries fall into specific categories, highlighting the need for targeted prevention strategies.
• Biomechanical Insights: Understanding the biomechanics of running gait is crucial for injury prevention and treatment.
• Clinical Application: Bridging the gap between biomechanics and clinical practice is essential for improving injury diagnosis and counseling.

Recommended Reading

• Biomechanics of Running Gait Reviews [16–21]
• James and Jones Studies [8,24]
• Biomechanics of Distance Running [22]

This structured approach aims to provide a clear understanding of the biomechanics of running gait and its implications for injury prevention and clinical practice.

The Gait Cycle

Walking Gait Cycle

• IC (Initial Contact): The moment when the foot first touches the ground.
• LR (Loading Response): The period immediately following initial contact where the body’s weight is transferred to the foot.
• TO (Toe Off): The moment when the toe lifts off the ground, initiating the swing phase.
• MS (Midstance): The middle of the stance phase where the body’s weight is fully supported by the foot.
• TS (Terminal Stance): The final part of the stance phase before toe off.
• PS (Preswing): The period between toe off and the initiation of the swing phase.
• IS (Initial Swing): The beginning of the swing phase where the foot is lifted off the ground.
• MS (Midswing): The middle of the swing phase where the leg is moving forward.
• TS (Terminal Swing): The final part of the swing phase before the foot makes contact with the ground again.

Running Gait Cycle

• IC (Initial Contact): The moment when the foot first touches the ground.
• TO (Toe Off): The moment when the toe lifts off the ground, initiating the swing phase.
• StR (Stance Phase Reversal): The transition point between stance phase absorption and generation.
• SwR (Swing Phase Reversal): The transition point between swing phase absorption and generation.
• Absorption: The period from swing phase reversal through initial contact to stance phase reversal.
• Generation: The period from stance phase reversal through toe off to swing phase reversal.

Key Differences Between Walking and Running

• In running, toe off occurs before 50% of the gait cycle is completed.
• There are no periods when both feet are in contact with the ground.
• Both feet are airborne twice during the gait cycle, referred to as double float.
• The timing of toe off depends on speed, with faster runners spending less time in stance.

Phases of Acceleration and Deceleration

• Absorption: The period where the body’s center of mass falls from its peak height during double float. This phase is divided into swing phase absorption and stance phase absorption.
• Generation: The period where the center of mass is propelled upward and forward, increasing kinetic and potential energy.

Stance and Swing Phases

• Stance will be plotted before swing for the purposes of this article, although some authors prefer to depict swing phase first.
• DeVita argued that toe off should mark the beginning of the gait cycle and that swing phase should be depicted before stance.

Figure References

• Fig. 2: Illustration of the gait cycle phases for walking and running.
• Fig. 3: Variation in gait cycle parameters with speed of movement.

EMG Activity in the Running Gait Cycle

Overview

Muscle activity during running is well-documented through electromyographic (EMG) studies. The EMG activity is represented by solid bars in relation to the gait cycle, as depicted in Fig. 4. Approximately 1.3 gait cycles are shown to better visualize the continuous nature of running gait, eliminating the artificial division caused by beginning and ending the cycle at initial contact (IC).

Key Observations

• Initial Contact (IC): There is a greater number of active muscle groups around the time of initial contact, indicating the body’s preparation for ground contact is more significant than the preparation needed to leave the ground.
• Transition from Swing to Stance: EMG activity is greater at the transition from swing to stance than from stance to swing, suggesting that the body’s preparation for ground contact is more critical than the act of leaving the ground.

Muscle Activity Patterns

Quadriceps and Rectus Femoris

• Quadriceps and Rectus Femoris: Both muscles fire from late swing to midstance to prepare the limb for ground contact and to absorb the shock of that impact during stance phase absorption.
• Cycle Time: The cycle time for the data presented in Fig. 4 is 0.6 seconds.
• Onset of Quadriceps Activity: The onset of quadriceps activity is at 87%, 78 ms before IC, consistent with the development of muscle force just before IC.
• Rectus Femoris Activity: Only the rectus femoris is active in midswing, essential to restrain the posterior movement of the tibia as the knee flexes.

Coaching Implications

• Preparation for Ground Contact: The body’s preparation for ground contact is more significant than the act of leaving the ground, emphasizing the importance of initial contact mechanics.
• Muscle Activation Timing: Understanding the timing of muscle activation is crucial for optimizing running mechanics and reducing injury risk.
• Energy Transfer: The biarticular rectus femoris plays a role in energy transfer between segments, highlighting the importance of coordinated muscle activity for efficient running.

Notes

• There is a delay (approximately 50 ms) between the onset of EMG activity and the development of muscle force.
• Muscle force is still present after EMG activity ceases, particularly for the gastrosoleus and quadriceps in midstance.

Kinematics of the Gait Cycle

Overview

These graphs illustrate the changing position of the joint listed for one complete gait cycle in all three planes. Each graph begins and ends at initial contact and therefore represents one gait cycle along the x-axis. The vertical dashed line represents toe-off for each condition.

• Left of the dashed line: Depicts joint motion during stance phase.
• Right of the dashed line: Depicts joint motion during swing phase.

The position of the joint or body segment in degrees is represented along the y-axis. Walking is represented by the lightly-dashed line, running by the solid line, and sprinting by the heavy-dashed line. The corresponding toe-off line is plotted using the same line style.

Data Representation

The continuous line connects fifty data points (every 2% of the gait cycle) and represents average data (15 strides) for each of the three conditions.

Joint Position and Motion

• Pelvis Position: Plotted relative to the horizontal and vertical coordinate system of the lab.
• Hip Position: Represents the position of the femur plotted relative to the position of the pelvis.
• Knee Flexion-Extension: Denotes the angle between the femur and the tibia. 0° indicates full extension (180° between the femoral and the tibial shafts).
• Dorsiflexion-Plantarflexion: Represents the position of the foot relative to the tibia with a 90° angle being plotted as 0°.
• Foot Progression Angle: Depicts the orientation of the foot relative to the lab.

Coaching Implications

Understanding the kinematics of the gait cycle is crucial for optimizing running performance and preventing injuries. Coaches can use this information to:

• Identify Biomechanical Issues: By analyzing joint angles and positions during stance and swing phases, coaches can pinpoint areas of inefficiency or potential injury risk.
• Develop Training Plans: Tailored training programs can be designed to address specific biomechanical needs, enhancing performance and reducing injury likelihood.
• Monitor Progress: Regular assessments using kinematic data can help track improvements in running form and efficiency.

Gait and Posture: Biomechanics Notes on the Running Gait Cycle

Sagittal Plane Ankle, Knee, and Hip Motion

Ankle Motion

• Timing: Elite 22%, Sprint 37%, Run 39%, Walk 62%
• Data collected at the Motion Analysis Laboratory at Gillette Children’s Specialty Healthcare (average data from 15 strides for each condition)
• Elite sprinting data adapted from Mann and Hagy [32] (average of two elite sprinters with similar velocities)
• Dorsiflexion-plantarflexion: Position of the foot relative to the tibia with a 90° angle plotted at 0°

Knee Motion

• Knee flexion-extension: Angle between the femur and the tibia
• 0° indicates full extension (180° between the femoral and the tibial shafts)

Thigh Position

• Thigh position: Position of the thigh relative to the vertical
• 0° angle indicates that the thigh is in a vertical position
• Comparable to the hip flexion-extension angle depicted in Fig. 5, but plotted in relation to the position of the pelvis

Anterior Tibialis

The anterior tibialis dorsiflexes the ankle to provide clearance in swing (concentric), to allow ground contact with the hindfoot initially, and to control the lowering of the forefoot to the ground during the first part of stance (eccentric).

Kinematics

Kinematics describe movement without considering the forces that cause it. Kinematic variables can be graphed as a function of the percentage of the total gait cycle or time. Patterns of movement are important, but peak values in degrees of movement are not as critical as the timing of extremes of motion. Kinematic data can be expressed in other ways, such as angle-angle diagrams [37,38], but these representations may have less meaning for clinicians. Motion in all three planes will be considered, and one must be aware of what the angular measurements represent.

Sagittal Plane Kinematics

When observing sagittal plane motion, there is a shift into flexion and the center of mass is lowered as the motion changes from walking to running to sprinting. The pattern of movement in the tilt of the pelvis is similar at all speeds (Fig. 5).

Gait and Posture in Running and Sprinting

Overview of Gait Cycle Dynamics

As speed increases in running and sprinting, the pelvis and trunk tilt further forward, lowering the center of mass. This adjustment maximizes the horizontal force produced in the propulsion phase.

Ground Reaction Force (GRF)

The foot and ground exert an equal and opposite force on one another, known as the ground reaction force (GRF). The position and acceleration of the runner’s center of mass determine the direction and magnitude of the GRF. For example, during the initial phase of acceleration from a standstill, the body is tilted forward, and the center of gravity falls far ahead of the contact point. After several gait cycles, the sprinter reaches maximum velocity, and the center of mass then moves backward. An athlete who tries to accelerate with an upright body would fall over backward due to the direction of the GRF. The forward trunk lean and pelvic tilt keep the GRF in a position to allow forward acceleration.

Sagittal Plane Hip Motion

Sagittal plane hip motion is essentially sinusoidal in walking. Maximum hip extension occurs just before toe-off, and maximum flexion occurs in mid to terminal swing. In running and sprinting, maximum hip extension is similar to walking but occurs slightly later in the gait cycle (at the time of toe-off). As velocity increases, so does maximum hip flexion, leading to a longer step length. Unlike walking, the hip extends during the second half of the swing phase during running and sprinting in preparation for initial contact. This difference is to avoid the excessive deceleration that would occur at the time of initial contact if the foot were too far ahead of the center of mass of the body. The ground reaction force vector would be directed excessively posteriorly.

Knee Motion

The pattern of knee motion in walking, running, and sprinting is very similar, but the extremes of motion are very different. In running, during the absorption period of stance phase, the knee flexes to approximately 45°. This is followed by knee extension to an average of 25° during the propulsion phase. In sprinting, the absorption period is shorter, and the knee flexes less. Greater knee extension occurs during the propulsion period, peaking at 20°. Swing phase also exhibits differences between walking, running, and sprinting. Maximum knee flexion during swing is about 60° in normal walking. This is much less than the average of 90° in running or the 105° in sprinting. A highly trained athlete in a full sprint may exhibit up to 130° of maximum knee flexion.

Initial Contact

Initial contact during walking and running occurs with the heel. For walking, this occurs despite ankle plantar flexion because of the position of the tibia. In running, greater ankle dorsiflexion is required to achieve initial heel contact. In sprinting, initial contact occurs on the forefoot. Tibial position allows the ankle to be in a more neutral or slightly dorsiflexed position.

Biomechanics Notes on the Running Gait Cycle

Sagittal Plane Kinematics

In the sagittal plane, the pelvis and hip motion play a crucial role in maintaining balance and equilibrium. During the stance phase, the hip is adducted, and the pelvis lowers to ensure foot clearance. Conversely, during the swing phase, the pelvis elevates to facilitate foot clearance. This nearly reciprocal motion, combined with slight lumbopelvic motion, minimizes shoulder and head movement. This mechanism is essential for decoupling intense lower extremity motion from the trunk and head, thereby maintaining balance and equilibrium.

Transverse Plane Kinematics

Motion in the transverse plane is less pronounced compared to the sagittal plane but is vital for energy efficiency. In walking, pelvic rotation is a key method for lengthening the stride, with maximal forward rotation at initial contact. However, in running and sprinting, the pelvis reaches maximal internal rotation in midswing to lengthen the stride, but by initial contact, it has rotated externally to maximize horizontal propulsion force and maintain speed.

The pelvis acts as a pivot between the counter-rotating shoulders and legs. For instance, when the right leg is maximally forward in midswing, the left shoulder is rotated forward, and the pelvis is neutral.

Pronation and Supination

Pronation and supination occur in an oblique plane in the foot. During the stance phase, the foot pronates during the absorption phase while the limb is loaded, and then supinates during the generation phase to provide a stable lever for push-off. The posterior tibialis muscle plays a significant role in controlling this motion.

Kinetics

Winter and Bishop outlined the major goals associated with athletic events, providing an overall framework for organizing the biomechanical principles discussed. The kinetic aspects of running and sprinting are crucial for understanding the forces and movements involved in these activities.

Gait and Posture: Biomechanics of the Running Gait Cycle

Ground Reaction Force (Vertical Component)

• First Peak: Passive force peak associated with the shock of contact with the ground, attenuated by the heel pad and shoe wear, and modified by the passive characteristics of the running surface. It is generally smaller and of shorter duration than the second peak.
• Second Peak: Centered about stance phase absorption, marking the end of deceleration and the beginning of acceleration. This peak is due to active muscle forces.

Energy Absorption and Power Generation

• Ankle Joint: Greater energy absorption in sprinting compared to running. The period of absorption is followed by a period of power generation, providing energy for forward propulsion. The magnitude of ankle power generation is directly related to the athlete’s speed.

Knee Moment Pattern

• Sprinting and Running: Similar knee moment patterns. Hamstrings become dominant in the second half of swing, producing a knee flexor moment. Shortly after initial contact, quadriceps become dominant, producing a knee extensor moment. The peak knee extensor moment is greater in running due to the runner’s greater degree of knee flexion as the limb is loaded.
• Running: Quadriceps contract eccentrically as the knee flexes following initial contact, reflecting their role as shock absorbers.
• Sprinting: The ankle plantarflexors absorb much of the shock of contact with the ground, resulting in little power absorption at the knee.
• Stance Phase: Knee extends in the second half of stance phase, with quadriceps contracting concentrically to generate power. In swing phase, muscles absorb power to control the movement of the swinging leg.

Hip Moment Pattern

• Forward Locomotion: Hip extensors are dominant just prior to and just after initial contact. Hip flexors are dominant in the second half of stance through the first half of swing. Both hip flexors and extensors are responsible for increased power generation in running and sprinting. Peak hip flexion occurs in the second half of swing in both running and sprinting.

Coronal Plane Joint Moments and Powers

Overview

Although the magnitudes of coronal plane moments are substantial, the muscles and ligaments that create them function primarily as stabilizers. There is minimal motion; therefore, power generated and absorbed are much less than in the sagittal plane. Coronal plane kinetic data is not graphically depicted in this review. The reader is referred to prior publications [31,39].

Stance Phase

• A continuous hip abductor moment is produced primarily by the gluteus medius.
• During the absorption phase, the hip adducts because the ground reaction force falls medial to the hip, and the hip abductor moment is less than the external adduction moment due to gravitational and acceleration loads.
• The gluteus medius contracts eccentrically to control this motion.

Propulsion Phase

• During the propulsion phase, the gluteus medius contracts concentrically, abducting the hip.

Biomechanics Notes on the Running Gait Cycle

Energy Sources and Power Generation

The energy sources for running are illustrated in Fig. 10, where the pie charts represent the total amount of positive work measured for the lower extremity joints. The main sources of power generation for forward propulsion are:

1. Hip Extensors: During the second half of the swing phase and the first half of the stance phase.
2. Hip Flexors: After toe-off.
3. Knee Extensors, Hip Abductors, and Ankle Plantarflexors: During the stance phase.

Kinetics and Muscle Contributions

As speed increases, the movement strategy changes. The primary muscle groups involved in power generation are:

• Hamstrings and Gluteus Maximus: Pull the body forward by actively extending the hip after swing phase reversal when the foot is ahead of the body.
• Quadriceps and Gastrocnemius-Soleus Complex: Contract to push the body forward by extending the knee and plantarflexing the foot.
• Hip Abductors: Contract to stabilize the hip and possibly provide lift (unproven).
• Psoas: Propels the limb into swing by pulling the thigh forward.

The total amount of power generated increases with speed, and the relative contribution from each muscle group changes such that relatively more power is generated proximally as speed increases.

Tendons and Muscle Efficiency

Tendons play a crucial role in energy efficiency. They stretch and then efficiently return most of that energy when they recoil. Muscles that are pretensioned and then contract generate more power per unit of activation than those that are not. Therefore, tendons can be considered as the springs and muscles as the tensioners of the springs.

Role of the Arms in Running

The role of the arms in running has been a subject of debate. Hinrichs concluded that the arms provide lift and do not contribute significantly to forward propulsion in distance running. They help maintain a more constant horizontal velocity by acting as a counterbalance.

Gait and Posture: Running Gait Cycle

Energy Efficiency in Running

Because of the difference in movement dynamics, the body alters its methods to maintain energy efficiency. Large fluctuations in total energy would be disadvantageous regardless of the pace of movement. In walking, efficiency is maintained by the effective interchange between potential and kinetic energy, which are out of phase. In running, however, potential and kinetic energy peak in midswing, and these energies are in phase, making this interchange impossible. Instead, efficiency is primarily maintained in two ways:

1. Storage and return of elastic potential energy by the stretch of elastic structures (especially tendons).
2. Transfer of energy from one body segment to another by two-joint muscles such as the rectus femoris and the hamstrings.

Hysteresis Curve for Tendon

Fig. 12. Hysteresis curve for tendon. Tendons efficiently recoil in a springlike fashion, returning approximately 95% of the energy stored when stretched. For any given amount of stretch (strain), the difference in stress is dissipated as heat.

Energy Conversion During Running

During running, potential and kinetic energy peak in midswing. As the center of mass falls toward the ground, potential energy is lost. As the foot contacts the ground, kinetic energy is lost. Much of the lost potential and kinetic energy is converted into elastic potential energy and stored in the muscles, tendons, and ligaments. During the generation phase, the center of mass accelerates upward, and both potential and kinetic energy increase. Energy for this movement is supplied by the active contraction of the muscles and the release of the elastic potential energy stored in the ligaments and tendons. The storage of energy in the elastic structures of the lower extremities thus plays a more important role in running and sprinting than in walking.

Tendons as Springs

Each musculotendinous unit absorbs power by stretching (eccentric) just before they shorten (concentric) to generate power. Recent animal studies have indicated that the changes in the length of the muscle belly itself are relatively minimal. Instead, they function as tensioners of the musculotendinous springs, their tendons. Most of the change in length comes from the stretch and recoil of their respective tendons. Therefore, most of the work is done by the tendons. An excellent source for information on this topic is provided by McMahon.

Tendons are, in fact, excellent biological springs. In this way, we should begin to think of tendons as springs and muscles as the tensioners of the springs. The analogy of a runner to a person on a pogo stick is apt.

Gait and Posture: Biomechanics of the Running Gait Cycle

Energy Storage and Return Mechanism

The Achilles tendon plays a crucial role in the stance phase of the gait cycle by storing and returning energy to the individual at the time of push-off. This mechanism is analogous to the spring of a pogo stick, where the tendon stretches under tension and returns the stored energy back to the system. According to R. McNeil Alexander, the total energy turnover in each stance phase of a 70 kg man running at 4.5 m/s is 100 J. Specifically, 35 J are stored as strain energy in the heelcord, 17 J in the arch of the foot, and more in the stretch of the quadriceps and patellar tendons. Consequently, less than half of the energy (approximately 48 J) has to be removed by the muscles acting as brakes and returned by them doing work. The muscles must still exert the tension, but they shorten and lengthen less. The idea that the body’s system of muscle, tendon, and ligament springs behaves like a single linear spring (‘leg spring’) is supported by the work of Farley and Gonzalez. They found that the leg spring stiffness increases by 2.3-fold from 7.0 to 16.3 kN/m as stride frequency increases from 26% below to 36% above preferred frequency. Additionally, vertical displacement decreases with increased stride frequency.

Biarticular Muscles

Transfer of Energy Between Body Segments

The second mechanism contributing to energy efficiency is the transfer of energy between body segments by biarticular muscles. Elftman is credited with first proposing this principle. For instance, the hamstrings in the second half of the swing phase extend both the hip and the knee while contracting. This results in an extensor moment at the hip and a flexor moment at the knee. Since the overall change in length of the hamstrings is minimal, they can be considered to neither absorb nor generate energy. Instead, the hamstrings function as an ‘energy strap’, transferring energy from the moving tibia to the pelvis to aid in hip extension. As the knee extends, energy from the tibia is supplied to the pelvis to augment hip extension. A similar analysis can be applied to the biarticular rectus femoris during the first half of the swing phase. This can be visualized by overlaying the power curves for the hip, knee, and ankle.

Jacobs et al hypothesize that biarticular leg muscles effectively transfer power from proximal joints to distal joints, causing an efficient conversion of successive rotational motions of body segments into translation of the body center.

Foot Biomechanics in Running Gait Cycle

Overview

Lay and sports medicine literature often attributes excessive pronation to a wide range of lower extremity and spinal issues. This perspective is based on the idea that abnormal movement of the foot joint over thousands of repetitive cycles can lead to overuse syndromes, such as increased internal rotation of the tibia via the mitered hinge effect [58]. Empirical clinical evidence supports this notion, as shoes or orthotics designed to reduce hyperpronation often alleviate painful conditions. However, there is a lack of quantitative evidence to substantiate this type of abnormal biomechanics [17].

Normal and Pathological Mechanics

Several review articles examine the normal and pathological mechanics of hind- and midfoot motion [59,60]. Roger Mann [61] has been instrumental in educating biomechanists and the medical community on this topic. Czerniecki’s review [58] correlates foot and ankle biomechanics with Perry’s three stance phase ankle rockers, integrating two areas of knowledge.

Ankle Motion and Foot Rotation

Sagittal plane ankle motion is accompanied by rotation in the transverse plane and rotation of the foot about its long axis due to the oblique orientation of the ankle joint. During gait, when the foot is fixed to the ground, ankle dorsiflexion causes internal rotation of the tibia and pronation of the foot. The subtalar joint also has an oblique axis of rotation, contributing to the complex movement of pronation-supination of the foot relative to the tibia. Rotational torques about the longitudinal axis of the foot are transmitted to the tibia, resulting in rotational torques about its longitudinal axis.

Stance Phase Mechanics

• Initial Contact: The hindfoot is typically inverted.
• Absorption Phase: Pronation occurs as the limb is loaded. Pronation ‘unlocks’ the transverse tarsal joint, increasing the flexibility of the foot, allowing it to function more effectively as a shock absorber. Peak pronation normally occurs at 40% of stance phase.
• Midstance to Propulsion: The foot begins to supinate and reaches a neutral position at 70% of stance. The transverse tarsal joint is then ‘locked’. The generation phase has been reached, and the foot is now more rigid, allowing it to act more effectively as a lever for push-off.

Coaching Implications

• Understanding Pronation and Supination: Coaches should understand the normal mechanics of pronation and supination to better assess and address potential overuse syndromes.
• Orthotic and Shoe Recommendations: Empirical evidence supports the use of orthotics and shoes designed to reduce hyperpronation for pain relief. However, quantitative evidence is lacking, so recommendations should be made with caution.
• Training and Rehabilitation: Training programs should consider the mechanics of the foot and ankle to enhance shock absorption and power generation phases of the gait cycle.

Biomechanics Notes on the Running Gait Cycle

Abnormal Excessive Pronation

• Time to Max Pronation: Delayed beyond 40% of stance.
• Prolonged Pronation Period: Delays the onset of supination.

Accuracy of Measurement Techniques

• 2-D vs. 3-D Models: Areblad et al. [64] showed that variables change by up to 1° for every 2° of change in the alignment angle when comparing 3-D model angles to 2-D model angles. This highlights the concern with using 2-D systems due to errors in foot alignment with the camera axis.
• Engsberg and Andrews [66]: Obtained 2-D data and reduced it to 3-D, acknowledging potential errors. The graphical presentation of 3-D data in 2-D format is confusing and limits utility to researchers, not clinicians.

Reporting Data

• Soutas-Little et al. [67]: Emphasized the importance of reporting rotations between body segments in a meaningful anatomical and functional way. However, they modeled the foot and shank as rigid bodies, highlighting limitations in defining rearfoot motion as the projection of angles on the posterior shank and heel.

Pronation and Injury Development

• Importance of Pronation Variables: It remains unclear whether the absolute degree of pronation, timing of pronation, or maximum velocity of pronation [68] is most crucial in injury development.

Running Shoes

• Shoe Analysis: Numerous publications have been written on running shoe analysis [69–75].
• Pink and Jobe [76]: Summarized the current thought on the interface between the foot and shoe. Shoes must be tested both in laboratories and in vivo to account for individual movement pattern changes in response to dynamic balance adjustments.
• Orthotic Intervention: Clinical experience suggests improvements due to adaptations in movement patterns rather than direct effects of orthotics or shoe alterations.

Gait and Posture: Biomechanics of Running

Introduction

They found that intra- and intersubject variability was large. The differences between subjects for a given condition were greater than the differences between conditions (different shoe designs) for a given subject. They concluded that the shoe must be on the foot to test its function and that dynamic function must be the basis for evaluation and design.

Function of Footwear

Winter and Bishop [26] stated that for runners, footwear is predicted to protect or attenuate the potential damaging forces in three ways:

1. shock absorption at heel contact reducing the initial spike of reaction force (protects against joint cartilage damage);
2. stance phase—protects against the rough ground surface;
3. aligning the forefoot to achieve a uniform force distribution at the major chronic injury sites.

Focus Areas for Shoe Design

For these reasons, the three main areas of focus for shoe design have been on the attenuation of the shock of heel strike, the control of hindfoot motion during loading response, and forefoot stability in stance phase. An ideally constructed shoe provides both shock absorption and stabilization of the foot. Intrinsic factors of each individual runner such as degree of pronation, flexibility of the foot, and body weight are all important factors which must be considered when selecting a running shoe.

Design Features for Stability and Motion Control

Stability and motion control are addressed in last design, stiffer heel counters, lacing systems, fiberglass midsole plates, and material combinations of varying density in the shoe’s midsole [77]. Design features that control the tendency for hyperpronation and maintain neutral forefoot position in midstance can minimize excessive stresses on the medial side of the Achilles’ tendon or plantar fascia. Forces may be more uniformly distributed and therefore the potential for injury minimized.

Cushioning and Rearfoot Control

Cushioning and rearfoot control require opposite design features. Therefore, a single shoe design cannot maximize both. For more cushioning, thicker-soled shoes are better than softer ones, but softer materials control pronation poorly.

Differences Between Racing and Training Shoes

Interestingly, quantifiable differences between racing and training shoes are negligible despite the commonly held belief that racing shoes provide less shock absorption and control of movement [43]. Perhaps runners adapt their running style to maintain acceptable force levels. On the other hand, actual differences may exist but are undetectable.

Mechanical Testing of Shoes

Mechanical testing of shoes for shock attenuation has shown a 33% difference between different shoe models [77]. In this report, 75% of shock attenuating capability was found to be retained after 75 miles and only 67% after 100—150 miles. In vivo testing in volunteers showed similar but less severe degradation with 70% retention of cushioning after 500 miles.

Development of Cushioning Systems

Running shoe manufacturers have attempted to develop a cushioning system that not only dissipates energy but also stores it to allow for passive energy exchange (to enhance performance).

Hip Abductors and Common Injuries in Distance Runners

It is notable that this list is comprised of many of the most common injury sites in distance runners. Inverse dynamics has indeed advanced the state of the art of biomechanical evaluation! It now seems more likely that most of the chronic injuries from jogging are related to the high forces that occur in mid- and late stance [79]. Based on these calculations, training with eccentric knee exercise and concentric plantarflexion can be recommended to help avoid injury. We now have an appreciation for the biomechanical stresses that can give us insight into the etiology of some of the most common injury patterns.

Even though inverse dynamics allows the evaluation of net joint moments about the hip, knee, and ankle, and provides insight into the location and timing of these soft tissue stresses [26,31,39], actual stress levels within specific musculotendinous structures cannot be measured unless strain gauges are implanted. Biomechanical link segment models can be used to estimate force and stress levels. For instance, Achilles’ tendon forces have been estimated to be approximately 6–8 times body weight [21,80] and patellofemoral contact forces between 7 and 11 times body weight [80]. The development of improved models will allow even more accurate calculation of these and other individual tissue stresses.

Concluding Remarks on Biomechanical Analysis

In the concluding remarks of his 1987 review article, Cavanaugh wrote, ‘It is this author’s firm belief that, in some few years time, it will be possible to write a fairly extensive review of the literature pertaining to the quantitative biomechanical analysis of running injuries’. A number of publications are now available regarding the biomechanical analysis of common injury patterns in runners [25,26,39,40,81,82]. Because of space constraints, only one injury pattern, Achilles’ tendinopathy, will be presented here.

Achilles’ Tendinopathy

The Achilles’ tendon and its insertion are frequent sites of chronic injury in athletes. Pain along the course of the tendon is the most frequent presenting complaint. Tenderness with or without swelling along its course is common. Acute ruptures are almost always preceded by a prodromal period of low-grade pain [10,11].

The Achilles’ tendon is one of the anatomic structures that stretches during the first half of stance phase and recoils later in a spring-like fashion. It stores energy as it is stretched and efficiently returns 90% at the time of push-off [21]. If initial contact is on the forefoot, the eccentric function of the gastrosoleus-Achilles’ tendon complex is exaggerated as the heel is lowered to the ground. The gastrosoleus generates large ankle plantar flexor moments during running compared to those generated during walking (Fig. 9). As mentioned, because there are few other structures involved, peak Achilles’ tendon forces have been estimated to be in the range of 6–8 times body weight [21,80]. Peak forces do not occur at initial contact, but in mid-stance.

Gait and Posture in Running

Introduction

Miller highlights the necessity of evaluating individual body segment contributions to running [38]. Techniques such as those reported by Kepple [84] may offer promising methods for determining the contributions of joint moments to the vertical and forward progression of the body’s center of mass.

Standardizing Terminology and Reporting Conventions

There is a need to standardize terminology and agree on reporting conventions, such as whether full knee extension is 0° or 180°. Presenting information in a format familiar to clinicians is crucial for its effective use. Data presented as tables of numbers or plots on graphs can be meaningless to clinicians.

Enhancing Communication

Electronic communication can enhance the use of animation, video, and live action to display data. It is the responsibility of the research community to present new biomechanical knowledge to clinicians in an understandable manner. Collaboration between biomechanists, pathophysiologists, and clinicians on the track can lead to significant advancements.

Acknowledgements

The author wishes to acknowledge Joyce Phelps Trost, RPT for her help in collecting, analyzing, and formatting the data, Mary Trost for her assistance in manuscript preparation, the staff of the Motion Analysis Laboratory at Gillette Children’s Specialty Healthcare for gathering the data, and Anna Bittner for photographic and computer graphics support.

References

1. Encyclopedia Britannica, 1952:234.
2. Cavanagh PR. The mechanics of distance running: a historical perspective. In: Cavanagh PR, editor. Biomechanics of Distance Running. Champaign, IL, Human Kinetics Publishers, 1990; Chapter 1:1–34.
3. Hanks GA, Kalenak A. Running injuries. In: Grana WA, Kalenak A, editors. Clinical Sports Medicine. Philadelphia: W.B. Saunders Company, 1982:458–65.
4. Renstrom PA. Mechanism, diagnosis, and treatment of running injuries. AAOS Instructional Course Lectures 1993;42:225–34.
5. O’Brien M. Functional anatomy and physiology of tendons. Clin Sports Med 1992;11(3):505–20.
6. Booth FW, Gould EW. Effects of training and disuse on connective tissue. Exer Sport Sci Rev 1975;3:83–112.
7. Leadbetter WB. Cell-matrix response in tendon injury. Clin Sports Med 1992;11(3):533–78.
8. James SL, Jones DC. Biomechanical aspects of distance running injuries. In: Cavanagh PR, editor. Biomechanics of distance running. Human Kinetics Books, 1990:249–269.
9. Brewer B. Mechanism of injury to the musculotendinous unit. AAOS Instructional Course Lectures, 1960;14.
10. Clement DB, Taunton JE, Smart GW. Achilles tendinitis and peritendinitis; etiology and treatment. Am J Sports Med 1984;12(3):179–84.
11. Galloway MT, Jokl P, Dayton DW

Biomechanics of the Running Gait Cycle

Introduction

The running gait cycle is a complex series of movements that involve the coordinated action of various body segments and muscles. Understanding the biomechanics of running is crucial for optimizing performance and preventing injuries. This section provides an overview of the key phases of the running gait cycle and their implications for training and injury prevention.

Key Phases of the Running Gait Cycle

1. Initial Contact

• Description: The first point of contact between the foot and the ground.
• Implications: The initial contact phase is critical for shock absorption and setting the tone for the rest of the gait cycle. Proper foot placement and flexibility in the ankle and foot are essential for effective shock absorption.

2. Loading Response

• Description: The period from initial contact to the point of maximum loading.
• Implications: During this phase, the body absorbs the forces generated by the impact of the foot hitting the ground. Efficient loading response involves optimal muscle activation and joint alignment to distribute forces effectively.

3. Midstance

• Description: The phase where the body is directly over the support leg.
• Implications: Midstance is crucial for stability and propulsion. Proper alignment of the knee and hip joints, along with adequate muscle strength and flexibility, are necessary to maintain balance and prepare for the next phase.

4. Terminal Stance

• Description: The period from the point of maximum loading to toe-off.
• Implications: Terminal stance involves the transition from stance to swing phase. Efficient transition requires optimal muscle coordination and joint mobility to initiate the forward motion of the swing leg.

5. Pre-swing

• Description: The phase immediately before toe-off.
• Implications: Pre-swing is characterized by the forward movement of the swing leg and the preparation for toe-off. Proper muscle activation and joint positioning are essential for an efficient transition to the swing phase.

6. Swing Phase

• Description: The period from toe-off to initial contact of the swing leg.
• Implications: The swing phase involves the forward movement of the leg and foot, preparing for the next initial contact. Efficient swing phase mechanics require optimal muscle coordination and joint flexibility to maintain momentum and stride length.

Biomechanical Considerations

• Leg Stiffness and Stride Frequency: Research indicates that leg stiffness and stride frequency are key factors in running economy (Farley CT, Gonzalez O, 1996). Adjusting these variables can enhance performance and reduce injury risk.
• Muscle and Reflex Properties: The spring-like properties of muscles and reflexes play a significant role in running efficiency (McMahon TA, 1990). Understanding and optimizing these properties can lead to improved performance and reduced injury incidence.
• Foot and Ankle Biomechanics: Proper foot and ankle mechanics are crucial for effective shock absorption and propulsion (Czerniecki JM, 1988). Addressing biomechanical issues in the foot and ankle can improve overall running efficiency and reduce injury risk.

Training Implications

• Stride Length Variation: Adjusting stride length can influence oxygen uptake and running economy (Cavanagh PR, Williams KR, 1982). Training programs should consider individual stride length optimization for improved performance.
• Muscle and Joint Flexibility: Enhancing flexibility in key running muscles and joints can improve shock absorption and propulsion, leading to more efficient running mechanics (Novacheck TF, 1997).
• Proprioceptive Training: Enhancing proprioception can improve joint stability and coordination, leading to more efficient and injury-resistant running mechanics (Novacheck TF, Trost JP, 1997).

Conclusion

Understanding the biomechanics of the running gait cycle is essential for optimizing performance and preventing injuries. By focusing on key phases and biomechanical considerations, endurance coaches can develop effective training programs that enhance running efficiency and reduce injury risk.