Biomechanics of Normal Gait

Overview and Description

Gait, or the way humans walk or run, is an orchestrated series of movements involving various muscles, joints, and biomechanical processes. Mastery of normal gait parameters is essential for physiatrists to evaluate and treat abnormal gait effectively. This chapter provides an overview of the gait cycle, important concepts used to understand gait, and gait analysis.

The gait cycle^1–3

The gait cycle is the sequence of events that occur from the initial contact of one foot with the ground to the subsequent contact of the same foot with the ground. Stance phase is the period of the gait cycle in which the foot is in contact with the ground. During stance phase, the lower limb accepts body weight and provides support while the body moves forward. Swing phase is the period in which the foot is off the ground and the limb is advancing forward.

Subphases of the Gait Cycle

The eight subphases, or divisions (terminology varies), of the gait cycle are described below. The timing of the subphases can be expressed as occurring at approximate percentages along the gait cycle, beginning with initial contact (0%), and ending with the most terminal portion of swing (100%).²

The subphases of stance phase and approximate timing during the gait cycle are:

Initial Contact (0% to 2% interval of the gait cycle) The moment the foot strikes the ground, and weight acceptance begins. In normal gait, the heel contacts the ground first. The hip is flexed, the knee is nearly fully extended, and ankle is at neutral. This phase is sometimes referred to as “heel strike.” In this phase, the hip extensors, knee flexors, and ankle dorsiflexors contract to position the foot and begin deceleration.

Loading response (2% to 12%) Body weight is transferred onto the limb (further weight acceptance). The foot plantarflexes to foot flat (referred to as the “first rocker” or “heel rocker”).³ The knee flexes to about 15° to absorb force and the knee extensors contract to stabilize the knee. The hip abductors contract to stabilize the pelvis.

Midstance (12% to 31%) Begins with lifting of the opposite foot. The body advances from behind the foot to slightly in front of the ankle, at about 5 degrees of dorsiflexion. The progression from foot flat to heel lift is referred to as the “second rocker,” or “ankle rocker.” The ankle plantar flexors contract to preserve momentum.

Terminal stance (31% to 50%) Begins when the supporting heel rises from the ground and continues until the heel of the opposite foot contacts the ground. The body advances forward beyond the supporting foot. As the body advances over the forefoot, the toes extend at the metatarsophalangeal joints (“toe break”). “Third rocker” or “forefoot rocker” refers to the ankle and foot positioning change from heel lift to toe break. The ankle plantar flexors contract to create acceleration.

Pre-swing (50% to 62%) Begins with initial contact of the opposite limb and ends with toe-off of the supporting limb (now the “trailing limb”). Body weight is transferred to the opposite limb. The hip flexors begin to contract in preparation for swing.

The subphases of swing phase are:

Initial swing (62% to 75%) Begins when the foot is lifted from the floor and ends when the swinging foot is opposite the stance foot. This subphase marks the beginning of single-limb support for the opposite limb. The hip flexors and ankle dorsiflexors contract to move the limb forward and help clear the foot, respectively.

Midswing (75% to 87%) Begins when the swinging foot is opposite the stance foot and continues until the swinging limb is in front of the body and the tibia is vertical. The ankle dorsiflexors remain contracted to help clear the foot.

Terminal swing (87% to 100%) Begins when the tibia is vertical and ends when the foot contacts the floor. The hip extensors, knee flexors and extensors, and ankle dorsiflexors contract to decelerate the limb and position the foot in preparation for initial contact.

Single limb support refers to periods in which only one limb is in contact with the ground (Midstance and Terminal stance). Double limb stance, or double limb support, refers to periods in which both limbs are in contact with the ground, which occurs during initial contact and loading response (“initial double stance”) and then again during preswing (“terminal double stance”). During ambulation at normal speeds, approximately 60% of duration of the gait cycle is spent in stance phase (about 40% in single limb support and 20% in double limb stance), and 40% in swing phase.²

Key Concepts for Understanding Gait^1,2,4

Walking gait is achieved by a complex, coordinated, and rhythmic motion of limbs to provide antigravity support of body weight, maintain balance, and progress the center of mass (COM) forward.

Stride length is the distance covered from the initial contact of one foot to the subsequent contact of the same foot. It reflects the distance traveled during one complete gait cycle. Step length is the distance between the initial contact of one foot and the initial contact of the opposite foot. It indicates the distance covered with each step.

Cadence is the number of steps taken per unit of time, typically measured in steps per minute. It reflects the rhythm or pace of walking.

Base of support (BOS) is the distance between the two feet in double limb stance. This is measured by choosing two fixed points, typically at the midpoint of the posterior heel or the center of the ankle joint.

Symmetry In normal gait, there tends to be symmetry in temporal and spatial gait characteristics.

Center of mass (COM) refers to the point within the body around which mass is evenly distributed in all directions. In standing, it is located around the pelvis, 5 cm (about 1.97 in) anterior from S2 vertebra. During gait, the COM deviates from the straight line in smooth vertical and lateral sinusoidal displacements.

The ground reaction force (GRF) is the force exerted by the ground on a body and is equal and opposite to the force exerted by that body on the ground (Newton’s Third Law).^5,6 When a person is standing still, the GRF is the equal and opposite force to their body weight. When a person is moving, the forces exerted on the ground, and thus the GRF, are more complex. The center of pressure (CoP) is the origination of the GRF, or where the GRF acts on the foot.⁷

A force applied to a body away from that body’s center of rotation (CoR; or pivoting point) creates a rotational force (a moment, also called torque).⁸ The moment created by a given force is the magnitude of that force times the distance of the force vector from the body’s center of rotation. If a given force is applied further from the CoR, the moment created by that force increases.

Normal and abnormal gait are often discussed in terms of joint moments, or rotational tendencies about joints.⁶ For example, a knee flexion moment creates a tendency for the knee to bend into flexion, which will result in knee flexion if unopposed (available range of motion permitting). A knee flexion moment could be normal in some situations, and abnormal in others – and the amount of knee flexion moment might be the difference between normal and abnormal.

Internal moments acting upon joints are created by forces generated by the body, for example by muscle contraction.⁸ External moments about joints result from external forces, such as the GRF. Often, when physiatrists refer to joint moments, they are referring to the sum of all internal and external moments, which add together to create the tendency for a joint to rotate.⁹

Six Determinants of Gait

In 1953, Saunders, Inman, and Eberhart described six determinants of gait, which were kinematic features posited to reduce energy expenditure during ambulation by minimizing displacement of the center of motion.¹⁰ With the increasing technological ability to monitor and measure gait kinematics, elements of the theory have been shown to be questionable.¹¹ However, the six determinants of gait theory remains a model used within some physiatry curricula, and therefore we will provide an outline:¹⁰

1. Horizontal pelvic rotation, with the swing limb’s hip moving forward faster
2. Tilting down of the swing limb’s hip
3. Knee flexion in early stance phase
4. Transfer of weight from the heel to the flat foot in stance phase
5. Knee flexion in late stance phase
6. Lateral movement of the pelvis towards the stance limb

Figure 1. Gait cycle, starting with left initial contact.

Relevance to Clinical Practice

Gait Analysis

Gait analysis is the systematic study of human locomotion, particularly walking and running, to assess biomechanical parameters and movement patterns. It aims to understand how the body move during the gait cycle and can be used for various purposes including diagnosis gait abnormalities, evaluating rehabilitation processes, optimizing athletic performance, and designing orthotic or prosthetic interventions.

Observational gait analysis (also referred to as informal visual gait analysis) is the assessment of gait without using equipment for measurement and interpretation.^4,12 The clinician observes characteristics of an individual’s gait, such as symmetry, smoothness of movements, or joint movements (e.g., amount of knee flexion in early stance). Some experts recommend a systematic segmental approach, starting with observation of the foot and ankle and moving upwards.¹² It is recommended to observe gait from front, back, and side, as gait abnormalities can be more apparent in certain planes. Video recording of gait is also a useful tool to supplement clinical observation.¹³

Quantitative gait analysis is the use of objective measurement techniques to assess kinematics (patterns of motion and related parameters), kinetics (forces produced during walking), dynamic muscle activation), and other gait characteristics.⁴ While quantitative gait analysis provides precise numerical data to characterize and understand gait accurately, it typically requires specialized equipment (e.g., motion capture systems, force plates) and expertise in data collection that may not be always readily available outside of research or clinical gait labs.

Functional measures of gait assess practical aspects of ambulation that can provide insights into an individual’s ability to perform activities of daily living (ADLs), navigate their environment, and maintain independence. Some functional measures of gait include:¹⁴

Table 1. Overview of selected functional measures of gait

Additionally, there are many patient-reported outcome measures that relate to gait parameters, including a variety of validated patient questionnaires, which are beginning to come into greater clinical use and grow in their utility to researchers and clinicians. This list is non-exhaustive as many such questionnaires exist for specific patient populations, some of which are highlighted here.

Table 2. Overview of selected patient-reported gait measures

Cutting Edge/Unique Concepts/Emerging Issues

• Wearable sensors utilize insertional measurement units or pressure sensors, or less commonly electromyography sensors, goniometers, inclinometers, or other sensors. This type of device can allow a longer period of observation, observation in varied settings, or real-time gait analysis. A wide variety of analytical techniques are used to process and interpret data from wearable sensors, such as rule-based (or threshold-based) algorithms or machine learning methods (e.g., hidden Markov models, random forests, support vector machines). Recent studies provide insight into the optimal type of sensor and processing strategy could depend on the intended use; for example, sensors with IMUs processed with rule-based algorithms provide a straightforward approach that could increase usability.
• Integration of multiple wearable devices or a wearable sensor with non-wearable methods has the potential to improve accuracy. For example, a technique integrating markerless optoelectronic motion capture and a wearable foot inertial measurement unit demonstrated improved accuracy in measurement of peak ankle joint angles compared to a markerless motion capture system alone.

Gaps in Knowledge/Evidence Base

• As a relatively “young” field, understandings of gait parameters and the ways in which modifications in various aspects of gait may lead to changes in the kinetic chain continue to evolve with the expansion of gait research and literature.
• The accuracy of gait analysis techniques can depend on the clinical population as well as the environment of use, and there is often limited research into the validity of devices in the real-world setting. For example, models and algorithms developed in a traditional gait laboratory may not translate well to analysis of data from wearable devices being worn during “free-living gait.” Validation studies of devices and analytical techniques is ideally done for both specific clinical populations and setting of use.  

Conclusion

Understanding the complexities of human gait involves delving into key concepts of biomechanical parameters, types of gait analysis, and the phases of the gait cycle. Embracing these concepts fosters a comprehensive approach to gait analysis, leading to improved outcomes and enhanced patient care.

References

1. Whittle M, Levine D, Richards J. Normal Gait. In: Richards J, Levine D, Whittle MW, eds. Whittle’s Gait Analysis. 6th ed. Elsevier; 2023:15-47.
2. Perry J, Burnfield JM. Gait Analysis:  Normal and Pathological Function. 2nd ed. SLACK; 2010.
3. Richards J, Thewlis D, Needham R, Chockalingam N. Motion and Joint Motion. In: Richards J, ed. The Comprehensive Textbook of Clinical Biomechanics. 2nd ed. Elsevier; 2018:79-103.
4. Esquenazi A, Talaty M. Gait Analysis:  Technology and Clinical Applications. In: Cifu DX, ed. Braddom’s Physical Medicine and Rehabilitation. 5th ed. Elsevier; 2016.
5. Boccardi S, Pedotti A, Rodano R, Santambrogio GC. Evaluation of muscular moments at the lower limb joints by an on-line processing of kinematic data and ground reaction. J Biomech. 1981;14(1). doi:10.1016/0021-9290(81)90078-6
6. Cerny K. Pathomechanics of stance: Clinical concepts for analysis. Phys Ther. 1984;64(12). doi:10.1093/ptj/64.12.1851
7. Richards J, Healy A, Chockalingam N. Ground Reaction Forces and Plantar Pressure. In: Richards J, ed. The Comprehensive Textbook of Clinical Biomechanics. 2nd ed. Elsevier; 2018:45-78.
8. Richards J. Forces, Moments, and Muscles. In: Richards J, ed. The Comprehensive Textbook of Clinical Biomechanics. 2nd ed. Elsevier; 2018:24-44.
9. Soutas-Little RW. Motion Analysis and Biomechanics. Gait Analysis in the Science of Rehabilitation. Published online 1998.
10. Saunders JB, Inman VT, Eberhart HD. The major determinants in normal and pathological gait. J Bone Joint Surg Am. 1953;35 A(3). doi:10.2106/00004623-195335030-00003
11. Kuo AD. The six determinants of gait and the inverted pendulum analogy: A dynamic walking perspective. Hum Mov Sci. 2007;26(4). doi:10.1016/j.humov.2007.04.003
12. Rancho Los Amigos National Rehabilitation Center. Observational Gait Analysis Handbook. Los Amigos Research and Education Institute, Inc.; 2001.
13. Whittle M, Jordon M, Levine D, Richards J. Methods of Gait Analysis. In: Richards J, Levine D, Whittle MW, eds. Whittle’s Gait Analysis. 6th ed. Elsevier; 2023:65-87.
14. Norasteh AA, Balayi E, Zarei H. Functional Gait Assessment Tests in Elderly: A Systematic Review. Casp J Neurol Sci. 2023;9(2). doi:10.32598/CJNS.9.33.295.3
15. Rose J, Gamble JG, eds. Human Walking. Williams & Wilkins; 1994.

Original Version of the Topic

Heakyung Kim, MD, Hannah Aura Shoval, MD, Teerada Ploypetch, MD. Biomechanic of gait and treatment of abnormal gait patterns. 9/20/2014

Previous Revision(s) of the Topic

Julio Vazquez-Galliano, MD, Ibtehal Kimawi, MD, Lawrence Chang, DO, MPH. Biomechanic of Gait and Treatment of Abnormal Gait Patterns. 8/3/2020

Author Disclosure

Ian J. Kim, MD
Nothing to Disclose

Michael J. Gallagher, MD
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Rebecca Ann Speckman, MD, PhD
Nothing to Disclose