Elsevier

Gait & Posture

Volume 21, Issue 4, June 2005, Pages 447-461
Gait & Posture

The evolution of clinical gait analysis part III – kinetics and energy assessment

https://doi.org/10.1016/j.gaitpost.2004.07.008Get rights and content

Abstract

Historically, clinical applications of measurements of force and energy followed electromyography and kinematics in temporal sequence. This sequence is mirrored by the order of topics included in this trilogy on the Evolution of Clinical Gait Analysis, with part I [Sutherland DH. The evolution of clinical gait analysis part I: kinesiological EMG. Gait Posture 2001;14:61–70.] devoted to Kinesiological EMG and part II [Sutherland DH. The evolution of clinical gait analysis part II – kinematics. Gait Posture 2002;16(2):159–179.] to Kinematics. This final review in the series will focus on kinetics as it relates to gait applications. Kinematic measurements give the movements of the body segments, which can be compared with normal controls to identify pathological gait patterns, but they do not deal with the forces controlling the movements. As a major goal of scientifically minded clinicians is to understand the biomechanical forces producing movements, the objective measurement of ground reaction forces is essential. The force plate (platform) is now an indispensable tool in a state-of-the-art motion analysis laboratory. Nonetheless, it is not a stand-alone instrument as both kinematic and EMG measurements are needed for maximum clinical implementation and interpretation of force plate measurements. The subject of energy assessment is also given mention, as there is a compelling interest in whether walking has been made easier with intervention. The goals of this manuscript are to provide a historical background, recognize some of the important contributors, and describe the current multiple uses of the force plate in gait analysis. The widespread use of force plates for postural analyses is an important and more recent application of this technology, but this review will be restricted to measurements of gait rather than balance activities.

Finally, this manuscript presents my personal perspective and discusses the developments and contributors that have shaped my thoughts and actions, and which I have found to be particularly noteworthy or intriguing. Just as in parts I and II, emphasis has been placed on the early development. All subtopics and important contributors, in this third and certainly most challenging of the review papers, have not been included. Some may find that my perceptions are incomplete. I accept responsibility for all deficiencies, as none were intended. Letters to selected contributors and their responses reveal how each contributor built on the work of others. The level of cooperation and sharing by these early investigators is extraordinary. Had they wished to withhold information about their own work, clinical gait analysis would have been severely delayed.

Introduction

The force that the human subject applies to the ground or floor is equally matched by the reaction of the floor or ground. Even primitive man made deductions about the activities of animals or humans from their paw or foot prints. Without any knowledge of Newton's formulae for the effects of gravity and the third law of motion that states, “for every force applied there is an equal and opposite reaction” [3], they understood that bodies have mass (weight), and could deduce much about the identity of animals or humans from the shape, depth, alignment and spacing of the prints they produced.

The search for scientific methods of recording the magnitude of foot/heel contact began in the 19th century. Carlet, of France [4], [5], and Ampar, his student, developed and utilized air reservoirs to measure the force applied to the heel and forefoot. Carlet started this work as a student of Marey, at his laboratory in Paris. A significant limitation of this method was that it gave only one-dimensional information. Surprisingly, a subject with normal heel/toe contact produced a cursive “m” shaped curve with fair resemblance to the vertical force curve produced by a modern force plate (see Fig. 1). The pressures applied by the body through the foot to the ground are vector forces. The earliest investigators understood this, but they lacked the technology to separate the ground reaction into three dimensions. Fischer [6], [7] of Germany deduced three-dimensional ground reaction forces from kinematic studies but did not measure them directly.

With another student, Georges Demeny, Marey went on to develop what would be considered as the first true force plate, which measured the vertical component of the ground reaction using a pneumatic mechanism similar to the one that Carlet had built into the shoe [8]. Jules Amar was a rehabilitation doctor working with amputees during and after the First World War in France. He developed the single component pneumatic force plate of Marey and Demeny to produce the world's first three-component (pneumatic) force plate, which is called the “Trottoire Dynamique” [9]. Wallace Fenn, working in Rochester, was the first to develop a mechanical force plate. This was a one-component device measuring only the fore-aft forces. In an article in which he describes his device, he makes clear the debt he owed to Amar's work [10]. Fenn was fundamentally interested in the consideration of the interchanges of kinetic and potential energy of the segments [11].

As a further development of Carlet's work, Plato Schwartz contributed significantly with his work with a pressure sole, and a device to measure movements of the pelvis. He called the instrument a basograph and used it to demonstrate abnormal pelvic movements associated with specific limps [12]. In 1932, the same authors wrote about “The Pneumographic Method of Recording Gait” refining the original concepts of Marey [13], Carlet [4], [5], and Ampar. A quotation from this article by Schwartz deserves mention, “Measurement is essential for the interpretation of normal and abnormal phenomena of the human body. Empiricism, fostered by trial and error, must continue to govern the therapy of abnormal function until measurement in some form improves the treatment of disabilities affecting the back and lower extremities” [14]. Fortunately, we now live in the era he envisioned. Many of his articles followed on foot function, both normal and abnormal using electrobasographic records of gait [15], [16], [17], [18], [19], [20]. Dr. Schwartz, an astute clinician–scientist, represents the type of individual so essential as a team member in a clinical gait laboratory.

Elftman was an early pioneer in measuring the forces in more than one plane. With a device he described in a 1934 publication [21], vertical force and the dynamic pressure distribution during a step could be shown, but by Dr. Elftman's own admission, quantification was lacking. In a 1938 publication in Science, a device capable of measuring the ground reaction in three planes was illustrated. An upper and a lower platform were suspended with calibrated springs that measured the ground reaction forces and separated them into components [22] (see Fig. 2). In a subsequent article, vertical force and shear forces in the sagittal plane are shown [23] (see Fig. 3). In this article Dr. Elftman discusses potential and kinetic energy, angular moments, and the influence of two-joint muscle action. His work, though hampered by a lack of technical sophistication, was highly creative and scientifically splendid.

It was not until the work of Cunningham and Brown that force plate development took on the features that lend themselves to clinical use [24]. Their plate or platform divided the ground reaction forces into four components. This was achieved with strain gage technology, but the strain gages at that time were quite sensitive to temperature changes. The construction of the platform was complex and constant calibration was necessary. Computer processing of the raw data was not yet available. More technical development would be required before a commercially available plate, suitable for clinical use, would appear. Reduction in the complexity of the platforms, and improvements in the accuracy and reliability of the sensing instruments, came through the efforts of scientists in several locations: San Francisco, California; Boston, Massachusetts; Philadelphia, Pennsylvania; Glasgow, Scotland; Winterthur, Switzerland.

In the mid-1960's, I requested development of a clinically useful, accurate and reliable force plate for the Shriners Hospital San Francisco Gait Laboratory. The challenge was given to John Hagy, an employee at Lockheed, Santa Cruz, California, who joined our research effort as a volunteer in 1965. His initial accomplishment was to design and implement a system to measure kinematics, using cinefilm and the Vanguard Motion Analyzer. A full description of this work is contained in part II [2]. With this success we turned our attention to the need for measuring the floor reaction forces. There were no commercially available force plates at that time. John Hagy used his considerable talent at eliciting help from within the Lockheed Missiles and Space Corporation. John Hawthorn, Supervisor of the Instrument Test Division, Santa Cruz, became an enthusiastic volunteer participant. I gave him a copy of the Cunningham and Brown article [24], and he remarked about the complexity and bulk of their instrument. John Hawthorn took a 2-week vacation from his employer and, during that time, experimented with the use of piezo-electric force transducers. At the end of his vacation, he showed up at our Shriners Gait Laboratory with a force plate under his arm. The force plate performed beautifully, but required the addition of charge amplifiers to maintain the signals. John Hawthorne, John Hagy, Cecil Keller, and Len Musil were the chief architects of the plate, which was completed and installed in April 1971, and issued a U.S. Patent on July 15, 1975 (see Fig. 4). The first plate was installed, tested, and put into clinical use in the Shriners San Francisco Gait Laboratory. The second force plate was provided to my new gait laboratory at San Diego Children's Hospital, the third was constructed for Dr. Edmund Chao at the Mayo Clinic, Rochester, Minnesota, and a fourth plate was constructed for Dr. Sheldon Simon at Boston Children's Hospital. These plates performed well, but commercial production of piezo-electric plates by The Kistler Corporation, Winterthur, Switzerland, put an end to further construction of the Shriners model. The first Kistler piezo-electric plate, which of course later became standard gait lab equipment, was installed for Dr. S.M. Perren at the Laboratorium fur Experiementelle Chirurgie in Davos, Switzerland, in 1969.

Prof. J.P. Paul, of the Bioengineering Unit Wolfons Centre, University Strathclyde, Glasgow, Scotland based his Ph.D., which was granted in 1967, on the measurements obtained with the force plate he built, and his key publication at that time, “Forces transmitted by joints in the human body” [25]. I have heard, but have been unsuccessful in documenting details of, his strain gauge force plate, patterned somewhat after that of Cunningham and Brown, which apparently was reliable and used for many years in clinical research. Two duplicate force plates were constructed and installed at the Limb Fitting Centre in Dundee in 1968 under the supervision of David Condie. Paul's use of strain gauges in the construction of pylon transducers, to measure forces within artificial limb prostheses, was based on earlier work by Bressler and Frankel at Berkeley. He contributed a number of articles regarding the use of motion analysis to study the gait of lower limb amputees [26]. His pioneer efforts in kinematics have already been discussed in part II.

The efforts in Boston began under the direction of Dr. Sheldon Simon. In part I, I mentioned Dr. Simon's Cave Traveling Fellowship that included a stay in San Francisco, and for a time at the San Francisco Shriners Gait Lab, then under the medical directorship of Roger Mann [1]. Upon his return to Boston, Dr. Simon established a gait laboratory on the sixth floor of Boston Children's Hospital in the Physical Therapy Department. John Hagy and his colleagues constructed a second piezo-electric force plate for Dr. Simon, but conditions on the PT floor were such that vibration (not handled well by the piezo-electric plate) was a tremendous problem. The space under the floor was not large enough to place the cameras in a position to illuminate the footprints through the transparent plate, necessitating the use of raised computer flooring. In addition to these problems, Dr. Simon wanted two plates and his budget restricted him to the price of a single plate from Hagy and colleagues. Dr. Simon was acquainted with Walt Synutis, Associate Professor of Electrical Engineering at M.I.T. and inventor of a new improved strain gage. Dr. Simon persuaded Mr. Synutis to design a new force plate utilizing strain gauges, and two of these plates were installed when the laboratory opened in September 1974. Using simultaneously recorded force plate readings, they were able to output a “butterfly pattern of normal walking, before Cappozzo did it.” (Personal communication from Dr. Simon) part II contains information about Dr. Simon and his contributions following his move to Ohio State University in 1986 [2], and further mention will come in this manuscript under the heading of gait data interpretation.

Roy Wirta, M.Sc., is another pioneer in force plate construction and analysis. Prior to the introduction of commercially available force plates, Mr. Wirta designed and constructed two plates for use in Moss Rehabilitation Center, Philadelphia, Pennsylvania. He also helped with the first calculations of mechanical work in an amputee study in the San Diego lab. We were using a single force plate at that time, so he added a right foot strike and a left foot strike from separate gait cycles together, and commented that ideally two or three force plates were needed to compute forces within a single trial [27], [28], [29], [30].

In a personal communication he states:

“As to details of the force plates, there were two side by side. Each was 60 inches long by 12 inches wide. Three forces were sensed: vertical, longitudinal shear and lateral shear, each with strain gauges mounted on thin aluminum strips. The long plates allowed us to record several gait cycles with one pass from test subjects who were mostly stroke patients. We could isolate the needed weight bearing events, and not require them to do many repetitions, to get enough information to evaluate the various ankle-foot braces in the studies. We worked closely with Case Western Reserve in Cleveland, specifically with Vic Frankel, MD to hone in on the design details of the plates. The major impact of the studies was identification of the merits of the molded ankle foot orthosis. Accordingly, orthotists began making these at that time, and they have become the most popular orthoses for stroke patients” (Personal communication from Roy Wirta.)

Though he has retired, Roy Wirta remains active professionally. He is a highly valued volunteer consultant at Children's Hospital, San Diego, for the Motion Analysis Laboratory and the Orthopedic Biomechanics Research Laboratory [31], [32].

Another outcome of the work at Moss Rehabilitation center was the development of a system to superimpose the vertical ground reaction force vector and the sagittal film image of the subject throughout the stance phase of a gait cycle [33]. A summary of the technical process is as follows: the center of pressure is determined, and the voltages representing the vertical force and sheer forces provide the necessary information to the force vector display circuitry. The force vector display is generated by application of sine waves having amplitudes proportional to the vertical and horizontal force components. The outputs of this circuitry are channeled to the vertical and horizontal inputs of an oscilloscope. An optical scanner is used to deflect the beam from a low power laser source onto a projection screen. The sagittal image of the subject on the screen, with the force vector superimposed, is recorded on cinefilm or videotape, so that it can be viewed dynamically. The authors, Cook et al., acknowledge that this technique has been used and published earlier in conjunction with the persistent image display by Cappozzo et al. [34], by Boccardi et al. [35], and Pedotti [36]. This visual tool has served very well in teaching the biomechanics of gait.

Concurrently, Tait and Rose, in their work at Oswestry, UK, in displaying the force vector, had developed a technique to superimpose the ground reaction vector on a standard video recording. They used this technique very effectively, particularly in examining the effect of orthoses on walking over a considerable period of time [37].

Section snippets

Commercial companies to the rescue

Although a number of the custom force plates mentioned did yeoman service and were valuable in clinical and research studies there were obstacles in the path of all new laboratories seeking to include force analysis. On-site engineering talent was optimal for construction, operation, and service of the custom plate or plates. Inordinate amounts of time could be consumed in this process, interfering with quality time for the preparation of research proposals, training of technical assistants and

Applications of force measurement technology

Now, you say, we have these reliable and readily available plates, with excellent support, but how have patients benefited from use of these plates in clinical studies? We will work our way into that later in this manuscript, but first, there are important scientific contributions to describe. A steady evolution of applications followed force plate introduction. Early on, force platforms were used primarily to measure 3D ground reaction forces. This was very important, for without this

Mechanical work

Can the global output of successive foot floor contact force measurements be used to determine mechanical work? Cavagna and Margaria thought so, and used two custom force plates to measure vertical and forward velocity of the center of mass of the human body in walking and running. Two platforms were inserted on a wooden track. One platform was sensitive to the vertical and the other to the forward component of the force impressed by the foot on the ground [58]. In a personal communication I

More about external work

Three models of calculating external work were compared with oxygen cost measurements in 26 subjects with myelomeningocele [61]. The models employed were (1) vertical excursion of the center of mass, (2) external work done by the center of mass, and (3) a full body model allowing energy transfers between segments within limbs. Although all three models showed significant difference between S1 and L4/L5 level involvement, there was not a significant correlation with oxygen cost in models 2 and

Oxygen consumption and oxygen cost

Sustained interest has been shown in the metabolic energy costs of human walking and other activities. To this day, oxygen consumption and oxygen cost measurements remain as the gold standard against which other methods of energy measurements are compared. Early references are found in German and English literature, but in keeping with the general format of this manuscript, which begins with the work of Inman et al., Henry J. Ralston, Ph.D., 1906–1993, and his contributions, will begin the

Acknowledgements

My gratitude goes to all of the individuals who responded to my letters and phone calls, supplying details and memories that gave life to this account. To Arnel Aguinaldo, for his professional and personal assistance with bioengineering details and accuracy. To John Hagy, whose foresight in cataloging historical papers has provided much documentation from the early days at the Gait Laboratory in San Francisco. I extend a special thanks to my administrative associate, Kit Holm, for her editing

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