Review paperThe biomechanics of running
Section snippets
Introduction/history
To avoid the misconception that the analysis of running is a new area of interest, one need only examine the art of Grecian vases and consider the writings of Aristotle, `Further, the forces of that which causes movement and of that which remains still must be made equal... For just as the pusher pushes, so the pusher is pushed—i.e. with similar force' [1]. Leonardo da Vinci's interest in accuracy in painting in the 15th and 16th centuries increased focus on human movement and was followed by
Gait cycle
How does one go from a standstill to maximum forward velocity during sprinting? How does the movement strategy change between walking and running locomotion? The demarcation between walking and running (Fig. 1, point A) occurs when periods of double support during the stance phase of the gait cycle (both feet are simultaneously in contact with the ground) give way to two periods of double float at the beginning and the end of the swing phase of gait (neither foot is touching the ground).
EMG
Muscle activity during normal walking [33]and running 30, 34, 35has been well documented. Typical electromyographic (EMG) activity for running is depicted in Fig. 4.
In general, muscles are most active in anticipation of and just after initial contact. Muscle contraction is apparently more important at that time than it is for the preparation for and the act of leaving the ground. This certainly is consistent with DeVita's contention that the events surrounding IC are more important than those
Kinematics
Kinematics are a description of movement and do not consider the forces that cause that movement. We can graph kinematic variables as a function of the percentage of the total gait cycle or time. For all of the kinematic graphic data presented in the next section, the patterns of movement are important (when in the gait cycle the joint in question is flexing or extending). The peak values in degrees of movement are not important as they depend on the athlete's level of training and speed. The
Kinetics
Winter and Bishop outlined the major goals associated with athletic events [26]providing an overall outline in which to organize one's thinking about the tasks that muscles must perform. They are
- 1.
shock absorption and control of vertical collapse during any weight acceptance phase;
- 2.
balance and posture control of the upper part of the body;
- 3.
energy generation associated with forward and upward propulsion;
- 4.
control of direction changes of the center of mass of the body.
The study of kinetics begins to
Potential and kinetic energy
The relationship between potential and kinetic energy is critically different between walking and running activities (Fig. 11). In walking, the two are out of phase. When potential energy is high, kinetic energy is low, and vice versa. Walking has been referred to as controlled falling (from the zenith of the center of mass in midstance to its nadir during double support) and is similar to a swinging pendulum. In running on the other hand, the two are in phase. Running has been likened to an
Tendons as springs
As mentioned above, each of these musculotendinous units 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 [46]. 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
Biarticular muscles
The second mechanism, transfer of energy between body segments by two-joint muscles, also contributes to energy efficiency. Elftman is the first to be recognized for proposing this principle. Consider the hamstrings in the second half of swing phase. The hip and knee are both extending (Fig. 5) while the hamstrings are contracting (Fig. 4). An extensor moment is produced by the hamstrings at the hip while they generate a flexor moment at the knee (Fig. 9, row 2). The moment produced at the knee
Economy of motion
It is generally accepted that one of the most important determining factors of the manner in which the individual moves is to maximize energy efficiency. In general it is held that for aerobic, steady state conditions, one chooses the movement strategies which are most economical in regard to energy usage. Economy of movement has also been felt to be a driving force for the evolution of limb structure in terrestrial animals. Despite these beliefs, interindividual variability in walking and
Foot biomechanics
Lay and sports medicine literature has blamed excessive pronation for nearly all maladies of the lower extremities (and the spine, for that matter). It is felt that abnormal movement of this joint occurring over the course of thousands of repetitious cycles leads to overuse syndromes due to increased internal rotation of the tibia via the mitered hinge effect [58]. There is a large amount of empiric clinical support for this notion in that shoes or orthotics designed to diminish hyperpronation
Shoes
Numerous publications have been written on the topic of running shoe analysis 69, 70, 71, 72, 73, 74, 75. Pink and Jobe [76]recently summarized the status of current thought about the interface between the foot and the shoe. It is essential that shoes not only be tested in the laboratories of shoe companies but also in vivo because individuals modify their movement pattern in complex ways in response to changes in their dynamic balance. This is undoubtedly under neurologic control. It certainly
Injuries
As has been shown, forces are not only higher but they must be attenuated in roughly one-third the time (as compared to walking). Even a slight biomechanical abnormality can induce injury [77]. It should be apparent that injured runners can not be tested to provide insight into the mechanisms by which they became injured. Dynamic analysis in that case would document the compensatory gait mechanisms employed by the runner to avoid pain rather than the gait pattern that lead to injury. Instead,
Future directions
Not to be a pessimist, but if one looks at concluding remarks by authors over the years, promises of future knowledge are routinely made. Authors commonly state that greater knowledge will lead to a decreased frequency of injury. These promises are oftentimes overstated and incompletely filled. As Nigg [83]has pointed out, there is, as yet, no evidence that biomechanical research in load analysis has contributed to a decreased frequency of running injuries. This author is hopeful for greater
Acknowledgements
The author withes to acknowledge Joyce Phelps Trost, RPT for her help in collecting, analyzing, and formatting this data (as well as her assistance in the development of this article), Mary Trost for her assistance in the preparation of this manuscript, the staff of the Motion Analysis Laboratory at Gillette Children's Specialty Healthcare (200 East University Ave., St. Paul, MN 55101) for gathering the data on which this article is based, and Anna Bittner for photographic and computer graphics
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