Biomechanics of Sport

Christopher L. Vaughan

• Publisher: CRC Press
• Year: 2020
• eBook ISBN: 9781000141931
• Topic: Medicine
• Subtopic: Medical Theory, Practice & Reference

This informative text features current and thorough reviews of the biomechanics of sport for improved performance, etiology, and pre-vention of injuries. Winter sports and aquatics are covered, with an emphasis on developing training programs for ski-jumping, alpine, and cross country skiing. Other sports featured include modeling perspectives in speed skating, swimming, and the mechanics of rowing and sculling. Track-and-field athletics, ball games, weight lifting, and training are examined in terms of per-formance, safety, and re-search methodology. Sports scientists and sports medicine specialists will find this book invaluable.

Chapter 1

SUBSTANTIVE ISSUES IN RUNNING

Carol A. Putnam and John W. Kozey

TABLE OF CONTENTS

I.	Introduction
II.	Running Efficiency A. Measuring Mechanical Work Done 1. Work Done by Internal Forces 2. Work Done by External Forces B. Interpreting Mechanical Efficiency 1. Work Done by RJMs vs. Individual Muscles 2. Type of Muscle Contraction 3. Storage and Reutilization of Elastic Energy 4. Nonmuscular Force Contribution to RJMs C. Muscular Effort D. Apparent Efficiency E. Summary
III.	Running Economy
IV.	External Forces A. Air Resistance B. Ground-Reaction Force
V.	Muscle Function in Running A. Resultant Joint Moment Patterns 1. Hip Moment 2. Knee Moment 3. Ankle Moment 4. Summary B. Functional Significance of RJMs and Segment Interaction C. Simulation of Running Gait D. Electromyography 1. Hip Musculature 2. Knee Musculature 3. Ankle Musculature 4. Co-contraction E. Muscle Length Changes
VI.	Performance Improvement
VII.	Running Injuries A. Sports Medicine 1. Patello-Femoral Syndrome 2. Achilles Tendinitis 3. Hamstring Strains B. Biomechanical Measurement and Injuries 1. Force Platform Data 2. Pressure Transducer Data 3. Electrogoniometer Data 4. Accelerometer Data
VIII.	Summary
References

I. INTRODUCTION

Running has received considerable attention from researchers in biomechanics, particularly over the last several decades. The number of publications or presentations at scientific meetings escalates yearly, adding to the more than 600 reported studies dealing with mechanical aspects of running. In addition, biomechanical considerations of running are being featured in popular journals with increased frequency, attempting to satisfy the curiosities of thousands of recreational and competitive runners about the mechanical implications and effects of running.

Consistent with the proliferation of literature in this area, several extensive reviews have been published.^1,2,3,4 The present paper is written to augment and update these reviews although some overlap will necessarily exist.

Research into the biomechanics of running is suffering the growing pains of being dominated by descriptive studies. While recognizing the importance of an extensive descriptive foundation, several investigators^2,5,6,7 have emphasized the importance of addressing more mechanistic issues — What fundamentally dictates the way we run? What forces are responsible for observed running patterns? What criteria dictate optimal performance? What are the mechanisms of injury? — etc. In the present paper we will attempt to review the literature on running mechanics in light of potential answers to these questions.

In the 1920s and 1930s, several papers, considered by many to be classics, were published which dealt with some of the basic, mechanistic aspects of running.^8,9,10,11 It is encouraging that the attention of present day researchers is being directed more and more towards these issues. Through these efforts we should start to see the development of a theoretical framework out of which should emerge general biomechanical principles relating to the fundamental mechanisms of human motion.¹²

It is impossible to understand fully the fundamental mechanisms of running from a biomechanical perspective without crossing over into several disciplines, including cardiovascular physiology, neuromuscular physiology, anatomy, and motor control. Space constraints make it impossible to span these areas in the present review so that the discussion will be restricted to a mechanical perspective of running. The reader is directed to an excellent book recently brought out by McMahon¹³ entitled Muscles, Reflexes, and Locomotion, in which many aspects critical to the fundamental understanding of running are presented in an integrated and lucid manner.

II. RUNNING EFFICIENCY

If one questioned runners or researchers interested in the mechanics of running on what fundamentally dictates the way we run, the answer would probably be efficiency. Efficiency, defined as the ratio of mechanical work done to metabolic energy expended^13,14 is one of the most extensively researched, yet poorly understood concepts of running mechanics. The problem of measuring efficiency is one that requires close cooperation between biomechanists and exercise physiologists, and is complex from both perspectives.^2,15 For the biomechanist, the challenge lies in correctly measuring mechanical work done and interpreting this measure in light of underlying principles which are likely to govern the way we run.

A. Measuring Mechanical Work Done

There is considerable confusion as to how mechanical work done should be measured. Much of this confusion stems from the fact that work done has been quantified in terms of energy changes. As will be pointed out below, this has resulted in both ambiguous and inaccurate measures of mechanical work done in running and consequently running efficiency.

Several investigators have measured mechanical work done in running solely in terms of the work done to cause changes in the energy state of the total body mass center.^{16,17,18,19,20,21,22,23,24,25} Winter²⁶ criticized this approach in that it oversimplified the system, and he suggested that the findings of these studies should be regarded with caution. He pointed out that consideration must be given to the mechanical energy changes of individual segments which are collectively responsible for changes in the energy state of the total body mass center. He emphasized that by doing this, the mechanical energy associated with reciprocal actions of body segments, which have no net effect on the motion of the total body center of mass, are not ignored.

One of the first attempts to account for mechanical energy changes of individual segments in running was by Fenn.^10,27 He suggested that the mechanical work done on a runner was the sum of the work done to cause changes in the energy of the total body center of mass (potential energy and kinetic energy due to translation), generally referred to as external work, and the work done to cause mechanical energy changes of individual body segments (potential energy and kinetic energy due to translation and rotation), generally referred to as internal work. This technique has since been employed in several investigations of running.^{28,29,30,31,32,33} This method of analysis treats segment motions as if they were independent of each other and of the movement of the total body mass center, which is clearly inappropriate. The body must be viewed instead as a constrained, linked system. As a result, the work done on the human body cannot be measured by changes in energies of individual segments and/or the total body mass center in the general case.³⁴

Measures of mechanical work done on the human body require the identification of individual forces which actually do work on the system and a quantification of the work done by these forces. Forces doing work on the human body system in running include those which arise from both internal and external sources.

1. Work Done by Internal Forces

Internal forces applied to individual body segments include those exerted by muscles (or musculotendinous units), ligaments, joint capsules, and articulating surfaces. Since it is impossible to quantity these forces individually,³⁵ they are represented by a resultant joint force (RJF) and a resultant joint moment (RJM) associated with each joint of the system. An RJF is the vector sum of all forces applied across or through a joint (including muscle, ligament, joint capsule and bony contact forces), while an RJM is the vector sum of the moments of these forces measured relative to the joint center. Simplified in this manner, the kinetics of the linked segment system can then be solved via an inverse dynamics approach.

The only internal forces that are associated with metabolic energy consumption are those exerted by muscles. The net effect of muscle forces acting on a system of body segments are reflected primarily by the RJMs of the system. It makes sense, therefore, that work done by internal forces be calculated in terms of the work done by the RJMs only. This was done as early as 1940 by Elftman⁹ and more recently by Winter³⁶ and Lin and Dillman³⁷ to analyze various aspects of the running gait. In each case, the work done by an RJM over a given period of time was quantified by integrating the power-time function of the RJM, where power is the RJM vector multiplied as a dot (or scalar) product with the joint angular velocity vector. This is equivalent to adding the algebraically signed scaler quantities of the work done by a RJM on both segments on which the RJM acts.³⁸

Running is periodic in nature, and thus the amount of positive work done by the RJMs will be equal to the amount of negative work done by these moments within any one cycle of constant-velocity-level running in the absence of externally applied forces which do work on the body (e.g., air resistance). From a mechanical perspective, the total work done by the RJMs...

Table of contents

• Cover
• Title Page
• Copyright Page
• Preface
• The Editor
• Contributors
• Table of Contents
• Chapter 1 Substantive Issues in Running
• Chapter 2 Swimming: Forces on Aquatic Animals and Humans
• Chapter 3 Rowing and Sculling Mechanics
• Chapter 4 Biomechanics of Speed Skating
• Chapter 5 Weight lifting and Training
• Chapter 6 The Throwing Events in Track and Field
• Chapter 7 Ski-Jumping, Alpine-, Cross-Country-, and Nordic-Combination Skiing
• Chapter 8 Tennis Strokes and Equipment
• Chapter 9 Mechanics of Cycling
• Index