on MSD Risk. Fatigue failure also offers the potential to incorporate certain personal characteristics into risk assessment. As an example, fatigue failure theory stipulates that the ultimate strength of a material determines the number of cycles to failure at different percentages of that strength. If an individual performs a lifting task resulting in a 2,500 N compressive load on the spine, they will incur damage more quickly if they have a spine ultimate strength of 6,000 N (say at age 60) as opposed to 8,000 N (at age 30). Factors such as age, anthropometry, sex, bone mineral density, and others could be considered to develop “personalized” risk assessments that may be more protective for workers based on their individual characteristics. Risks associated with personal characteristics are discussed in Chapter 12.
The preceding examples provide a sampling of the opportunities that may be realized with the use of the fatigue failure approach to MSD risk, many of which would be difficult to realize with previous approaches. There are numerous other useful applications of this model as will be described in detail later in the book.
In summary, fatigue failure is a universally accepted causal mechanism of damage nucleation and propagation for nonbiological materials, and there is ample evidence to suggest that the same process occurs in musculoskeletal tissues. Much of what has been learned regarding the process of material damage resulting from repeated stress appears applicable to the assessment of musculoskeletal risk, and many techniques developed in this theory appear to provide ready solutions to challenging problems faced by musculoskeletal researchers. These include simple methods of estimating the cumulative impact of multiple tasks having highly variable loading conditions. Techniques are also available for assessing cumulative damage associated with complex loading curves that will be useful soon as real‐time exposure assessment methods for MSDs become available. Furthermore, models incorporating the effects of healing and other biological processes critical to musculoskeletal health have been put forth, thus allowing the complexity of the fatigue failure process in the biological environment to be more fully understood.
As indicated by the earlier discussion, there are many topics to be discussed and implications to be addressed when evaluating the effects of a fatigue failure process in a biological environment and the roles of damage and healing in overall musculoskeletal health. We have structured the 16 chapters in a logical order, and the chapters are grouped into four general themes. Chapters 2–5 provide detailed information regarding common MSDs and the components of the musculoskeletal system, including the structure and function of musculoskeletal structures, the material properties of these tissues, and the important role of nerves and the nervous system in the musculoskeletal system. Chapters 6–9 cover fundamental concepts of biomechanics, evidence of fatigue failure processes in musculoskeletal tissues, and fundamental concepts in fatigue failure analytical methods relevant to the assessment of MSD risk. Chapters 10–12 discuss concepts related to the unique aspects of fatigue failure in a biological environment, addressing the body’s healing capacity and the influence of personal characteristics and psychosocial stress on MSD risk. The final four chapters (Chapters 13–16) provide methods for assessing risk using fatigue failure methods, implications for MSD prevention, suggestions for optimizing musculoskeletal health, and assessment of the status of knowledge and the need for future research in this area. We would note that the book need not be necessarily consumed in the order in which it was written, as many chapters can be read on their own without loss of meaning.
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