ABSTRACT
This chapter explores the concept of biological safety factors and trade-offs as a key component of human performance, health and disease. The initial discussion focuses on the relationship between adaptations and exaptations, along with introducing the concept of symmorphosis. A key concept in the study of human performance is the proposition that biology has limitations, which we interpret to mean that we seldom, if ever, exceed these limits, at least in health. Various engineering concepts and biological tissues as examples are used to show that safety factors are likely to be specific and developed in accordance with the expected use and loading throughout the lifespan. Notably, safety factors are altered in a range of situations and sometimes temporarily in order to maximise the potential for survival. Since the central component of this book is human performance, this chapter mainly explores the safety factors associated with bone and skeletal muscle, which undergo enormous changes over the lifespan and in disease states. Finally, as an example, the biological trade-off between endurance and speed is examined.
