Introduction

Why we move

Living organisms show an enormous range of movement — from a fly's escape reflex to the gentle blink of a human eyelid to a marathon runner covering 20 km. Locomotion is the specific case where the whole organism relocates from one place to another, typically to find food, shelter or a mate, or to escape a predator. Because locomotion directly affects survival and reproduction, it carries real evolutionary significance — animals better able to move efficiently toward resources and away from danger are favoured by natural selection.

Movement in the body is never the job of muscle alone. The skeletal system (bones and cartilage), the muscular system (which can only generate a pulling force, never push) and the nervous system (which times and coordinates contraction) act as one integrated unit. This chapter builds that picture from the smallest scale outward: the types of cellular movement, the microscopic structure of a muscle fibre and how it contracts, and then the bones and joints that convert that contraction into locomotion.