apparatus is disclosed for monitoring strain and / or load applied to the body of a vertebral mammal . the apparatus includes means for measuring position of the body relative to an inertial frame of reference and for providing first data indicative of the position , wherein the means for measuring position includes at least one inertial sensor such as an accelerometer . the apparatus includes means for measuring muscle activity and for providing second data indicative of the muscle activity . the apparatus also includes means for storing the data and means for processing the data to provide a measure of strain and / or load to the body . the strain and / or load is typically applied to the back of the mammal . a method of monitoring strain and / or load applied to the body of the vertebral mammal is also disclosed .