Apparatus is disclosed for monitoring strain and/or load applied to the body of a vertebral mammal. The apparatus includes means (10, 11) 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 (12, 15-19) 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.