In addition to work analyses during the use of ambulance cots, the strain on the circulatory system of 12 professional carriers was measured in 4 standardized carrying tests: carrying of the stretcher in a staircase at normal speed and at increased speed, lifting of the stretcher onto the gurney, and loading the ambulance cot into as well as unloading it from an ambulance. Additionally, static and dynamic components of the muscle strain of 6 muscle groups were determined electromyographically. The tests consisted of “normal” carrying as well as explicitly rapid carrying of a dummy (78 kg) up and down a flight of stairs using 3 different commercially available ambulance cots (roll-in systems – stretchers with incorporated transporter which weighed between 48.5 and 50 kg including a pad for the patient). The paramedics had to carry both the front and the rear of all the stretchers. The “normal” carrying times to cover one floor (the typical real-life situation) were approximately 35 to 40 s. Rapid carrying reduced the carrying times by approximately 10 s.
Model-specific influences of the roll-in systems aside, the rapid carrying led to substantially increased strain on the circulatory system (work-related increases of approximately 10 beats per minute (bpm)). The “lifting of the stretcher onto the gurney” and the “loading/unloading of the roll-in system” cause significantly less strain, but still lead to substantial “extra physiological costs” of approximately 50 bpm. The strain on the flexor digitorum, the upper part of the trapezius muscle, and the erector spinae substantially exceeds the strain on the 3 parts of the delta muscle in all tests. Increased speed significantly increases muscle strain. The static components of the standardized electromyographic activity sEA [%] with values of 50 % and more (especially for the flexor digitorum) show that even carrying times of only approximately 30 s cause fatigue. It is well known that just 50 % of maximum output over 30 s already require recovery times of approximately 400 %, i.e., approximately 2 min. Carrying the rear of the stretcher upstairs leads to significantly increased strain on the erector spinae related to the carrying position at the front. Similarly, the carrier at the front of the stretcher experiences substantially higher strain while bearing the stretcher downstairs. Even though model-specific influences cause some differences, they are not displayed consistently across all work elements.
The data can be used by job analysts to grade the level of muscle activity required by different carrying tasks during the transport of a patient, and by product designers to justify changes in the design of ambulance cots to reduce muscular strain on the upper extremities and the back.