What is heavy?-Friday April 21st, 2017

After figuring out that it requires less energy, and is safe for your back to perform a stoop lift for a light load, the next logical question is what is heavy? And how long will it take for your lower back to fatigue? This will be different for every person. Originally, I envisioned taking the formula from Garg's method and deriving it, like a maximization problem in calculus. Unfortunately, the formulas from Garg's method are straight lines so calculus doesn't make sense to use. In fact, the stoop lift will always require less energy than the squat lift, but there are weights where the load can only be lifted by performing a squat lift. A second way to determine when a lift is too taxing is by monitoring physiological signs while the subject performs the lift. This is also difficult to do because it requires certain facilities, it is time consuming, and ultimately the results only apply to one person. To avoid this bulky one result process, Snook's Liberty Mutual psychophysical tables were developed. These tables are used in the field of ergonomics to help determine when a job is too physiological demanding to perform. This table is helpful to employers, but it certainly doesn't help the everyday person. So how can you apply this information to everyday life? Well most likely, you don't need a table to tell you when something is heavy. The difficulty lies in knowing your back will fatigue faster than your quads. Take moving boxes for example. For the most part moving boxes aren't too heavy. If you only had to move one box, you could get away with performing the stoop lift to move that box inside. But continuing to use the stoop lift to move 30 or 40 boxes will tire your back well before you can even start to unpack! By starting from box one with the squat lift(which will feel awkward, and is all too easy to forget), you can save your back a lot of discomfort.