You have decided to redesign a shovel for shoveling snow. In normal shoveling, p

Question

You have decided to redesign a shovel for shoveling snow. In normal shoveling, people typically flex their trunks by ~ 90 degree and the distance from the L4/L5 joint to the blade of the shovel is about 60 cm. In your redesign, the handle is lengthened, so that person leans forward by only 20 degree. However, the loaded blade now 1.2 m from the L4/L5. Given the following body dimensions: M_upper body= 40 kg Horizontal distance of upper body COG from L4/L5 = 45cm. Would you say that your redesign is an improvement, given that when the blade of the shovel is laden with snow it weighs 5kg? Explain your answer from the perspective of muscle and joint (L4/L5) loads.

Explanation / Answer

This topic is related to Ergonomics, although i am not a expert of Ergonomics, I have answered this as per my understanding, blow are the answers of both part - find these

as per subject - it is about Shovel -Spinal Compression - and question is about redesigning a shovel.

given values are - distance fromL4/L5 joint = 60 cm or = 0.6 m

loaded blade distance = 1.2 m

load on upper body - M_{upper body} = 40 kg

horizontal distanceof upper body COG from L4/L5 = 45 cm = 4.5 m

a) blade of shovel load weigh = 5 Kg

Yes, redesigen is an improvement, as angle vareies from 90° to 20° for person forward lean- as for snow shoveling - it is difficult and typical for a person who is straight forward.

for finding spinal compression - we can use simple mechanical model - as per it

F = ma or we can say - force = mass *acceleration

here we use g - which is acceleration due to gravity at surface of earth = 9.81m/s² nearly equivalent to 10 m/s²

so mass of1 kg resting on earth results force of-

f = 1(Kg) * 9.81(m/s²) = 9.81 N = nearly equivelent to 10m/s²

now total compressive force C_t = (Compressive force due to upper body weight +compressive force due to load + compressive force due to back muscle contraction needed to maintain posture.

now compressive force due to upper body weight = 400N as body weighs 40 Kg and it also attaches with distance so - 400 = 400N

compressive force due to load =

for an erect posture - force = 50N as load weigh 5 kg

for it muscle contraction is needed for load moment and unit of load moment- should be Nm

so load moment about spine = 50(N)*1.2(m) = 60Nm

now asuming lower arm of back muscle = 0.06m or 6 cm

back muscle forcefor posture stability = 60(Nm)/0.06(m) = 1000 N

now total spinal compression = 400+60+1000 = 1460N

b) muscle joint load results only a 5 Kg load asit is at a particular distance from the body from spine. due to it back muscle force required for balacing load as muscle is at disadvantage of ratio 10:1

as main goal is to minimize the adverse effect or redesigen or we can say redesigen for improvement to prevent the dangerous

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