$2.$ Spine Loading

Estimate the force $($in terms of body weight$)$ acting in the erector spinae muscles $($spine

extensors$)$ for holding a weight of one$-$tenth body$-$weight with arms outstretched and

back bent forward by $20$ degrees. Use the FBD$/$Graphical models from Nordin &

Frankel; Anthropometric calculations using Bartel et al$.$ may also be required. State any

other assumptions.