![]() ![]() Fig 2.2-1 A line drawing shows the forces across the hip in single-leg stance. However, even sedentary activities generate significant forces across the joint with straight-leg raise 1.0−1.8 × BW and bed-to-chair transfer 0.8−1.2 × BW. This value increases to 4.8−5.5 × BW when jogging, and almost 8 × BW with inadvertent stumbling. The JRF during stance when walking on level ground averages about 2.5−2.8 × BW and about 0.1−0.5 × BW during swing phase. The joint reactive force (JRF) represents the sum of mechanical forces acting across the hip joint and is also expressed as a vector on the free body diagram. ![]() The abductor force (ABD) is greater than BW owing to a shorter moment arm, so that in the steady state (BW × a) = (ABD × b) ( Fig 2.2-1). During single-leg stance, these two forces reach equilibrium. Forces across the joint itself are greatest during mid-stance and are derived from two primary sources: body weight (BW) and abductor moment. Mechanical forces acting across the hip joint are complex and not easily quantified precisely. However, the joint is complex in both the forces crossing the joint as well as the distribution of forces within it. The hip joint appears to be a simple ball-and-socket articulation. ![]()
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