PhD Fekete - SZIE version - 2.2 - Szent István Egyetem

Materials and Methods
Ys [cm]
40
30
Horizontal movement of center of gravity
Average Ys function
Standard deviation
Mason et al. - Standard squat
20
10
0
Flexion angle [°]
40 60 80 100 120 140 160
Figure 3.28. Y s(α) function with its standard deviation
As it is seen, the difference between the two graphs is quite significant. In order to show how
the two models differ in numbers, a small calculation has been carried out as follows:
⎛ K ⎞
∆ =
non standard
⎜1
−
−
K ⎟⋅100
(3.38)
⎝ Kstandard
⎠
Where, K can be any quantity (force, moment or displacement). ∆K can provide a percentage
difference of a standard quantity compared to a non-standard quantity (here standard and nonstandard
relates to the type of squat motion). The results were summarized in Table 3.8.
FLEXION ANGLE
∆Ys
40° 21%
80° 25%
120° 31%
160° 41%
Table 3.8. Ys difference between standard and non-standard squat
The displacement of center of gravity line, as it was mentioned earlier in the introduction, is
usually bounded to external non-human geometric quantities. The novelty of these graphs that
they present functions, which are easy to apply in any mathematical model, since they are only
dependent on one physical quantity: the flexion angle of the knee joint.
Although Mason et al. [Mason et al., 2008] also created a similar function (Eq. (2.4)), their
function supposes that:
−
−
the movement of the femur and the tibia are always symmetric to each other,
the center of gravity does not move horizontally.
These hypotheses are major simplifications and the difference evidently appears.
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