Biomechanics and Medicine in Swimming XI

may be assumed that the most difficult element of monofin swimming
is the proper range of motion in the ankle joints; (4) an analysis of the
differences between value of errors performed, suggests the parameter
most differentiating the fastest from the slowest swimmer, is the angle
of bend of the feet in relation to the shanks (19.5%). The angle of attack
of distal part of the fin (11.5%) placed second in the ranking mentioned.
The differences between values of errors in terms of the angle of bend in
the proximal part of the fin (7.3%) and angle of attack of the entire fin
(6.8%) was the lowest, even when most similar. (5) The errors estimated
high correlated to swimming intracycle velocity.
Angular Displacement [deg]
220
200
180
160
140
M900 4 16 20 30
ERROR ERROR
M600 5 17 27 29
ERROR ERROR
120
M300 4 21 24 33
TIME [s] (Sampling frequency 50Hz)
ERROR ERROR
100
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37
KAT1ER
KAT6ER
KAT1COR
KAT6COR
KAT3ER
KAT9ER
KAT3COR
KAT9COR
Ma M100 4
ERROR
17 19
ERROR
33
M-HIGHEST SPEED
SUMM OF ERRORS [%]
M-LOWEST SPEED AVERAGE SD
KAT
58,1
77.6
71,5
8,4
ATM
26,4
33,7
34,6
6,1
HME
22,4
33,6
34,6
6,1
HTE
29,8
36,6
42,5
8,5
Figure 2. Graph illustrating scope of errors (ER) in angle of the foot
flexion in relation to shank (KAT) in time function. At left are sequences
of movement illustrating the range of errors showed in the graph.
Sum of errors by fastest and slowest swimmers compared to average
value calculated for all swimmers.
Table 1. Pearson’s correlation coefficients between value of error in cycle
made by all subjects on 100-m sections, and average velocity (ranked by
average velocity). (KAT) – angle of bend in foot at ankle joint; (ATM) –
angle of bend in tail of monofin; (HME) – angle of attack of distal part
of fin, (HTE) – angle of attack of entire surface of fin.
SUBJECT KAT ATM HME HTE SUBJECT KAT ATM HME HTE
M -0,94 -0,99 -0,62 -0,99 P -0,66 -0,88 -0,90 -0,89
A -0,99 -0,55 -0,72 -1,00 S -0,79 -0,96 -0,85
B -0,71 -0,94 -1,00 -0,70 N -0,77 -0,52
The following determinant movement sequences were estimated. The
end of the downbeat movement, where the knee joints straighten, the
legs are straight, the feet are in their lowest downbeat position, the tail
is at maximum bent at the maximum angle of attack of the entire surface
of the fin (Table 2(1)). The change ankle joint angle and the angle
between proximal part of the fin and the feet is during the downbeat
– beginning of the phase where the legs are maximally flexed and the
segments of the fin are more or less parallel (Table 2(3)) and finally, during
upbeat – the last part of upward movement, with legs straightened,
just before flexing at the knees, at the maximum bend of the tail of the
fin (Table 2(2)). The determinant movement sequence referring to the
change of angle of the distal part of the fin and its entire surface is in the
downbeat - the second part of legs straightening at the knees, where the
shanks are more or less parallel to the direction of swimming and the
monofin is more or less straight in the maximum angle of attack (Table
2(4)). During upbeat – the second part of the lifted legs straightened
with the knees up, until the legs are placed more or less parallel to direction
of swimming and the monofin is at maximum bend in the middle
(Table 3(5)). The key elements in the movement structure of legs and
monofin were also described (Table 1).
chaPter2.Biomechanics
Table 2. The determinant sequence of leg movements and monofin
(1,2,3,4,5) arranged with the key elements in the structure of monofin
and leg movements (A,B,C,D).related to occurrence of errors.
dIscussIon
Errors in propulsive movement structure and their impact on swimming
speed, are relevant to the principle of equilibrium of momentum
due to the interaction between the water and swimmer. Without errors
momentum transfer between the subsequent leg segments and the
monofin, is most effective (Rejman, 2006). Therefore, the determinant
sequence initiated in the category of quality of momentum transfer, occurs
between subsequent elements of the feet - parts of the monofin‘s
chain.
The swimmers tested in this study show a low level of control over
feet movement while executing propulsion actions. The angle of bent
of the feet in relation to the shanks is the most difficult element of the
movement structure (Figure 2). Additionally, changing this angle in
the function of time and layout of errors, demonstrates the least mutual
similarity among the parameters tested. The dominant role of foot
movement in generating propulsion is revealed in results gained from
the construction of a neural network (Rejman and Ochmann, 2009) as
well as research on factors supporting maintenance of consistent high
infracycle monofin swimming velocity (Rejman, 2006). The aim of
these suggestions was to avoid placing the fin parallel to the direction of
swimming. The results confirmed that, the feet as an active (under total
control of the swimmer) element in the biomechanical chain are the
final link of torque transfer from the legs to the surface of the fin (Rejman,
2006). Hence, correct movement in this element of the sequence
structure of propulsion seems to be important. Cognitive control of foot
movement allows for self-correction of swimming technique. The tendency
toward excessive plantar flexion of the feet (observed generally,
not only in the research group) thus seems unjustified from the point of
view of swimming efficiency
An analysis of the value of sum of errors made by swimmers indicated
similarities between angle of bend in the tail of the monofin
(ATM) and angle of attack of the distal part of the fin (HME) (Figure
2). Similarities were also noted when comparing the values of difference
between angle of bend in the tail of the monofin (ATM) and angle of
attack of the entire surface of the fin (HTE) This may indicate that
the bending of the tail of the fin, influences the change in shape of the
monofin’s surface. It is accepted that the tail is the place where transfer
of torque, generated by the legs, to the surface of the fin is performed
(Rejman, 2006). With this in mind, the tail is the key element in analyzing
the biomechanical chain, dividing it into parts consisting of leg segments
and monofin segments. Supporting this thesis are results showing
that the optimal plantar flexion during downbeat, limits the bend of the
tail, as a result optimizing the angle of attack of the proximal part of
the fin. Optimal dorsal flexion of the feet during upbeat causes greater
tail bending and consequently, the angle of attack of the distal part and
entire fin, achieves optimum range in both phases of the cycle (Rejman
and Ochmann, 2009). These suggestions are confirmed in the present
work. Greater optimization of tail bend, within limits established in the
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