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Measurement of propulsion by the hand during competitive swimming

Authors:
Hideki Takagi at University of Tsukuba
Hideki Takagi
Ross Sanders at The University of Sydney
Ross Sanders
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Abstract and Figures

The purpose of this study was to evaluate propelling technique quantitatively in the four swimming strokes and at different velocities and performance levels by estimating forces from direct pressure measurements at a swimmer's hand surface. Six college students (three novice swimmers and three competitive swimmers) volunteered for this study. On each subject's right hand, four micro pressure sensors were attached on a palmar and dorsal sides at the metacarpophalangeal joints II, III, IV and V. The pressures were sampled over a 15 s period at 100 Hz, and the data during five completed strokes for front crawl, backstroke, breaststroke and butterfly were processed. Force components normal and across the palm plane were obtained. Differences in patterns of force output, were apparent across strokes, ability levels and velocities.
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Measurement of propulsion by the hand during
competitive swimming
Hideki Takagi
Institute of Health and Sports Sciences, University of Tsukuba, Ibaraki,
Japan
Ross Sanders
Department of Physical Education Sport and Leisure Studies, The
University of Edinburgh, Edinburgh, UK
Adjunct Professor, Edith Cowan University, Perth, Western Australia.
ABSTRACT: The purpose of this study was to evaluate propelling technique
quantitatively in the four swimming strokes and at different velocities and
performance levels by estimating forces from direct pressure measurements at a
swimmer's hand surface. Six college students (three novice swimmers and three
competitive swimmers) volunteered for this study. On each subject's right hand, four
micro pressure sensors were attached on a palmar and dorsal sides at the
metacarpophalangeal joints II, III, IV and V. The pressures were sampled over a 15 s
period at 100 Hz, and the data during five completed strokes for front crawl,
backstroke, breaststroke and butterfly were processed. Force components normal and
across the palm plane were obtained. Differences in patterns of force output, were
apparent across strokes, ability levels and velocities.
INTRODUCTION
Except for the breaststroke, the majority of propulsive force during swimming is
produced by the hands and forearms. For improving the propulsive technique, it is
important to evaluate the stroking movement qualitatively and also to analyze the
hydrodynamic force generated by a swimmer’s hands quantitatively. In previous
studies, this hydrodynamic force has been measured in two ways. The first uses
3D-video analysis techniques (Schleihauf et al., 1983; Schleihauf et al., 1988; Berger
et al., 1995; Berger et al., 1999). This method is inconvenient for providing
feedback to swimmers and coaches because much time is required to digitize points
on the hand to determine the orientation of the hand with respect to the direction of
motion of the hand and with respect to the external reference frame. In addition, the
accuracy of this method has not been established yet (Pai and Hay, 1988; Toussaint,
2000). The second method uses differences in pressures between the palmar and
dorsal surfaces of the hand. Hence, the hydrodynamic force can be estimated if a
whole pressure distribution on the hand surface is measured precisely. Some
researchers have measured a particular point of pressure on the hand surface using a
631
pressure transducer and discussed about a pressure profile during stroking ( Boicev K.
and Tzvetkov A.,1975; Van Manen, J. D. and Rijken, H.,1975; Svec, O. J.,1982; Loetz
et al. 1988). However, these studies did not evaluate whether the location of pressure
transducers on the hand accurately reflected the overall pressure distribution. To
confirm a relationship between a particular point’s pressure and a whole
hydrodynamic force acting on the hand, Thayer (1990) attempted to measure both
pressure and force at the same instant using a hand model. Although Thayer found a
tendency to synchronize the pressure with the force, the locations that best reflected
force for the whole hand were not obtained. Takagi and Wilson (1999) measured the
pressure and position of 88 points on the hand model. An integration of all pressure
values over the surface was calculated and defined as a representative pressure value
of a whole hand model. They found a significant correlation (r=0.962) between the
overall pressure values and the pressure differentials of four particular points. These
were the metacarpophalangeal (MP) II, III, IV and V joints. In addition, Takagi and
Wilson suggested that the hydrodynamic force acting on the hand could be estimated
by using the four-point pressure differential values. However, this study was
conducted only for front crawl using a single subject.
Therefore, the purpose of this study was to modify Takagi and Wilson’s method
and to evaluate a propelling technique quantitatively in various kinds of strokes,
velocities and performance levels by measuring the pressure distribution over a
swimmer's hand surface.
METHOD
SUBJECTS
Three competitive swimmers and three novice swimmers volunteered for this study,
with one male and two females in each group. The three competitive swimmers were
in the regional collegiate levels, and the other three swimmers were physical
education students who have no competitive careers. The participants were
characterized (M ± SD) by an age of 21.5 ± 1.9 years and height of 1.66 ± 0.07 m, and
weight of 61.8 ± 17.8 kg. Their physical characteristics and competitive career are
shown in Table 1. The participants were informed of the purpose of the study, and
their consents obtained.
MATERIALS AND PROCEDURES
A total of 8 water-proofed micro pressure sensors, 6 mm diameter and 1 mm thick,
(KYOWA PS-2KA) were attached to the MP joint of the hand and covered by a
surgical nylon glove (See Figure 1). The definitions of angle and direction of pressure
are shown in Figure 2. A line through the MP II and V joints was defined as the
standard axis. At each pressure sensor, an angle between the surface of sensor and the
standard axis was scaled and defined as
θ
. Surface area of the hand including both
sides of the hand (A) was also measured.
632
Table 1 The subjects' physical characteristics and competitive career.
Subject Sex Age (yrs) Height (m) Weight (kg)
*Total hand
and surface
area (m
2
)
Competitive
Career (yrs)
A Male 22 1.72 76.0 1.56 x10
-2
17
B Male 24 1.71 95.0 1.60 x10
-2
0
C Female 19 1.72 52.0 1.25 x10
-2
11
D Female 19 1.58 47.0 1.13 x10
-2
12
E Female 23 1.69 54.0 1.20 x10
-2
0
F Female 22 1.54 47.0 1.10 x10
-2
0
Average 21.5 1.66 61.8 1.31 x10
-2
6.7
SD 1.9 0.07 17.8 1.99 x10
-3
6.9
*Total hand surface area=(Front +back)
Fig. 1 Pressure sensors attached on the MP joints.
The pressure sensor measures only pressure acting normal to the surface. By
multiplying by surface area to obtain a force normal to the surface the mean force
components normal to the palm plane (F
V
) and across the palm (F
H
) over the surface:
F
V
= P
n
Cos
θ
n
A
8
n=1
8
∑
, (1)
F
H
= P
n
Sin
θ
n
A
8
n=1
8
∑
. (2)
where P
n
is the real pressure value measured at the sensor n.
The measurement of the pressure during stroking was conducted in the
circulating water channel (CWC) in NKK Corporation. This CWC is 3m width,
633
7m length and 1.5m depth and was controlled by a microcomputer for solving peculiar
problems such as an unbalanced flow distribution, an incline in the water surface, and
an occurrence of regular wave. The subjects were asked to swim by four kinds of
strokes, front crawl, breaststroke, backstroke and butterfly in the CWC. The water
temperature was set at 28 degrees and the water flow velocity (U) was set at three
relative levels for each subject, approximately 70%, 80% and 90% of the best record in
a standard 50 m pool for each stroke event. The pressures were sampled over a 15 s
period at 100 Hz, and input to the PC, then the data during five completed strokes were
processed. Each stroke movement and duration of stroke for the five strokes were
unsteady, especially in novice swimmers. Therefore, to obtain the mean pressure and
error value during the five strokes, a duration from entry to exit for each stroke was
normalized as 100 percentage, then mean and standard deviation were calculated.
F
n
F
Vn
F
Hn
θ
n
U
θ
n
Fig.2 Position of sensors, definitions of angles and force components
RESULTS AND DISCUSSION
Typical examples of the F
V
and F
H
in four kinds of strokes for a skilled swimmer
(Sub. A) at U=80% are shown in Figure 3. Except for the backstroke, F
V
is greatest
towards the end of the stroke when the swimmer sweeps the arm down and in
towards the body. F
H
did not change dynamically as much as F
V
. Although the
magnitude of F
V
directly corresponded to propulsion, F
H
reflected the direction of
motion of the hand. Except for the backstroke, a positive F
H
value implied that the
hand was moving toward the little finger. Conversely a negative F
H
implied that the
hand was moving toward the thumb. In the cinematographic method, a contribution
of lift and drag to the propulsion has been discussed. The current pressure
measuring method cannot identify the lift and drag, but does provide valuable insights
into the temporal pattern of forces produced by the stroking pattern of a hand. The
force-time curve profiles were similar to the results of Sevec (1982) and Loetz et al.
(1988). The results were also similar to those obtained by 3D-video methods
634
(Schleihauf et al., 1988; Berger et al., 1999), except for the backstroke.
An example of differences between a competitive swimmer and a novice
swimmer and in front crawl are shown in Figure 4. The novice swimmer produced
peak force in the middle of a stroke whereas the competitive swimmer produced peak
force late in the stroke. The variability of the novice swimmer’s force, indicated by
the standard deviations, was greater than that of the competitive swimmer.
80%@Front crawl
U=1.6m/s
-10
0
10
20
30
40
50
60
70
0 20406080100
%stroke
Force
（
N
）
80%@Breast stroke
U=1.1m/s
-10
0
10
20
30
40
50
60
70
0 20406080100
%stroke
Force
（
N
）
80%@Butterfly
U=1.3m/s
-10
0
10
20
30
40
50
60
70
0 20406080100
%stroke
Force
（
N
）
80%@Back stroke
U=1.2m/s
-10
0
10
20
30
40
50
60
70
0 20406080100
%stroke
Force
（
N
）
Fig. 3 Mean vertical and horizontal components of force over five complete strokes
in four kinds of strokes for Sub. A (U=80%@best record).
Combining qualitative analysis with the force data yields an effective diagnostic
system for improving a swimmer’s stroke. For example, the qualitative analysis
shows that, in general, novice freestyle swimmers are inclined to push their hand
downward immediately after entry. This means that the force produced would be
upward rather than in the desired forward direction. Thus, even if the swimmer
tried to push the water more strongly there would not be a substantial increase in
propulsion unless a change the direction of pull to the so-called ‘straight pull’ is
executed.
Competitive swimmer
80%@Front crawl
U=1.6m/s
-10
0
10
20
30
40
50
60
0 20406080100
%stroke
Force
（
N
）
F
H
F
V
Novice swimmer
80%@Front crawl
U=0.9m/s
-10
0
10
20
30
40
50
60
0 20 40 60 80 100
%stroke
Force
（
N
）
F
H
F
V
Fig. 4 Force profiles of a competitive swimmer (Sub. A) and a novice swimmer
(Sub. B) in front crawl.
635
F
V
-10
0
10
20
30
40
50
60
70
0 20406080100
%stroke
Force (N)
0.9m/s
1.0m/s
1.1m/s
F
H
-10
-8
-6
-4
-2
0
2
4
6
8
10
0 20406080100
%stroke
Force (N)
0.9m/s
1.0m/s
1.1m/s
Fig. 5 Force component profiles of Sub. A at velocities of 0.9, 1.0, and 1.1
m/s in breaststroke.
The change of hydrodynamic force production in breaststroke of competitive
swimmer due to an increase of velocity is shown in Figure 5. As velocity increased,
forces increased, and the time from entry to the peak value decreased.
CONCLUSION
While this study has shown that the pressure transducer method combined with
qualitative analysis of video is a useful tool for showing differences in force
generation across ability levels and across swimming velocities, we also need to
consider the direction of the forces produced.
This ‘pressure difference’ method is increasing our knowledge of forces acting
across the palmar to dorsal surfaces of the hand. However, we are not yet able to
quantify forces along the long or transverse axes of the hand. Further, determining the
extent to which the palmar to dorsal forces were in the desired direction of travel
requires quantification of the orientation of the hand with respect to an external
reference frame. Therefore, the method requires further refinement so that directions
of the forces produced by a swimmer’s hand during swimming can be obtained.
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Literature Review - Strength and Power Training For 100m Front Crawl Swimmers
Conference Paper
  • Mar 2012
Journal of the International Society of Swimming Coaching 2(1) Fast swimming, either in the pool, in open water swimming, or in water polo, requires maximizing the efficiencies with which the human body can move through a liquid medium. A multitude of factors such as power and strength can affect the ability to swim fast as well as the final outcome. Strength and conditioning are tools used by sports scientists and coaches to enhance strength, power and, subsequently, to improve performance.
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Hydrodynamic Characteristics of a Swimmer’s Hand
Article
Full-text available
  • Feb 1999
  • J APPL BIOMECH
The main purpose of this study was to develop a model for calculating forces produced by a swimmer's hand, with the thumb adducted, accelerating in the direction of flow. The model included coefficients to account for the velocity and acceleration of the hand. These coefficients were designed to calculate forces in the direction opposite the motion (drag) and two components of lift orthogonal to the direction of motion. To determine the coefficients, three-dimensional forces acting on a resin cast of a swimmer's hand were recorded while accelerating the hand from rest to 0.45 m · s-1 and 0.6 m · s-1 in a towing tank. The hand orientation was varied throughout the entire range at 5°increments. Three-dimensional surfaces describing the magnitude of the coefficients as functions of pitch and sweepback angle were produced. It was found that acceleration coefficients as well as velocity coefficients are required for accurate modeling of the forces produced by the hand in swimming. The forces generated by the hand are greatest when pitch angles approach 90°due to the large contribution by the drag component. However, at pitch angles near 45°and sweepback angles near 45°and 135°, lift forces contribute substantially.
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Determining propulsive force in front crawl swimming: A comparison of two methods
Article
Full-text available
  • Mar 1999
To evaluate the propulsive forces in front crawl arm swimming, derived from a three-dimensional kinematic analysis, these values were compared with mean drag forces. The propulsive forces during front crawl swimming using the arms only were calculated using three-dimensional kinematic analysis combined with lift and drag coefficients obtained in fluid laboratories. Since, for any constant swimming speed, the mean propulsive force should be equal to the mean drag force acting on the body of the swimmer, mean values of the calculated propulsive forces were compared with the mean drag forces obtained from measurements on a Measuring Active Drag (MAD) system. The two methods yielded comparable results, the mean difference between them being only 5% (2 N). We conclude that propulsive forces obtained from three-dimensional kinematic analysis provide realistic values. The calculation of the propulsive force appears to be rather sensitive to the point on the hand at which the velocity is estimated and less sensitive to the orientation of the hand.
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A hydrodynamic study of the oscillation motion in swimming
Article
  • Dec 1987
  • J BIOMECH
The purpose of this study was to determine the validity of the quasi-static assumption—that fluid forces exerted under unsteady flow conditions are equal to those exerted under similar steady flow conditions—in the case of a cylindrical model oscillating in a vertical plane about a transverse axis normal to the flow. The findings indicated that the quasi-static approach is applicable only to cyclic motions with low frequencies and small accelerations. For swimming motions that involve high frequencies and high accelerations, like those that occur in competitive swimming, the vortex shedding effect and the added mass effect must be taken into account if accurate values are to be obtained for hydrodynamic forces.
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Hydrodynamic drag and lift forces on human hand/arm models
Article
  • Mar 1995
  • J BIOMECH
Forces acting on the forearm and hand during swimming can be decomposed into drag forces and lift forces. In this study drag and lift forces were measured on two models of a human hand and forearm when towed in a towing tank. To compare the results of models with different size at different velocities force data were normalized to drag and lift coefficients (Cd and Ct). Influence of the orientation of the model with respect to the flow, velocity, size of the model and the relative contribution of the hand and forearm on Cd and Ct were studied. The orientation of the model with respect to the line of motion was varied by rotating the models around three axes, and quantified using the angle of pitch (AP: the angle between the hand plane and flow) and the sweep-back angle (SB: the orientation of the flow vector when projected on the hand plane). Cd was maximal when the palm of the hand is almost perpendicular to the flow (AP = 65 degrees, SB = 342 degrees). Ct shows maximal values at two different orientations: with the hand in a thumb-leading position, AP = 31 degrees, SB = 358 degrees, and with the hand in a little finger-leading position, AP = 48 degrees, SB = 193 degrees. The orientation of the hand was very critical in generating lift forces. By contrast, the influence of velocity and size of the model on the values of Cd and Ct was limited.(ABSTRACT TRUNCATED AT 250 WORDS)
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Propulsive techniques: front crawl stoke, butterfly, backstroke, and breaststroke
  • Jan 1988
  • 53-59
  • R E Schleihauf
  • J R Higgins
  • R Hinrichs
  • D Luedtke
  • C Maglischo
  • E W Maglischo
  • A Thayer
Schleihauf, R.E., Higgins, J.R., Hinrichs, R., Luedtke, D., Maglischo, C., Maglischo, E.W. & Thayer, A. (1988). Propulsive techniques: front crawl stoke, butterfly, backstroke, and breaststroke. In: Swimming Science V, (Ed. By B.E. Ungerechts, K. Reischle & K. Wilke), pp. 53-59. Human Kinetics, Champaign, IL.
Three-dimensional analysis of hand propulsion in the sprint front crawl stroke
  • Jan 1983
  • 173-184
  • R E Schleihauf
  • L Gray
  • J De Rose
Schleihauf, R.E., Gray, L. & De Rose, J. (1983). Three-dimensional analysis of hand propulsion in the sprint front crawl stroke. In: Biomechanics and Medicine in Swimming, (Ed. By A.P. Hollander, P.A. Huijing & G. de Groot), pp.173-184. Human Kinetics, Champaign, IL.
Hand pressures as predictors of resultant and propulsive hand forces in swimming
  • Jan 1990
  • A M Thayer
Thayer, A.M. (1990). Hand pressures as predictors of resultant and propulsive hand forces in swimming. Unpublished Ph.D. dissertation, The University of Iowa, Iowa city, IA.
The evaluation of highly skilled swimmers via quantitative and qualitative analysis
  • Jan 1988
  • 361-367
  • C Loetz
  • K Reischle
  • G Schmitt
Loetz, C., Reischle, K. & Schmitt, G. (1988). The evaluation of highly skilled swimmers via quantitative and qualitative analysis. In: Swimming Science V, (Ed. by B.E. Ungerechts, K. Reischle & K. Wilke), pp.361-367. Human Kinetics, Champaign, IL.