Biomechanics and Medicine in Swimming XI

BiomechanicsandmedicineinswimmingXi
Influence of Swimming Speed on the Affected- and
Unaffected-Arm Stroke Phases of Competitive
Unilateral Arm Amputee Front Crawl Swimmers
osborough, c.d. 1 , Payton, c.J. 1 , daly, d.J. 2
1 Manchester Metropolitan University, Alsager, United Kingdom
2 Katholieke Universiteit Leuven, Leuven, Belgium
The purpose of this study was to determine whether the arm stroke
phases used by competitive unilateral arm amputee crawl swimmers
differed between their affected and unaffected sides and whether these
phases changed with an increase in speed. Thirteen highly-trained
swimmers were video-taped underwater from two side-views during five
increasingly faster 25 m front crawl trials. At all swimming speeds, the
stroke phases of the affected and unaffected arms differed significantly.
As speed increased, the duration of the affected-arm’s Entry and Glide
phase and the unaffected-arm’s Pull phase decreased significantly; the
duration of both arms’ Push phase increased significantly. The amputees
used a coordination strategy that asymmetrically adjusted
their arm movements to maintain the stable repetition of their
overall stroke cycle at different speeds.
Key words: swimming; disability sport; Motor control; Biomechanics
IntroductIon
Stroke phases have been frequently used to describe the propulsive and
non-propulsive arm actions of able-bodied front crawl swimmers. Maglischo
et al. (1988) reported that while there were four propulsive phases
in the front crawl underwater arm stroke action: (1) Downsweep; (2)
Insweep; (3) Outsweep; and (4) Upsweep, able-bodied swimmers were
unable to generate large propulsive forces in more than two of these phases.
Later, Chollet et al. (2000), when formulating the Index of Coordination
for front crawl, separated the complete action of the arm stroke cycle
into four distinct phases: (A) Entry and Catch; (B) Pull; (C) Push; (D)
Recovery, of which they assumed, B and C were propulsive and A and D
were non-propulsive.
For competitive swimmers with a single elbow-level amputation, the
roles that the affected- and unaffected-arm have within the front crawl
arm stroke cycle may differ from each other. It would be expected that the
primary function of the unaffected-arm is to generate propulsion. However,
uncertainty remains as to whether the affected-arm of a unilateral
arm amputee can contribute effectively to propulsion at swimming speeds
higher than 1 m∙s -1 . Rather, the affected-arm might simply function to
control inter-arm asymmetry so that stable repetition of the overall arm
stroke cycle is maintained. Understanding the roles of both the affected-
and unaffected-arm during the stroke phases would be of great practical
importance to swimmers, teachers and coaches. No examination of the
arm stroke phases has been undertaken with a single homogenous group
of highly-trained swimmers with a single-arm amputation.
For unilateral arm amputee front crawl swimmers, increases in swimming
speed are achieved by increasing stroke frequency (Osborough et al.,
2009). However, it is unclear how these swimmers vary the duration of
their arm stroke phases in order to accommodate an increase in stroke frequency
and swimming speed. The purpose of this study was to determine
if the arm stroke phases used by competitive unilateral arm amputee front
crawl swimmers differed between their affected and unaffected sides and
whether these phases altered with an increase in swimming speed.
Methods
Thirteen (3 male and 10 female) competitive swimmers (age 16.9 ± 3.1
yrs) participated in this study. All participants were single-arm amputees,
at the level of the elbow. The mean 50 m front crawl personal best
time was 32.7 ± 3.1 s. Twelve of the swimmers competed in the Inter-
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national Paralympic Committee S9 classification for front crawl; one
male swimmer competed in the S8 classification. The procedure for the
data collection was approved by the Institutional Ethics Committee. All
participants provided written informed consent before taking part in
the study.
Participants completed five 25 m front crawl trials. Seven of the
swimmers performed the trials from slow to maximum swimming speed
(SS max ); the remainder performed the trials from maximum to slow
swimming speed. To control for the effects of the breathing action on
the swimming stroke, participants were instructed not to take a breath
through a 10 m test section of the pool.
Two digital video camcorders (Panasonic NVDS33), sampling at
50 Hz with a shutter speed of 1/350 s were used to film the participants.
Each of the camcorders was enclosed in a waterproof housing
suspended underwater from one of two trolleys that ran along the side
of the pool, parallel to the participants’ swimming direction. This set-up
enabled the participants to be video-taped under the water, from opposite
sides, over the 10 m test section.
The digital video footage was transferred to a laptop computer and
analysed using SIMI Motion 7.2 software. Three consecutive, nonbreathing
stroke cycles for each participant, were then selected for
analysis. The estimated locations of the gleno-humeral joint centre and
the elbow joint centre of both the affected and unaffected arms were
digitised at 50 Hz to obtain the angular position of the upper-arms, as
a function of time. Before filming, the skin overlaying the joint centres
was marked with black pen to help estimate their location.
At 80%, 85%, 90%, 95% and 100% of each participant’s SS max individual
arm stroke phases, expressed as a percentage of the duration of
the complete arm stroke cycle, were determined from the angle made by
the shoulder-to-elbow position vector relative to the horizontal. Each
upper-arm movement was divided into four phases (Fig. 1): Entry and
Glide (A); Pull (B); Push (C); and Recovery (D):
(A) Entry and Glide: from where the elbow joint centre entered
the water (0°) to where the shoulder-to-elbow position vector made an
angle of 25° with the horizontal. This latter position corresponded to a
point where typically the swimmers actively initiated extension of their
affected-arm.
(B) Pull: from the end of the Entry and Glide (25°) to where the
shoulder-to-elbow position vector made an angle of 90° with the horizontal.
(C) Push: from the end of the Pull (90°) to where the shoulder-toelbow
position vector made an angle of 155° with the horizontal. This
latter position corresponded to a point where, as a result of the rolling
action of the swimmers’ trunk and the bow-wave created by the swimmers’
movement through the water, the most-distal part of the swimmers’
affected-arm typically exited the water.
(D) Recovery: from the end of the Push (155°) to where the elbow
joint centre entered the water (360°).
Figure 1. Divisions of the arm stroke phases: (A) Entry and Glide; (B)
Pull; (C) Push; and (D) Recovery for a unilateral arm amputee front
crawl swimmer.