|
|
MAKING A
SPLASH: The VIII International Symposium of
Biomechanics and Medicine in Swimming, Jyvaskyla,
Finland
Andy
Stewart,
Scottish Institute of Sports Medicine and
Sports Science, University of Strathclyde, Glasgow,
Scotland; and Hideki
Takagi,
Faculty of Education,
Mie University, Tsu, Japan
Sportscience News Sept-Oct
1998
http://www.sportsci.org/news/news9809/isbms.html
|
|
|
More than 160 delegates from around the globe gathered at the
University of Jyvaskyla for the VIII International Symposium of
Biomechanics and Medicine in Swimming from June 28-July 2,
1998. Over 130 presentations in various formats (podium,
poster, pool demonstration) were given at the symposium. For
those of you interested in obtaining more detailed information than
what we present here, there is a
book of
abstracts available for purchase at the conference web site, and
proceedings will be published early in 1999. The next swim
research conference is FINA's (Federation Internationale de Natation
Amateur) in April, 1999 in Hong Kong, and the next International
Symposium of Biomechanics and Medicine in Swimming is scheduled for
St Etienne, France in 2002.
We've chosen a few presentations to highlight in this conference
report; among them, keynote addresses by David Costill and Mitsumasa
Miyashita. First, Costill's presentation on training intensity
and tapering.
Intensity and Tapering
The opening session of the conference was an invited lecture given
by David Costill (Ball State University) entitled "Training
adaptations for optimal performance in swimming".
Development of upper body strength is related highly to swim
performance; and in looking at effects of training on muscular power
and strength, Costill discussed the issue of quality vs quantity (or
intensity vs volume). He pointed out that training volume
is not related to performance and showed evidence that in periods of
high-volume training, muscle power was actually less than during
periods of no training. Thus the only way to recover that power
in time for competition was for swimmers to taper. Although
there is debate surrounding the optimal taper period and how it
should be constructed, Costill suggested that if athletes respond to
training as expected, the taper should last approximately 14 to 21
days and consist of high-intensity sessions with a gradual reduction
in volume. For those athletes who show signs of overtraining,
training volume should be reduced immediately in one large step, and
then maintained at a low level until athletes start to show positive
signs of adapting to the training stimulus.
Costill presented several theories that attempted to explain the
mechanisms behind the effectiveness of tapering, but ruled out
psychological and motor unit recruitment theories for lack of
convincing evidence. Instead, muscle fiber contractility
appeared to be the more likely explanation behind tapering
effectiveness. Single muscle fiber studies that he and Scott
Trappe performed at Ball State supported the view that tapering
worked primarily through an increase in power (brought about by an
increase in the muscle protein, myosin) in the fast twitch
fibers. They also found some increase in the power output of
slow twitch fibers.
In addition, Costill touched upon the debate surrounding the
use of dry-land training for swim performance. While such
training is common practice in the swim world, Costill presented
evidence that supported the view that there does not appear to be any
further benefit to swim performance from dry-land training performed
in addition to water-based workouts.
Historical Perspectives
Mitsumasa Miyashita (Toyo Eiwa Woman's University, Japan) has been
involved in the scientific study of swimming for many years, and he
has participated in this symposium since the first meeting in
1970. Therefore, he was well-qualified to provide an historical
perspective in his presentation entitled "Biomechanics of swimming:
Past, present, and future". During his talk, Miyashita
discussed propulsive and resistive forces, factors in determining
swimming velocity. He pointed out that a swimmer's velocity
varies during a single stroke cycle: it increases when the propulsive
force exceeds the resistive force, and it decreases when the
propulsive force falls below resistive force.
The measurement of propulsive and resistive forces has been a
matter of concern to many researchers over the years, because
accurate measurement of these forces would allow stroke technique to
be evaluated quantitatively. The history of biomechanical
research in swimming has been one of trying to improve scientific
methodology in order to measure propulsion and resistive force
accurately. In the early 1900s, resistive force was measured as
passive drag and assessed while towing a swimmer behind a
rowboat. We now know that passive drag is somewhat different
from active drag, which is the resistive force acting on a
self-propelling swimmer.
Considerable developments have been made over the years in the
techniques of biomechanical analysis. Since 1970,
three-dimensional cinematography has allowed propulsive forces in
free swimming to be estimated. In 1980, researchers in the
Netherlands developed a system to measure active drag and the
propelling efficiency of the front crawl stroke. Miyashita
pointed out that, even though such developments have taken
place, the relationship between propulsion, resistive force,
and stroke technique is still not completely understood. (See the
Sportscience article on swim
biomechanics by Ross Sanders.) Miyashita also suggested
that the relationship between mean velocity and fluctuation of
velocity during a single cycle stroke should be investigated,
especially in breaststroke and butterfly.
Technique and Efficiency
Minoru Fujishima (Tokyo University, Japan) tried to clarify the
effect of intracycle velocity fluctuation on average sustainable race
velocity (a problem pointed out by Mitsumasa Miyashita). By
assuming that resistive drag is proportional to the square of the
velocity, he showed that the smaller the fluctuation in velocity
during a stroke cycle, the greater the average velocity. He
suggested that the reduction of resistive force would increase the
velocity in strokes with a large resistive component (i.e.
breaststroke and butterfly), and pulling equally with the left and
right arm would reduce oscillations in velocity during freestyle and
backstroke. Swimmers should therefore concentrate on
maintaining constant velocity within a stroke cycle by avoiding
surges from a dominant limb (e.g. right arm) or a particular part of
a stroke cycle (e.g. breaststroke kick).
Training
Load Model
Jean-Claude Chatard (St Etienne, France) presented a model of
training loads, which consisted of a combination of intensity,
volume, frequency, and dry-land training. Individual differences must
be taken into account, and he agreed with David Costill's earlier
presentation that intensity was the key to successful swim
performance, not volume. Much of the work that he presented was
based upon the research of Mujika et al. (1995) Can. J. Appl.
Physiol. 20: 395-406. We questioned Jean-Claude about the
theoretical basis of his new modeling approach, as it was based on
Eric Bannister's original TRIMP (training impulse) model, which was
developed on only two subjects. His response was that his model
held for the majority of the time, but it needed training data from
at least 12 swimmers in order for it to work. His model:
MITS = (1*km1 + 2*km2 + 3*km3 + 5*km4 + 8*km5 +
dry-land equivalent)/(training volume)
where MITS is the mean intensity of training session, and 1*km1,
2*km2, etc. are the "stress indices" for each intensity times the km
swum at that intensity. The stress index ranges from 1 (corresponding
to a blood lactate concentration of 2 mmol/L) through 8 (maximum
intensity sprint swimming). For dry-land training, sessions composed
on average 50% warmup and stretching (intensity = 1), 25% submaximal
strength workouts (intensity = 4), and 25% maximal strength training
(intensity = 8). Coaches and swimmers estimated that 1 hr of dry-land
training was equivalent to 1 km swum at intensity 1, 0.5 km at
intensity 4, and 0.5 km at intensity 5.
Jean-Claude also noted that the better the performance at the
start of the season, the better the performance at end-of-season
competition. In addition to advocating year-round
high-intensity workouts, he suggested that medley swimming and weight
training should be avoided during the taper period.
3-D
Techniques
Jane Cappaert (International Center for Aquatic Research, USA)
discussed the application of 3-D analysis to quantifying swim
technique. Such analysis has allowed her group to acquire a
greater understanding of the underwater technique of all four swim
strokes than conventional biomechanical analyses had previously
allowed. The knowledge gained from 3-D analysis formed the
basis of all the biomechanical support given to the US swim
team. Jane explained that 3-D analysis of a swimmer's stroke
was possible from the film footage of four cameras: two cameras in
underwater housing and two cameras placed in the spectator stands.
Separate direct linear transformations (DLT) were performed for the
above-water and below-water views to determine the 3-D coordinates of
body landmarks from the sets of 2-D coordinates digitized from each
video frame of each camera. Various body angles, displacements,
and velocities of swimmers were then obtained to determine
differences between swimmers of different abilities in each of the
four strokes. Jane indicated that, within each stroke, swimmers
differed in their stroke patterns. She pointed out that elite
athletes did not always possess great strength and power, but the
common trait among all elite swimmers was that they had the ability
to apply power to the water more effectively than less-skilled
swimmers. In addition, elite swimmers would rather have
better whole body streamlining that reduces resistive forces than use
significantly higher propulsive force. In short, reducing
active drag is essential.
Altitude
Futoshi Ogita (National Institute of Fitness and Sports, Japan)
reported positive effects from a train-high live-low study.
Nine well-trained swimmers were exposed to hypobaric conditions
(simulated 3000 m above sea level) for two, two-hour sessions per day
for five days per week for two weeks. During each session the
swimmers performed repeated bouts of 20-s exercise at 130% of maximal
oxygen uptake, with 10-s rest intervals. There was no
change in maximal oxygen uptake following the intervention period,
but anaerobic capacity (as assayed by maximal accumulated oxygen
deficit) improved by 10%.
Drafting
Jean-Claude Chatard presented work that he and his colleagues had
undertaken on the effects of drafting on swim performance and
resistive drag in triathletes. They found that drafting
enhanced performance by an average of nearly 10 s in a 400-m race
(more than a 3% improvement in performance). Gains in
performance were greater for faster swimmers. In another
drafting study, Gregoire Millet (University of Besancon, France)
indicated that kicking frequency of the lead swimmer, that is 2-beat
or 6-beat, had little effect on the advantage gained by a drafting
swimmer.
Swim
Tests
New underwater system and tests. A group from
Finland, lead by Kari Keskinen (University of Jyvaskyla) developed a
new system of underwater pace-maker lights to control swim speed
during tests. The system was used to investigate the
appropriateness of a new non-invasive test of performance utilizing a
combination of stroke length, stroke rate, and swim velocity
data. The major finding: aerobic training intensities could be
obtained from swimming velocity versus stroke length curves at the
point where stroke length attained a maximum.
Non-invasive vs invasive testing. Masaru Matsunami
(Beppu Women's Junior College) led a group of Japanese scientists
comparing swimming speed during non-invasive and invasive testing
protocols. The non-invasive tests were a 30-min swim test,
600-m swim test, 2000-m swim test, and critical speed test. The
invasive protocol consisted of lactate measurements taken during an
incremental 7x200 m swim test. The non-invasive test that
elicited the most comparable swim speed to that of the so-called
anaerobic threshold (as determined by lactate deflection point) was
that of critical speed.
Don Maclaren (Liverpool John Moores University, UK) presented data
on critical swim speed and how it could be used to track changes in
training status. He found that a two-distance (100-m and 200-m)
model could be used to obtain critical swim speed rather than
conventional three- or four-distance models. He suggested that
a 50-m swim could be used in a three-distance model, as long as the
longest distance in the model was at least 200 m (although preferably
at least 400 m). He also found a significant increase in
critical swim speed for sprinters following a period of aerobic
training in tandem with a reduction in their anaerobic
capability. It seems, therefore, that aerobic training will
benefit performance in the endurance-based events (200 m and
greater), but not the sprint events (50 m and 100 m).
Training
and Performance
Training practices survey. Andy Stewart presented the
results of a survey that he conducted with Will Hopkins on the
training practices of most of the top swim coaches in New
Zealand. Twenty-four coaches and almost 200 age-group
competitive swimmers completed the questionnaires, mailed out at the
end of a summer and winter season. Periodization of training and
differences in training between sprint and middle-distance were
broadly in accord with principles of specificity.
Middle-distance swimmers were prescribed higher mileage and longer
repetitions of lower intensity than sprinters. Repetition intensity
and rest duration increased as competition approached. In the taper,
repetition intensity increased while repetition volume and distance
decreased. Average session volume for sprint and middle-distance
swimmers reduced gradually from 5000 m at the beginning of the season
to around 2000 m at the end of taper, while the average intensity of
interval workouts rose steadily from around 83% of seasonal-best pace
at the start of the season to approximately 90% by the time of
competition. These effects ranged in magnitude from small to
very large.
Some training practices showed a lack of specificity. For
example, the proportion of easy swimming increased from 25% of volume
in the build-up to 35% by the end of taper. Easy and moderate
swimming together accounted for slightly more than 50% of volume.
Interval training decreased steadily from 40% of volume during the
build-up to 30% by the end of the season. And more than half of
the volume was prescribed in the front crawl stroke for those
swimmers who did not specialize in that stroke!
On the relationship between training and performance... well,
there wasn't much! Coaches preferred the long, slow,
distance method over the race-specific approach. But this
was a descriptive study--good to find out what's going on, but not to
find out what ought to be going on. For that you need to do
experiments.
Intervals, velocity, and rest. Kohji Wakayoshi
(Nara University of Education, Japan) led a group investigating
various physiological responses to different combinations of swimming
velocity and rest period during interval swimming. The
investigators used typical interval sets to determine whether there
was a threshold of fatigue during interval swimming. The test
involved nine sets of 10x100 m at three velocities, with three rest
durations. From those intervals, it was shown that swimmers
could perform the workouts without exhaustion at a pace equivalent to 105% of the mean
swim velocity obtained during a maximal-effort 20-min test, with 20-s
rests between intervals; they could also manage 110% of the mean swim
velocity with 55-s rests.
A novel approach to the estimation of 200-m freestyle performance
from 100-m freestyle bests was presented in poster form by Teruo
Nomura (Kyoto Institute of Technology, Japan). Performance data
were collected from 232 national-class swimmers at the Japanese
National Championships over a four-year period. Stroke rates,
stroke lengths, and various start, turn, and finishing split times
within the 100-m and 200-m events were also recorded. The
multiple regression equations for estimating 200-m performances were:
Males:
200 m performance = 2*100 m record + 1.707*type + 9.890
Females:
200 m performance = 2*100 m record + 1.719*type + 8.872
where performance and records are in seconds, and type = 0, 1, or
2 for swimmers specializing in both 100-m and 200-m freestyle events,
or only the 100-m, or only the 200-m respectively. The 95%
confidence intervals for estimated performances were 1.6 s for male
and 1.4 s for females. The authors speculated that swimmers
whose 200-m performance is beyond the upper confidence limit of the
predicted time should concentrate on the shorter events and/or
increase the endurance component of their training program. On
the other hand, those swimmers whose 200-m performance is below the
lower confidence limit of the predicted time
should concentrate on longer events and/or increase the
sprint component of the training program.
High intensity prevails. Albert Termin (University of
Buffalo, USA) provided further evidence of high-intensity
training favoring better performance outcomes than traditional
high-mileage programs. In his study, 22 male university
swimmers were followed for a four-year period, during which they
performed various high-intensity workouts. He compared
performance to a group of swimmers who followed the traditional
mileage program. Favorable changes in stroke rate and stroke
length were noted in the experimental group, but the most important
change was that the experimental group improved their performance
three to four times (~9% as opposed to ~2 to 3%) that of those
swimmers following traditional training methods.
Estimating Hydrodynamic Forces
Hideki Takagi introduced a new method to evaluate
hydrodynamic forces acting on the hand during swimming. Most
often the 3-D cinematographic analysis technique (Scheihauf, 1979)
has been used for estimating forces on the hand, but this method
involves the lengthy process of digitizing. Hideki developed a
new pressure-difference method that estimated the hydrodynamic force
by using the pressure difference between the palm and the back of the
hand. The hydrodynamic force was obtained by multiplying
the entire mean pressure difference by hand plane area. A key
characteristic of the new method is that it's possible to measure the
hydrodynamic force more correctly than traditional techniques by
using a total of eight waterproof micro pressure sensors.
Moreover, the new method has the advantage of immediate visual
diagnostics and continuous monitoring. It may become a useful way to
improve stroke effectiveness.
Reducing Drag During Glides
Does a swimmer's depth in the water make
a difference in glide speed?
Andrew Lyttle (University of Western
Australia, Australia) performed trials with 31 experienced
male swimmers towed in a prone position through the water using a
pulley system to determine the optimal depth for the glide and
push-off phase. Drag force acting on each swimmer was
measured in trials performed at four depths (surface, 0.2, 0.4, and
0.6 m). The drag at the surface was significantly higher than
at depth for all towing velocities (range from 1.6 m/s to 3.1
m/s). For velocities of 2.2 to 3.1 m/s, the drag at 0.2 m
underwater was significantly higher than the drag recorded at 0.4 and
0.6 m, but no significant difference was found between 0.4 and 0.6 m
underwater. Conclusion: it may be beneficial for swimmers to
perform their glides at a depth of approximately 0.4 m to gain
maximum benefit from reduction of resistance.
Flume
Swimming
Are swimming flumes as effective as pools for swimming
research? Scientists have conducted experiments in swimming
flumes assuming that there is no
hydrodynamic difference between pool and flume. Barry Wilson
(University of Otago, New Zealand) compared stroke rates in front
crawl for flume swimming and free swimming. Fourteen
experienced swimmers swam at five different speeds in the pool and
flume on each of two separate days. The mean stroke rate was
determined at each swimming speed for each condition. A
repeated measures within-subjects design was used to compare stroke
rates in the two environments at the same swimming speed. The findings: no meaningful difference in
stroke rate for flume or free swimming. However,
it is essential to have adequate familiarization sessions in the
flume prior to any experiment if you are to have confidence in your
flume data.
newseditor=AT=sportsci.org · webmaster=AT=sportsci.org · Homepage
· Copyright
©1998
Edited by Mary Ann Wallace and Ross
Sanders · Webmastered by
Jason Nugent
Last updated 17 Sept 1998