Biomechanics and Medicine in Swimming XI

BiomechanicsandmedicineinswimmingXi
was i) to emphasize the importance of effective breathing and breath
control (in any stroke), and ii) to quantify the burden of added resistance
when swimming breaststroke with the head continually above the surface,
considered in a survival context.
Lastly the point must be made that survival is often a matter of
efficiency of movement (or good technique). It has nothing to do with
swimming fast, although efficient movement is also faster. At any given
velocity, the more efficient the movements, the less energy they will require.
The less energy required per unit time or distance, the longer one
will be able to continue in any necessary pursuit of survival whether it be
to swim or to remain in the same place. This is a point sadly overlooked
by many swimming instructors, who often express the idea that good
technique is only important for the competitive swimmer. Most aquatic
experts (e.g. Cureton, 1943, The USA Navy, 1944, Lanoe, 1963, Wilke,
2007, Stallman, 2008 ) consider breathing in an optimal way, the most
important aspect of efficient technique.
Methods
While quantifying energy expenditure under the two conditions named
above was the primary goal of the study, it was recognized that several
factors might influence it. Factors considered possible confounders
were: skill level, buoyancy, endurance, drag characteristics and motivation.
From 40 volunteers, 20 were selected (12male, 8 female) to give a
broad, representative sample with relation to buoyancy and ankle drag.
This would reduce any bias because of these two factors. The subjects
were university physical education students, average age 26.1 (range
19.5-35.0).
Buoyancy was determined by hydrostatic weighing as described by
Katch et al. (1967). As function was of greatest interest, weight at both
full inspiration and full expiration was recorded uncorrected for trapped
air spaces and residual volume. Body density as determined by Brozek et
al. (1963) was calculated but not included in the study. The term functional
buoyancy (Stallman, 1971) is used for the uncorrected values.
Ankle drag was measured as described by Cureton (1943). The subject
adopted a stretched prone position, arms forward and together, with full
inspiration. A Salter spring scale registered the weight of the ankles resting
on a horizontal rod just below the surface, heels under water. Skill
level was defined by a composite of two values: the number of strokes
required to swim 25m (as few as possible) and the fastest time possible
for 25m. Twenty five meters was chosen to minimize the influence of
endurance and to maximize the influence of technical skill. All trials
were repeated 3 times and the best performance was used in the analysis.
Energy cost was measured by classical Douglas Bag respirometry
while swimming in a flume. The sub-maximal velocity of 0.5 m·s -1 was
used for all subjects. If this velocity resulted in unusually high levels of
plasma lactate, the subject was eliminated. Given that these were physical
education students, few were eliminated for this reason. The subjects
swam approximately 10 min. unhindered to reach a steady state. They
then immediately entered the flume where they swam for approximately
3 min. with gas collection during the last min. This same operation was
repeated twice for each subject. Half of the group was randomly selected
to swim first with the head up while the other half swam first with normal
breathing. A blood sample to determine plasma lactate levels (La)
was taken after each trial.
Lastly, the ability to swim for a longer period of time (simulating a
survival situation) was measured by swimming to exhaustion. It was hypothesized
that when swimming with the head up, the swimming time
to exhaustion would be shorter. Each subject swam to exhaustion on
two different occasions. Again, half randomly with head up first and half
with normal breathing first. The subject swam easily first for 5 min. Then
five min. at 0.5 m·s -1 . If the subject was able to continue, the velocity was
increased by 10% and they swam for an additional two min. If after these
two min. the subject was still swimming, the velocity was again increased
by 10%. They swam in military trousers and shirts.
380
results
When swimming with the face constantly above the surface, the oxygen
uptake (VO 2 ) expressed in ml/meter was significantly higher than with
normal breathing (p=