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Lecture 4

Kinesiology 2241A/B Lecture Notes - Lecture 4: Front Crawl, Parasitic Drag, Butterfly Stroke

Course Code
Kinesiology 2241A/B
Thomas Richard Jenkyn

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Kin 2241b Introductory Biomechanics Keenan Vanderkooi
Lab 4 250866706
The purpose of this lab is to analyze different swimming strokes and techniques to see the effects
that drag and lift has on the swimmer. These swim strokes include the head-up and head-down front crawl, as
well as underwater and above water dolphin kick. In hydrodynamics compared to aerodynamics, water is
much heavier than air, meaning the swimmer does not have to be moving fast for these forces to take effect.
By orienting the body in different positions, the swimmer can increase or decrease the drag forces acting
upon them, therefore affecting their time, perceived effort, and stroke length.
Swim Stroke
Distance (m)
Time (seconds)
# Of Strokes
Head-Up Front Crawl
Head-Down Front Crawl
2. A) The average stroke frequency (strokes per time) for the head-up front crawl was 28 strokes/18.6
seconds, or 1.5 strokes per second. The average stroke length (strokes per distance) of the swimmer for the
head-up front crawl was 28 strokes/25m, or 1.12 strokes per meter.
B) The average stroke frequency (strokes per time) for the head-down front crawl was 24 strokes/16.3
seconds, or 1.47 strokes per second. The average stroke length (strokes per distance) of the swimmer for the
head-down front crawl was 24 strokes/25m, or 0.96 strokes per meter.
3. During the head-down front crawl, the time, stroke frequency, and perceived effort was less. This is
because you are enhancing the overall streamline of your body, minimizing profile drag and allowing water to
flow past you faster and closer to the body. This cannot be said for the head-up front crawl, as the technique
does not allow you to be optimally streamlined. Therefore, profile drag is increased and the water will not get
back together directly behind youcreating a low-pressure area that sucks you backwards. Having the head
up caused stroke lengths to be shorter, as the subject uses more strokes to swim the same distance. This is
because they had to waste some of their energy expenditure keeping their head up, making their perceived
effort higher as the low-pressure area behind them becomes larger. Some elements of wave drag may exist
when the head is kept up as well, as it wastes some energy by creating a small amount of waves. Keeping the
head-down makes the area presented to the oncoming flow smaller, therefore making profile drag smaller.
Keeping the head down was a much more efficient method for the subjecttheir stroke length became longer
as profile drag was reduced by the body being more streamlined, and their strokes became more efficient as
there was less of a low pressure area pulling them backwards.
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