Biomechanics and Medicine in Swimming XI

Performance Level Differences in Swimming:
Relative Contributions of Strength and Technique
havriluk, r.
Swimming Technology Research, Tallahassee, USA
The purpose of this study was to compare the relative contributions of
strength (measured by force, F) and technique (measured by the active
drag coefficient, Cd) to swimming performance. Male (n = 40) and female
(n = 40) swimmers were tested with Aquanex+Video swimming
four trials (one of each stroke) over a 20 m course. Underwater video,
hand force data, and swim time were collected over the last 10 m. The
magnitude of the difference between faster and slower swimmers in
both F and Cd was calculated as an effect size (ES). The mean ES for the
Cd was almost double the ES for F, indicating that the advantage faster
swimmers have over slower swimmers is derived more from technique
than strength. Coaches can use this information to implement the most
appropriate interventions for continued improvement.
Key words: strength, technique, hand force, active drag coefficient,
biomechanics
IntroductIon
The drag equation explains swimming performance as: v ≈ √(F/C d ),
where v is swimming velocity, F is force, and C d is the active drag coefficient.
Consistent with this equation, previous research found that v increases
with √F (Havriluk, 2004), and that faster swimmers have a lower
C d than slower swimmers (Havriluk, 2003). Other testing protocols (e.g.
Takagi et al., 1983; Toussaint et al., 1988; White & Stager, 2004) also
reported significant relationships of F and C d with v.
The importance of both strength (as measured by F) and technique
(as measured by C d ) to swimming performance (as measured by
v) is well established both theoretically and empirically. The relative contributions
of F and C d to performance, however, have not been determined.
The purpose of this study was to determine how faster swimmers
perform better than slower swimmers due to the relative contributions
of strength (F) and technique (C d ), so that coaches can implement the
most appropriate interventions for continued improvement.
Method
Swimmers from 21 teams volunteered to participate in the study. Male
(n = 40) and female (n = 40) swimmers were tested with Aquanex+Video,
swimming four trials (one of each stroke) over a 20 m course. The standard
Aquanex testing protocol as described in previous research (e.g.
Havriluk, 2003, 2004, 2006b) was used (see Figure 1).
Informed consent was obtained. Descriptive statistics for the male
swimmers include: age in yrs (M = 18.0, SD = 1.3), height in cm (M =
180, SD = 7.7), mass in kg (M = 74.2, SD = 8.5) and for the females:
age in yrs (M = 17.7, SD = 1.0), height in cm (M = 168, SD = 6.0), mass
in kg (M = 62.1, SD = 6.5). Underwater video, hand force data, and
swim time were collected over the last 10 m of each trial. The C d was
calculated as: C d = F/(.5ρXv 2 ), where F is the average normal hand force,
r is the mass density of water, X is the cross-sectional area of the body,
and v is swimming velocity. Previous research found an almost perfect
correlation between normal and propulsive force (r = .98) with a minor
overestimation (6 N) of propulsive force (Havriluk, 2006b).
chaPter5.education,adviceandBiofeedBack
Figure 1. Captured screen of an Aquanex+Video image of swimmer T09
at .53 sec in the second stroke of butterfly. The vertical lines on the force
curves are synchronized with the video image.
results
Regression analyses found significant (p