Presented at the 2012 Spin Summit, October 1-3rd, 2012 , Vancouver, Canada. For further information

please contact Mads Hansen at mbh84hotmail.com or Dr. J. Barden at john.barden@uregina.ca.

Determination of Peak Body Acceleration using a Body-Fixed Sensor in

Competitive Front Crawl Swimming

Mads B. Hansen and John M. Barden

Neuromechanical Research Centre, Faculty of Kinesiology and Health Studies

University of Regina, Regina, Saskatchewan, Canada

Methods

Procedures

• Participants were instructed to swim 25 meters as fast as possible.

• In order to look at stroke phases with a minimum of interference, the participants

were instructed not to breathe during the 25 meter sprint.

Data Collection

• Tri-axial accelerometers were placed on the left wrist and lower back, at the 3rd

lumbar vertebrae (L3) of the swimmer.

• Accelerometers sampled the data at 60 Hz.

• The participants were also video recorded using an underwater camera (Kodak

PlaySport Zx5) that recorded at 60 Hz.

• The accelerometer data was smoothed with a low-pass digital filter (3 Hz cutoff).

Data alignment

• In order to align the data, subjects were instructed to jump on land, thereby creating

a point of reference for both the accelerometers and the video.

References

Methods (Cont.)

Stroke phase identification

• After synchronizing the data, stroke phase events in the wrist accelerometer data

were identified using video.

• The following stroke phases were determined, by aligning peak data points with the

recorded video:

• Entry – when the hand enters the water.

• Down sweep – when the hand sweeps down and in to the catch

position.

• Pull phase – when the hand and forearm move from the catch, until the

forearm is vertical and aligned with the shoulder.

• Push phase – the hand and forearm move from a vertical to a

horizontal position in preparation to exit the water.

• Recovery – the arm is moved over the water until the hand re-enters

the water.

• The effect on the forward acceleration of the hip/trunk was determined for each

phase.

Results (Cont.)

Discussion & Conclusions

• The change in hand orientation from horizontal to vertical, causes gravity to change from

the z-axis to the y-axis of the accelerometer.

• The swimmer was kicking as well as arm stroking, which will have an effect on the

positive and negative forward accelerations of the hip. Studies are ongoing that will

attempt to quantify the contribution of the kick to the forward acceleration of trunk/hip.

• The intent of this research is to provide coaches with the opportunity to identify specific

deficiencies in the various stroke phases/patterns of individual swimmers.

In competitive swimming, improving stroke technique makes it possible to gain an

advantage on an opponent. Stroke analysis is often based on subjective criteria, due to lack

of data regarding propulsion. By using waterproof accelerometers, sport scientists can

measure accelerations of the hand and wrist and analyze the impact these accelerations have

on the forward motion of the body.

Previous studies show that the duration and acceleration of the different phases of the

freestyle stroke cycle can be determined using accelerometers attached to the swimmers

wrists (Oghi et al., 2003). The accelerations of the body in a forward direction have also

been analyzed using waist mounted accelerometers (Davey et al., 2008). Other studies have

used both wrist and back mounted accelerometers (Bachlin & Troster, 2011), but none have

determined the effect that the different phases of the arm stroke cycle have on the forward

propulsion of the body.

Introduction

1. Bächlin, M., & Tröster, G. (2011). Swimming performance and technique evaluation with

wearable acceleration sensors. Pervasive and Mobile Computing. doi:10.1016/j.pmcj,

2011.05.003

2. Davey, N., Anderson, M., & James, D. A. (2008). Validation trial of an accelerometer-

based sensor platform for swimming. Sports Technology, 1(4–5), 202–207.

3. Ohgi, Y., Ichikawa, H., Homma, M., & Miyaji, C. (2003). Stroke phase discrimination in

breaststroke swimming using a tri-axial acceleration sensor device. Sports Engineering,

6, 113–123.

Figure 2: Lower back (L3) accelerometer axis orientation. The position of this accelerometer

represents the forward motion of the swimmer’s centre of mass (COM).

Figure 3: The graph shows two full stroke cycles of freestyle. Data is from the accelerometers placed on the

left hand and at L3 showing motion of the trunk/hip. Black vertical lines ilustrate peaks used for stroke phase

identification..

Results are shown for a representative participant.

• The pull and push phases of the stroke cycle cause the greatest positive (i.e., forward )

acceleration of the hip/trunk.

• The downsweep, from the point at which the hand enters the water until the catch, is

the longest single phase of the stroke.

• As the left hands enters the water, the right hand is stroking and causing positive

forward acceleration of the hip.

• Peak accelerations in each of the three axes, can be used to determine specific stroke

phases.

Results

Figure 1: Left hand accelerometer axis description.

X +

Y +

Z +

Y +

Acknowledgement: The authors would like to thank GENEActiv for their

assistance in making this study possible by supplying accelerometers and

software. Without their product, this study could not have been conducted.

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