Josh neely

An investigation into the differences in stroke parameters through statistical and movement analysis

Josh Neely

Falmouth Marine School

Marine Sport Science

Year 2

Abstract The aims to discover the differences in stroke parameters, speed and body posture between the Impact vest and the Buoyancy aid through movement and statistical analysis and provide a recommendation to water users about which one is better for swimming in. the method was to swim 20 meters in both the buoyancy aid and impact vest. The times of the swims were recorded and they were videoed as a source for movement analysis and collecting other data. The data collected was then analysed through calculations and statistical analysis in the form of a paired t-test.

The results showed that there was no significant difference in stroke rate, distance per stroke, swimming speed and time taken to swim 20 meters. The movement analysis showed that the body posture and technique different when in the different PFD’s with the impact vest having a more horizontal position in the water than the buoyancy aid Key words: impact vest, buoyancy aid, stroke rate, personal flotation device INTRODUCTION

While participating in water sports of any kind safety is one of the main considerations that must be observed and wearing a Personal Flotation Device (PFD) can significantly increase chances of survival. ‘In 2009, the U.S. Coast Guard received reports for 4,730 boating incidents; 3,358 boaters were reported injured, and 736 died. Among those who drowned, 9 out of 10 were not wearing life jackets’ (U.S. Coast Guard, 2009). Personal flotation devices are defined as ‘any device designed to keep a person afloat in the water’. (Sayour, 2011). ‘A variety of buoyancy aids have therefore been constructed to support the body in water and to maintain the body afloat without difficulty’ (Dowdeswell, 1988). These devices are

majorly important in keeping us safe when partaking in water sports. However, the ways in which they affect our ability to swim are questionable This experiment aims to discover the differences in stroke parameters between two of these devices the Impact vest and the Buoyancy aid through movement and statistical analysis and provide a recommendation to water users about which one is better for swimming in. The stroke parameters being measured are stroke rate (SR), distance per stroke (DPS) and speed. The impact vest ‘is designed with tough materials including multiple heavy-duty straps/buckles and with a longer design that will sit down to your waist covering and protecting your vital organs.’ (Personal Watercraft Partnership, anon). The buoyancy aid however is of a more bulky design and is designed mainly for floatation rather than impact protection. This must mean that there will be a difference in how they affect the way we swim.

The buoyancy provided by the PFD’s in the torso area may affect the swimmers body posture. Having a horizontal body position is extremely important when trying to swim, as it minimizes drag and makes the body more streamline. When swimming with a bad posture it can cause people to swim ‘slower than they are capable or work MUCH harder to swim at the same speed.’ (Michael Collins, anon) H0: There will be no significant difference in stroke parameters between the two PFD’s H1: There will be a significant difference in stroke parameters between the two PFD’s

Methods and materials

Location: Falmouth Water Sports Centre Date: 21st March 2012 Time: 9:00am Temperature: Air: 9-10째C Water: 10.2째C Cloud cover: 66% Wind strength and direction: Easterly 9 mph The experiment was designed to test stroke rate over a 20 meters in a straight line front crawl swim. The subjects are 4 asymptomatic college students aged 20 to 26 years of age. They were selected from a class of students at Falmouth marine school. The equipment will be collected and brought to the Falmouth Water Sports centre for the experiment. A distance of 20 meters between the pontoon and harbour wall will be measured with a 15 metre (m) Ronson tape measure. For validity, this will be done by 2 assistants chosen from the participants. The subject will put on a 5mm wetsuit and Naish Impact vest. The subject will then enter the water at a temperature of 10.2 degrees centigrade. Once in the water the subject will prepare themselves to swim and from a resting position and without pushing off the wall the subject the will swim the distance of 20 metres in a straight line as fast as possible

using the front crawl stroke. The subjects will then give the impact vest to the next person and the process will be repeated for each participant. Whilst the subject is swimming the 2 assistants will be positioned at the midpoint of the course on the slipway. One of the assistants will use a Sony handy cam to film the subject whilst swimming to provide a source for data collection(stroke rate.) The camera will follow the swimmer by moving round on a pivot controlled by the assistant. Each swim will be filmed and timed separately. The other assistant will time each swim from start to finish with a Casio stopwatch and record the results in the table provided. Once all the impact vest swims have been completed the first subject will put on the Gill buoyancy aid. The swims will then be repeated with the same process and distance as done with the impact vest. the data collected will be formatted into tables and different results will be calculated.

These results will then be statistically tested using the Paired T test.

Results Participant A B C D Mean

Impact Vest 26.18 22.39 22.39 25.00 23.99

Buoyancy Aid 27.62 22.63 23.70 25.44 24.85

Table 1: showing time in seconds of each swim and means

This table shows the times of each of the swims done in both the impact vest and the buoyancy aid. The mean times show that the buoyancy aid is 0.86 seconds slower than the impact vest. A paired t-test was performed on the two means. The paired t test show that the mean time of the impact vest and is not significantly different from the mean time of the buoyancy aid at the 0.05 significance level Participant A B C D Mean

Impact Vest 0.764 0.893 0.893 0.8 0.838

Buoyancy Aid 0.724 0.884 0.844 0.786 0.809

Table 2: showing speed in metres per second (m/s) of each swim and means

This table shows the speed in m/s for all the swims in both PFD’s and the mean speeds show that the Impact vest is quicker than the Buoyancy aid at a speed of 0.838 m/s. A paired t-test was performed on the two means. The paired t test shows that the mean time of the impact vest and is not significantly different from the mean time of the buoyancy aid at the 0.05 significance level Participant A B C D Mean

Impact Vest 47.12042 48 50.420 57.508 50.455

Buoyancy Aid 45.685 51.136 53.097 50.847 50.847 -1

Table 3: showing strokes per minute (strokes.min ) and means

This table shows stroke rate in stroke.min-1 and the means show that when wearing the impact vest the swimmer uses less strokes.min-1 (50.455) than when wearing the

buoyancy aid (50.847). A paired t-test was performed on the two means. The paired t test shows that the mean time of the impact vest and is not significantly different from the mean time of the buoyancy aid at the 0.05 significance level Participant A B C D Mean

Impact Vest 0.191 0.19 0.178 0.156 0.18

Buoyancy Aid 0.197 0.176 0.169 0.165 1.177

Table 4: showing distance per stroke in meters per stroke (mps)

This table shows the distance each stroke (when one arm enters the water and does a full 360 degrees until it enters the water again) takes the swimmer in meres. It shows that there is a higher mean DPS for the impact vest than the buoyancy aid. A paired t-test was performed on the two means. The paired t test shows that the mean DPS of the impact vest and is not significantly different from the mean DPS of the buoyancy aid at the 0.05 significance level Discussion and movement analysis In order to reach the aim of discovering which PFD is the better to swim in, movement analysis of the body posture and stroke movement must be done

Figure 1: impact vest mid stroke

Figure 2: buoyancy aid mid stroke

Body posture As can be seen in the figures 1 and 2, the postural angle when wearing the impact vest is at a more horizontal angle to the water when compared with the buoyancy aid which is at a more vertical angle. Body position ‘affects the whole stroke’ (British Swimming Association, anon) when swimming so it is very important to get it right.

When swimming with a bad posture it can cause people to swim ‘slower than they are capable or work MUCH harder to swim at the same speed.’ (Michael Collins, anon). A more horizontal swimming posture will make swimming easier. Huijing et al 1988 found a high degree of correlation between body cross section and active drag which means that the greater the angle of the body to the water surface the more drag created

As the body posture when wearing the impact vest is more horizontal to the water surface it would suggest that it would be faster to swim in and use less effort. This can be seen in the results as the mean time for the swims done in the impact vest is lower than the mean time for the buoyancy aid. There is also a slightly lower mean stroke rate when wearing the impact vest at 50.455 stroke.min-1 showing that fewer strokes are used than the buoyancy aid which has a mean of 50.847 stroke.min-1.

The difference in body posture could be explained by the difference in the aesthetics of the jackets. The buoyancy aid is much more bulky and provides more buoyancy whereas the impact vest is much more compact and provides a little less buoyancy.

This means that the buoyancy aid will be pushing the torso of the body up upwards with more force than the impact vest causing a noticeable difference in posture

Stroke movement ‘During front crawl the continuous alternating arm action provides the majority of the power and propulsion of the entire swimming stroke.’ (www.swim-teach.com, 2012).

This makes it a very important part of the stroke. In figures 1 and 2 measurements of the distance from the wrist to the water have been taken (measurements to picture scale). The impact vest measured at a size of 0.9 cm and the buoyancy aid measured at a scale size of 1.1 cm. From this it can be seen that there is a difference of 0.2cm between the 2 devices. This could be due to the amount of buoyancy in the vests. As the buoyancy aid provides more flotation it lifts the torso further out of the water causing the clavicle, scapula and the humerus to be higher thus creating a gap > 0.9cm. The body posture will also add to this as a more upright position will cause the top half of the torso to be further out of the water. The impact vest has less buoyancy than the buoyancy aid therefore the torso is lower in the water causing there to be less distance between the Glenohurmeral joint (shoulder joint) and the water

Figure 3: impact vest end of stroke

Figure 4: buoyancy aid end of stroke

In figures 3 and 4 the angle of the arm to the water and the flexion of the arm have been observed. In figure 3 wearing the impact vest, the arm enters the water at a

much more downward angle than in figure 4.the arm is also fully extended meaning that there will be a greater DPS which can be seen in the results as the mean DPS for the impact vest is 1.863mps and 1.938mps. This shows that the impact vest provides a wider range of movement causing the arm to move freely and in a more natural movement. In figure 4 the angle of the arm is more upward and there is flexion at the elbow joint. This shows that there is less range of movement in the buoyancy aid and it causes a less natural stroke. This is due to the extra buoyancy that is provided, changing the posture of the body and affecting the stroke movement. The flexion at the elbow means that the stroke length will be decreased thus causing the DPS to be reduced. This means that more effort will have to be used to travel a distance than if the full stroke length was used Time and speed The results show that the impact vest has a mean time of 23.99 secs and the buoyancy aid has a mean time of 24.85 secs. This impact vest has a faster mean time than the buoyancy aid meaning that it is quicker through the water. This is shown in the mean speeds of the impact vest at 1.20mps and the buoyancy aid had a mean speed of 1.24mps. These differences were shown not to be significantly different. However the small differences that there may due to the fact that the buoyancy aid is considerably more bulky than the impact vest which is very small and compact in comparison. The bulkiness of the buoyancy aid means that there will be more drag created in the water. This lack of laminar flow means that the buoyancy aid will be slower through the water and need more effort to propel the user through the water. This is also because of the bad posture that it puts the user in whilst swimming with the legs lower in the water

Stroke rate (SR) The mean stroke rate for the buoyancy aid is 50.45 stroke.min-1 showing that fewer strokes are used than the buoyancy aid which has a mean SR of 50.85 stroke.min-1.

The paired t-test showed that these results were not significantly different there are still small differences. These differences show that when wearing the buoyancy aid strokes are taken within a minute than the impact vest. ‘This increase in SR will be detrimental to the stroke length’ (Dekerle J, 2005) which will affect DPS. These results suggest that a person wearing the buoyancy aid is likely to use more energy to push themselves through the water.

Distance per Stroke (DPS) The mean DPS for the impact vest is 0.180mps and the mean DPS for the buoyancy aid is 0.177mps. Distance per stroke is a good measure of how well a person is swimming. Craig et al found that on average the better swimmer distinguishes themselves from the poorer by distance per stroke rather than stroke frequency. The paired t-test showed that there was no significant difference between the two PFD’s. the small differences however show that with one stroke a person wearing the impact vest will travel slightly further than a person wearing a buoyancy aid. This is due to a number of factors that have been mentioned previously such as body posture, range of movement and drag that is created Evaluation of experiment If doing the experiment again things that would be done differently would be to use more participants and do more swims in each PFD. This would provide a larger amount of data to statistically analyse. This would mean that there would be more

likely hood of finding a difference between the two different PFDs. The timing of the experiment would also be changed to when the tide is high as there was very little water for the experiment to take part in. using buoys instead of harbour walls as markers for the start and finish would be better as it would reduce the factor of subjects pushing of the wall. The location could be changed to a swimming pool to reduce variables further and provide more accurate results.

Conclusion To conclude this report there is no significant difference in stroke parameters speed or time. This means that there is not enough evidence to reject the H 0. The movement analysis however showed differences in body posture and explained the small differences that did occur. The recommendation that come out of this is that for swimming short distances either PFD will work, but if you’re looking for more protection rather than buoyancy for sports such as windsurfing for example go for an impact vest as it protects your vital organs. If more buoyancy is what you need for sports like kayaking for example then buoyancy aid is the correct choice

References 1. British

Swimming

Association.

(anon).

Swimming

Strokes.

Available:

http://www.sportcentric.com/vsite/vfile/page/fileurl/0,11040,4716-160290177506-79387-0-file,00.pdf. Last accessed 24 Mar 2011.

2. Craig et al. (1985). Velocity, stroke rate and distance perstroke in elite swimming competition. Med Sci Sports. 17, 625-34 3. Dekerle j et al. (2005). Stroking parametres in front crawl swimming and maximal lactate steady speed. Int j Sports Med. 26 (53), 8 4. Georg Thieme ET al . (2006). 2006; 27(11): . International Journal Sports Medicine. 27 (11), 894-899.

5. George Sayour. (2011). PFD: Personal Flotation Device.

Available:

http://paddling.about.com/od/paddlingdefinitions/g/PFD.htm. Last accessed 7th Dec 2011.

6. Keskinen KL et al. (1988). The stroking characteristics in four different exercises in freestyle swimming. Biomechanics XI-B. 1 (1), 839-43 7. M. Toussaint et al. (1982). Effect of a triathlon wetsuit on drag during swimming. Medicine and Science in Sport and exercise. 21 (3), 3.

8. Micheal

Collins.

(anon).

Swimming

Posture.

Available:

http://www.alexandriamasters.com/articles/posture.htm. Last accessed 24 Mar 2012 9. Newsome, P.. (2009). Breathing technique in the freestyle stroke. Available: http://www.swimsmooth.com/breathing.html. Last accessed 09/12/2011

10. Per-Ludvik Kjendlie. (2008). Drag characteristics of competitive swimming children and adults. Journal of Applied Biomechanics. 24 (1), 35-42 11. Personal Watercraft Partnership. (anon). Safety and personal kit for your PWC. Available: http://www.pwpulse.co.uk/page4.htm. Last accessed 24th Mar 2011.

12. Pinnington, H. C et al. (1987). Cardiorespiratory responses of water polo players performing the head-in-the-water and the head-out-of-the-water front crawl swimming technique. Australian Journal of Science and Medicine in Sport (AJSMS). 19 (1), 1-19.

13. Richard Dowdeswell. (1990). Non Inflatable buoyancy aid. . (1), .

14. Swim-Teach.com.

(2011).

How

to

Swim

Front

Crawl.

Available:

http://www.swim-teach.com/front-crawl.html. Last accessed 24 Mar 2012.

15. U.S. Coast Guard, Department of Homeland Security (US). Recreational Boating Statistics – 2009 [online]. [cited 2011 Apr 11]. Available from http://www.uscgboating.org/assets/1/workflow_staging/Publications/394.PDF. . Last accessed 24 Mar 2012 16. www.swim-teach.com. (anon). How to Swim Front Crawl: Arm Technique.

Available:

http://www.swim-teach.com/front-crawl-arm-action.html.

Last

accessed 24 Mar 2012 authors notes used: The Journal of Sports Science and Medical Fitness: Instruction to

authors.

Available

fitness/notice-to-authors.php

at

http://www.minervamedica.it/en/journals/sports-med-physical-