Bachelor Thesis
HALMSTAD
UNIVERSITY
Exercise Biomedicine, 180 credits
Associations between dolphin kick
performance and lower extremity muscle strength, abdominal muscle strength and foot length in active competitive swimmers
Biomedicine, 15 credits
Halmstad 2020-05-27
Jakob Sundén
Associations between dolphin kick performance and lower extremity muscle strength, abdominal muscle strength and
foot length in active competitive swimmers
Jakob Sundén
2020-05-27
Bachelor Thesis 15 credits in Biomedicin inriktning fysisk träning Halmstad University school of business, Engineering and science Thesis supervisor: Emma Haglund
Thesis examiner: Eva Strandell
Abstract
Background: Maximal muscle strength and body proportions are some of the key attributes to be a fast swimmer. Even though dolphin kick (DK) has become essential to be a fast
swimmer little is known of its associations to muscle strength and body proportions.
Moreover, the effect of feet size has been stated to be a primary contributor to dolphin kick thrust production, but scientific evidence is still scarce.
Aim: The aim of this study was to examine the correlation between lower extremity muscle strength, abdominal strength and feet length with dolphin kick performance over 15 meters in active competitive swimmers 15-20 years old
Method: Twelve Test subjects (six male and six female) participated. Test subjects performed four 15 meters dolphin kick trials. Lower extremity muscle strength was tested with a three repetition maximum strength test and abdominal strength with brutal bench test.
The muscles tested were rectus femoris, biceps femoris and rectus abdominis. Feet length was measured with a measuring tape. The correlations between lower extremity strength,
abdominal strength and feet length with dolphin kick performance were calculated with spearman’s correlation.
Results: Twelve test subjects between ages 15-20 years old participated. Spearman correlation test showed that lower extremity strength (rectus femoris: rs=-0.57 and biceps femoris: rs=-0.66) had a large association with dolphin kick performance. Abdominal strength (rs=-0.46) and feet length (rs=-0.35) had a moderate association with dolphin kick
performance.
Conclusion: The present study conclude that lower extremity strength is important for DK performance over 15 meters and that abdominal strength and feet length also is important but is less associated to it. The finding from this study can be used for making training programs for improving DK performance and for scouting swimmers with beneficial traits for specific swimming technique.
Abstrakt
Bakgrund: Maximal muskelstyrka och kroppsproportion är två av det viktigare egenskaper för att vara en snabb simmare. Delfinkick har visat sig vara en viktig faktor för att vara en snabb simmare, men lite är känt om hur muskelstyrka och kroppsproportioner påverkar dess prestationen. Foten är en av de största kraftproducenterna för delfinkick men inget
vetenskapligt bevis kunde hittas på storlekens effekt.
Syfte: syftet med denna studie var att undersöka associationerna mellan nedre extremitets styrka, abdominal styrka, fotlängd med delfinkicks prestation över 15 meter för aktivt tävlande simmare 15-20 år gamla.
Metod: Tolv testdeltagare varav sex män och sex kvinnor deltog. Test deltagarna hade fyra försök på sig att sätta en så snabb tid på 15 meter delfinkick som möjligt. Nedre extremitets muskelstyrka testades med ett tre repetitions max test (kg) och abdominal styrka med ett brutal bänktest (repetitioner). Muskler som mättes var rectus femoris, biceps femoris och rectus abdominis. Fotlängd mättes med ett måttband (cm). För att räkna ut associationerna mellan nedre extremitets styrka, abdominal styrka, fotlängd och delfinkicks prestation användes spearmans korrelation test.
Resultat: De tolv testdeltagarna var mellan åldrarna 15–20 år. Resultaten från spearmans korrelations test visade att nedre extremitets styrka (rectus femoris och biceps femoris) hade en stark association till delfinkicks prestation (rs=-0,57, rs=-0,66). Abdominal styrka och fotlängd hade båda en måttlig korrelation (rs=-0,46, rs=-0,35).
Slutats: Från dessa resultat kan man dra slutsatsen att nedre extremitets styrka är viktigt för delfinkicks prestanda över 15 meter. Abdominal styrka och fotlängd visade sig också vara viktig för att delfinkicks prestation men möjligtvis inte lika betydande som nedre extremitets styrka. Resultaten från denna studie kan användas för att göra träningsupplägg för att förbättra delfinkick och för att kunna hitta simmare med utmärkande egenskaper för undervattenkick.
Table of contents
Background ... 1
Introduction ... 1
Biomechanics of dolphin kick ... 1
Body proportions ... 2
Strength correlation with swimming ... 3
Aim ... 4
Research questions ... 4
Method ... 4
Study design ... 4
Subjects ... 4
Procedure ... 4
Measurements ... 5
DK kick performance ... 5
Lower extremity muscle strength... 5
Abdominal muscle strength ... 6
Data collection... 6
Ethical and social consideration ... 7
Statistics ... 7
Results ... 8
Discussion ... 11
Limitations ... 13
Conclusion ... 14
References ... 15
1
Background
Introduction
Dolphin kick (DK) was first performed in the 1980 Moscow olympic games where some swam a whole 25 meter under water after the start. DK is a technique used to propel the swimmer under water after starts and turns in all strokes except breaststroke (Shimojo, Sengoku, Miyoshi, Tsubakimoto, & Takagi, 2014). After a start or turn, 15 meter of underwater kick is allowed. When swimming, underwater drag (the amount of water that hinders the body) is lower than when you swim at the surface, therefore DK is very important to swim fast (Willems, Cornelis, Deurwaerder, Roelandt, & De Mist, 2014). According to Yamakawa, Shimojo, Takagi, Tsubakimoto, & Sengoku, (2017) start and turn speed is very much related to DK performance. After the introduction of DK in competitive swimming it spread quickly and has become essential to be a fast swimmer. Even though DK is widely used over the world, factors such as strength and body proportion and range of motion that determine the effectiveness of DK is still not yet fully understood. Willems et al., (2014) argue that differences in performance between swimmers depended a lot on the swimmer’s skill with DK.
Biomechanics of dolphin kick
DK is a cyclic motion using both legs to kick up and down simultaneously and is performed in a prone position with the back either facing down, up or lateral depending on the preference and stroke performed with arms above the head (Kobayashi, Takagi, Tsubakimoto, &
Sengoku, 2016). When swimming DK in a ventral position swimmer facing down, it consist of two phases; extension kick (knee extension, legs moving downward) and a flexion kick (knee flexion, legs moving upward), this is repeated to produce thrust. Most of the thrust is created by the feet because of their position at the end of the legs and by the extension kick.
DK is performed in a complex wave like whip motion using flexion and extension of hip, knee and ankle joints (Willems et al., 2014). Some of the primary muscles used when performing DK are muscles in the core like rectus abdominis, erector spinae and in lower extremity like rectus femoris, biceps femoris, gastrocnemius and tibialis anterior (Yamakawa et al., 2017).
2 With the swimmer in a prone position facing down, the toes at the up peak the highest point (compared to the pool floor) of the kick, the hips hyper extended and knees flexed slightly.
From this position the kick will begin with extension kick. The extension kick motion begins by flexing the hip joint and extending the knee joint using the lower extremity muscle rectus femoris bringing the lower legs down (Akima, Tomita, Ando., 2019 ;Atkison, Dickey, Dragunas, Noltes., 2013 & Yamakawa et al., 2017). With the knee joint fully extended and hips flexing, the movement will stop with the toes at the down peak lowest point of the kick.
Flexion kick phase starts by activation of the trunk muscle, erector spinae and lower extremity muscles, gluteus maximus, and bicep femoris, extending at the hip joint and with knee joint still extended (Yamakawa et al., 2017 & Akima, Tomita, & Ando, 2019). The kick then ends with bicep femoris flexing the knee joint to the up-peak start position, concluding the kick.
The feet will be in a plantarflexed position with the help of gastrocnemius throughout the whole motion of the kick. The internal abdominal muscles will act as a stabilizer and the external abdominal muscles, such as rectus abdominis and erector spinae, helps with the whip movement through the body either flexing to bring the legs forward or extending to bring them backward (Atkison, Dickey, Dragunas, & Noltes, 2013; Guilhem, Giroux, Couturier, &
Maffiuletti, 2014; Urquhart, Hodges, & Story, 2005 & Nakashima, 2009). The effectiveness of a swimmer’s movement is very much related to the anthropometrics of the swimmer. Taller swimmers can exert more force on the water because of the longer limbs they have. The effect of differences in force production due to differences in body proportions has been studied but not specifically its effect on DK performance (Nevill, Oxford, & Duncan., 2015).
Body proportions
The size and proportions of a swimmer are very important for performance. Greater arm length can contribute with longer lever action and consequently higher force can be produced each stroke compared with swimmers with shorter arm length, but more strength is needed.
Longer foot length has also been found to contribute positively by increasing the surface area which water can be pushed, increasing thrust produced (Nevill, Oxford, & Duncan, 2015).
Thrust produced from the feet in DK is a major contributor of forward momentum in DK (Willems et al., 2014). To maximize DK performance a balance between force generated and minimizing resistance that acts on the swimmer is the optimal way to increasing propulsion (Cohen, Cleary, & Mason, 2012). Longer lower legs were found to be a swimming detriment.
Longer lower legs may be able to create more force but because of the altered floatation and
3 increased inclination bringing the legs downward creating more resistance in the water
hurting movement efficiency (Nevill, Oxford, & Duncan, 2015). Thus, greater foot length could be considered a major factor of DK speed. Longer limb length is generally better for swimming performance, but greater strength is needed to move a longer lever (Nevill, Oxford,
& Duncan., 2015).
Strength correlation with swimming
Péraz-Olea, Valenzuela, Aponte, & Izuquierdo, (2018) have found that dryland exercises could be used to predict swimmer’s performance, develop their swimming and to evaluate the different strengths of the swimmer. According to Amaro, Morouqo, Marques, Batalha, Nieva,
& Marinho, (2018) strength and power is very important to swimmers, particularly in short distances. Swimmers and coaches have used strength training to increase performance and to prevent injury for decades. Keiner, Yaghbi, Sander, Wirth, & Hartmann, (2015) show that strength training has a positive effect on start and turn times. Maximum strength in upper and lower extremity is strongly related to swim performance which can be seen in two ways by either allowing the swimmer to increase the frequency or the length of the swim stroke. High maximum strength has shown to lengthen time to fatigue by increasing the beginning impulse of the stroke/ kick decreasing the muscle effort rest of the stroke/ kick length carrying the momentum with it. When swimming, an optimal stroke length and frequency is important to maintain for better performance. Hawley, Williams, (1991) and Smith, Norris & Hogg, (2002) both show that swimmers with higher strength could maintain stroke length and frequency for longer times than swimmers with lower strength. Aspenes, Kjendelie, Hoff, & Helgrud (2009) found that higher strength was highly associated with swimming velocity. Keiner et al., (2015) also found an especially strong correlation between one repetition maximum squat strength to short distance performance.
Several studies (Amaro et al., 2018; Keiner et al., 2015; Péraz-Olea, Valenzuela, Aponte, &
Izuquierdo, 2018; Hawley, Williams, 1991 & Smith, Norris & Hogg, 2002) have investigated swimmers’ strength and general performance in various distances and strokes but not
specifically DK. No study was found that studied the efficiency of larger feet on DK
performance. With the advantage of less drag, DK has the potential to be faster than surface strokes and when considering that in a 25-meter pool, 15 meters of DK is allowed, it becomes clear that an efficient DK is essential. The efficiency of DK is unclear in short distances and is
4 often dependent on the practitioner’s skill or physical attributes such as strength and body proportion therefore further studies of DK is needed.
Aim
The aim of this study was to examine the correlation between lower extremity muscle
strength, abdominal strength and feet length with dolphin kick performance over 15 meters in active competitive swimmers 15-20 years old.
Research questions
- How strong are the associations between lower extremity strength and dolphin kick performance time over 15 meters?
- How strong are the association between abdominal strength and dolphin kick performance time over 15 meters?
- How strong are the association between feet length and dolphin kick performance time over 15 meters?
Method
Study design
The study used a cross-sectional study design, measuring the strength of the lower extremity muscles (e.g. rectus femoris, biceps femoris) and abdominal muscle (e.g. rectus abdominis), feet length and DK performance over 15 meters.
Subjects
Test subjects consisted of 12 active competitive swimmers between the ages 15-20 years old with a time qualifying them in their district championship. To be classed as active or
competitive they had to be training at least five times a week and to compete regularly at a district level in any stroke or length. Subjects was recruited by the head coach of a swim club in the west district of Sweden. Swimmers with a time qualifying them to the district
championship was then later asked to take part in the study. Exclusion criteria were that recently injured or sick test subjects could not participate in the study.
Procedure
Before any test or data collection informed consent was given out and obtained from all test subject with risks and information of the study before testing was done. The tests were
5 performed at two sessions and the second session was held within 72 hours of the first
session. The test was done in a pool in the west Sweden district. Rectus/biceps femoris and rectus abdominis was measured at a gym which the test subjects had access to. The first test was the 15 meters DK test. Here foot size centimeter (cm), age and DK speed seconds (s) with two decimals precision was measured. Before testing, test subjects performed a moderately intense 1000-meter warmup. Test subjects was asked to have regular training swim clothes, swim goggles and a swim cap during testing. The second session consisted of a three- repetition maximum strength test (3RM) for lower extremity in kilograms (kg). Rectus abdominis was tested with brutal bench. At this session, a five minutes jog or stationary cycling was performed as warm up. The test subject was instructed to maintain their normal diet. Dry land, gym work, smoking, alcohol consumption was not allowed 48h before and during the test schedule to prevent performance losses.
Measurements
DK kick performance
Test subject performed a 15 meters maximal effort DK underwater in a ventral prone position.
The test subjects started from the pool wall pushing of under water when given a signal. They were asked to be swimming at least one meter under the water during the trials. The test subjects time was taken with a stopwatch and recorded from the point where the feet left the wall to when the feet passed the 15 meter mark to subtract the effect of the reaction time. The test subjects were given 4 attempts to set a fast as possible time. (Yamakawa et al., 2017 &
Keiner et al., 2015) The fastest time was recorded as the test subject’s result. Time was recorded with two (K5000, Freker, Helsingborg, Sweden) stopwatches. Handheld stopwatch was found to have reasonable reliability compared to electronic timekeepers. Reliability could be increased with more stopwatches (Hetzler, Stickley, Lundquist & Kimura 2008).
Lower extremity muscle strength
For the lower extremity strength test, rectus femoris and biceps femoris were tested. Rectus femoris was tested with a leg extension machine (SZ06, Free motion, Colorado Spring, USA).
Before testing the leg extension machine was set up so that the test subjects knees were at the edge of the seat and the ankles were just below the foot pad. The test subject was asked to sit with their back against the backrest and to firmly grasp the handles. To perform one
repetition, the test subject was instructed to extend their legs fully and then bring back the leg to starting position (Julio, Panissa, & Franchini, 2012).
6 Biceps femoris was tested with a leg curl machine. The test subject was asked to lie down facing down, on the leg curl machine (F814, Free motion, Colorado Springs, USA), with the padded lever placed right at the achilles tendon. The knees were placed at the edge of the bench and the test subjects were instructed to have a firm grasp of the handles for stability. To perform a repetition, the test subject kept the hips down to the bench, while flexing the knees to bring the padded lever towards the gluteus, and then lowered the padded lever to the starting position (Julio, Panissa, & Franchini, 2012).
To reach 3RM test subjects first performed 5-10 repetitions on a moderately easy weight then increased the weight by 10-20% to perform a set of 5 repetitions. From here the weight was increased 20-30% to then increase progressively 10-20% at each successful attempt until 3RM is reached. If the test subject was unsuccessful with the current weight 5-10% of the weight was taken off. The subject was given five attempts with 3-5 minutes of rest between trials to achieve maximum load. Test subjects chose the pace at which they performed the exercise. This test protocol was found to be highly reliable and valid for testing maximal strength (McCurdy, Langford, Cline, Doscher & Hoff, 2004).
Abdominal muscle strength
Abdominal strength was tested with the “brutal bench” (EI3001404-010, Eleiko, Halmstad Sweden). Test Subjects started by hanging with the back against the back rest, feet stuck to the bench, hands at the sides of the ears holding a band around the back of the head. To perform one repetition, the test subject lifted the upper body towards the legs so that the elbows touched the patella, then the test subject lowered the body back to starting position touching the scapula against the backrest. Test subjects was asked to do as many as possible till failure and to complete the next repetition within three seconds from the previous one (Sveriges Olympiska Kommitté, 2016a). During this study, no validity or reliability reference was found, but the test is used for testing Swedish athletes´ physical ability (Sveriges
Olympiska Kommitté, 2016b).
Data collection
Data that was collected from the subjects was age, rectus/biceps femoris strength, abdominal strength, feet length and DK time. Feet length was measured with measuring tape with one decimals precision and DK time was taken with a stopwatch by two test leaders and the mean of the two was the time recorded. This data was collected from a swimming pool in western Sweden. Rectus/biceps femoris and rectus abdominis strength was measured at a gym which
7 the test subjects had access to. Rectus femoris strength was measured with a knee extension machine and biceps femoris with a leg curl machine, this was measured in kilograms. Rectus abdominis strength was tested with the brutal bench test and the number of repetitions was counted and recorded.
All data collected was handled with confidentiality and stored in a digital document only accessible to test leader. To get access to the data test subjects could send a message to the test leader to gain access to their results. All names were coded to FP1,2,3 etc. All collected data will be stored on a USB stick for 10 years after testing in a safe locker at Halmstad University.
Ethical and social consideration
This study followed the rules and guidelines of the declaration of Helsinki 2013 (World Medical Association, 2018) and CODEX (CODEX, 2020). Before testing informed consent was given out and collected from participants. All recorded data was stored in a digital document. This document was coded, and access was only granted to the test leader. All results were presented at a group level so no individual could be identified. All test subjects had the right to at any time withdraw from the study, all data from the withdrawn test subject was deleted.
There was some risk of injury because of the maximal effort performed. Test subjects were given information on the risks that may occur during testing such as muscle tears and stress on joint and ligaments. To avoid injury test leader thoroughly explained the test and how to perform them. One important factor was that no injured or sick test subjects were tested. Test subjects was asked of their physical state the last week. If they were found to be either sick or injured participants was then excluded from the tests.
The findings of this study could improve coaches and swimmers understanding of how muscle strength and body proportion affect DK performance. With the increased
understanding of how muscles contribute to DK coaches could use these results to improve training programs for increased DK performance. The findings could also help with scouting swimmers with beneficial traits for DK.
Statistics
Data was tested for normality with Shapiro-Wilks test, one variable was found to be
significantly different to a normality curve. Hence non- parametric test was used to analyse the data with Spearman correlation (rs) and data are presented as median (min- max).
8 Correlation threshold values was set to small (0.1), moderate (0.3), large (0.5), very large (0.7), and nearly perfect correlations (0.9) as shown in table 1 (Yamakawa et al., 2017). The data was analyzed using Spss 25 (IBM SPSS Statistics version 25, IBM corp., Armonk, New York, USA) and excel (Excel version 12730.20270, Microsoft Corporation, Washington, USA) on Windows 10.
Table 1. Correlation threshold
___________________________________
Correlation thresholds rs No correlation 0<0.1
Small correlation 0.1<0.3 Moderate correlation 0.3<0.5 Large correlation 0.5<0.7 Very large correlation 0.7<0.9 Nearly perfect correlation 0.9<1.0 (Yamakawa et al., 2017)
Results
Twelve test subjects between the ages of 15- 20 years participated in the study. Six were male and six were females. The median (min-max) of the DK performance test was 10.08 s (7.34- 12.13 s). For the lower extremity muscles rectus femoris, strength was tested with leg
extension the median was 89 kg (75-130 kg) and for biceps femoris, tested with leg curls, the median was 56 kg (41-93 kg). The abdominal muscle strength tested with brutal bench test, resulted in a median of 16 repetitions (5-25 repetitions). The feet length was 24 cm (23–31.50 cm) (table 2).
9 Table 2. Test results from leg extension, leg curl, brutal bench and feet length tests.
presented as min, max, median (n=12).
Min Max Median
Leg extension (kg) 75 130 89
Leg curl (kg) 41 93 56
Brutal bench (reps) 5 25 16
Feet length (cm) 23.00 31.50 24.40 DK-performance (s) 7.34 12.13 10.08
Leg extension (rectus femoris strength) & leg curl (biceps femoris strength) (kg) measuring lower extremity strength, Brutal bench repetitions performed measuring abdominal muscle strength, Feet length (cm) and DK- performance (seconds)
The lower extremity muscle strength for rectus femoris had a large association to DK performance (rs= -0.57) and a determining coefficient (r²) of 0.32 which means 32% of DK performance could be explained by biceps femoris strength or vice versa (table 3 and figure 1). The negative value means that lower DK performance times is associate to higher strength values. Lower extremity muscle strength of biceps femoris also had a large association (rs= - 0.66, r²= 0.44) to DK performance (Table 3 and figure 2). Abdominal strength had a moderate correlation (rs= -0.46, r²= 0.21) to DK performance (table 3 and figure 3). Feet length also had a moderate association (rs= -0.35, r²= 0.12) to DK performance (table 3 and figure 4).
Table 3. Spearman’s correlation results between DK- performance and lower extremity strength of rectus femoris (leg extension) and biceps femoris (leg curl), Abdominal strength of rectus abdominis (brutal bench) and feet length (n=12)
p- value rs- value r²-value Leg extension 0.66 -0.57 0.32 Leg curl 0.02 -0.66 0.44 Brutal bench 0.13 -0.46 0.21 Feet length 0.27 -0.35 0.12
10 Figure 1. Correlation between 3 RM leg extension and DK performance
(rs= -0.57, r²= 0.32)
Figure 2. Correlation between 3 RM leg curl and DK performance (rs= -0.66, r²= 0.44)
Figure 3. Correlation between brutal bench performance (number of repetitions) and DK performance (rs= -0.46, r²= 0.21)
6 7 8 9 10 11 12 13
60 70 80 90 100 110 120 130 140
Dolphinkick performance (s)
Leg extension performance (kg)
Lower extremity strength in rectus femoris
6 7 8 9 10 11 12 13
40 50 60 70 80 90 100
Dolphinkick performance (s)
Leg curl performance (kg)
Lower extremity strength in biceps femoris
6 7 8 9 10 11 12 13
0 5 10 15 20 25 30
Dolphinkick performance (s)
Brutal bench performance (repetitions)
Abdominal strength in rectus abdominis
11 Figure 4. Correlation between feet length and DK performance (rs= -0.35,
r²= 0.12)
Discussion
This study attempted to study the association of lower extremity strength, abdominal strength and feet length to DK performance over 15 meters. This study shows that muscle strength in the lower extremity (bicep femoris & rectus femoris), abdominal strength (rectus abdominis) and feet length all had a moderate to large negative association to DK performance. Meaning that higher lower extremity strength, abdominal strength and longer feet length all correlated to shorter DK performance times over 15 meters. This indicate that biceps femoris and rectus femoris strength, abdominal strength and feet length all are important for DK performance.
This was expected but the interesting result was how large the correlations were to DK performance.
Results from previous studies on DK has shown some conflicting data on what phase is the most important. Cohen, Cleary, & Mason (2012) & Loebbecke, Mittal, Mark, & Hahn (2009) found that the extension kick provided most of the thrust produced by the DK and could be seen as the more important phase compared to the flexion kick but concluded that at high speeds flexion kick also is an important phase to DK. According to Higgs, Pease, & Sanders (2016) the flexion kick phase is the most important to develop and especially to increase flexion kick velocity. Atkison, Dickey, Dragunas, & Noltes (2013) found that faster DK swimmers tends to have a faster flexion kick and spend less time with knees flexed reducing resistance in the water which is a similar conclusion to that of Higgs, Pease, & Sanders (2016). Having a stronger biceps femoris may be a contributing factor to a faster flexion kick though it could also be that more skilled DK swimmers utilize the flexion kick better with an
6 7 8 9 10 11 12 13
20 22 24 26 28 30 32 34
Dolphinkick performance (s)
Feet length (cm)
Feet length
12 improved technique. The reduction in time spent in the flexion kick phase might be a result of a faster deceleration of the knee flexion a result caused by a stronger antagonist to the
movement rectus femoris or a combination of both. Considering these studies show that rectus femoris and bicep femoris muscle strength could be considered as important to DK
performance by increasing velocity, power production and deceleration of the flexion kick spending less time in the phase. The key to dolphin kick may perhaps lie in the development of a better flexion kick especially for less skilled swimmers making strength gains in biceps femoris more important for them (Atkison, Dickey, Dragunas, & Noltes, 2013; Keiner, Rähse, Wirth, Hartmann, Fries, & Haff, 2018 & Smilios, Sotiropoulos, Christou, Douda, Spaias, &
Tokmakidis, 2013). West, Daniel, Owen, Nick, Cunningham, Dan, Cook, Christian, Kilduff
& Liam. (2011) found a large association between sprint speed over 15 meters, one repetition maximum squat strength (r= 0.62) and peak power (r=0.79). Their results are in line to the results of this study where rectus femoris (rs= -0.57) and bicep femoris (rs= -0.66) muscle strength association with DK over 15 meters and shows the importance of lower extremity strength in short distances. From the results of the current study and previous studies it is shown that rectus femoris and biceps femoris muscle strength are equally important to DK- performance over 15 meters because for their part in extension and flexion kick. More strength of these two muscles could not only increase thrust production of both phases but decrease time spent in the flexion kick phase making it possible to begin the extension kick faster. Coaches who train swimmers for better DK should therefore aim to increase lower extremity strength equally, but less skilled DK swimmers should maybe focus on
strengthening the biceps femoris muscle to increase flexion kick performance.
Keiner et al., (2015) tested the association between one repetition max sit up strength to sprint speeds over 100 meters. They found that a moderate correlation to performance in 15 meter Freestyle (r= -0.51), 50 meter breaststroke (r= -0.39) and backstroke (r= -0.31) to one repetition max sit up strength. These results mirror the results of the moderate association of brutal bench to DK- performance over 15 meters (rs= -0.46) that this study has. Even though two of them is measured over 50m and none of them are DK they do show the importance of abdominal strength in short distance sprinting. With its double use of both as an agonist for the extension kick the most thrust producing phase (Cohen, Cleary, & Mason, 2012 &
Loebbecke, Mittal, Mark, & Hahn, 2009) and as a stabilizer (Urquhart, Hodges, & Story, 2005) it could be considered one of the more important muscle in the movement. So, based on these facts’ stronger rectus abdominis could increase extension kick performance and help
13 stabilize the DK better. Further research on core musculature such as back and internal core muscles impact on DK performance would help clarify its importance of these muscles and their effect on DK.
Studies that investigated foot length and its effect on swimming found that longer feet were positive for swimming. Nevill, Oxford, & Duncan (2015) & Sammoud, Negra, Chaabene, Bouguezzi, Attia, Granacher, Younes, & Nevill, (2020) investigated the association between greater foot length to 100m free style speed (r= 0.337, r=0.264) and found that it was an significant contributor to increased performance which are similar to our result (rs= -0.35).
Their results especially mention that a longer foot to shorter lower leg ratio is positive not just because of the bigger force that the swimmer could generate from the foot but of the less drag a shorter lower leg caused. But Sammoud, Nevill, Negra, Bougezzi, Helmi, & Hachana, (2018) found that longer leg length was a positive variable for backstroke speed. Having a longer foot can thus be stated to be positive for kick performance but leg length might have a stroke specific effect in swimming making it of interest to study for DK in the future.
Limitations
Twelve test subjects participated though more were interested but could not participate due to the covid- 19 outbreak that limited non- essential social activities. The test subjects consisted of swimmers with a time qualifying them to their district championship, but there was a difference between the test subject’s performance level. Some competing at a national level and having a better DK technique compared to some making the group less homogeneous.
This could be seen as selection bias, but test leader was not actively selecting swimmers to increase skewness and the gap between test subject’s performance was not great. But this could make the results less trustworthy and enhance the results making them look better than what they really are. Having older swimmers with a more developed DK technique and a faster time for exclusion, would help to homogenize the group, but because of the scarcity of these swimmers it would be hard to find a moderate sized test group. Some of the test subject were not as familiar with strength training and the machines used in the study, which may have decreased their performance. Body weight was not taken from the test subjects which was a mistake in hindsight. Better descriptive, such as weight and length of the swimmers, would make it easier to compare results with other studies and could be used to calculate values to describe the test subjects. The methods used for evaluation of rectus femoris and biceps femoris is both valid and reliable (McCurdy, Langford, Cline, Doscher & Hoff., 2004
& Julio, Panissa, Franchini, 2012) but DK performance and abdominal strength test were both
14 lacking of validity and reliability. Handheld stopwatches was found to have some reliability in a trained user of them but does not have the precision of electronic timekeepers which would make this study more reliable (Hetzler, Stickley, Lundquist, & Kimura, 2008) To better the DK performance test cameras or some kind of gate system could have been used to increase the reliability of the time gathered. The DK performance test was based on (Shimojo et al., 2014 & Yamakawa et al., 2017) and a variant of this test was used to fit the resources present.
In search of a way to measure the abdominal muscle strength, a lack of tests was found. Most abdominal tests, that was found during this study, only tested the endurance of the abdominal muscles by either testing them isometrically or with easily repeated movements. The brutal bench test was therefore used because it is a testing tool for Swedish sports developed by the Swedish olympic committee (Sveriges Olympiska Kommitté. 2016b). Stopwatch and brutal bench were used because it was the best methods that could be performed from the resources present. These two methods were also still well standardized and described (Sveriges
Olympiska Kommitté. 2016a; Hetzler, Stickley, Lundquist, & Kimura, 2008; Yamakawa et al., 2017 & Keiner et al., 2015). A study to find a new way of measuring abdominal strength in a reliable and valid way is needed. Keiner et al., (2015) used an ab bench to test one repetition maximum abdominal strength which could have been a better alternative to the brutal bench. To give a more complete picture of the importance of the different associated factors to DK performance more muscles such as erector spinae, gluteus maximus,
gastrocnemius and anthropometrics such as leg length, torso length and body length could have been measured and a regression analysis could have been used to tell which factor effect DK performance the most.
Conclusion
This study investigated the correlations between the lower extremities, abdominal strength, feet length and DK performance. The present study conclude that lower extremity strength had a large association to DK performance over 15 meters and can be stated to be important for DK. Abdominal strength and feet length both had a moderate association to DK
performance over 15 meters and although important may have less of an effect on DK. The finding from this study could be used for making training programs for improving DK performance by focusing on the development of the lower extremity muscles strength and abdominal muscle strength. The results could also be used for scouting swimmers with
beneficial traits for DK like strong lower extremity muscles, abdominal muscles and long feet.
15
References
Akima, H., Tomita, A., & Ando, R. (2019). Effect of knee joint angle on the neuromuscular activation of the quadriceps femoris during repetitive fatiguing contractions. Journal of Electromyography abd Kinesiology, 49. Doi:10.1016/j.jelekin.2019.102356
Amaro, N.M., Morouqo, P.G., Marques, M.C., Batalha, N., Nieva, H., & Marinho, D.A.
(2019). A systematic review on dry-land strength and conditioning training on swimming performance. Science & Sport, 34(1), 1-14. Doi: 10.1016/j.scispo.2018.07.003
Aspenes, S., Kjendlie, P. L., Hoff, J., & Helgerud, J. (2009). Combined strength and endurance training in competitive swimmers. Journal of sports science & medicine, 8(3), 357–365.
Atkison, R. R., Dickey, J. P., Dragunas, A., & Nolte, V. (2013). Importance of sagittal kick symmetry for underwater dolphin kick performance. Human Movement Science, 33, 289–311.
Doi: doi.org/10.1016/j.humov.2013.08.013
CODEX. (2020). Regler och riktlinjer för forskning. Retrieved 2020-05-29 from http://www.codex.vr.se/forskningmanniska.shtml
Cohen, R.C., Cleary, P.W., & Mason, B.R. (2012). Simulations of dolphin kick swimming using smoothed particle hydrodynamics. Human Movement Science, 31(3), 604-619. Doi:
https://doi.org/10.1016/j.humov.2011.06.008
Guilhem, G., Giroux, C., Couturier, A., & Maffiuletti, N. A. (2014). Validity of trunk extensor and flexor torque measurements using isokinetic dynamometry. Journal of Electromyography and Kinesiology, 24(6), 986- 993. Doi: /10.1016/j.jelekin.2014.07.006
16 Hawley, J. A., & Williams, M. M. (1991). Relationship between upper body anaerobic power and freestyle swimming performance. International journal of sports medicine, 12(1), 1-5.
Doi:10.1055/s-2007-1024645
Hetzler, R. K., Stickley, C. D., Lundquist, K. M., & Kimura, I. F. (2008). Reliability and Accuracy of Handheld Stopwatches Compared With Electronic Timing in Measuring Sprint Performance. Journal of Strength & Conditioning Research, 22(6), 1969-1976.
Doi:10.1519/JSC.0b013e318185f36c
Higgs, J. A., Pease, L. D., & Sanders, H. R. (2016). Relationships between kinematics and undulatory underwater swimming performance. Journal of sports sciences, 35(10), 995-1003.
Doi: 10.1080/02640414.2016.1208836
Julio, U.F., Panissa, V.L.G., & Franchini, E. (2012). prediction of one repetition maximum from the maximum number of repetitions with submaximal loads in recreationally strength- trained men. Science & sport, 27(6), 69-76. Doi: 10.1016/j.scispo.2012.07.003
Keiner, M., Rähse, H., Wirth, K., Hartmann, H., Fries, K., & Haff, G. G. (2018). Influence of Maximal Strength on In-Water and Dry-Land Performance in Young Water Polo Player.
Journal of Strength and Conditioning Research, 34(6). Doi: 10.1519/JSC.0000000000002610
Keiner, M., Yaghbi, D., Sander, A., Wirth, K., & Hartmann, H. (2015). The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performance in adolescent swimmers. Science & Sports, 30(6), 147-154. Doi:
10.1016/j.scispo.2015.05.001
Kobayashi, K., Takagi, H., Tsubakimoto, S., & Sengoku, Y. (2016). Actication of trunk, thigh and lower leg muscles during underwater dolphin kick in skilled female swimmers.
Conference on biomechanics in sports, Tsukuba, Japan July 18-22
17 Loebbecke, A., Mittal, R., Mark, R., & Hahn, J. (2009). A computational method for analysis of underwater dolphin kick hydrodynamics in human swimming, Sports
Biomechanics, 8(1), 60-77. Doi: 10.1080/14763140802629982
McCurdy. K., Langford. G. A., Cline. A. L., Doscher. M., & Hoff. R. (2004). The reliability of 1-and 3RM Test of Unilateral Strength in trained and untrained men and women. Journal of sport science & Medicine, 3(3), 190-196. PMC: 3905302
Nakashima, M. (2009). Simulation Analysis of the Effect of Trunk Undulation on Swimming Performance in Underwater Dolphin Kick of Human*. Journal of biomechanical Science and Engineering, 4(1), 94-104. Doi: 10/1299/jbse.4.94
Nevil, M. A., Oxford, S. W., & Duncan, M. J. (2015). Optimal Body Size and Limb Length Ratios Associated with 100-m Personal-Best Swim Speeds. Medicine & science in sports & exercise, 47(8), 1714-1718. Doi: 10.1249/MSS.0000000000000586
Pérez-Olea, J. I., Valenzuela, P. L., Aponte, C., & Izuquierdo, M. (2018).
Relationship Between Dryland Strength and Swimming Performance: Pull-Up Mechanics as a Predictor of Swimming Speed. Journal of strength and conditioning research, 32(6), 1637- 1642. Doi: 10.1519/JSC.0000000000002037
Sammoud, S., Negra, Y., Chaabene, H., Bouguezzi, R., Attia, A., Granacher, U., Younes, H.,
& Nevill, A. M. (2020). Key Anthropometric Variables Associated With Front-Crawl Swimming Performance in Youth Swimmers: An Allometric Approach, Journal of strength and conditioning research, 34(6) Doi: 10.1519/JSC.0000000000003491
Sammoud, S., Nevill, A.M., Negra, Y., Bougezzi, R., Helmi, C., & Hachana, Y. (2018). Key somatic variables in young backstroke swimmers. Journal of Sports Sciences, 37(10), 1162- 1167. Doi: /10.1080/02640414.2018.1546547
18 Shimojo, H., Sengoku, Y., Miyoshi, T., Tsubakimoto, S., & Takagi, H. (2014). Effect of imposing changes in kick frequency on kinematics during undulatory underwater swimming at maximal effort in male swimmers. Human Movement Science, 38, 94-105.
Doi:10.1016/j.humov.2014.09.001
Smith, D.J., Norris, S.R., & Hogg, J.M. (2002). Performance Evaluation of Swimmers. Sports Medicine, 32, 539–554. Doi: 10.2165/00007256-200232090-00001
Smilios, I., Sotiropoulos, K., Christou, M., Douda, H., Spaias, A., & Tokmakidis, S. (2013).
Maximum Power Training Load Determination and Its Effects on Load-Power Relationship, Maximum Strength, and Vertical Jump Performance. Journal of Strength & Conditioning Research, 27(5), 1223-1233. Doi: 10.1519/JSC.0b013e3182654a1c
Sveriges Olympiska Kommitté. (2016a) Fysprofilen. Collected 2019-12-01 from
http://fysprofilen.se/sv/Utmanardokument/Testbeskrivningar_Fysprofilen_Utmanare%201312 16.pdf
Sveriges Olympiska Kommitté. (2016b) Fysprofilen. Collected 2020-05-29 from http://www.fysprofilen.se/sv/default.aspx?PageID=1074
Urquhart, D. M., Hodges, P. W., & Story, I. H. (2005). Postural activity of the abdominal muscles varies between regions of these muscles and between body positions. Gait & Posture, 22(4), 295- 301. Doi: 10.1016/j.gaitpost.2004.09.012
West, D. J., Owen, N. J., Cunningham, D. J., Cook, C. J., & Kilduff, L. P. (2011). Strength and Power Predictors of Swimming Starts in International Sprint Swimmers. Journal of Strength & Conditioning Research, 25(4), 950-955. Doi: 10.1519/JSC.0b013e3181c8656f
19 Willems, T. M., Cornelis, J. A.M., Deurwaerder, L. E.P. De., Roelandt, F., & De Mist, S.
(2014). The effect of ankle muscle strength and flexibility on dolphin kick performance in competitive swimmers. Human Movement Science, 36, 167-176. Doi:
10.1016/j.humov.2014.05.004
World Medical Association. (2018). WMA- Decleration of Helsinki – Ethical Principles for Medical Research Involving Human Subjects. Retrieved 2020-05-29 from
https://www.wma.net/policies-post/wma-declaration-of-helsinki-ethical-principles-for- medical-research-involving-human-subjects/
Yamakawa, K. K., Shimojo. H., Takagi, H., Tsubakimoto. S., & Sengoku, Y. (2017). Effect of increased kick frequency on propelling efficiency and muscular co.activation during underwater dolphin kick. Human Movement Science, 54, 276-286. Doi:
10.1016/j.humov.2017.06.002
(Appendix 1)
Information till forskningsperson för studien
Vi vill tillfråga dig om du vill delta i denna studie. Detta dokument innehåller information till dig som testperson om studien ” Correlation between underwater dolphinkick and lower limb, abdominal muscular strength and foot length in active competetiv swimmers ” och samtyckes formulär.
Vad är det för projekt och varför vill ni att jag ska delta?
Delfinkick är viktigt för en tävlande simmare vid start och vändning. Kicken är till för att simmaren ska kunna behålla farten från start och vändning och eftersom delfinkicken sker under vattenytan kommer simmaren uppleva mindre motstånd än vid ytan. Detta gör att delfinkick är otroligt effektivt och har potential at vara snabbare än det andra fyra simsätten.
Delfinkick utförs antingen på mage eller rygg med händerna över huvudet, båda benen
sparkandes upp och ner. Mestadels av farten från delfinkicken kommer från nedåt sparken och fötterna. Styrketräning bland simmare har blivit väldig prevalent för att med väldigt små marginaler mellan toppsimmare måste simmaren få ut allt från sina lopp från start, vändning till målgång. Det är välkänt att sim prestation är beroende på muskelstyrka och power. Styrka i övre, undre extremiteter har visat på samband mellan simmarens styrka och sim-prestation speciellt starka samband mellan undre extremiteters styrka och till sim-prestation.
Syfte
Denna studie har som mål att undersöka korrelationen mellan ben, bål styrka, fot längd och 15 meter delfinkick prestation undervattnet på aktivt tävlande simmare 16-30 år.
Hur går studien till?
Datainsamlingen kommer utföras vid två tillfällen, vid det första tillfället kommer vi att mäta 15 meter delfinkick tid (sekunder). Här kommer vi också samla in fot storlek och ålder. Innan mätning av 15 m delfinkick kommer simmare utföra en måttligt intensiv 1000 meter
uppvärmning. Detta testtillfälle beräknas ta 1 timma. Det andra tillfället kommer vi testa simmarnas ben styrka med ett test som mäter den maximala vikten man kan ha när man utför 3 repetitioner på sittande knäextension och knäflexion. För att testa bålen kommer vi göra ett
brutal bänktest. Innan start av sessionen kommer testpersonerna göra en 5 minuter joggning på rullband eller cykling på en stationär cykel. Det andra tillfället beräknas ta 1,5 timmar och kommer att hållas inom 72 timmar efter den första testtillfället.
Vi kommer också utföra ett brutal bänktest där testperson kommer vara hängandes med ryggen mot bänken, fötterna fast i ställningen, händerna ska vara vid öronen hållandes ett band bakom huvudet. Här ska de utföra så många repetitioner som möjligt.
Risker
Det finns en viss risk för skador tack vare den maximala insats du ska utföra. För att undvika skador som kan åstadkommas av dessa tester kommer testledare grundligt gå igenom testen och ha koll på den som utför testet. Det är också viktigt att inte har några tidigare skador eller sjukdomar som kan förvärras eller orsaka problem under testet. Det kan finnas viss obehag med användning av test instrument och utförandet av maximala test. För att undvika att du kommer skadad eller sjuk kommer vi fråga ut dig innan test om ditt hälsotillstånd den senaste veckan.
Fördelar
Det kommer möjligt få en bättre förståelse om sin delfinkick och hur man tränar den bäst samt hur mycket fotlängd påverkar sin delfinkick. Det kan också få en bättre förståelse av 3-RM test och sin egen styrka i ben och bål. Svagheter hos personen kan framkomma av dessa test och vad man bör träna på för att få en bättre delfinkick.
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personuppgifter kommer att behandlas av ansvariga för studien enligt gällande lagstiftning.
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Du kan få del av dina resultat direkt efter testtillfälle eller genom att begära det skickat till dig av Forskningsledare. Du kommer även kunna se dem i kostnadsfritt i studien ”Correlation
between underwater dolphin-kick and lower limb, abdominal muscular strength and foot length in active competitiv swimmers”.
Deltagandet är frivilligt
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Om du vill avbryta ditt deltagande ska du kontakta den ansvariga för studien.
Ansvariga för studien
Den ansvarige för studien Jakob Sundén, Nyhemsgatan 24, 0701455590, Jaksun17.student@hh.se & Emma.haglund@hh.se
Samtycke till att delta i studien
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Jag har fått muntlig och skriftlig informationen om studien och har haft möjlighet att ställa frågor. Jag får behålla den skriftliga informationen.
☐ Jag samtycker till att delta i studien Correlation between underwater dolphin-kick and lower limb, abdominal muscular strength and foot length in active competitiv swimmers.
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Jakob Sundén
