Freestyle Swimming (Front-Crawl)
In international competition, swimming races are held in each of the competitive strokes including freestyle (usually front crawl), backstroke, breaststroke, and butterfly. Freestyle is the most economical of the strokes, followed by backstroke, butterfly, and breaststroke (Barbosa et al., 2006). Competitions are held either in short-course pools (25 m) or long-course pools (50 m). During the short-course season of international competition, race distances of 50, 100, and 200 m are held for each of the four stroke styles. In addition, freestyle events of 400, 800, and 1,500 m are also swum (Pyne and Sharp, 2014). Because of the different distances in competitive swimming, the swimmers can be classified as sprinters or distancers, which usually requires different type of physical qualities (Stager and Coyle, 2005). In our thesis, the main stroke of our research will be focused on freestyle (Front-crawl) and during a sprint distance of 50m (Sprinter swimmers). Freestyle is the most common swimming stroke used, particularly at elite level. Performance is controlled by the stroke technique, physiology, and anthropometry. Together they determine how the swimmer interacts with the fluid in order to generate both propulsion and drag (Cohen, 2015). The contribution of the arms to total propulsion during freestyle has been reported to exceed 85% of the total thrust in studies by (Bucher, 1975) and (Hollander et al., 1988). The legs were shown using swimming trials with and without leg kicking to contribute only about 10% to maximal freestyle speed (Deschodt et al., 1999).
Achieving high performance in swimming requires the specific development of different qualities that will characterize the swimmer. Performance, thus, becomes the product of the whole human being biologically functioning, but also the cognitive, attentional, motor, energetic and functional processes. Since 2006, a new trend in swimming research emerged called the “Interdisciplinary assessment”(Barbosa et al., 2010 ; Vilas-Boas et al., 2010). It is based on the “holistic approach” and “the deterministic model.” It is defined as the interplay of several scientific and the deeper understanding of the variables that determine swimming and how they interplay to enhance performance (Figure 1) (Barbosa, 2013).
Elite swimmers have been shown to be tall, have a long trunk and arms, broad-shouldered and have more muscle mass in the upper body and trunk compared to other athletes (Reilly et al., 2005
; Reis et al., 2012). This increase in length and upper body dominance is due to the majority of propulsive forces in swimming being generated by the upper body with the legs being essentially used to maintain body position in the water (Seifert et al., 2010 ; Barbosaa et al., 2013).
Several studies have investigated the impact of morphological characteristics on the hydrodynamic resistance (Chatard et al., 1990 ; Benjanuvatra N, 2001), undulating movements (Connaboy et al., 2009; Arellano and al., 2002), energy cost, swimming economy(Chatard et al., 1990 ; Kjendlie et al., 2004) and swimming technique (Naemi, 2010). These studies have confirmed that morphological characteristics have a big impact in swimming quality and may vary from each individual. According to Charles (2009), world records were broken in sprint events because of the swimmer’s morphology getting bigger.
Dufour (1988), reported in a study about gender that the time difference was more related to gender dimorphism than to swimming technique. The study concluded that the difference in performance is mainly due to the differences in size between both sexes, rather than a different swimming quality.
Freestyle swimming can be divided into propulsive- and recovery phase. Propulsive phase is when the hand enters the water above the head and goes backward against the hips and upward toward the surface of the water (Fig.1). The upper body muscles used in the beginning and the end of the propulsive phase are primarily latissimus dorsi, pectoralis major and biceps brachii (Fig.2) (Mcleod, 2010). During the main propulsive phases, termed the pull and push, the hand moves in an underwater “s” shape. This is usually considered to be an effective way to maximize the amount of still water the hand comes into contact with and therefore maximize the propulsion (Counsilman, 1968).
Swimmers partake in both endurance and resistance training concurrently and utilize all three energy systems, therefore exhibit a full range of fiber types. Motor units are recruited in a ramp-like fashion, and the energy demands of the length of the event determine which fiber types are preferentially recruited (Feiereisen et al., 1997).
In swimming, elite sprinters are characterized by a high proportion of type II fibers, while distance athletes have a high distribution of type I fibers. Muscles can contain a combination of the fiber types, which is desirable in middle-distance swimming (Stager and & Tanner, 2005). Sprint events utilize all three fiber types (Troup, 1999), Intramuscular adenosine triphosphate (ATP), phosphocreatine (PCr), and glycogen stores are the main fuel sources during high-intensity exercise (Bergstrom, 1972). Type IIb fibers are preferentially recruited due to the explosive forces required in sprint events. Type IIb fibers produce high forces in short times, but they are fatigue sensitive (Burke, 1981), which will limit performance during sprint swimming.
According to Zamparo (1996), swimming efficiency is influenced by the length of the body segments. He added that children, with a short distance between the centre of gravity and the buoyancy centre comparing to adults, performed slower. Chatard also showed that length (1985), mass (1985) and body surface (1990) affected the energy costs.
According to Ben-Zaken (2017), efforts to identify significant genes that promote athletic excellence are difficult, mainly because each possible gene makes only a small contribution to the overall heritability. Nevertheles, they showed that IGF 1245Y and MSTN 153R genes were more present among long-distance swimmers than sprinters. Previously, the same team (Ben Zaken, 2015) found no significant differences in the presence of the ACTN3 R577X gene between long-distance and short-distance swimmers
In another hand, Anthero-Jacquemin J (2013) reported a strong link between familiar genes and performance. A study by Costa et al. (2009) highlighted that the angiotensin converting enzyme (ACE) D allele seems to be overrepresented among elite athletes, who compete in power oriented events (Nazarov I et al., 2001), and the I allele among elite endurance athletes (Collins, 2004). Furthermore, Woods (2001) reported an excess frequency of the D allele overall among competitive swimmers,, with no significant variation in I allele frequency by event distance (>400m and < 400m). Nazarov I et al. (2001) stratified swimmers in three event groups with different durations (<1min, 1-20min, >20min) not by regular trial distance, and found an excess of the D allele in short distance swimmers (P = 0.042) and of the I allele in middle distance swimmers (P = 0.042).
Athletes with a favourable genetic profile and interacting in a suited environment are more likely to reach the very high level, but there are several conditions which reduces predictability. Our difficulty to understand this complexity makes genetics of performance a difficult variable to use (Roth, 2012).
Psychology & social variables
Motivation is another important variable that differentiates young athletes. It seems that a good sport and education system, providing opportunities for all and the autonomy to choose your own path at the right time, remains the best way to improve performance and join the high level sphere (Gonçalves et al., 2011)
The importance of good sprint performance is evident in team competitions in swimming, as not only are there many points scored from multiple short individual events, but sprinters contribute vitally important relay points. These individuals appear to be able to sprint for 20-30 s (swim the 50 or 100 m) and fatigue at distances less than 100 m. Aquatic sprint events rely heavily on energy provision mainly from muscle stores of high-energy phosphates (adenosine triphosphate, adenosine diphosphate, creatine phosphate). There is evidence that the capacity, power, and recovery of this energy system can be modified with appropriate training (Hirvonen, 1987) and diet (Greenhaff and K., 1993). Consequently, training using repeated supramaximal efforts is often used in an attempt to create adaptations of this energy system as a means to enhance muscle’s ability to reach peak velocities as quickly as possible and maintain race speeds for the duration of the event (Pyne and Sharp, 2014).
Arm span (from finger tip to finger tip with the arms perpendicular to the body) is generally equal to body height. In talented sprinters, arm span tends to be 6-10% greater than height. Hand size is important, as is foot size. Surprisingly, the best sprinters are also shown to be the best kickers, and maximal kick velocity correlates with sprint swim time very highly (Stager, 2005). However, this does not mean that these specific traits are absolute requirements for outstanding sprint performance, as there are always successful individuals who might be seen as exceptions to these generalities. In these cases, it may be the intangible factors that contribute the most to outstanding performance.
Swimmer Level (Elite/Sub-elite)
Elite-level athletes have been well characterized compared with sub-elite adolescents. According to several studies, Elite competitors have larger anaerobic capacities and smaller rates of adjustment (larger use of the anaerobic system) during high-intensity exercise as compared to their sub-elite counterparts (Medbo, 1990 ; Troup, 1991). For example, the world-class swimmer has a larger anaerobic ability and will derive more energy from anaerobic sources to meet the energy demands of the exercise; thus, the rate of change of his or her oxygen kinetic curve will be relatively flat. On the other hand, the national caliber swimmer will not be able to rely on his or her anaerobic energy stores for very long (because they are relatively small), and the slope of his or her oxygen kinetic curve will be relatively steep.
From 12 years on, top‐elite swimmers progressively outperformed swimmers of similar age, and there is a wide variety in the age at which male and female top‐elite swimmers start to perform at high‐competitive, sub‐elite, elite and top‐elite level (Post, 2020). This progressive trend not only characterizes the differences between performance groups, but also the variety within the top‐elite
performance group (Post, 2020).
Factors determining swimming performance
The dynamics of performance in professional sport requires a systematic improvement of the training process. Researchers are constantly trying to find and classify factors which determine the highest precision in performance. Competitive swimming is one of the popular sports to be researched extensively. The aquatic environment presents specific challenges for humans. Hence, the huge research has given special emphasis for a multifactorial process that involves several scientific domains, such as the anthropometric (Geladas et al., 2005 ; Latt et al., 2010), hydrodynamics (Kjendlie and Stallman, 2008), Biomechanics (Jurimae et al., 2007 ; Barbosa et al., 2010) and physiological/ energetics (Poujade et al., 2002 ; Greco et al., 2007 ; Barbosa et al., 2008) as the major determinants in enhancing swimming performance. But since 2006, the trend in swimming research is the “Interdisciplinary assessment” (Barbosa et al., 2010 ; Vilas-Boas, 2010). This “Interdisciplinary assessment” is based on the “holistic approach.” This can be defined as the interplay of several scientific domains and how those variables determine a given outcome (for the case, the swimming performance).Thus, a performance indicator is a selection, or combination of variables that aim to define some (or all) aspects of a performance (Hughes and Bartlett, 2008)
Swimming as an individual discipline requires special predisposition of an athlete. One of them is the body shape and composition. Nowadays, sport at the highest level makes higher demands on athletes.
In competitive swimming especially sprint front crawl, athleticism characterized by high rates of strength as well as slenderness and a long swimmer’s body is well recognized (Christensen and Smith, 1987 ; Chatard et al., 1990 ; Latt et al., 2010 ; Morouco et al., 2011).
Anthropometric assessment included on a regular basis the measurement of lengths (e.g., height, arm span, limbs’ lengths, segments diameters, etc.), areas (e.g., body surface area, hand’s area, feet area), volumes and masses (e.g., body mass body volume, lean mass, fat mass)(Barbosaa et al., 2013).
The influence of anthropometric properties such as lean body mass (LBM), total length or length of body parts (BL) are considered as essential for achievements in age-group swimmers (Taylor, 2003). These properties in mature swimmers become indispensable factors and are the basis in top-level racing in front crawl (Chollet, 1990). Swimmers specializing in sprint have higher both body mass (BM) and LBM as well as more favorable BL qualities than swimmers with endurance predispositions (Grimston Sk and Hay, 1985 ; Chatard et al., 1990 ; Jurimae et al., 2007 ; Strzala and Tyka, 2009). For example, Geladas et al. (2005), found that total upper extremity length, leg power and handgrip strength could be used as predictors of 100 m front crawl performance in 12-14-year-old boys.
Additionally, the arm span (AS) is also considered a major performance determinant. It is known that swimmers should have a high AS. Practitioners suggest that a ratio of 1/1.03 should exist between the height and the AS (i.e. AS should be ~3% higher than the height). It is also correlated with stroke mechanics, namely the stroke length (SL) and stroke index (SI) (Jurimae et al., 2007). Certain anthropometric characteristics must be taken into consideration in analyzing sprint swimming performance, including body height (BH), AS and LBM (Jurimae et al., 2007). Zampagni et al. (2008) studied the effects of anthropometrical parameters: body weight, BH, lengths of the arm and forearm, circumferences of the arm and forearm muscles on swimming performance. They found that in a short distance of 50 m the important parameters were: age, the handgrip strength and BH.
The best anatomical landmark to use as reference point to perform a race analysis is the head/vertex, the hip or the centre of mass (CM) (Arellano, 2000 ; Jesus et al., 2011). Hip is mainly used during race analysis or training session (Barbosaa et al., 2013). The CM is mainly selected during training session or control and evaluation session (Figueiredo et al., 2009). Swimming is a locomotion technique characterized by the movement of the limbs, trunk and head. So, the location of the CM within a stroke cycle might not be at a fixed position. On the other hand, both the head/vertex and the hip have fixed locations, no matter the segment’s range of motion. However, some studies reported the presence of a moderate-large bias assessing a fixed-point kinematics (Barbosa et al., 2003 ; Figueiredo et al., 2009 ; Psycharakis and Sanders, 2009). There is 0.1 s (i.e. ~10%) time-delay (Barbosa et al., 2003), a 7% and 3% bias, for forward velocity and displacement (Fernandes et al., 2012) in the hip’s vs CM’s assessment, respectively.
These somatic attributes are largely inherited and determine swimming technique to a high degree.
Biomechanics / Hydrodynamics
A performance indicator is a selection, or combination of variables that aim to define some (or all) aspects of a performance (Hughes and Bartlett, 2008). Performance in competitive swimming is dependent on the generation of propulsive forces by upper and lower limbs. Thus, biomechanics looks at the fine details of sports techniques based on mechanics and anatomy (Hughes and Bartlett, 2008). Previous work in biomechanics has tended to break into two sections, focusing on Kinematic and Kinetic factors of the stroke (Toussaint and Truijens, 2005 ; Barbosa et al., 2011)
The goal of competitive swimming is to travel the event distance at the maximal velocity (Vs.) since the performance is assessed by the time spent to cover that same distance (Wakayoshi et al., 1996): Vs. = SL x SF (1)
Where Vs represent the mean swimming velocity, SL the stroke length, and SF the stroke frequency. The three kinematical variables from equation (1) are considered for most biomechanical assessments of swimming techniques. Besides these, there are a couple of other variables computed on a regular basis to estimate the swimming efficiency based on the Vs, SL and/or SF, such as the stroke index (SI) (Costill et al., 1985 ; Fritzdorf et al., 2009): SI = Vs. x SL (2)
It is considered that a swimmer that can achieve a given velocity with a higher SL instead of SF will be more efficient. And the propelling efficiency (ƞp) (Zamparo et al., 2005): ƞp = [( 2 0.9 ) 2] x 100 (3)
Where Vs represent the swimming velocity, SF the stroke frequency, and “l” the arm’s length.
Body velocity depends from SF and SL as reported in equation (1).
SL and SF have been the focus of much research due to their importance in producing maximal speed (Toussaint et al., 2006). SF and SL are independent of each other (Hay 1993) and depend on the partial duration and distance covered within each stroke cycle. As SL increases, swimmers will tend to find they need longer to complete the stroke, leading to a decrease in SR (Hay, 1993 ; Sanders, 2002).
Many studies have highlighted the importance of SL in improving swimming performance (Smith et al., 2002 ; Girold et al., 2006 ; Figueiredo et al., 2011) and therefore maintaining mechanical propulsive efficiency throughout the race. SF has been determined as a key factor in 50m performance compared with other swimming distances (Girold et al., 2007), and has also been shown to influence Vs. Increases or decreases in Vs are due to a combined increase or decrease in SF and SL (Toussaint et al., 2006). Swimmers also can have « highly individual » combinations of SL and SF (Toussaint et al., 2006) further pointing towards the need for coaches to coach the individual rather than focus on changes or improvement program for groups of swimmers (Rushall, 1985 ; Cross, 1999).
Besides these variables for an “overall” assessment of the swimmers’ kinematics (i.e., v, SF and SL) and efficiency (SI and ƞp) some other variables are selected to a deeper understanding of the biomechanical behavior.
The actual speed fluctuates within a stroke cycle due to the propulsive actions of the arms and legs, body-roll and breathing during swimming (Toussaint and Beek, 1992 ; Tella et al., 2008). These fluctuations are known in the literature as intra-cyclic velocity fluctuations or variation (IVV). IVV is considered an index of skill level and technique, with lower IVVs indicating higher skill levels (Schnitzler et al., 2010 ; Matsuda et al., 2014). The assessment of the IVV within a stroke cycle
is another approach to make an overall mechanics’ assessment and estimation of the swimming
In biomechanical terms, a swimmer should be able to generate high propulsive forces while keeping the opposing drag forces low, resulting in efficient swimming (Toussaint and Beek, 1992). When propulsive and drag forces are in balance, a constant speed is reached.
Swimming is a cyclic form of locomotion in the aquatic environment whereby propulsion is generated to overcome resistive forces. Therefore, the goal for competitive swimmers is to maximize propulsion while minimizing drag, given a finite metabolic capacity (Seifert et al., 2010).
Table of contents :
LES EXIGENCES DE LA NATATION COMPÉTITIVE
La nage en Crawl
Caractéristique du nageur compétitive:
a) Morphologie du nageur
b) Genetique du nageur
c) Aspects psychologiques et socio-culturels
Le niveau du nageur
Les facteurs déterminants de la performance
Les accessoires d’entrainement de sprint dans l’eau
a) Le Pull-Buoy et les plaquettes de natation
b) Les parachutes
c) La méthode du « Power-Rack »
d) La méthode du « Tethered Swimming »
e) Maillot d’entrainement de resistance
Échauffement “à sec”
Échauffement dans l’eau
Les mécanismes de l’échauffement
a) Les mécanismes liés à la température
1) Diminution de la résistance des muscles et des articulations
2) Augmentation de la performance des fibres musculaires
3) Augmentation du métabolisme musculaire
4) Augmentation de la vitesse de conduction des fibres Musculaires
b) Mecanismes metaboliques
1) Élévation de la consommation d’oxygène (VO2)
c) Mécanismes psychologiques
d) Mecanismes neuronaux
Post-Echauffement (Période de Transition)
Échauffement pour les épreuves de sprint
A brief History about PAP
Les mécanismes et facteurs de PAP
a) Les mécanismes neuromusculaires du PAP
1) Les facteurs centraux et PAP
2) Les facteurs périphériques et PAP
3) La chaine légère du Myosine
4) Force musculaire et distribution des fibres
7) Le niveau des athletes
8) Charge de travail et intensité
9) Taux de développement de la force
10) L’angle de Pennation
Facteurs modulateurs de PAP
Type de contraction
PAP et Fatigue
a) La fatigue neuromusculaire
b) PAP and Fatigue coexistance
Procédures de PAP et Performance
Natation et PAP / PAPE
Résumé des études PAP en natation
G/ CONTRIBUTION PERSONNELLE
OBJECTIFS ET HYPOTHÈSES
Etude 1: Do Thirty-Second Post-Activation Potentiation Exercises Improve the 50-m
Freestyle Sprint Performance in Adolescent Swimmers?
Etude 2: Individual effect of post-activation potentiation after a re-warm-up: Statistically
not significant but clinically meaningful
Etude 3: Effect of Tethered Swimming as Postactivation Potentiation on Swimming
Performance and Technical, Hemophysiological, and Psychophysiological Variables in
H/ DISCUSSION GENERALE
I/ CONCLUSION & PERSPECTIVES