Frantisek Zahalka

Body Composition of Elite Female Players in Five Different Sports Games

Abstract The goal of this study was to identify and compare body composition (BC) variables in elite female athletes (age ± years): volleyball (27.4 ± 4.1), softball (23.6 ± 4.9), basketball (25.9 ± 4.2), soccer (23.2 ± 4.2) and handball (24.0 ± 3.5) players. Fat-free mass (FFM), fat mass, percentage of fat mass (FMP), body cell mass (BCM), extracellular mass (ECM), their ratio, the percentage of BCM in FFM, the phase angle (α), and total body water, with a distinction between extracellular (ECW) and intracellular water, were measured using bioimpedance analysis. MANOVA showed significant differences in BC variables for athletes in different sports (F60.256 = 2.93, p < 0.01, η2 = 0.407). The results did not indicate any significant differences in FMP or α among the tested groups (p > 0.05). Significant changes in other BC variables were found in analyses when sport was used as an independent variable. Soccer players exhibited the most distinct BC, differing from players of other sports in 8 out of 10 variables. In contrast, the athletes with the most similar BC were volleyball and basketball players, who did not differ in any of the compared variables. Discriminant analysis revealed two significant functions (p < 0.01). The first discriminant function primarily represented differences based on the FFM proportion (volleyball, basketball vs. softball, soccer). The second discriminant function represented differences based on the ECW proportion (softball vs. soccer). Although all of the members of the studied groups competed at elite professional levels, significant differences in the selected BC variables were found. The results of the present study may serve as normative values for comparison or target values for training purposes.

Kinematic Analysis of the Take-Off and Start of the Early Flight Phase on a Large Hill (HS-134 m) during the 2009 Nordic World Ski Championships

Kinematic Analysis of the Take-Off and Start of the Early Flight Phase on a Large Hill (HS-134 m) during the 2009 Nordic World Ski Championships The take-off is often considered the most significant and difficult phase of a ski jump. Thus, the purpose of this study was to compare three groups of ski jumpers representing different skill levels during the execution of the take-off and start of the early flight phase in ski jumping. A total of 30 athletes, recruited from competitors performing ski jumps on an HS-134 m jumping hill, were categorized into three groups based on jump-length execution. Two-dimensional (2-D) kinematic data were collected from the lower extremities, trunk, and skis of the ski jumpers. Findings indicated that the ski jumpers with shorter jump length demonstrated significantly smaller in-run velocity (p < .05), while the elite and mediocre level ski jumpers exhibited a significantly faster shift of the thigh at the transition from take-off into the early flight of the jump (p < .05) than did the low-level ski jumpers. In addition, the centre of body mass (CoM) of the elite group shifted significantly more forward over the skis (p < .01) than did that of the other two groups. Finally, interindividual differences existed among ski jumpers at similar performance levels. The largest coefficients of variation (CVs) were found for the position changes of the trunk and shank behind the jumping hill edge.

Asimetría de Fuerzas Unilateral e Ipsilateral en Jugadores de Fútbol de Elite Juveniles con Respecto al Grupo Muscular y a la Dominancia de Miembros

The purpose of study was to identify the presence of strength asymmetries (SA) in young elite soccer players in relation to muscle group (knee extensors (KE) and flexors (KF)) and limb preference (dominant vs. non-dominant limb). Forty-one U16 national team soccer players (mean age 15.7 ±0.3 years, body height 177.9 ±6.6 cm, body weight 68.2 ±7.9 kg) participated in this study. Assessments were performed on a Cybex Humac Norm isokinetic dynamometer in concentric contraction. We noted the degree of SAs in the bilateral ratio of quadriceps and hamstrings and in the ipsilateral ratio of the dominant (DL) and non-dominant (NL) leg s. Bilateral deficits of KFs were higher (9.02–12.61 %) than those of KFs (6.32–7.15 %). The percentage of SA (>10 %) in knee extensors was 19.5– 31.7 %. The percentage of SA (>10 %) in knee flexors was 36.6–51.2 %. At the lowest velocity, there was a significantly higher p revalence of SAs in KFs than in KEs ( χ= 4.11, p<.05). The ipsilateral ratio was lowest at the lowest velocity regardless of limb dominance (DL: 58.95–63.27 %, NL: 56.58–60.11 %). At each velocity, the percentage of SA was higher for the non-dominant limb (12.2–24.4 %) th an for the dominant one (4.9–14.6 %). Despite these differences, we did not find any significantly higher prevalence of SA in the nondominant limb than in the dominant one ( χ= .35–2.04, p>.05). The results of the study suggest that more than 73.2 % of players have at least one SA. More attention should be paid to knee flexors, where a higher percentage of strength asymmetries were observed; f urthermore, a higher percentage of strength asymmetry was seen in the non-dominant lower limb.

Seasonal Variation of Agility, Speed and Endurance Performance in Young Elite Soccer Players

The aim of this study was to investigate changes in the linear running speed (LRS) for 30 m, change of direction speed (CODS), and endurance in young elite Czech soccer players. The following tests were conducted to assess CODS and endurance: Agility 505 turning toward the dominant (A505DL) and non-dominant lower limb (A505NL); Illinois Agility Test (IAT); and intermittent test (Yo-Yo IRT1). During the soccer season, we investigated performance at the following time periods: the start (t1) and the end of the pre-season period (t2); during (t3) and at the end of the competitive period (t4). Repeated measurement analysis of variance revealed a significant effect of time period on selected fitness parameters (p < 0.05). Post hoc analysis for test A505DL revealed significant improvements of performance at t3 (2.71 ± 0.08 s) and t4 (2.72 ± 0.06 s) compared to t1 (2.81 ± 0.09 s). A505NL was significantly different between t1 (2.83 ± 0.09 s) and t2 (2.76 ± 0.09 s), t3 (2.7 ± 0.07 s) and t4 (2.71 ± 0.09 s). Performance of CODS at t1 for the IAT (18.82 ± 0.56 s) was significantly lower (p < 0.05) than any other time period (t2 = 18.52 ± 0.63 s, t3 = 17.94 ± 0.51 s, t4 = 17.89 ± 0.66 s). The power of LRS was significantly different at t3 (4.99 ± 0.15 s), and t4 (4.98 ± 0.17 s) compared to t1 (5.15 ± 0.21 s), and t2 (5.07 ± 0.14 s). For the Yo-Yo IRT1 test, we observed a significant increase in performance between t1 (625.26 ± 170.34 m), t2 (858.95 ± 210.55 m), and t3 (953.68 ± 229.88 m). These results show the impact of soccer season time period on young soccer player performance and may further serve as a basis for comparison with similar research conducted by peers. These results may aid sports practice for clinicians, conditioning coaches, soccer coaches and physiotherapeutic coaches.

A Comparison of Methods for Evaluating Body Composition in Elite Female Soccer Players

Abstract The aim of the research was to determine an accuracy of measurement based on intra-trial concurrent and convergent validity of body composition (BC). Measurements were obtained via bioelectrical impedance analysis (BIA) in comparison with the hydrodensitometry (HD) method in elite female soccer players (n = 14). BC was measured using three methods: bioelectrical impedance methods BIA 2000M and In Body 3.0, and HD. The fat mass (FM) measured by HD was 16.96±3.86 percent, whereas it was 21.26±5.77 percent when measured with BIA 2000M, and was even higher when measured by the In Body 3.0 device at 23.33±3.52 percent. Effect size between BIA and HD was >0.87, convergent validity was lower than r<0.65, coefficient of determination was lower than R2<0.65, and a standard error of estimation was higher than >2.8. The results of the research showed that, without proper prediction equations for the specific population, the selected bioelectrical impedance analysers cannot be considered valid enough to assess the fat mass of elite female soccer players.

The bilateral strength and power asymmetries in untrained boys

Abstract The aim of the study was to identify the level of isokinetic strength and power of lower limbs in 13-year- old untrained boys (n=22, height: 158.5±8.0 cm, mass: 49.1±12.6 kg), to determine bilateral deficit between the limbs in the tests and examine their mutual relationship. Maximum peak muscle torque of knee extensors (PTQ) and flexors (PTH) on dominant (DL) and non-dominant leg (NL) were measured by isokinetic dynamometer. Three types of a vertical jump: countermovement jump with (CMJFA) and without arms (CMJ) and squat jump (SJ) were performed on two force platforms. We found the significant effect (p<.01) of independent vari- ables (knee extensors, flexors, AV) and their interaction on PT. AV did not indicate any significant effect on bilat- eral ratio of knee extensors (F4,84=.74, p>.05, ηp2=0.03), however a significant effect of AV was found in knee flexors (F4,84=2.70,p<.05, ηp2=.114). The type of jump had no effect on the difference between force exerted by DL and NL (F1,21=.102, p>.05, ηp2=.01). Bilateral deficit (Q:Q, H:H) did not significantly correlate with bilateral deficit in jumps (p>.05). Despite the possibility of identifying muscle asymmetries in the sense of strength imbalances, their mutual relation- ship with results in isokinetic dynamometry and power jump tests is still unclear.

ISOKINETIC STRENGTH OF KNEE FLEXORS AND EXTENSORS IN VERY YOUNG SOCCER PLAYERS

Background Monitoring of physical fitness characteristics in very young players could be helpful for the selection of talented youth or identification of the strengths and weaknesses in motor predispositions for physical performance. Muscular strength tested on an isokinetic dynamometer belongs to the most widely used methods of the identification of knee extensors (KE) and flexors (KF) strength in adult soccer players It appears that there is the lack of information concerning monitoring of isokinetic strength of lower limbs and its parameters in very young soccer players. The purpose of the study was to find out the level of isokinetic strength (IS) of KE and KF and to compare the selected characteristics of IS related to the movement velocity and limb dominancy in very young players. Methods Young players (n=16, age 8.8±0.4 years, body height=137.5±6.2 cm, body weight=30.7±4.1 kg) were tested on an isokinetic dynamometer Cybex Humac Norm. Maximum peak muscle torque (PT) of KE and KF, their mutual ratio (H:Q) and bilateral ratio between Q:Q or H:H were assessed during concentric contraction at different velocities (60,180,300°.s-1) in the dominant leg (DL) and non-dominant leg (NL). Mixed-design ANOVA was used for evaluation of PT differences between the factors (angular velocity, limb dominancy, muscle groups–KE, KF). For multiple comparisons we used Bonferonnis post-hoc test. Statistical significance was set at p≤0.05. Effect size was assessed using the ηp2 coefficient. Results The results of PT during 60,180 and 300°.s-1 were (KE [DL]: 60.9±11.6, 39.2±7.3, 30.9±5.4 N•m, [NL]: 60.8±12.2, 41.1±7.8, 33.6±6.3 N•m and for KF [DL]: 34.5±6.2, 24.5±4.1, 19.7±4.3 N•m, [NL]: 33.2±5.7, 24.6±5.8, 20.0±4.8 N•m). Movement velocity had a significant effect on the level of PT (peak torque) in the players F(1.3, 77.9)=414.9, p<0.01, ηp2=0.874 and HQ ratio (F(1.7, 49.8)=7.6, p<0.01, ηp2=0.202. With increasing velocity, significant differences were revealed in PT (L vs M, L vs H, M vs. H p<0.01) and HQ ratio (L vs M, L vs H p <0.05). Limb dominancy did not significantly influence the level of PT F(1, 60)=0.180, p>0.05, ηp2=0.687 or H:Q F(1, 30)=0.760, p>0.05, ηp2=0.025. Movement velocity and limb dominancy did not have any significant effect on the bilateral ratio between QQ and HH in young soccer players (p>0.05). Conclusion The results indicated significant differences in PT and HQ in relation to movement velocity. On the contrary, no significant differences were found in bilateral ratio (Q:Q, H:Q). Limb dominancy did not significantly affect any of the observed characteristics. The presented data may contribute to comparison or establishment of standards for strength profile in this age category. Supported by GAČR P407/11/ P704 and MSM 0021620864.

ELITE SOCCER'S LOWER LIMBS EXPLOSIVE STRENGTH ASYMMETRY

Background A vertical jump is one of essential motor skills in many sports (Vanezis & Lees, 2005). Monitoring and description of vertical jumps is based on both external movement structure and explosive strength of lower limbs as a basic driving impulse for its performance. Explosive strength is one of the most important components for the body increasing and vertical jump (Aragon, 2000). Methods The research group consisted of elite soccer players (n=138, age=25,1±4,7 years, height=184,2±7,2 cm, weight=79,7±8,1 kg). For recording force effect of lower limbs on the surface, two force platforms Kistler B8611A (KISTLER Instrumente AG, Switzerland) were used. All participants performed three types of a vertical jump, T1–countermovement jump with arms included, T2–countermovement jump with arms excluded, T3–squat jump. Evaluation parameters were: high of the jump (cm), maximal strength produced by separate lower limb FmaxR(L) and strength impulse produced by separate lower limb during the take off (Ns-1). Results The heights of the jumps were CMJ-FA=42.83±4.88 cm, CMJ=37.55±4.18 cm a SQJ=35.97±3.97cm. Maximal strength produced by separate lower limb was recalculated by dividing to weight of every player as a strength for one kilogram; FmaxPT1=1.32±0.11 N.kg-1 resp. FmaxLT1=1.27±0.11 N.kg-1; FmaxPT2=1.33±0.14 N.kg-1 resp. FmaxPT2=1.28±0.16 N.kg-1; FmaxPT3=1.12±0.12 N.kg-1 resp. FmaxLT3= 1.09±0.09 N.kg-1. The level of asymmetry was evaluated by percentage difference between maximal strength of right or left lower limb per one kilogram of boy weight. Percentage difference between maximal strength was T1=5.86±4.58%; T2=9.61±7.92, T3=5.47±6.49%. Evaluation of lower limbs asymmetry by help of strength impulse using the take off was T1=9.91±10.49 N.s-1, T2=8.55±7.34 N.s-1, T3=5.69±4.73 N.s-1. Discussion/Conclusions The best results were achieved in the first type of the vertical jump (T1). Results of the countermovement jump without arm swing (T2) and squat jump without arm swing (T3) are more comparable, although it could be expected that squat position could improve the height of absolute value of the vertical jump. The biggest asymmetry by maximal strength point of view was found in the jump T2. Jumps T1 and T2 had asymmetry by maximal strength point on were similar and the absolute value was only half according to jump T1 asymmetry. The biggest asymmetry by strength impulse was in the jump T1, rest jumps aszmmetry were lower (T2-13%; T3-42%). Project was supported: MSM 0021620864, GACR P407/11/P784, PRVOUK 38.

Effect of Muscular Strength, Asymmetries and Fatigue on Kicking Performance in Soccer Players

The aim of this study was to determine the effect of muscular strength, strength asymmetries, and fatigue on the speed and accuracy of an instep kick in soccer players. We measured ball velocity (BV) and kicking accuracy (KA) in the preferred (PL) and non-preferred leg (NPL) before (PRE) and after (POST) physical load in the PL. Maximum peak muscle torque of the knee extensors and flexors in the PL and NPL as well as ipsilateral knee flexors and knee extensors ratio (H:Q ratio) for both legs were assessed. BV was significantly decreased in POST physical load (5.82%, BVPRE=30.79±1.70 m·s-1, BVPOST=29.00±1.70 m·s-1, t19=3.67, p=0.00, d=1.05). Instep kick accuracy after the physical load worsened by an average of 10% in the most accurate trials. Results revealed a significant decrease in instep kick accuracy after physical loading (KAPRE=2.74±0.70 m, KAPOST=3.85±1.24 m, t19=-3.31, p=0.00, d=1.10). We found an insignificant correlation between H:Q ratio and KA in PRE test value, whereas a lower ipsilateral ratio (higher degree of strength asymmetry) in the POST physical load significantly correlated with KA in all angular velocities (r=-0.63 up to -0.67, p=0.00).

Performance and Kinematic Differences in Putting Between Healthy and Disabled Elite Golfers

Abstract Golfers with disability are limited in the execution of the full golf swing, but their performance in putting may be comparable because this stroke does not demand significant strength, balance and range of motion. Therefore, the aim of this study was to compare putting performance, kinetic and kinematic consistency between golfers with different disabilities and healthy athletes. The participants consisted of three disabled athletes (perinatal cerebral palsy, multiple sclerosis, below knee lower limb amputee) and three healthy golfers (age 34 ± 4.5 years, body height 178 ± 3.3 cm, body mass 83 ± 6.2 kg). The golfers’ movements were recorded by active 3D markers for kinematic analyses; the subjects performed 10 trials of a 6 m putting task while standing on separate force platforms placed under each lower limb. Putting performance was measured by the distance of the final ball position to the centre of the hole. ANOVA analyses did not show any differences in clubhead speed and total ball distance from the hole. The consistency of those two parameters expressed by the coefficient of variation (CV) was CV = 0.5% or better in both groups for clubhead speed and ranged from CV = 0.40 to 0.61% in healthy and CV = 0.21 to 0.55% in disabled athletes for total error distance. The main effect ANOVA showed differences in weight shift, hip and shoulder kinematics (p < 0.05) between healthy players and all players with disability. All disabled athletes shifted their weight toward the healthy side (towards the healthy lower limb) and alternated the end of the swing. The player with below knee amputation had the lowest range of motion in the shoulder joint during the putting stroke. The players with perinatal cerebral palsy and multiple sclerosis had the largest range of motion in the hips. Putting performance of disabled golfers was similar to healthy athletes. During training of disabled players, coaches should pay attention to the specificity of a particular disability when focused on putting performance. However, individual technique should achieve the same consistency as observed in healthy players.