MkaouerB., Jemni M., Amara S., Chaaben H., Tabka Z. KINEMATIC AND KINETIC ANALYSIS... Vol. 4 Issue 3: 61 - 71 KINEMATIC AND KINETIC ANALYSIS OF COUNTER MOVEMENT JUMP VERSUS TWO DIFFERENT TYPES OF STANDING BACK SOMERSAULT 12 1 1 Bessem Mkaouer , Monem Jemni, Samiha Amara , Helmi Chaaben , Zouhair Tabka3 1Higher Institute of Sport and Physical Education of Ksar Said, Tunisia School of Science, University of Greenwich, London, United Kingdom 3Faculty of Medicine of Sousse, Tunisia Original research article Abstract The aim of this study was to compare the take-off's kinetic and kinematic variables between three types of jumps from a standing position: counter movement jump with arm swing (CMJa), standing back somersault with landings on the spot (BSls) and standing back somersault with rear displacement at landing (BSld). Five elite level male gymnasts (age 23.17 ± 1.61 years; height 165.0 ± 5.4 cm; weight 56.80 ± 7.66 kg) took part in this investigation. A force plate and a 3D movement analysis system were synchronized and used for data collection. Statistical analysis via non-parametric Kruskal-Wallis test showed a significant difference between the take-off variables. The vertical component of force, peak power, impulse and displacement of the centre of mass were significantly different (P<0.01). Similarly, the horizontal component of force, maximum speed, peak power and displacement of the centre of mass were significantly different (P< 0.01). However, vertical velocity remained relatively constant. In conclusion, the standing back somersaults performed on the spot's variables (without back displacement) were very similar to the ones analysed during counter movement jump with arm swing. The standing back somersault with landing on the spot allowed better force impulse. This was facilitated by a take-off closer to the centre of mass, unlike the standing back somersault with rear displacement in landing. Analysing kinetic and kinematic together, allowed the endorsement of linear regression equations enabling the prediction of some variables from others. Keywords: gymnastics, take-off, thrown off centre, reaction force. INTRODUCTION Jumps take an important part of gymnastics men and women's daily routines. Gymnasts' ability to transmit their impulse from their feet to their upper bodies following rebounds is crucial, allowing acrobatic skills such somersaulting and twisting. Artistic gymnastics has seen amazing evolution throughout the last five decades (Jemni, Friemel, Sands & Mikesky, 2001). Exhibited strength, power, flexibility and spatial awareness via the incredible complicated aerial skills have contributed in shaping a new profile of the modern gymnast (Jemni, 2011; Jemni, Sands, Friemel, Cooke & Stone, 2006). This lately is nowadays able to perform triple tacked Science of Gymnastics Journal 61 Science of Gymnastics Journal MkaouerB., Jemni M., Amara S., Chaaben H., Tabka Z. KINEMATIC AND KINETIC ANALYSIS... Vol. 4 Issue 3: 61 - 71 somersaults and even quadruple twists in one straight back. How could they do it? How important is to learn the "perfect" jumping technique? Are there any variables to analyse enabling coaches to dissociate the "good", the "bad" and the "useful" jumps? Vertical jumps are used in a plenty of sports. Their primary goal is usually to reach the greatest possible height (Psycharakis, 2012). Other goals could also include rotation in acrobatic somersaulting. Gymnasts' jumping ability is often linked to successful performance (especially in floor routines and vault) and is sometimes considered as an overall indicator of gymnastics proficiency. Gymnastics' performance is largely defined by the ability to successfully jump complex forward and backward rotating skills. Video analysis of world-class gymnastics competitions has shown gymnasts performing more backward rotation skills than forward ones (McNitt-Gray, 1992; Munkasy, McNitt-Gray, Michele & Welch, 1996; Harski, 2002; Sadowski, Boloban, Wisniowski, Mastalerz, & Niznikowski, 2005). This current study would put some more insight on the nature of the backward take-offs. Analysing the mechanics of ground reactions forces during different jumping cases could add significant understanding and tools for coaching. Reaction force passes through the centre of mass (COM) during vertical jump; meanwhile this force would be thrown off centre forward during a backward rotation. Performing somersaults from a standing position requires a production of significant amount of force and velocity during take-off phases. The transfer of force depends on the gymnast's ability in backward rotating skills. Relatively large number of authors have analysed various executions of backward somersaults (Payne & Barker, 1976; Bruggemann, 1983; Lacouture, Junqua, Duboy, & Durand, 1989; Knoll, 1992; Newton, Turner, & Greenwood, 1992; Hong & Bruggemann, 1993; McNitt-Gray, Munkasy & Welch, 1994; Duboy, Junka, & Lacouture, 1994; Medved, Tonkovic & Cifrek, 1995). Conversely, there is a paucity of literature that explores ground reaction forces during take-offs. Mc Nitt-Gray, Hester, Mathiyakom and Munkasy (2001) studied the mechanical demand during landing after three skills: the forward somersault, the backward somersault and the drop jump. Medved (2001) has studied ground reaction force during gymnasts' take-off while performing two skills: backward somersault and straddle jump, both performed from a standing position. Lebeuf, Lacouture and Bessonnet (2003) analyzed the COM path during a successful and a failed backward somersault. Other studies have examined the vertical jump as in artistic gymnastics (Marina, Jemni & Rodriguez, 2012; Sands, 2011; Sands, Stone, McNeal, Jemni & Haff, 2006; Swartz, Decoster, Russell & Croce, 2005; Marina, Busquets, Padulles & Camps, 2005; Marina, 2002). Very recently, Marina, Jemni, Jimenez & Rodriguez (2012) have thoroughly investigated jumping abilities in significant number of gymnasts and compared them to a matching control group. They have came-up with a very important conclusion showing that studying jumping ability should take few variables into consideration. Flight time, contact time and power output are not enough to dissociate gymnasts; other variables such as Bosco expression and flight to contact times ratio should also be calculated for a more significant profiling purpose. For these reasons, the current study has not only analysed dynamic data acquired by a force plate but also kinematic data collected by synchronised cameras. The purpose of this study was to compare the take-off's kinetic and kinematic variables underpinning gymnasts' ability to perform the counter movement jump with arms swing (CMJa), the standing back somersault with landing on the spot (BSls) and the standing back somersault with rear displacement in landing (BSld). METHODS Five elite level male gymnasts (age 23.17 ± 1.61 yrs; height 165.0 ± 5.4 cm; weight 56.80 ± 7.66 kg) took part in this Science of Gymnastics Journal 62 Science of Gymnastics Journal MkaouerB., Jemni M., Amara S., Chaaben H., Tabka Z. KINEMATIC AND KINETIC ANALYSIS... Vol. 4 Issue 3: 61 - 71 study. The inclusion criteria were: to be ranked at international level with participation in world cups and/or championships; average training volume around 25 hours per week; healthy without any muscular, neurological or tendinitis injuries; able to perform back somersaults on the spot. After being informed on the procedures, methods, benefits and possible risks involved in the study, each subject reviewed and signed a consent form to participate in the study. The experimental protocol was performed in accordance with the Declaration of Helsinki for human experimentation and was approved by the university ethical committee. The investigation's design contained a dual approach: kinematic and kinetic of three types of take-offs from a standing position. The direction of reaction forces was different between the three skills during the push-off phases (Figure 1): - It passes through the centre of mass (COM) during the counter movement jump with arm swing (CMJa) (Figure 1a); - It is thrown off centre forward but close to the COM during the standing back somersault with landings on the spot (BSls) (Figure 1b); - It is very thrown off centre forward during the standing back somersault with rear displacement at landing (BSld) (Figure lc). (a) CMJa (b) BSls (c) BSld Figure 1. Kinogrammes of three types of take-off from a standing position. (a) counter movement jump with arm swing; (b) standing back somersault with landings on the spot; (c) standing back somersault with rear displacement in landing. Kinetic data were acquired using a 60*40 cm Kistler force plate (Kistler Instruments, Switzerland. Ref. 9281C). Sampling frequency was 500 Hz, and the measuring range was set between 10 to 20 kN. Vertical (Fy) and horizontal (Fx) force variables, the COM displacement (dx; dy), velocity (vx; vy), peak power (Px; Py) and impulse (Ix; Iy) were analysed. Analysis was performed with a Bioware Performance Software 5.1.1 (Kistler Instruments, Switzerland). Kinematic data were acquired using two high-speed cameras (NAC HSV-500C3; 250 Hz) in NTSC format with VCR C3D and SVHS tape. A motion analysis software (Movias, NAC Corp, Santa Rosa, CA) was used to process the data. 20 retro-reflective body markers were attached to the gymnasts' bodies allowing digitisation using a video based data analysis system (Movias for Windows 2.0.4). The body segments' centres of mass were computed using Matshui model (1983). Take-off angle (aT), shoulder angle (aS), hip angle (aH) and knee joint angle (aK) were analysed and compared at the different take-offs. Angular displacements of these respective joints (9S, 9h and 0K) and their angular velocities (raS, raH and raK) were calculated in the sagittal plane. Data acquisition and testing were carried out in a laboratory setting. All tests were performed within a 3-day period, starting at 4:00PM up to 6:00PM under the following environmental condition: average temperature 23°C (minimum 20, maximum 26°C). The force plate was synchronized with the two high-speed cameras. The first camera was placed in front of the subject and the second sideways, each at 5m from the centre of the force plate (figure 2). All participants wore only a short during testing to allow digitising. They were given ten-minute warm-up period including light jog, stretching and several jumps and somersaults with stable landing. Each gymnast performed each jump three times in separate days. The choice of jumps and/or somersaults was randomised using Latin Square randomisation protocol (Zar, 1984). The execution of each skill was separated by a two-minute recovery period between repetitions. Two international Science of Gymnastics Journal 63 Science of Gymnastics Journal MkaouerB., Jemni M., Amara S., Chaaben H., Tabka Z. KINEMATIC AND KINETIC ANALYSIS... Vol. 4 Issue 3: 61 - 71 judges marked each somersault by referring to the Code of Points FIG (2009). Only the best somersault was retained for analysis and comparison. Figure 2. Experimental setup. Data are reported as mean ± standard deviation (SD). The distributions' normalities, estimated by the Kolmogorov-Smirnov test, varied between variables. Therefore, we used the non-parametric Kruskal-Wallis test to compare all take-offs' variables, while the U test of Mann-Whitney was applied to pair-wise the somersaults and CMJ comparison. Spearman correlation analysis was performed to check any relations between the CMJ and the back somersaults. The results are considered significantly different when the probability is less than or equal to 0.05 (P<0.05). Statistical analyses were performed using the software package SPSS version 13.0 (SPSS Inc., Chicago, IL, USA). RESULTS All kinetic data for the BSld have almost doubled in comparison to the tow other conditions. Significant statistical increases were noticed in all horizontal components: the horizontal force component (Fx) has increased by 63.36% during the BSld when compare to the CMJa and by 39.18% when compared to the BSls (P<0.01) (Table 1). Similar results were noticed for the horizontal velocity (vy): [+41.36% compared to CMJa (P<0.05), (+51.49% compared to BSls (P<0.01)], the horizontal peak power (Px): [+50.87% compared to CMJa (P<0.01) and +50.34% compared to BSls (P<0.01)] and the horizontal impulse (Ix): [+36.23% compared to CMJa (P<0.05) and +51.03% compared to BSls (P<0.01)] (Table 1). The magnitude of change has ranged between 10% to 22% when it came to compare the vertical components. Force vertical component (Fy) has significantly increased by 10.04% during the CMJa in comparison to the BSld (P<0.01). Similarly, peak power's vertical component (Py) has significantly increased during the same take off compared to the tow other conditions: [by 19.031% compared to BSld (P<0.01) and by 11.81% compared to BSls (P<0.05)]. Looking at the absolute data, the CMJa and BSls showed the highest level of vertical force, followed by BSld (1808.89 ± 97.06 N; 1806.87 ± 78.08 N; 1625.55 ± 62.64 N respectively). Moreover the horizontal component of force was the highest during the BSld take-off (very thrown off centre). The BSld developed more force than the BSls and the CMJa (209.44 ± 4.80 N; 126.65 ± 22.14 N; 127.38 ± 7.97 N respectively) (Figure 3). : Fx (N) □ Fy (N) r Figure 3. Horizontal and vertical forces produced during the three take offs. Vertical axis' variables were different during the impulse of the three take-offs (214.91 ± 9.37 N/s; 194.72 ± 3.82 N/s; 176.31 ± 20.82 N/s respectively for CMJa, BSls and BSld). Moreover, the horizontal axis of the impulse was higher during the BSld compared to the BSls and to the CMJa (23.80 ± 3.84 N/s; 18.28 ± 2.68 250 2500 200 2000 1500 1000 50 500 0 Science of Gymnastics Journal 64 Science of Gymnastics Journal MkaouerB., Jemni M., Amara S., Chaaben H., Tabka Z. KINEMATIC AND KINETIC ANALYSIS... Vol. 4 Issue 3: 61 - 71 N/s; 17.91 ± 6.09 N/s respectively) (Figure 4). Impulse's vertical component of (Iy) has significantly increased during the BSls compared to the other conditions: [by 21.89% compared to BSld (P<0.01) and by 10.37% compared to CMJa (p<0.05)]. Vertical velocity was almost the same between BSls, Bsld and CMJa (3.05 ± 0.04 m/s, 3.40 ± 0.40 m/s; 3.57 ± 0.37 m/s respectively); however, and as expected, the horizontal velocity was the highest during BSld, followed by the BSls and CMJa (0.41 ± 0.07 m/s; 0.29 ± 0.05 m/s; 0.20 ± 0.04 m/s respectively). This increase is indeed a basic condition allowing backward rotation, and is supported by the fact that power generated on the horizontal axis was greater during the BSld compared to BSls and CMJa (279.00 ± 60.34 W; 138.08 ± 35.00 W; 137.54 ± 27.62 W respectively). In contrast, the peak power produced on the vertical axis was more important during CMJa and BSls than during BSld (4774.12 ± 231.98 W; 4269.72 ± 245.65 W; 4010.94 ± 368.00 W respectively) (Figure 5). Table 1. Comparative statistics of the three take-offs. Kruskal Wallis Mann-Whitney Test Variables Test CMJa vs. BSls CMJa vs. BSld BSls vs . BSld K2 Sig. Z Sig. Z Sig. Z Sig. Fx (N) 9.517 0.009** -0,522 0,602 -2,619 0,009** -2,619 0,009** Fy (N) 9.380 0.009** -0,104 0,917 -2,611 0,009** -2,611 0,009** Vx (m/s) 11.060 0.004** -2,193 0,028* -2,402 0,016* -2,611 0,009** Vy (m/s) Kinetic dx (m) 5.840 0.054 -2,402 0,016* -1,358 0,175 -0,94 0,347 9.500 0.009** -0,522 0,602 -2,611 0,009** -2,611 0,009** dy (m) 7.620 0.022* -1,358 0,175 -1,567 0,117 -2,611 0,009** Px (W) 9.380 0.009** -0,104 0,917 -2,611 0,009** -2,611 0,009** Py (W) 8.340 0.015* -2,193 0,028* -2,611 0,009** -0,731 0,465 IFx (N/s) 10.640 0.005** -2,402 0,016* -1,984 0,047* -2,611 0,009** IFy (N/s) 11.180 0.004** -2,611 0,009** -1,984 0,047* -2,611 0,009** Œt (°) 12.50 0.002** -2,611 0,009** -2,611 0,009** -2,611 0,009** «S (°) 8.960 0.011* -2,402 0,016* -2,611 0,009** -0,731 0,465 «H (°) 2.060 0.357 -0,313 0,754 -1,567 0,117 -0,731 0,465 aK (°) 9.380 0.009** -2,611 0,009** -2,611 0,009** -0,104 0,917 6s (°) 6.720 0.035* -0,731 0,465 -2,611 0,009** -1,567 0,117 Kinematic 6h (0) 12.500 0.002** -2,611 0,009** -2,611 0,009** -2,611 0,009** 6k (°) 1.820 0.403 -0,104 0,917 -1,358 0,175 -0,94 0,347 ffls (°/s) 7.580 0.023* -0,731 0,465 -2,402 0,016* -2,193 0,028* ®H (°/s) 0.420 0.811 -0,522 0,602 -0,313 0,754 -0,522 0,602 ®K (°/s) 7.460 0.024* -1,984 0,047* -2,611 0,009** -0,94 0,347 Significant at P < 0.05; ** Significant at P < 0.01 Kinematic study has provided the following results: the take-off angle (aT) relative to the vertical axis was significantly decreased in the BSld condition in comparison to the two other conditions (P<0.01): by 5.01% and by 13.45% compared to BSls and to CMJa respectively. Similarly, the angle of shoulder joint at take-off (aS) was also significantly decreased by 18.22% during the BSld compared to the CMJa (P<0.05). The angle of knee joint at take-off (aK) was significantly decreased at almost a similar percentage during the same skill compared to CMJa (18.72%) (P<0.01) (Figure 6). Science of Gymnastics Journal 65 Science of Gymnastics Journal MkaouerB., Jemni M., Amara S., Chaaben H., Tabka Z. KINEMATIC AND KINETIC ANALYSIS... Vol. 4 Issue 3: 61 - 71 Furthermore, the angular displacement of the shoulder joint (0S) was significantly increased by 9.65% in the CMJa condition compared to BSld (P<0.01). More considerable change was noticed in the hip joint. Its angular displacement (0H) has significantly increased compared to the two other conditions (P<0.01): by 34.50% and by 14.70% compared to BSld and to BSls respectively. □ X (N/s) □ ly (N/s) BSls BSld CMJa BSls BSld CMJa Figure 4. Horizontal and vertical impulse generated during the three take-offs. I BSls BSld CMJa BSls BSld CMJa Figure 5. Horizontal and vertical peak power generated during the three take-offs. 132.7° Figure 6. Joint angles during the three takeoffs. Angular displacement of the arms was larger during the CMJa compared to the BSld (157.51±6.77° and 128.81±7.63° respectively) and the flexion of the hip joint was also more important (55.48±2.05°; 47.32±2.36° and 36.33±2.65° respectively for CMJa, BSls and BSld). Angular velocity of the knee joint (raK) was likewise increased during the CMJa compared to the other situations by 27.95% v BSld (P<0.01) and by 19.70% v BSls (P<0.05). The angular velocity of the shoulder joint (roS) was itself, significantly increased in the BSld condition with respect to the two others (P<0.05): by as high as 65.53% compared to BSls and by 71.86% compared to CMJa (Figure 7). Angular velocity of shoulder joint (°/s) 3000 2500 ^ 2000 g> 1500 1000 500 0 Figure 7. Angular velocity of shoulder joint during the three take-offs. Lastly, the centre of mass's (COM) vertical velocity (vy) and the angular velocity of the knee joint (raK) did not vary during the different take-offs. In the same way, the hip joint's angle (aH) at take-off and its angular displacement (0H) remained Correlation analysis showed only one significant relation (P<0.05) across all data. It was between the BSls and CMJa and in particular between the vertical component of force (Fy) and displacement (dy) of the COM (r = -0.900 and r = 0.884 respectively) (Figure 8a and b). Correlation between the kinematic and kinetic variables showed a significant relation at (P<0.05), between the take-off angle (aT) and the horizontal displacement (dx) of the COM (r = -0.900). Similarly, there was a significant correlation at (P<0.05), between force's vertical component (Fy) and the angular displacement of the knee joint (0K) (r = -0.900). A highly significant correlation at (P<0.001) was also found between the 30 250 25 200 150 100 50 0 0 400 6000 350 5000 300 4000 250 200 3000 150 2000 100 1000 50 Science of Gymnastics Journal 66 Science of Gymnastics Journal MkaouerB., Jemni M., Amara S., Chaaben H., Tabka Z. KINEMATIC AND KINETIC ANALYSIS... Vol. 4 Issue 3: 61 - 71 vertical peak power (Py) and the angle of the hip joint (aH) (r = 1.000). (a) Vertical component of force (Fy) tn m 120 124 128 132 CMJa Fy (N) (b) Vertical component of displacement (dy) ■a