BUILDING A PROFILE OF SPECIFIC FITNESS INDICES FOR MALE TEENAGE CHINESE SPRINTERS

Objectives: This study aimed to construct a profile of specific fitness indices for male teenage sprinters on the Chinese National Team to provide sprinting fitness assessments for teenage training. Material and Methods: 229 male teenage sprinters at the same level were recruited to participate in this test for the indices. The t- and Kruskal-Wallis tests were conducted for the first selection of fitness indices. In the second selection, principal components analysis was applied to select common factors with greater characteristic values. The fitness indices chosen were height, leg length, measurement B (ankle circumference/heel length×100%) and measurement A (thigh circumference/leg length×100%), hemoglobin, 60m sprint time, 100m sprint time, countermovement jump (CMJ), maximum countermovement jump velocity, CMJ flight time, CMJ maximum force, and CMJ force. Results: Thirteen indices were chosen for the specific fitness of male teenage Chinese male sprinters with 3 general categories and 9 subcategories. The weight of each fitness index was confirmed and used to construct a standard fitness assessment scale. Conclusion: Anthropometric indices indicate the athlete’s innate limits in the structure of the sprinting motion. Physiological indices indicate the athlete’s potential to expend energy and recover in a short time. Motor indices indicate the athlete’s maximum sprinting ability, lower limb reaction strength, power, and maximum strength. Level of evidence II, Diagnostic studies - Investigation of a diagnostic test. m, tiempo sprint de 100 m, salto de contramovimiento (CMJ), velocidad máxima del salto de contramovimiento, tiempo de vuelo del CMJ, fuerza máxima del CMJ, fuerza del CMJ. Resultados: Se seleccionaron 13 índices para evaluar la aptitud física específica de los velocistas del estudio, divididos en 3 categorías principales y 9 subcategorías. Se confirmó la ponderación de cada índice de aptitud física y se utilizó para crear una escala estándar de evaluación de la aptitud. Conclusión: Los índices antropométricos reflejan los límites innatos de los atletas en la estructura del movimiento del sprint. Los índices fisiológicos indican el potencial del atleta para gastar energía y recuperarla en un corto período. Los índices motores indican la capacidad máxima del atleta en el sprint, la potencia de reacción de las extremidades inferiores, la fuerza y la potencia máxima. Nivel de evidencia II, Estudios diagnósticos - Inves-tigación de un examen para diagnóstico. movimiento; atlético.


INTRODUCTION
Performance of sprinting events relies on athletes' level of comprehensive fitness capacity. [1][2] Despite sprinting specific fitness indices for training assessment being scientifically mature to a certain extent, research concerning sprinting fitness was majorly based on elite or collegiate athletes. [3][4] Furthermore, these studies were mostly focused on single factors such as psychological ability, 5 speed structure, 6 strength of knee extension and flexion, 7 stride and frequency. 8 Little research regarding specific fitness was focused on teenage sprinters. Establishing sprinters' specific fitness indices for assessment in training is vital to enhance teenage sprinters' performance. This study aimed to determine important specific fitness indices for teenage Chinese male sprinters through testing large samples with a view to provide practical uses for sports science, talent identification in sprinters and teenage sprint training.

METHODS Subjects
A total of 229 male teenage sprinters from the teenage training base of China National Team were recruited in the study. The project was approved by the Ethics Committee on Human Research. Passive informed consent was applied. The participants subjects were divided into made of two groups: the elite group was made of elite teenage sprinters (n=57) and the control group was made of physical education students (n=172). Average 100m sprint time 100m performance of the elite group was sub 11.74s, while the performance of control group was between11.75-12.64s. The subjects' information is provided in Table 1. This study was approval by ethic committee of China University of Mining and Technology.

Measurement
For the integrity of the testing fitness parameters, fitness-related references were studied and accessed to possible relating parameters. Expert interviews were carried out with professionals in national athletics teams, elite teenage athletics training bases and schools with athletics teams. Questionnaires regarding testing parameters were then designed according to the results of fitness-related references and expert interviews. Afterward, 12 experts were invited to check confirm the content validity and structure of questionnaires. Consequently, 92% of experts confirmed the content validity of questionnaires regarding the testing parameters. Three rounds of selections were carried out for the determination of final testing parameters. The overall recovery ratio of 57 questionnaires was 92.98%. 33 testing parameters were chosen in the final selection, which could be categorized into 3 general categories and 10 subcategories. The final 33 testing parameters were: height (H), leg length A (LLA) (vertical distance from subjects' anterior superior iliac spine to the floor), leg length B (LLB) (vertical distance from subjects' greater trochanter to the floor), shank length A(SLA), Aachilles tendon length (ATL), ilium width (IW), shoulder width (SW), thigh circumferences (TC), ankle circumferences (AC), weight, body fat, resting heart rate, cardiac effort indices, vital capacity weight indices, red blood cell count, Hemoglobin (HGB), human growth hormone (HGH), testosterone, 30m, 60m,

Statistical analysis
All statistical analyses were conducted using the SPSS (Version.22.0, SPSS Inc, USA). Analyses were as follow: Fitness parameters for anthropometry, physiological function and motor ability. Independent sample T-test or Kruskal-Wallis H test were applied to compare differences between two groups. Factor analysis and Principal Components was respectively used for second round of parameters determination and selection of common factor. The relative percentile method was used to make the final specific fitness assessment scale of teenage male sprinters.

RESULTS
As mentioned, teenage athletes' specific fitness is a complex system, which can be generally classified into anthropometry, physiological function, and motor abilities. Specific fitness is a combination of inborn and acquired ability that makes the difference in athletes' performance in the event. 9 Accordingly, a significance test of the differences was conducted on 33 parameters of two groups in the study in order to eliminate the parameters with low discrimination and distinction. However, potential parameters suggested by professionals (height) were kept for the second selection. As result of the first selection, 26 fitness indices were chosen. (Table 3) KMO value of anthropometry, physiologic function, and motor abilities were respectively 0.669, 0.607 and 0.782. Mean values were all greater than 0.6 and reported significantly different when using the Bartlett test (p<0.001). (Table 4) Accordingly, factor analysis was able to be carried out. According to the default standard in which eigenvalues should be greater than 1.0 (Figure 1), factor rotation was conducted. Consequently, three parameters were chosen for anthropometry (cumulative proportion: 74.66%). Two parameters were chosen for physiologic function (cumulative proportion: 75.29%). Three parameters were chosen for motor ability (cumulative proportion: 83.789%).
According to the size of factor rotation value characteristic and experts' opinions, the final 13 parameters were determined, which could be categorized into 3 general categories and 9 subcategories. (Table 5)

DISCUSSION
For years, talent identification through scientific means has become a focus among coaches, researchers and specialists. Anthropometrics is critical in talent identification and in teenage athletes. Previous study reported the anthropometric characteristics of elite sprinters are mesomorph figure, low body fat (5-10%), long legs, small length ratio of thigh and shank, strong gluteus, long Achilles tendon etc. 10 This sort of figure gives athletes a better structure for muscle contracting efficiency in sprinting conditions, increasing speed through leg stride length. As the sprint event and its technique developed, world elite sprinters became taller. Hence, longer stride and slower frequency were developed for the height trend, decreasing muscle work to increase sprinting efficiency. 11 Studies also indicate Achilles tendon length is correlated with the power of lower extremities. TC/ LLA×100% indicates the strength of quadriceps and growth of LL. In the sprinting cycle, strength of quadriceps and hamstring are crucial for the swing and push technique. 12 Research suggest short thigh and long shank shorten the swing radius  and decrease the resisting moment, increasing sprinting efficiency by creating more horizontal distance and less vertical displacement. [13][14][15] An athlete's physiological function is influenced by numerous factors and genetics from an early age. Thus, to find the physiological indices correlated with performance the elite teenage sprinters' specific physiological state. In sprinting events, the respiratory and circulatory system function to create an ideal internal environment for athletes' bodies by catabolic buffering, enduring and adapting. It increases musculoskeletal capacity in anaerobic sprinting, delaying occurrence of fatigue and to maintain the balance of the body. As a result, the oxygen usage of muscle and recovery ability helps to promote the effects of training. [16][17] Szygula 3 found VO 2 max is highly correlated with HGB. In sports, the increment of HGB results in better VO 2 max and ability to resist fatigue. Hypoxia of central nervous system could be detrimental to ability of repeated sprinting. Better anaerobic ability could reduce the neuromuscular fatigue. The ability for muscles to use oxygen could be beneficial to long-time repeated sprinting. Resting heart rate, a simple and easily controlled way to evaluate and compare, is widely used in health assessment, physiological assessment, training monitoring and talent identification in sports. Studies show the decrease of resting heart rate shows less myocardial consumption of oxygen and improves myocardial blood supply. The cardiac effort index is an important factor in physiological indices because it reveals the ability of myocardial recovery, meaning the individual potential and cardiovascular system athletes show and recover in short time.
Hristo 18 suggested the distance of maximum velocity training should base on ATP-PC energy system (6-8 sec). 60m sprinting is an ideal way to develop sprinters' speeds, and it could be an indicator for 100m sprinter talent identification. Maćkała et al. 19 stated that the ability to accelerate and maintain maximum velocity is crucial in 100m performance. Tyson Gay and Derrick Atkins's decreasing percentage of velocity in the 100m final in 2007 Athletics World Champion were 1.69% and 1.53%. The Chinese sprinter decreased their velocity by 7.54% in the last 20m of the 100m sprint. 20 It indicates maximum velocity is highly correlated to 100m performance. CMJ parameters including CMJMV, CMJMS, CMJP indicate lower extremity explosive power to jump in a vertical downward direction. It shows an athlete's ability to use lower extremities to move from a static to dynamic state. The stretch-shortening cycle is the way muscles express strength in sprinting, which makes it a good way to evaluate teenage sprinters' lower extremity power. [21][22][23] Kukolj 24 reported the height of CMJ and maximum velocity is correlated positively with the peak power of lower extremities. We concluded that muscle strength and its contraction speed result from the individual difference of reactional strength, which makes reaction strength an influential factor for different level of teenage sprinters. Expert questionnaires using the Likert scale were conducted to determine the weight of the indices. Experts were asked to grade each parameter. Normalization and the main component analytical method were used to determine the weight of indices and the 3 general categories. (Table 6) Where W_i is the weight of i factor in fitness. Pij is the experts' and coaches' grading of i factor. (i=1,2,3) According to the normal distribution, deviation and relative percentile method were applied to transform the values of parameters into scores. The chosen parameters were calculated into scoring points. Equation for scoring was used by: Indices sorces= WCG is the weight of the 3 general categories. WCP is the weight of chosen parameter. RL is the relative level.
Subjects' testing data were transformed to total points based on relative points. According to P90, P70, P30, P10, the final teenage Chinese male sprinters' fitness indices ranking scale was made. (Table 7) The relative percentile method was applied to grade subjects into elite group (<P90, n=18), good group (P70-P90-△, n=32)and normal group (P30-P70-△, n=57). Ultimately, the assessment standard scale of teenage Chinese male sprinter specific fitness indices was established. (Table 8) Afterward, a retrospective test was conducted for 107 subjects. Results of the test indicate subjects who reached level 5 in the elite group were significantly better than good and normal group. Talent identification for the good and normal groups was based majorly on level 4 and 5. It suggests the fitness scale made in the study demonstrates suitably to identify different level of athletes in a similar age group. Results of the retrospective test demonstrate the differences in different fitness levels of each group. (Figure 2)

CONCLUSIONS
13 parameters were chosen for teenage Chinese male sprinters' specific fitness indices, which could be categorized into 3 general categories and 9 subcategories. The final scale for teenage Chinese male sprinters' specific fitness has established the relationships and influences between parameters. Indices regarding teenage Chinese male sprinters' specific fitness can be categorized generally to anthropometric, physiological function and motor ability. Anthropometric indices indicate innate limits in high-speed sprinting motion structure; physiological indices indicate athletes' potential to express energy and recover in a short time; motor abilities indicate athletes' ability of maximum sprinting, reaction strength of lower extremities, power and maximum strength. Coaches and practitioners should emphasize teenage sprinters' ability of acceleration, maximum velocity, speed endurance and lower extremity strength. Moreover, when developing muscle strength for sprinting specific abilities in teenagers, motor ability should be focused on.

ACKNOWLEDGEMENTS
We thank Beijing Sport University lab for the help with experimental data collection and the financial support from Fundamental