Lower Body Strength and Power Characteristics Influencing Change of Direction and Straight-Line Sprinting Performance in Division I Soccer Players: An Exploratory Study

The purpose of this dissertation was to investigate the influence of lower body strength characteristics on change of direction (COD) performance in NCAA Division I soccer athletes. Specifically, this dissertation served to examine: 1) whether the lower body strength and power were related to COD performance, 2) whether stronger athletes had superior COD performance than weaker athletes, 3) whether the force production asymmetry and strength dominant (SD) associated with COD performance, and 4) weather sex differences existed in kinetic variables during the stand phase of cutting. The major findings of this dissertation include: 1) strength and power characteristics were moderately to strongly related to COD performance. Furthermore, soccer athletes’ straight-line sprinting times were significantly related to COD performance outcomes. 2) Stronger athletes demonstrated the tendency to perform superiorly in modified 505 COD test when compared to weaker athletes. 3) Athletes who had more lower body force production asymmetry were more likely to perform asymmetrically during a COD test. However, the SD and the magnitude of asymmetry were not limiting factors for athletes’ COD performance.4) Male athletes demonstrated statistically significantly less COD total time, longer ground contact time (GCT), and better ability to apply forces and impulses while performing cutting. Based on the results, vertical forces and impulses during both the braking and propulsive phases of cutting ranged from 2.51 to 3.14 times larger than horizontal direction. In summary, stronger and more powerful soccer athletes were able to perform in a superior manner for both the COD tasks and straight-line sprinting. This may be due to the ability to produce high force and power during the critical time periods. Although force production asymmetry during related to the asymmetrical performance during COD tasks, the SD and the magnitude of asymmetry did not limit the COD performance. Finally, statistical differences existed between sexes in kinetic variables during cutting may be due to the different approaches to apply force in this task. Moreover, the ability to generate higher force and impulse in the vertical direction could affect COD performance

THE RELATIONSHIP OF FORCE PRODUCTION ASYMMETRY AND PERFORMANCE IN ATHLETES OF DIFFERENT STRENGTH LEVELS

The purpose of this study was to evaluate the relationship between force production asymmetry and performance of athletes with differing strength levels in males and females. Collegiate athletes (n=129) from various sports were ranked according to isometric mid-thigh pull peak force and the top (‘strong’) and bottom (‘weak’) 25% were used for analysis. Symmetry index (SI) scores were calculated and correlated with their respective force-time characteristics using bivariate correlations. For the weaker males, several negative moderate correlations were observed; however, no statistically significant correlations were observed for the females in either group. These findings indicate that force production asymmetry is inversely related to performance in weaker male athletes during isometric strength testing; however, similar to previous findings, this relationship is not apparent in stronger males

Isometric Force Production Symmetry and Jumping Performance in Collegiate Athletes

Objectives: The purpose of this study was to identify the relationship between isometric force production symmetry and jumping performance in weighted and un-weighted static and countermovement jumps (SJ and CMJ). Design: Bivariate correlation between isometric force production symmetry and vertical jump performance variables. Methods: Collegiate athletes were evaluated for this study (n=36). Subjects performed SJ, CMJ, and isometric mid-thigh pulls (IMTP). Jumps were analyzed for jump height (JH) and peak power (PP). IMTP was analyzed for peak force (PF) for left and right sides, and values were calculated to produce a peak force symmetry index (PF-SI) score. Correlational statistics were performed examining the relationship between PF-SI and jump variables. Results: Moderate statistically significant negative correlations were observed between PF-SI and all jump variables, indicating that as asymmetry increases jump performance decreases. SJ correlations weakened in weighted conditions (JH r=-0.52 @ 0 kg/r=-0.39 @ 20 kg, PP r=-0.43 @ 0 kg/r=-0.34 @ 20 kg), but CMJ produced similar correlations for both conditions (JH r=-0.47 @ 0 kg/r=-0.49 @ 20 kg, PP r=-0.28 @ 0 kg/r=-0.34 @ 20 kg). Unlike the SJ, which only contains the propulsive or concentric portion of the jump, the CMJ also contains the eccentric portion and performance contributions of the stretch-shortening cycle (SSC). The addition of the SSC may play a role in the maintaining the magnitude of asymmetry in the CMJ weighted condition. Conclusions: The results indicate that force production asymmetry may be detrimental to bilateral vertical jumping performance. The findings should be considered for further investigation on sport-specific tasks

DESIGN OF SIMULATIVE PITCHING MACHINE AND IT'S EFFECT

The purpose of this study was to design a simulative device that attached on pitching machine to create the similar pitching motion of real pitcher, and to investigate the subsequent training effect. A photo sensor and automatic switch were used in the design of a simulative device in this study. When light from the photo sensor was cut off by the pitcher's throwing arm, the automatic switch would be turned on immediately and allow a ball to roll down into the pitching machine. Twelve collegiate baseball batters were divided into three groups. A cross-over experimental design was used. Each group involved one of three types of practice after one days rest. The three groups were Type-A: do nothing. Type-B: batting practice by traditional pitching machine. Type-C: batting practice by simulative pitching machine. Each batter hit six balls before and after batting practice for investigating training effect and two baseball experts evaluated batting performance. The results showed that there was significantly increased batting performance after Type-B and Type-C practice (p < .05). Type-C achieved significantly higher batting scores than type-A and Type-B (p < .05) methods. The results suggest that batting practice using a pitching machine with simulative device was an effective batting training method

The Effects of Strength Training on Isometric Force Production Symmetry in Recreationally Trained Males

Objectives: The purpose of this investigation was to determine what effect a bilateral strength training regimen has on isometric force production symmetry and if changes in force production symmetry can be accounted for by differences in pre-intervention strength levels. Design: Sixteen recreationally trained males (1-RM squat: 146.8 ± 23.0 kg.) were assigned to two groups for the 7-week training intervention: strong (S) and weak (W) based on pre-training squat isometric peak force allometrically scaled (IPFa) at 120° knee angle. Methods: Subjects completed a 7-week training intervention following a block-periodized model and were tested on measures of dynamic (1RM squat) and isometric (isometric squat at 90° and 120° knee angle) strength pre- and post-intervention. The degree of bilateral lower limb asymmetry was calculated as a percentage where 0% symmetry index (SI) indicates perfect symmetry on the isometric squat.Results: ANCOVA results showed no statistical difference between groups for all dependent variables when pre-intervention IPFa 120° scores were used as the covariate. Paired t-tests results showed both groups statistically improved 1RM squat and IPFa 120° (p \u3c 0.05). IPFa 120° SI decreased statistically from pre-training in the W group (p = 0.03). Independent t-test results showed the W group had statistically larger pre-intervention SI scores for IPFa 90° (p = 0.045) and IPFa 120° (p = 0.007); however this difference was no longer present following strength training. There was a strong inverse relationship between pooled IPFa 120° and IPFa 120° SI (r = -0.64, p = 0.004). Conclusions: The findings of the current study support the notion that weaker individuals can augment lower limb symmetry with strength training. The same does not seem to be true for stronger individuals who already have a low symmetry index score. These findings indicate that strength training improves force production symmetry in relatively weak males, which may be important for bilateral tasks and injury potential reduction

The Relationship of Force Production Asymmetry and Performance in Athletes of Different Strength Levels

The purpose of this study was to evaluate the relationship between force production asymmetry and performance of athletes with differing strength levels in males and females. Collegiate athletes (n=129) from various sports were ranked according to isometric mid-thigh pull peak force and the top (‘strong’) and bottom (‘weak’) 25% were used for analysis. Symmetry index (SI) scores were calculated and correlated with their respective force-time characteristics using bivariate correlations. For the weaker males, several negative moderate correlations were observed; however, no statistically significant correlations were observed for the females in either group. These findings indicate that force production asymmetry is inversely related to performance in weaker male athletes during isometric strength testing; however, similar to previous findings, this relationship is not apparent in stronger males

LEG DYNAMIC STRENGTH PREDICTORS OF A PRE-PLANNED CHANGE OF DIRECTION TASK IN NCAA DIVISION I SOCCER PLAYERS

The purpose of this investigation was to evaluate the relationships between two types of vertical jumps and change of direction (COD) test in collegiate soccer players (n=24). 5-5 COD test was utilized to measure soccer athletes’ COD ability. 3m acceleration (3mAcc), Total time (TT) and Partial time (PT) were measured by two sets of timing gates. Countermovement jump (CMJ) and static jump (SJ) with 2 different loading conditionings (0kg and 20kg) were employed to evaluate athletes’ leg dynamic strength. Strong statistically significant relationships were found between COD test variables (r =0.71 to 0.90), and between vertical jump variables with PT and TT (r = -0.41 to -0.81). These results suggest that leg dynamic strength is vital for NCAA Division I soccer players’ COD performance and SJ 0kg jump height can be used to predict for COD performance

Leg Dynamic Strength Predictors of a Pre-Planned Change of Direction Task in NCAA Division 1 Soccer Players

The purpose of this investigation was to evaluate the relationships between two types of vertical jumps and change of direction (COD) test in collegiate soccer players (n=24). 5-5 COD test was utilized to measure soccer athletes’ COD ability. 3m acceleration (3mAcc), Total time (TT) and Partial time (PT) were measured by two sets of timing gates. Countermovement jump (CMJ) and static jump (SJ) with 2 different loading conditionings (0kg and 20kg) were employed to evaluate athletes’ leg dynamic strength. Strong statistically significant relationships were found between COD test variables (r =0.71 to 0.90), and between vertical jump variables with PT and TT (r = -0.41 to -0.81). These results suggest that leg dynamic strength is vital for NCAA Division I soccer players’ COD performance and SJ 0kg jump height can be used to predict for COD performance