Objectives: The primary purpose of this study was to examine the difference in peak force (PF) production with and without the inclusion of lifting straps (LS) during an isometric mid-thigh pull (IMTP). An additional goal of this study was to identify potential asymmetry during the two protocols while evaluating the potential use of a dual force plate IMTP as a tool for player monitoring programs. Methods: Twenty-one NCAA division I men (n=10) and women (n=11) soccer players performed a maximal IMTP over dual force plates with and without the assistance of LS. The PF total between the two plates for both conditions was used to examine the effect of LS. Asymmetry was assessed by the PF of the separate force plates by calculation of a symmetry index (SI). Results: The PF achieved with the assistance of LS was significantly greater for males (strapped: 2102.3±506.2N, unstrapped: 1468.6±286.0N; p 1105.0±294.7N, unstrapped: 940.6±155.7N; pConclusion: The inclusion of LS on the IMTP allowed for a significantly greater PF production for male and female soccer athletes. However, the increase in PF with the inclusion of LS was greater in the males who saw a large effect size (d=1.959, pp=0.024). Both male and female soccer players possessed some level of asymmetry that did increase with the inclusion of LS, but no significant difference was found between conditions.

Research has demonstrated a clear relationship between dynamic strength and vertical jump (VJ) performance; however, the relationship of isometric strength and VJ performance has been studied less extensively. The aim of this study was to determine the relationship between isometric strength and performance during the squat jump (SJ) and countermovement jump (CMJ). Twenty-two male collegiate athletes (mean ± SD; age 21.3 ± 2.9 years; height 175.63 ± 8.23 cm; body mass 78.06 ± 10.77 kg) performed isometric midthigh pulls (IMTPs) to assess isometric peak force (IPF), maximum rate of force development, and impulse (IMP) (I100, I200, and I300). Force-time data, collected during the VJs, were used to calculate peak velocity, peak force (PF), peak power (PP), and jump height. Absolute IMTP measures of IMP showed the strongest correlations with VJ PF (r 0.43-0.64; p ≤ 0.05) and VJ PP (r 0.38-0.60; p ≤ 0.05). No statistical difference was observed in CMJ height (0.33 ± 0.05 m vs. 0.36 ± 0.05 m; p 0.19; ES-0.29) and SJ height performance (0.29 ± 0.06 m vs. 0.33 ± 0.05 m; p 0.14; ES-0.34) when comparing stronger to weaker athletes. The results of this study illustrate that absolute IPF and IMP are related to VJ PF and PP but not VJ height. Because stronger athletes did not jump higher than weaker athletes, dynamic strength tests may be more practical methods of assessing the relationships between relative strength levels and dynamic performance in collegiate athletes.

For an ideal impact energy absorber, the initial peak force should be low and the average crushing force should be high. Also, a long stroke and a stable force history are expected. The thin-walled tube under axial loads is a kind of energy absorber that can produce controlled progressive collapse during a crash. It is a promising collapse mechanism for energy absorption with demonstrated success in industry. But the conventional thin-walled tubes still have high initial peak force and force fluctuations during a crushing process. To help to achieve a better energy absorbing structure, a research work has been carried out in this thesis. The aim of the present research is to achieve an improved understanding of the crushing behaviour of thin-walled tubes under axial loads. In the study, the entire crushing process, including the initial stage of collapse, its localization and the subsequent progressive folding has been carefully investigated by experiment. The relation between the localized plastic deformation and the corresponding crushing force is built by comparing the cross section of series of specimens and their load-displacement curves, which give a deep insight of the collapse mechanism of circular thin-walled tube under axial loads. Then some trigger systems are proposed, which is proved to be a good way to reduce the initial peak force and influence the collapse behaviour. To achieve higher energy absorbing efficiency, the multi-cell thin-walled tube has been investigated. Finally, based on the analysis in this study, a new multi-cell profile which is composed of coaxial tubes with different lengths and dented grooves is proposed. The new design is proved to be a good energy absorber with low initial peak force and very high energy absorption efficiency.

The purpose of this dissertation was to determine if a periodized strength and conditioning program resulted in long-term adaptations in NCAA Division I women’s volleyball athletes, and if these changes related to the team’s competitive performance. Specifically, this dissertation serves to: 1.) describe the changes in body composition and performance variables of 2 female volleyball athletes over a 4-year collegiate career, 2.) determine the degree and magnitude of change in performance variables after about 1, 2, and 3 years of periodized resistance training, and 3.) infer if volleyball performance characteristics are related to a team’s competitive success. The following are major findings of this dissertation. 1.) Positive changes in vertical jump height, strength, and explosiveness may be possible throughout 4 years of collegiate volleyball training even with increased body mass and percent body fat. Moreover, impaired ability to perform heavy lower-body resistance training exercises due to chronic injury negatively impacts long-term physical performance adaptations over 4 years. 2.) A combination of traditional resistance training exercises and weightlifting variations at various loads, in addition to volleyball practice, appear to be effective at increasing maximal strength by 44% and vertical jump height by 20%-30% in NCAA Division I women’s volleyball athletes after about two and half years of training. Furthermore, these characteristics can be improved in the absence of additional plyometric training outside of normal volleyball-specific practice. 3.) A rating percentage index RPI ranking ratio and unweighted match score ratio appear to be better predictors of overall team competitive season success than a weighted match score ratio. On the contrary, a weighted match score ratio may be better for determining an association between team match performance and volleyball-specific fitness. A considerable amount of research is needed to develop a volleyball-specific performance index that best quantifies team performance and whether or not a measurable association exists between improved fitness characteristics and increased overall team competitive success. The findings of this dissertation provide evidence that analyzing and monitoring volleyball-related performance variables over time can assist the sport performance group in making training based decisions as well as promote the successful development of an athlete.

The purpose of this study was to determine the acute effects of stretching and local vibration on flexibility and explosive strength in competitive female gymnasts. Flexibility was measured in the forward-split position and jump characteristics were recorded using a force plate. Analysis included flight time (FT), jump height (JH), peak force (PF), instantaneous forces, and rates of force development (RFDs). Randomly assigned and counterbalanced groups were: simultaneous vibration-stretching (VS) (n=22), stretching-only (n=7), and vibration-only (n=8). VS showed statistically greater measures of flexibility in both the right and left leg, favored and non-favored legs pre- versus post-treatment. Vibration-only group resulted in statistically greater right forward-split flexibility and non-favored leg flexibility. There were no statistical differences in JH, FT, PF, instantaneous forces, or RFDs in the VS, stretching-only, and vibration-only groups' pre- versus post-treatment tests. The conclusion was simultaneous vibration-stretching greatly increased flexibility while not altering explosive strength.

This study compared peak force, peak power, peak velocity, impulse, work, and vertical displacement between the high bar back squat (HBBS) and low bar back squat (LBBS). Six trained males performed each using 20, 30, 40, 50, 60, 70, 80, and 90% of their recent training 1 repetition maximum. Dual force plates recorded force-time curve characteristics of ground reaction forces and four potentiometers tracked vertical and horizontal barbell displacement. Repeated–measures analysis of variance revealed a significant main effect for load (p<0.01) across all variables, but no significant effects for condition or interaction. The HBBS generated higher peak force in loads 20%–80%, higher peak power in loads 20%–60% and 80%–90%, higher peak velocity at every load, and greater vertical displacement at every load. The LBBS generated a larger impulse at loads 30%-90% and the HBBS generated more work at loads 20%, 40%, and 60%–90%.

Sprinters are always looking for an improvement in their time, from the gun going off until the finish. An effective start can lead to reaching top velocity sooner and a decreased finish time. New developments in starting blocks, more specifically the width of the starting block pedal, has allowed for variation in foot placement in the blocks. With the ability to change how wide an athlete can place their feet in the blocks, this study looked at trying to find an optimum spacing for college level sprinters. Thirteen Male College Sprinters (mean age = 23.08 years) participated in this study. Subjects self selected their longitudinal block spacing with 3 different lateral positions being tested. In position 1, the feet were placed as narrow as was allowed by the starting block, simulating the width of a traditional set of blocks. Position 2 was defined by the hip width of the individual, distance between right ASIS to left ASIS. Position 3 was the preferred foot width of the subject as determined by completing a vertical jump. Measurements of peak force on the blocks at the time of the start as well as time to 10 m were taken. Neither peak force nor time to 10 m were different between conditions (p = .887, p = .135). The normal condition, position 1 (20cm), was measured to be the narrowest width with position 3 (mean = 37.6cm) being the widest in all subjects. The use of wider pedals on starting blocks is a fairly new idea in track and field, and is something that many athletes have not had the chance to practice with. Since the older style of starting blocks only allowed for a narrow stance that is what track athletes have become accustomed to and could possibly explain why there was no significant difference seen between the 3 starting positions. More research should be done after a time of adaptation to the new starting blocks by the athletes.

No description available.

The use of the isometric squat as a measure of strength and explosiveness. J Strength Cond Res 29(5): 1386–1392, 2015—The isometric squat has been used to detect changes in kinetic variables as a result of training; however, controversy exists in its application to dynamic multijoint tasks. Thus, the purpose of this study was to further examine the relationship between isometric squat kinetic variables and isoinertial strength measures. Subjects (17 men, 1-repetition maximum [1RM]: 148.2 ± 23.4 kg) performed squats 2 d·wk−1 for 12 weeks and were tested on 1RM squat, 1RM partial squat, and isometric squat at 90° and 120° of knee flexion. Test-retest reliability was very good for all isometric measures (intraclass correlation coefficients > 0.90); however, rate of force development 250 milliseconds at 90° and 120° seemed to have a higher systematic error (relative technical error of measurement = 8.12%, 9.44%). Pearson product-moment correlations indicated strong relationships between isometric peak force at 90° (IPF 90°) and 1RM squat (r = 0.86), and IPF 120° and 1RM partial squat (r = 0.79). Impulse 250 milliseconds (IMP) at 90° and 120° exhibited moderate to strong correlations with 1RM squat (r = 0.70, 0.58) and partial squat (r = 0.73, 0.62), respectively. Rate of force development at 90° and 120° exhibited weak to moderate correlations with 1RM squat (r = 0.55, 0.43) and partial squat (r = 0.32, 0.42), respectively. These findings demonstrate a degree of joint angle specificity to dynamic tasks for rapid and peak isometric force production. In conclusion, an isometric squat performed at 90° and 120° is a reliable testing measure that can provide a strong indication of changes in strength and explosiveness during training.

Purpose: To determine the reliability of early force production (50, 100, 150, 200, and 250 ms) relative to peak force (PF) during an isometric mid-thigh pull and to assess the relationships between these variables. Methods:: Male collegiate athletes (N = 29; age 21.1 [2.9] y, height 1.71 [0.07] m, body mass 71.3 [13.6] kg) performed isometric mid-thigh pulls during 2 separate testing sessions. Net PF and net force produced at each epoch were calculated. Within- and between-session reliabilities were determined using intraclass correlation coefficients and coefficient of variation percentages. In addition, Pearson correlation coefficients and coefficient of determination were calculated to examine the relationships between PF and time-specific force production. Results:: Net PF and time-specific force demonstrated very high to almost perfect reliability both within and between sessions (intraclass correlation coefficients .82–.97; coefficient of variation percentages 0.35%–1.23%). Similarly, time-specific force expressed as a percentage of PF demonstrated very high to almost perfect reliability both within and between sessions (intraclass correlation coefficients .76–.86; coefficient of variation percentages 0.32%–2.51%). Strong to nearly perfect relationships (r = .615–.881) exist between net PF and time-specific net force, with relationships improving over longer epochs. Conclusion:: Based on the smallest detectable difference, a change in force at 50 milliseconds expressed relative to PF > 10% and early force production (100, 150, 200, and 250 ms) expressed relative to PF of >2% should be considered meaningful. Expressing early force production as a percentage of PF is reliable and may provide greater insight into the adaptations to the previous training phase than PF alone.