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.

Aim: The aim of this study was to investigate the effects of performing an isometric conditioning contraction (CC) consisting of two sets of five seconds maximal voluntary contraction in physically active individuals prior to three sets of Loaded Squat Jumps (LSJ). Method: 5 males and 4 females (mean ± SD: age 25 ± 2 years, height 175 ± 10 cm, body mass 70 ± 15 kg) were assessed on their power output, force production, jump height and velocity on three sets of LSJ on two separate sessions. Each participant attended two sessions in randomized order: a control session (CON) and an experimental session (EXP) separated by at least two hours. The EXP session consisted of a 10 min warm-up followed by 2 x 5 seconds isometric CC, this was proceeded by another two minutes of rest before three sets of LSJ were performed, each set separated by a two-minute rest. During the CON session a two-minute rest, followed by three sets of LSJ, replaced the isometric CC sequence. Results: No significant improvement was found on any of the physical parameters assessed, comparing the CON and EXP session (p > 0.05). The results showed a variance on individual response were some subjects performed better after the CC and others did not . Conclusion: In conclusion, this study evaluated the effect of performing an isometric CC prior three sets of LSJ. The results indicate that an isometric CC consisting of two sets of five seconds maximal voluntary contraction is insufficient to enhance the performance in an LSJ.

The purpose of this study was to understand the relationship between back squat one-repetition maximum relative to body mass (1RMrel), countermovement jump height (CMJH), and optimal drop height in drop jump (DHopt). Fifteen male participants with various sport backgrounds and training experience completed a one repetition maximum (1RM) back squat, maximum countermovement jump (CMJ), and drop jumps (DJ) from incrementally increasing drop heights to determine which drop height elicited the greatest jump height. The DHopt testing protocol was unique in that smaller increments were used to determine DHopt compared to what has been reported in literature previously. Pearson correlation coefficients revealed that DHopt had small (r=0.214) and moderate (r=0.464) relationships with 1RMrel and CMJH, respectively. A second analysis (n=13) was conducted after two participants (i.e. powerlifters) were identified as possibly being representative of a different population. The second analysis found that DHopt had strong relationships with 1RMrel (r=0.645) and CMJH (r=0.690). Results from this study seem to suggest that individuals with greater 1RMrel and CMJH tend to have a higher DHopt. However, this relationship may not be observed among all populations due to likely differences in sport background, genetics, and/or training experience.

A great deal of research has shown decrements in force and power following static stretching. There has been little research investigating the acute effects of static stretching of the antagonist on the expression of strength and power. The purpose of this study was to investigate the effects of static stretching of the antagonist muscles on a variety of strength and power measures. Sixteen active males were tested for vertical jump height and isokinetic torque production in a slow knee extension (KES) at 60°/s and a fast knee extension (KEF) at 300°/s. Electromyography was taken during knee extension tests for the vastus lateralis and the biceps femoris muscles. Participants performed these tests in a randomized counterbalanced order with and without prior antagonist stretching. All variables for stretching and non-stretching treatments were compared using paired t tests at an alpha of .05. Paired samples t tests revealed a significant (p = .034) difference between stretch KEF and non-stretch KEF conditions. There was no significant (p > .05) difference between KES stretch and non-stretch conditions. Vertical jump height was significantly (p = .011) higher for the stretching treatment than the non-stretching treatment. Vertical jump power was also significantly higher (p = .005) in the stretch versus the non-stretch condition. Paired samples t test indicated no significant (p > .05) difference between testing conditions for electromyography, represented as a percentage of maximal voluntary contraction (MVC). These results suggest that stretching the antagonist hamstrings prior to high speed isokinetic knee extension increases torque production. It also demonstrated that stretching the hip flexors and dorsi flexors may enhance jump height and power. Practitioners may use this information to acutely enhance strength and power performances.

Background: Jump height, utilization of the stretch-shortening cycle (SSC) and knee stability is key qualifications and important factors for athletic performance. This is usually practiced with the help of plyometric training. However, plyometric training is considered as an exercise with high-impact that adds stress on the body. Trampoline training is an activity with a growing number of adolescent’s performers, and with the ability to train the same qualities that plyometric training. However, few studies have investigated trampoline trainings effect on jump height, utilization of the SSC and the knee stability in comparison to ordinary plyometric exercises. Aim: The aim of the study was to investigate whether the jump height in a countermovement jump (CMJ) and a squat jump (SJ), the use of SSC and knee stability at landing is different in adolescents who are training using a trampoline and adolescents training using plyometric exercises. Methods: Thirty (n=30) participants, 19 handball players and 11 trampoline practitioners, aged 14-18 years, completed this cross-sectional study. This study involved three tests, a CMJ and a SJ for measuring the jump height and SSCand a double leg drop jump test for measuring the knee stability. Results: The result showed a significant difference in relative jump value between the groups, were the handball group showed a higher value in the CMJ and the SJ compared to the trampoline group. In the utilization of the SSC there were no significant difference between the groups. The result showed that there was a significant difference between the groups knee stability, were the handball group showed a greater knee degrees of varus compared to the trampoline group. Conclusion: Findings from this study suggests that adolescents might benefit from performing plyometric training to achieve a greater jump height and trampoline training to achieve a greater knee stability. Both activities had the same effect on the utilization of theSSC. More studies are needed, including a more homogenous group with larger sample sizes, to support the present results and investigate whether the results are reliable.

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 compare the phase characteristics of the countermovement jump (CMJ) force-time (F-t) curve between athletes based on jumping ability. An initial sample of one-hundred fifty Division-I collegiate athletes were ranked based on CMJ height. Three performance groups were then formed by taking the top, middle, and lower 30 athletes (15 men and 15 women) from the sample. Phases of the CMJ F-t curve were determined and then characterized by their duration, magnitude, area (impulse), and shape (shape factor). A series of 3-way mixed analysis of variance were used to determine statistical differences in phase characteristics between performance groups as well as between male and female athletes. Statistically significant phase-by-performance group interactions were observed for relative phase magnitude (p < 0.001), relative phase impulse (p < 0.001), and shape factor (p = 0.002). Phase-by-sex interactions were statistically significant for both relative phase magnitude (p < 0.001) and relative phase impulse (p < 0.001). Post hoc comparisons indicated that higher jumpers exhibited larger relative magnitude and impulse in the phases contained within the positive area of the F-t curve. Similarly, relative phase magnitude and impulse were the only phase characteristics to be statically different between men and women. Finally, the relative shape of the phase representing the initial rise in force was found to relate to jump height. These results provide some information regarding the diagnostic value of qualitative analysis of the CMJ F-t curve.

PURPOSE: To determine the relative contribution of vastus lateralis (VL) and lateral gastrocnemius (LG) cross-sectional area (CSA) to countermovement jump height (JH) in collegiate athletes. METHODS: Sixty-nine male (n=33, 20.43 ± 1.68 y, 180.34 ± 11.39 cm, 77.54 ± 14.45 kg) and female (n=36, 19.79 ± 1.09 y, 168.46 ± 10.07 cm, 67.33 ± 9.48 kg) collegiate athletes competing in basketball, tennis, cross-country, weightlifting, and volleyball were recruited for the study. Testing was conducted as part of an on-going athlete monitoring program. Athletes were tested on measures of VL and LG CSA using β-mode ultrasonography, and JH measured on force platforms sampling at 1000Hz. Jump height was regressed on age, sex, body mass, VL and LG CSA using a simultaneous multiple linear regression after testing regression assumptions. A relative importance analysis was conducted to determine the relative contribution of each independent variable. The alpha level for all analyses was set at p≤0.05. RESULTS: The model explained 48% of the variance in JH (p<0.001, observed statistical power=0.99). Body mass (B=-0.16, p=0.01), sex (B=-5.10, p<0.001), and VL CSA (B=0.66, p<0.001) were statistical predictors of JH. Age, LG CSA, body mass, sex, and VL CSA contributed 3%, 3%, 7%, 32%, and 55% of the total variance explained by the model, respectively. CONCLUSIONS: Vastus lateralis CSA has a greater contribution to JH than LG CSA while controlling for the variance of age, sex, and body mass. Therefore, greater emphasis should be placed on developing VL CSA than LG CSA for athletes whose goal is to improve JH. Athletes who lose body mass without losing VL CSA may also improve JH.

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