Relationships among Maximal and Explosive Strength Production of the Leg Extensors and Vertical Jump Peak Power Output in Female Youth Volleyball Athletes

ABSTRACT Architectural and physical performance measurements are commonly implemented to identify various physical capacities in many populations. However, previous research has suggested architectural measures, notably in the leg extensors, are ineffective predictors of vertical jumping (VJ) performance. Given the functional relevance of rapid strength development on explosive dynamic tasks, further research is warranted examining, a) the presence of associations of maximal (e.g., peak torque; PT) and, in particular, explosive (e.g., rate of torque development; RTD) strength-related characteristics with jumping performance in the leg extensors, and b) the extent to which PT and RTD either uniquely, or synergistically contribute to VJ performance. The purpose of this study was to examine the relationships between isometric maximal and explosive strength measures of the leg extensors and VJ peak power (PP) output in female youth volleyball athletes. Thirty (mean ±SD, range: age= 13.73±1.11, 12-17 years, height=162.53±6.39 cm, body mass=57.84±12.05 kg) female youth competitive volleyball players reported to the laboratory on two occasions, with the first visit being a familiarization session. The second visit involved experimental testing, in which participants performed two isometric maximal voluntary contractions of the leg extensors on a dynamometer at a leg angle of 60º, followed by three countermovement VJ trials. Subjects performed countermovement jumps, starting in a standing position and feet firmly on the ground. Following the descent to the midpoint position and without pause, the subjects exploded upward as hard and fast as possible. PT and RTD were calculated as the highest 500ms epoch and the slope of the rise in torque in the first 200ms from onset, respectively. Lower-body PP was assessed using a linear velocity transducer, which was attached to the posterior side of a belt that was securely fastened to the subjects’ waistline. Pearson correlation (r) and stepwise linear regression analyses were performed to examine the relationships. Results indicated that both PT (r=0.7) and late RTD (r=0.62) were significantly correlated to PP (p≤0.01). However, linear regression analysis revealed that PT was the only variable entered into the stepwise regression model (R=0.71; R²=0.50). These findings showed that while both maximal and explosive strength variables correlated with VJ performance, only PT was necessary to effectively predict PP output with no additional explained variance from RTD. Thus, training regimens aimed at development of high force production of the leg extensors may enhance PP production during explosive vertical jump tasks more so than enhancing early rapid force production

Leg Lean Mass Adaptations Following Short-Term Barbell Training in Women

Participation in a resistance training program results in both neural adaptations and increases in lean body mass, the latter of which is considered a slow process. The majority of previous investigations that have examined the time course associated with muscular adaptations have utilized exercise machines or single-joint movements. Furthermore, the adaptations associated with resistance training in women are not as well understood as those for men. The purpose of this investigation was to examine the effects of a four week resistance training intervention on changes in leg lean mass in untrained, college-aged women. Thirty-five women (mean ± SD age = 21 ± 3 years; body mass = 61.9 ± 10.4 kg) with no previous lower-body strength training experience were randomly assigned to high volume training (n = 11), low volume training (n = 10), and control (n = 14) groups. The training groups performed the barbell back squat and deadlift twice per week for four weeks. The low volume training group performed five repetitions of two sets per exercise; the high volume group performed an additional two sets per exercise. The external loads were increased progressively during each training session. The mean ± SD external loads used in this study increased from 27.9 ± 8.2 to 51.4 ± 14.0 kg for the barbell back squat and from 34.2 ± 7.7 to 60.2 ± 10.1 kg for the deadlift. Body composition analyses were performed during pre- and post-testing with dual X-ray absorptiometry. Manufacturer provided software was used to determine the appropriate region of interest in the assessment of leg lean mass. An analysis of covariance was used to compare the post-test data, and the pre-test data were used as the covariate. The results indicated that there was a statistically significant difference among the adjusted post-test means. Specifically, when the pre-test scores served as the covariate, the mean leg lean mass for the high volume training group was 0.503 kg greater than that for the control group (p = 0.031, 95% CI for adjusted mean difference = 0.038 to 0.968 kg). The pre-test – post-test effect sizes for the high volume training and low volume training groups were 0.31 and 0.29, respectively. Collectively, these findings demonstrated that a four week, high-volume training program involving barbell back squats and deadlifts produced small increases in leg lean mass in previously untrained women

Isokinetic Fatigue Characteristics for the Leg Extensors versus Flexors

Maximal isokinetic muscle actions are often used in research studies to examine fatigability and even estimate muscle fiber-type. However, the majority of previous investigations have examined these topics for the leg extensors (i.e., quadriceps), and we are unaware of investigations that have specifically assessed the fatigue characteristics for the flexors (i.e., hamstrings). The purpose of this study was to compare the percent decline values for the leg extensors versus flexors for 50 and 100 repeated, maximal concentric isokinetic muscle actions. Fifteen healthy men (mean ± SD age = 23 ± 3 years; body mass = 94.1 ± 11.9 kg) with previous lower-body strength training experience volunteered to participate in this study. All of the subjects were familiarized with the testing procedures prior to data collection. For data collection, each subject performed 100 repeated, maximal concentric isokinetic muscle actions of the left leg extensors and flexors in a reciprocal manner. Each muscle action was performed at 180 degrees/second through a full 90 degree range of motion. Strong verbal encouragement was provided throughout testing. Percent decline was determined using the mean peak torque values of the initial and final three muscle actions for each muscle group (i.e., extensors versus flexors) and condition (i.e., 50 versus 100 repetitions). A two-way repeated measure analysis of variance was used to examine the data. The mean ± SD percent decline for the leg extensors was 61.8 ± 7.8 and 71.2 ± 6.5% for the 50 and 100 conditions, respectively (Cohen’s d = 1.31). For the leg flexors, these corresponding values were 48.0 ± 12.2 and 54.3 ± 11.7 % (Cohen’s d = 0.53). There was no significant muscle group × condition interaction (p= .114; partial eta squared = .169) There were, however, main effects for both factors. The bonferroni marginal mean pairwise comparisons indicated that when collapsed across condition, the leg extensors fatigued more so than the flexors (66.5 vs. 51.2%). Similarly, when collapsed across muscle group, the percent decline values were greater following 100 (62.8%) versus 50 (54.9%) repetitions. These finding demonstrated greater isokinetic fatigue characteristics for the leg extensors versus flexors. Furthermore, the additional decline in peak torque from repetitions 50-100 was more pronounced for the extensors. We speculate that these findings could be related to differences in muscle fiber-type, lower absolute strength and mass for the posterior aspect of the thigh, and/or unfamiliarity with single-joint testing of the leg flexors

Relationships Between Anthropometric and Performance Variables in Youth: Predictors of Lower-Body Vertical Jump Peak Power

ABSTRACT Anthropometric and physical performance measurements are commonly used for identifying specific physical traits in youth. Laboratory-based tests (e.g., linear velocity transducers), while accurate, provide practical limitations due to high costs and technical necessities. Thus, commonly used field tests may be useful alternatives for assessing fitness/performance characteristics of youth. The purpose of this study was to examine the relationships between anthropometric measures and lower-and upper-body power and strength measures; and to assess the predictive ability of these measures for lower-body vertical jump peak power (PP) output in youth. Thirty-nine pre-adolescent (mean±SD, range: age=7.8±1.7, 5-12 years) children volunteered to participate in this investigation. Subjects were measured for body mass and stature on a calibrated physicians scale. Lower-body PP was assessed using a linear velocity transducer, which was attached to the posterior side of a belt that was securely fastened to the subjects’ waistline. Subjects performed countermovement jumps, starting in a standing position, with hands placed on hips and feet firmly on the ground. Following the descent to the midpoint position and without pause, the subjects exploded upward as hard and fast as possible. Broad jump testing involved subjects performing a countermovement jump in the horizontal direction, on a scaled mat. Maximum isometric hand grip strength of the dominant hand was assessed using a dynamometer. For all testing, 1-2 practice trials were performed, followed by testing consisting of 2-3 trials. The highest trial was used for analyses. Peak power values were normalized to body mass using allometric scaling procedures (PP· body mass-0.67). Pearson correlation (r) and stepwise linear regression analyses were performed to examine the relationships. Results indicated all variables (age, stature, body mass, broad jump and grip strength) were significantly correlated (r=0.38-0.64) to PP. Age was correlated to all variables (r=0.39-0.82) and stature and body mass were correlated to all variables (r=0.37-0.77) except broad jump. Broad jump was correlated only to age (r=0.39) and PP (r=0.38). Linear regression for all variables revealed that stature was the only variable entered into the model (R=0.64; R2=0.41). With the anthropometric variables removed, grip strength was the only variable entered into the model (R=0.57; R2=0.32). These findings suggest that while all the anthropometric and performance variables may be correlated to PP, only stature and grip strength were effective, and thus, necessary to predict PP abilities. Interestingly, broad jump performance was not a good predictor of lower body vertical PP

Linear Progression for Increased External Loads during Strength Training

Improvements in muscular strength require an individual to train with progressively increased external loads over time. While it is well documented that the initial adaptations to strength training occur rapidly, previous researchers have not thoroughly examined the most effective means of inducing these changes. The purpose of this study was to examine the ability to add 2.27 kg to the barbell for 20 consecutive training sessions, and to compare these responses between the sexes. Thirty-four subjects ([mean ± SD age = 23 ± 3 years] men, n = 17; women, n = 17) participated in this study. The subjects were taught how to perform the barbell deadlift exercise, and received individual instruction and verbal feedback regarding their technique throughout the entire investigation. The subjects visited the laboratory twice per week for ten weeks. The external loads corresponded to the maximum weight that each subject could use to perform five sets of five repetitions with correct technique. If five sets of five repetitions were performed, 2.27 kg were added to the barbell for the following training session. The mean external load for each training session was recorded. The data were analyzed with bivariate regression and repeated measures analyses of variance (ANOVAs). The mean ± SD external loads used in this study increased from 66.2 ± 22.3 to 123.1 ± 21.8 kg for the men and 37.8 ± 7.0 to 70.7 ± 12.2 for the women. The results from the repeated measures ANOVAs indicated that men were able to add 2.27 kg to the barbell for 17 consecutive training sessions. For the women, however, the progress stalled at roughly week six. As a result, the coefficient of determination for the external load versus training session number relationship was r2 = .960 for the men and r2 = .881 for the women. These findings demonstrated that adding 2.27 kg to the barbell for each training session was an effective method for progressively increasing the external load over a ten week period. Many of the women had a difficult time with this gradual increase after week six, however, suggesting that smaller absolute changes with fractional plates (e.g., 0.91 kg) may be necessary

Effects of a Ten Week Barbell Deadlift Training Program on Vertical Jump Height in College-Aged Women

The barbell deadlift is a large muscle mass exercise that primarily involves extension at the hip and knee joints. Although it is often incorporated into strength training programs with a variety of other exercises (e.g., back squat), no previous studies have examined the effects of deadlift training on strength or power adaptations. The purpose of this investigation was to examine the effects of a ten week barbell deadlift training program on vertical jump height in previously untrained women. Twenty-eight women (mean ± SD age = 22 ± 2 years) were randomly assigned to either the training group (n = 17) or the control group (n = 11). The training group visited the laboratory for supervised exercise twice per week for ten weeks. Each training session involved five sets of the barbell deadlift, and each set utilized the heaviest external load that allowed for five repetitions with proper exercise technique. If all repetitions were performed with correct technique, additional weight (≤ 2.27 kg) was added to the barbell during the next training session. The control group was asked to refrain from lower-body exercise throughout the course of the study. Vertical jump height was assessed with a Vertec before and after the ten week intervention. An analysis of covariance (ANCOVA) was used to examine the data, and the pretest and posttest values were used as the covariate and dependent variable, respectively. The ANCOVA indicated that the posttest mean for the training group (42.5 cm) was significantly greater than that for the control group (39.0 cm) after adjusting for the pretest vertical jump height scores (p = .012, η² = .229). The effect size for the unadjusted mean increase for the training group (3.6 cm) was considered small-to-moderate (Cohen’s d = .37). These findings demonstrated that a ten week exercise training program using only the barbell deadlift significantly improved vertical jump height in college-aged women

Influence of hamstring fatigue on the estimated percentage of fast-twitch muscle fibers for the vastus lateralis

A previous study has demonstrated the ability to roughly estimate the percentage of fast-twitch muscle fibers for the vastus lateralis through the analysis of peak torque values during fatiguing isokinetic testing. We examined whether use of the hamstrings influenced peak torque and electromyographic (EMG) responses for the quadriceps during fatiguing isokinetic muscle actions. On 2 separate occasions, 21 men (mean age = 23 years) performed 50 repeated, maximal concentric isokinetic muscle actions of the left leg extensors at a velocity of 180°·s−1. For 1 trial, the subjects maximally flexed the knee joint after each full extension to bring the dynamometer\u27s lever arm back to the starting position. For the other trial, the subjects relaxed after each maximal extension and an investigator assisted in returning the lever arm. Surface EMG signals were detected from the vastus lateralis and biceps femoris throughout testing. Dependent variables that assessed the decline in peak torque and EMG mean frequency for the vastus lateralis were examined using dependent samples t-tests, effect size statistics, and the number of subjects who exceeded the minimal difference needed to be considered real. Our results showed small mean differences between the trials (Cohen\u27s d ≤0.136). For the estimated percentage of fast-twitch fibers, none of the subjects showed a difference between trials that we considered meaningful. The mean estimated percentages of fast-twitch fibers were 61.6 and 60.1. Collectively, use of the hamstrings during fatiguing isokinetic testing of the quadriceps had little influence on peak torque and EMG

Peak torque and electromyographic amplitude response to short-term barbell training in women

We investigated the time course of neuromuscular and hypertrophic adaptations associated with only four weeks of barbell squat and deadlift training. Forty-seven previously untrained women (mean ± SD, age = 21 ± 3 years) were randomly assigned to low volume training (n = 15), moderate volume training (n = 16), and control (n = 16) groups. The low and moderate volume training groups performed two and four sets, respectively, of five repetitions per exercise, twice a week. Testing was performed weekly, and included dual X-ray absorptiometry and vastus lateralis and rectus femoris B-mode ultrasonography. Bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis and biceps femoris during isometric maximal voluntary contractions of the leg extensors. Significant increases in lean mass for the combined gynoid and leg regions for the low (+0.68 kg) and moderate volume (+0.47 kg) groups were demonstrated within three weeks. Small-to-moderate effect sizes were shown for leg lean mass, vastus lateralis thickness and pennation angle, and peak torque, but EMG amplitude was unaffected. These findings demonstrated rapid muscular adaptations in response to only eight sessions of back squat and deadlift training in women despite the absence of changes in agonist–antagonist EMG amplitude

Evidence of muscular adaptations within four weeks of barbell training in women

We investigated the time course of neuromuscular and hypertrophic adaptations associated with only four weeks of barbell squat and deadlift training. Forty-seven previously untrained women (mean ± SD, age = 21 ± 3 years) were randomly assigned to low volume training (n = 15), moderate volume training (n = 16), and control (n = 16) groups. The low and moderate volume training groups performed two and four sets, respectively, of five repetitions per exercise, twice a week. Testing was performed weekly, and included dual X-ray absorptiometry and vastus lateralis and rectus femoris B-mode ultrasonography. Bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis and biceps femoris during isometric maximal voluntary contractions of the leg extensors. Significant increases in lean mass for the combined gynoid and leg regions for the low (+0.68 kg) and moderate volume (+0.47 kg) groups were demonstrated within three weeks. Small-to-moderate effect sizes were shown for leg lean mass, vastus lateralis thickness and pennation angle, and peak torque, but EMG amplitude was unaffected. These findings demonstrated rapid muscular adaptations in response to only eight sessions of back squat and deadlift training in women despite the absence of changes in agonist–antagonist EMG amplitude

Barbell deadlift training increases the rate of torque development and vertical jump performance in novices

The primary purpose of this study was to examine the effects of 10 weeks of barbell deadlift training on rapid torque characteristics of the knee extensors and flexors. A secondary aim was to analyze the relationships between training-induced changes in rapid torque and vertical jump performance. Fiftyfour subjects (age, mean 6 SD = 23 6 3 years) were randomly assigned to a control (n = 20) or training group (n = 34). Subjects in the training group performed supervised deadlift training twice per week for 10 weeks. All subjects performed isometric strength testing of the knee extensors and flexors and vertical jumps before and after the intervention. Torque-time curves were used to calculate rate of torque development (RTD) values at peak and at 50 and 200 milliseconds from torque onset. Barbell deadlift training induced significant pre- to post-increases of 18.8–49.0% for all rapid torque variables (p , 0.01). Vertical jump height increased from 46.0 6 11.3 to 49.4 6 11.3 cm (7.4%; p , 0.01), and these changes were positively correlated with improvements in RTD for the knee flexors (r = 0.30–0.37, p , 0.01–0.03). These findings showed that a 10-week barbell deadlift training program was effective at enhancing rapid torque capacities in both the knee extensors and flexors. Changes in rapid torque were associated with improvements in vertical jump height, suggesting a transfer of adaptations from deadlift training to an explosive, performancebased task. Professionals may use these findings when attempting to design effective, time-efficient resistance training programs to improve explosive strength capacities in novices