Effects of deceleration-focused exercise strategies on shoulder range of motion and throwing velocity in baseball and softball athletes.

This study examined the effects of deceleration-focused exercises on shoulder range of motion and throwing velocity in both softball and baseball players. Volunteers included 28 Division III William Paterson University baseball and softball athletes (18 females and 10 males), who were evenly distributed across two groups both undertaking 14 sessions of either resistance band or handheld medicine ball exercises (band vs. ball group). A pre-test and post-test measured participants' best active internal/external shoulder rotation and best throwing velocity at a target 40 ft away. A two-tailed, independent t-test showed no significant differences in velocity, internal rotation or external rotation (p < 0.01) between the band and ball groups. However, the average change in velocity in the ball group was double that of the band group (1.50 ± 2.06 m/s versus 0.73 ± 2.24 m/s). For change in both internal and external rotation the band group (2.86 ± 5.27° and 3.29 ± 3.87°, respectively) was greater than the ball mean (1.93° ± 3.32° and 1.29 ± 6.52°, respectively). These findings suggest that overhead athletes aiming to increase throwing velocity can benefit from performing deceleration training with weighted balls whereas resistance bands appear to improve shoulder rotation.

A new geometric-based model to accurately estimate arm and leg inertial estimates.

Segment estimates of mass, center of mass and moment of inertia are required input parameters to analyze the forces and moments acting across the joints. The objectives of this study were to propose a new geometric model for limb segments, to evaluate it against criterion values obtained from DXA, and to compare its performance to five other popular models. Twenty five female and 24 male college students participated in the study. For the criterion measures, the participants underwent a whole body DXA scan, and estimates for segment mass, center of mass location, and moment of inertia (frontal plane) were directly computed from the DXA mass units. For the new model, the volume was determined from two standing frontal and sagittal photographs. Each segment was modeled as a stack of slices, the sections of which were ellipses if they are not adjoining another segment and sectioned ellipses if they were adjoining another segment (e.g. upper arm and trunk). Length of axes of the ellipses was obtained from the photographs. In addition, a sex-specific, non-uniform density function was developed for each segment. A series of anthropometric measurements were also taken by directly following the definitions provided of the different body segment models tested, and the same parameters determined for each model. Comparison of models showed that estimates from the new model were consistently closer to the DXA criterion than those from the other models, with an error of less than 5% for mass and moment of inertia and less than about 6% for center of mass location.

A comparison of self-administered proprioceptive neuromuscular facilitation to static stretching on range of motion and flexibility.

Stretching is known to be an effective method for increasing range of motion. Proprioceptive neuromuscular facilitation (PNF) is a stretching technique that is often associated with a partner. The goal of this study was to examine the changes in hip range of motion (ROM) and hip, back and shoulder flexibility (HBSF) after an intervention of self-administered PNF vs. traditional static stretching. Nineteen healthy college-aged individuals (ages 19-25 years) completed the study. Participants were tested preintervention and postintervention for hip ROM and HBSF using a goniometer and sit-and-reach test, respectively. Interventions included static or self-PNF hamstring stretching 2 × 40 seconds on each leg for 6 weeks. Participants were randomly placed in a group, and upon completion of the intervention and a 1-week rest period, they repeated the process with the other intervention. Statistical analysis revealed that there was a significant difference (p < 0.01) in the change in hip ROM and HBSF between the static stretch and self-PNF group. Mean and SD changes in the hip ROM were -6.2 ± 6.6° vs. 0.6 ± 4.5° for the PNF and static groups, respectively (where a negative value indicates an increase in ROM) and 5.2 ± 3.3 cm vs. 2.0 ± 2.6 cm, respectively, for HSBF. In addition, significant improvements (using 99% confidence intervals) were found in the 2 measures after the PNF intervention but only in HBSF after the static stretching intervention. These results suggest that self-PNF can be used in place of static stretching, does not require a partner, and gives control of the stretching to the individual.

Comparison of pitching kinematics between youth and adult baseball pitchers: a meta-analytic approach.

Coaches teach proper mechanics at a young age in an effort to increase pitching efficiency (i.e., proper pitching mechanics). Unfortunately, the mechanics taught to beginning pitchers are based on the findings from adult pitchers and may result in techniques that are detrimental to younger pitchers. The purpose of this study was to compare kinematics published for pitchers across various ages in an effort to determine whether the pitching techniques vary across developmental periods. A meta-analysis of papers published describing pitching kinematics for youth and adult pitchers was conducted. Maximal rotational velocity of the trunk and maximum external rotation of the shoulder were observed during the arm cocking phase. Peak magnitudes for abduction, horizontal adduction, and shoulder internal rotation were observed during the deceleration phase of the movement. In addition, by comparing previously published data across youth and adult pitchers, valuable insight into the differences in mechanics was gained. The results demonstrated that there are some distinct differences between youth and adult pitching mechanics. This finding may allow increased focus to be applied to those parameters observed to differ across age, increasing the knowledge base available for coaches to properly instruct youth pitchers.

Influence of the volume and density functions within geometric models for estimating trunk inertial parameters.

The geometric method combines a volume and a density function to estimate body segment parameters and has the best opportunity for developing the most accurate models. In the trunk, there are many different tissues that greatly differ in density (e.g., bone versus lung). Thus, the density function for the trunk must be particularly sensitive to capture this diversity, such that accurate inertial estimates are possible. Three different models were used to test this hypothesis by estimating trunk inertial parameters of 25 female and 24 male college-aged participants. The outcome of this study indicates that the inertial estimates for the upper and lower trunk are most sensitive to the volume function and not very sensitive to the density function. Although it appears that the uniform density function has a greater influence on inertial estimates in the lower trunk region than in the upper trunk region, this is likely due to the (overestimated) density value used. When geometric models are used to estimate body segment parameters, care must be taken in choosing a model that can accurately estimate segment volumes. Researchers wanting to develop accurate geometric models should focus on the volume function, especially in unique populations (e.g., pregnant or obese individuals).

Biomechanical analysis of forearm pronation and its relationship to ball movement for the two-seam and four-seam fastball pitches.

This study examined forearm pronation in relation to both the vertical and horizontal ball movement measured for 2 variations of the fastball pitch. Ten healthy collegiate baseball pitchers participated in the study (age: 19.4 +/- 0.7 yr, height: 1.90 +/- 0.06 m, mass: 88.50 +/- 9.05 kg). Reflective markers were placed at the level of each joint center's location, and standard high-speed video techniques were used to record the participants as they threw 10 maximal effort fastball pitches. Marker positions were digitized in each video frame from which forearm pronation data were calculated. Across all pitchers, magnitude of both the vertical and horizontal ball movement was observed to be greater for the 2-seam fastball than for the 4-seam fastball. Regardless of pitch type, positive relationships were observed between all forearm pronation parameters and both vertical and horizontal ball movement. A significant positive correlation (r = 0.583, p < 0.01) was identified between forearm pronation acceleration at ball release and the magnitude of vertical ball movement regardless of pitch type. These results suggest that pitchers may be able to manipulate the magnitude of vertical ball movement by altering pronation accelerations at ball release. In addition, it appears that pitchers should alter their current training techniques so as to increase the endurance capabilities of the primary pronator muscles of the forearm. In doing so, they may be able to limit the effects of fatigue on these muscles during pitching, thus preventing a decrease in the magnitude of vertical ball movement that typically occurs late in a pitching performance.

A comparison between a new model and current models for estimating trunk segment inertial parameters.

Modeling of the body segments to estimate segment inertial parameters is required in the kinetic analysis of human motion. A new geometric model for the trunk has been developed that uses various cross-sectional shapes to estimate segment volume and adopts a non-uniform density function that is gender-specific. The goal of this study was to test the accuracy of the new model for estimating the trunk's inertial parameters by comparing it to the more current models used in biomechanical research. Trunk inertial parameters estimated from dual X-ray absorptiometry (DXA) were used as the standard. Twenty-five female and 24 male college-aged participants were recruited for the study. Comparisons of the new model to the accepted models were accomplished by determining the error between the models' trunk inertial estimates and that from DXA. Results showed that the new model was more accurate across all inertial estimates than the other models. The new model had errors within 6.0% for both genders, whereas the other models had higher average errors ranging from 10% to over 50% and were much more inconsistent between the genders. In addition, there was little consistency in the level of accuracy for the other models when estimating the different inertial parameters. These results suggest that the new model provides more accurate and consistent trunk inertial estimates than the other models for both female and male college-aged individuals. However, similar studies need to be performed using other populations, such as elderly or individuals from a distinct morphology (e.g. obese). In addition, the effect of using different models on the outcome of kinetic parameters, such as joint moments and forces needs to be assessed.

Estimating segment inertial parameters using fan-beam DXA.

Body segment inertial parameters are required as input parameters when the kinetics of human motion is to be analyzed. However, owing to interindividual differences in body composition, noninvasive inertial estimates are problematic. Dual-energy x-ray absorptiometry (DXA) is a relatively new imaging approach that can provide cost- and time-effective means for estimating these parameters with minimal exposure to radiation. With the introduction of a new generation of DXA machines, utilizing a fan-beam configuration, this study examined their accuracy as well as a new interpolative data-reduction process for estimating inertial parameters. Specifically, the inertial estimates of two objects (an ultra-high molecular density plastic rod and an animal specimen) and 50 participants were obtained. Results showed that the fan-beam DXA, along with the new interpolative data-reduction process, provided highly accurate estimates (0.10-0.39%). A greater variance was observed in the center of mass location and moment of inertia estimates, likely as a result of the course end-point location (1.31 cm). However, using a midpoint interpolation of the end-point locations, errors in the estimates were greatly reduced for the center of mass location (0.64-0.92%) and moments of inertia (-0.23 to -0.48%).

Trunk density profile estimates from dual X-ray absorptiometry.

Accurate body segment parameters are necessary to estimate joint loads when using biomechanical models. Geometric methods can provide individualized data for these models but the accuracy of the geometric methods depends on accurate segment density estimates. The trunk, which is important in many biomechanical models, has the largest variability in density along its length. Therefore, the objectives of this study were to: (1) develop a new method for modeling trunk density profiles based on dual X-ray absorptiometry (DXA) and (2) develop a trunk density function for college-aged females and males that can be used in geometric methods. To this end, the density profiles of 25 females and 24 males were determined by combining the measurements from a photogrammetric method and DXA readings. A discrete Fourier transformation was then used to develop the density functions for each sex. The individual density and average density profiles compare well with the literature. There were distinct differences between the profiles of two of participants (one female and one male), and the average for their sex. It is believed that the variations in these two participants' density profiles were a result of the amount and distribution of fat they possessed. Further studies are needed to support this possibility. The new density functions eliminate the uniform density assumption associated with some geometric models thus providing more accurate trunk segment parameter estimates. In turn, more accurate moments and forces can be estimated for the kinetic analyses of certain human movements.

A pilot study of a dynamical systems approach to examining changes in static balance of adolescents.

In a dynamical systems model, movement patterns are dictated by several variables, called control parameters. The goal of this pilot study was to assess whether changes on a static balance task can be described by a dynamical systems model with body inertial properties as one of the potential control parameters. Three aspects of a dynamic system were examined in relation to a 2-ft. static balance task: a relation between the changes in the balance pattern and the control parameter, a relation between the stability of the balance pattern and the stability under perturbed conditions (1-ft. balance task), and during the perturbation lack of relation between the balance pattern and the control parameters. Nine adolescent boys, 15.3 +/- 1.0 yr. old were examined twice over a 14-wk. period. During each testing session, participants' body mass, moments of inertia, and radius from the ankle to the center of mass were calculated, after which 1- and 2-ft. balance tasks were performed. Center of pressure coordinates were recorded using a Kistler force plate. The body parameters were used to calculate the natural frequency of the body to represent the control parameter. Significant relations among all three aspects of a dynamic system examined in both the lateral and anterior-posterior axes were found. This investigation was designed for exploratory purposes and limited to correlational analysis; therefore, no concrete conclusions could be drawn. The results, however, suggest a dynamical systems approach to the study of static balance patterns may be possible.