Jumping and Landing Techniques in Elite Women's Volleyball

Volleyball has become one of the most widely played participant sports in the world. Participation requires expertise in many physical skills and performance is often dependent on an individual's ability to jump and land. The incidence of injury in volleyball is similar to the rates reported for sports that are considered more physical contact sports. Though the most common source of injury in volleyball is the jump landing sequence, little research exists regarding the prevalence of jumping and landing techniques. The purpose of this study was to quantify the number of jumps performed by female volleyball players in competitive matches and to determine the relative frequency of different jump-landing techniques. Videotape recordings of two matches among four volleyball teams were analyzed for this study. Each activity was categorized by jump type (offensive spike or defensive block) and phase (jump or landing). Phase was subcategorized by foot use patterns (right, left, or both). Each of the players averaged nearly 22 jump-landings per game. Foot use patterns occurred in unequal amounts (p < 0.001) with over 50% of defensive landings occurring on one foot. Coaches, physical educators, and recreation providers may utilize the findings of this inquiry to help prevent injuries in volleyball. Key PointsThe incidence of injury in volleyball is nearly equivalent to injury rates reported for ice hockey and soccer.Most injuries in volleyball occur during the jump landing sequence, but few data exist regarding jump landing techniques for elite female players.Our data indicate that the vast majority of jumps utilize two feet, but approximately half of landings occur with only one foot.Coaches, physical educators, and recreation providers may utilize the findings of this inquiry to prevent possible injuries in athletes, students, or those who participate in volleyball for recreational purposes.

Variable-ratio pushrim-activated power-assist wheelchair eases wheeling over a variety of terrains for elders11A commercial party with a direct financial interest in the results of the research supporting this article has conferred or will confer a financial benefit on the author or 1 or more of the authors

OBJECTIVES

To test (1) whether a prototype variable-ratio pushrim-activated power-assist wheelchair would decrease effort and perceived exertion associated with wheeling and (2) whether the prototype would be acceptable to elders.

DESIGN

Repeated-measures design.

SETTING

Biomechanics laboratory.

PARTICIPANTS

Eleven elderly wheelers (mean age +/- standard deviation, 70.7+/-7.8 y).

INTERVENTIONS

Wheelers propelled their own wheelchairs and the prototype on a level surface, a carpet, and an incline.

MAIN OUTCOME MEASURES

Surface electromyographic activity from upper limb and torso, heart rate, number of pushes, category-ratio scale of perceived exertion, and Consumer Assessment of Power Assist Wheelchairs.

RESULTS

Compared with subjects' own manual wheelchairs, the prototype was associated with lower heart rate elevation (P<.0125), lower perceived exertion (P<.0125), and reduced electromyographic activity in 5 of 8 muscles. Of the 11 participants, 10 found the prototype to be "very easy" or "easy" to push on level and inclined surfaces; 9 gave that assessment on carpeted and inclined surfaces. Seven would "definitely" or "probably" trade their manual chairs for the power-assist chair if given the opportunity. Nine thought they would venture to new and different places in a power-assist wheelchair. Time and number of pushes to complete tasks did not differ significantly between chairs.

CONCLUSIONS

The prototype reduced the effort associated with wheeling and was an acceptable alternative to manual wheelchairs. Further testing outside the laboratory is warranted.

Braking impulse and muscle activation during unplanned gait termination in human subjects with parkinsonism

Persons with parkinsonism (PD) are known to have difficulty with both rapid force production and declination, and may not be able to adjust force levels during bimanual tasks in the upper extremity. We proposed that these deficits might underlie the problems experienced by those with PD when attempting to rapidly terminate locomotor activity. Rapid gait termination requires concomitant increases in braking impulse and decreases in propulsion impulse. We hypothesized that those with PD would be less able to modulate muscle activity and the associated braking impulse during gait termination. Muscular activity of soleus, tibialis anterior and gluteus medius, and braking impulse were compared between a group of subjects with PD and age and gender matched control subjects. Subjects with PD had similar patterns of muscular activation to control subjects although at dramatically reduced levels of amplitude. Consequently, PD subjects were unable to generate sufficient net braking impulse under time-critical conditions.

Force and repetition in cycling: possible implications for iliotibial band friction syndrome

This study examined force and repetition during simulated distance cycling with regard to how they may possibly influence the on-set of the overuse injury at the knee called iliotibial band friction syndrome (ITBFS). A 3D motion analysis system was used to track lower limb kinematics during cycling. Forces between the pedal and foot were collected using a pressure-instrumented insole that slipped into the shoe. Ten recreational athletes (30.6+/-5.5 years) with no known history of ITBFS participated in the study. Foot-pedal force, knee flexion angle and crank angle were examined as they relate to the causes of ITBFS. Specifically, foot-pedal force, repetition and impingement time were calculated and compared with the same during running. A minimum knee flexion angle of approximately 33 degrees occurred at a crank angle of 170 degrees. The foot-pedal force at this point was 231 N. This minimum knee flexion angle falls near the edge of the impingement zone of the iliotibial band (ITB) and the femoral epicondyle, and is the point at which ITBFS is aggravated causing pain at the knee. The foot-pedal forces during cycling are only 18% of those occurring during running while the ITB is in the impingement zone. Thus, repetition of the knee in the impingement zone during cycling appears to play a more prominent role than force in the on-set of ITBFS. The results also suggest that ITBFS may be further aggravated by improper seat position (seat too high), anatomical differences, and training errors while cycling.

Effect of ball size on player reaction and racket acceleration during the tennis volley

The purpose of this study was to examine the effect of ball size on reaction time (from ball projection to initial racket movement), movement time (from ball projection to ball-racket impact), mean rectified acceleration and vibration frequency of the racket during the impact phase (100 ms duration after ball-racket impact) of the tennis volley. Twenty-nine beginning to intermediate level tennis players performed volleys under 18 experimental conditions including variations in lateral contact location (forehand and backhand), ball type (Penn oversize, Wilson oversize, regular size), and ball speed (fast, medium, slow). A ball machine was shielded so that the subjects could not predict the ball trajectory before it was released from the machine. Outcome measures were determined using a miniature uni-axial accelerometer and a Photogate timing device. ANOVA with repeated measures and Tukey's post hoc tests were used in statistical analyses (p < .025). The reaction times for the fast speed were significantly shorter than the corresponding times for the slow speed and the reaction times for the forehand volley were significantly shorter than that of the backhand volley. The significant interaction in movement time between ball speed and ball type indicates that the benefits of the larger ball (to slow the game down) increase as the ball speed increases. No significant effect of ball type or ball speed, or interactions were found on mean rectified acceleration and vibration frequency. These results suggest that oversized balls would not cause an increased load to the hitting arm while executing a tennis volley.

Differences in three intercondylar notch geometry indices between males and females: a cadaver study

The primary purpose of this unique evaluation of cadaveric skeletal geometry was to compare intercondylar notch geometry between males and females. One hundred male skeletons and 100 female skeletons were evaluated. Three indices of notch geometry were calculated from digital photographs of the distal femur: notch width index, notch area index, and notch shape index. Notch shape index for males exceeded that for females (P<0.004). The intercondylar notch appears less round in females and may play a role in causing ACL injuries. Future studies are required to confirm any link between notch geometry and ACL injury.

An insole pressure measurement system: repeatability of postural data

This study analyzed the ability of an in-shoe plantar pressure measurement system to provide repeatable measurements of postural sway data for both healthy and clinical patients. Each participant's in-shoe pressure data were recorded for three trials during each test session during quiet stance. Healthy individuals (n = 9) participated on three consecutive days while clinical participants (n = 5) were tested on one day. Nine response variables were measured to assess their postural stability. Intrasubject measures were evaluated using the Kerlinger reliability procedure. Values provided directly by the Parotec System for a single day of testing yielded the following average coefficients: r = 0.95 (left), r = 0.97 (right) with mean coefficient values from the three day tests of: r = 0.98 (left), r = 0.98 (right). Variables calculated from raw data on a single day produced mean coefficients of: r = 0.77 (left), r = 0.76 (right) and over three days of: r = 0.65 (left), r = 0.66 (right). The ability to record highly reproducible data of postural sway parameters should assist clinicians to treat patients more confidently for balance deficiencies.

Limit of detection (LQD)/limit of quantitation (LOQ): comparison of the empirical and the statistical methods exemplified with GC-MS assays of abused drugs

The limit of detection (LOD) for any analytical procedure, the point at which analysis is just feasible, may be determined by a statistical approach based on measuring replicate blank (negative) samples or by an empirical approach, consisting of measuring progressively more dilute concentrations of analyte. The limit of quantitation (LOQ), or concentration at which quantitative results can be reported with a high degree of confidence, may likewise be determined by either approach. We used both methods to determine LOD and LOQ for forensic gas chromatographic-mass spectrometric (GC-MS) analyses of abused drugs. The statistically determined LOD and LOQ values for these assays underestimated the LOD because of the large imprecision associated with blank measurements and the inability of blank samples to meet typical GC-MS acceptance criteria. The empirical method provided much more realistic LOD values, supported by reasonable experimental data, and are 0.5-0.03 the magnitude of the corresponding statistical LODs. The empirical LODs and LOQs are identical for these GC-MS assays. The observations made here about the LOD/LOQ for specific forensic GC-MS procedures are generally applicable to any type of analysis.

Limit of detection (LQD)/limit of quantitation (LOQ): comparison of the empirical and the statistical methods exemplified with GC-MS assays of abused drugs

The limit of detection (LOD) for any analytical procedure, the point at which analysis is just feasible, may be determined by a statistical approach based on measuring replicate blank (negative) samples or by an empirical approach, consisting of measuring progressively more dilute concentrations of analyte. The limit of quantitation (LOQ), or concentration at which quantitative results can be reported with a high degree of confidence, may likewise be determined by either approach. We used both methods to determine LOD and LOQ for forensic gas chromatographic-mass spectrometric (GC-MS) analyses of abused drugs. The statistically determined LOD and LOQ values for these assays underestimated the LOD because of the large imprecision associated with blank measurements and the inability of blank samples to meet typical GC-MS acceptance criteria. The empirical method provided much more realistic LOD values, supported by reasonable experimental data, and are 0.5-0.03 the magnitude of the corresponding statistical LODs. The empirical LODs and LOQs are identical for these GC-MS assays. The observations made here about the LOD/LOQ for specific forensic GC-MS procedures are generally applicable to any type of analysis.