TACTICAL APPLICATION OF BIOMECHANICS TO VOLLEYBALL USING INTERACTIVE COMPUTER SOFTWARE

Biomechanics of the techniques of volleyball players have been studied in several research papers (Coleman et aI, 1993, Huang et ai, 1998), but the application of fluid dynamics to the behaviour of volleyballs after spiking impact has only been investigated in one study (Kao et ai, 1994). The tactical uses of information on the flight of volleyballs were considered briefly in Kao et al.'s paper, but there were some omissions and errors concerning players' tactical capabilities. It was therefore the aim of this study to design and construct computer software which would allow coaching staff (or their support teams) to make objective decisions about defensive and offensive tactics in volleyball

The measurement of maximal power output during short-term cycle ergometry

One of the most popular methods of assessment of power output during short-term maximal of exercise is the Wingate Anaerobic Test (WAnT), but this test suffers from serious conceptual limitations. Therefore, the first aim of this study was to investigate the theoretical underpinnings and practical implementation of correct power measurement in the WAnT. The second aim was to design and construct a pair of force pedals, and the last objective was to use these pedals to analyse the force application and power output of elite sprint cyclists during maximal ergometry. The inertial and frictional characteristics of Monark ergometer flywheels were assessed using 'run-down' techniques. Moments of Inertia of 0.411 (±0.001) and 0.396 (±0.002) kg.m. 2 were found for the two Monark 864 ergometers measured, with the newer 814 ergometer possessing a value of 0.962 (±0.003) kg.m. 2 . Frictional torques of 0.0025 (±0.0030) to 0.1720 (±0.00 16) N.m. were found, depending on the attachments to the flywheel and chainset. These values were then utilised to correct the power outputs obtained during the WAnT. Corrected powers were found to produce significantly (P<0.001) larger peak and mean power outputs than those obtained using uncorrected methods. The methods used also produced significantly different (P<0.01) corrected power outputs to those of Lakomy (1986), who utilised an incorrect method of'acceleration-correction'. The force pedals were found to be highly linear in calibration and force measurement, as well as suitable for ergometer cycling. These were then used to test elite sprint cyclists on a modified Monark ergometer. The results of the sprint testing of cyclists found no overall significant difference between power measured indirectly (at the flywheel) and that measured at the pedals. There were significant differences between flywheel and pedal power outputs at high pedal velocity, and this was attributed to large crank torques, in agreement with Sjøgaard (1978). Also noted were differences in force application patterns between cyclists, indicating the use of a variety of pedalling techniques. It was concluded that inertial correction of the WAnT is mandatory for the accurate measurement of power output, and that this needs to be based on sound mechanical principles. This study has also shown that is possible to measure power accurately using indirect methods. However, if the individual techniques of elite sprint cyclists are to be examined in detail, it is necessary to utilise force pedals

THE USE OF FORCE PEDALS FOR ANALYSIS OF CYCLING SPRINT PERFORMANCE

INTRODUCTION: Force application patterns in cycling have been studied using cadences between 60-100 rpm, but not during sprint cycling. The aim of this study was to investigate the force application patterns during sprint cycling (above 135 rpm), and to compare these with those obtained for constant velocity exercise in other studies. METHODS AND PROCEDURES: Two piezoelectric force transducers (Kistler 8067) were incorporated into two specially-designed pedals, and statically calibrated for vertical loads of 0 to 2000N and antero-posterior and medio-lateral loads of -2000 to 2000N. Crank and pedal angles were measured with continuous turn potentiometers. 9 national and international sprint cyclists (mean age 26.5 ñ 2.7yr, height 1.80 ñ 0.06m, mass 82.0 ñ 6.6kg) performed a 10s sprint on a Monark 864 ergometer against a load of 9% body mass (to simulate a track 200m sprint). Data were sampled at 100Hz. Specially-written software calculated Effective and Ineffective crank forces, and computed the Index of Effectiveness (Sanderson, 1991) RESULTS AND DISCUSSION: Two distinct pedalling styles emerged. Two subjects demonstrated smooth application of pedal forces throughout the whole pedal cycle; whereas, others applied very large forces (up to 1100N) only in a small range of crank angles (90 to 135ø past TDC). ‘Smooth’ pedallers had a greater Index of Effectiveness, suggesting more mechanically efficient cycling. No subjects showed an upward ‘pull’ on the pedals during recovery (BDC to TDC), in contrast to earlier studies examining steady state cycling. CONCLUSIONS: The force pedals realised interesting aspects of force application during sprint cycling. Further study should be carried on actual bicycles and, if possible, in track situations. Previous research on steady-state cycling cannot be generalised to sprinting at high cadences. REFERENCES: Sanderson, D. J. (1991). The Influence of Cadence and Power Output in the Biomechanics of Force Application During Steady-Rate Cycling in Competitive and Recreational Cyclists. Journal of Sports Sciences 9, 191-203

LANDING FORCES IN VOLLEYBALL SPIKING AND BLOCKING

The present study sought to investigate Vertical Ground Reaction Forces during landings from volleyball spiking and blocking actions. 16 players from Scottish Division 1 and 2 teams performed 10 spikes, 10 blocks from the right and 10 from the left, landing on two Kistler force plates. Kinematic data were also obtained using a 6-camera Qualisys motion capture system. The spike resulted in significantly larger VGRF than either of the blocks, probably due to the greater maximum height attained in the jump. Analysis of the significant interaction between action and feet showed that in the block to the right, the right foot experienced a significantly larger VRGF than the left. There were large inter-individual differences and coaches need to examine techniques closely before making recommendations about landings

INITIAL BALL SPEED AND FORCE ESTIMATION AT IMPACT IN VOLLEYBALL AND FOOTBALL

This study was undertaken to show how with a simple electronic design we could estimate the initial speed of a ball at impact as well as the force exerted on it. The system has been used for top elite, top university and beginners volleyball and football players. The electronic system can provide the time of flight of ball and also the time of impact. From the time of flight, the initial ball speed can be obtained while from the time of impact the force exerted to ball can be estimated. The results showed that highly skilled players apply larger forces and produce higher ball speeds than lower- level athletes. The values of initial speeds and forces achieved by this simple arrangement are very comparable to those obtained by other researchers

Skyrmions from a Born-Infeld Action

We consider a geometrically motivated Skyrme model based on a general covariant kinetic term proposed originally by Born and Infeld. We introduce this new term by generalizing the Born-Infeld action to a non-abelian $SU(2)$ gauge theory and by using the hidden gauge symmetry formalism. The static properties of the Skyrmion are then analyzed and compared with other Skyrme-like models.Comment: 11 pages, 4 figures (not included), revtex v3, LAVAL-PHY-11-9

The WATER study: Which AquaTic ExeRcises increase muscle activity and limit pain for people with low back pain?

ObjectiveAquatic exercise therapy is used for the treatment and management of chronic low back pain (CLBP). However, to the authors’ knowledge, no studies to date have compared muscle activity between different aquatic exercises performed by people with CLBP. As such, this study assessed and compared muscle activity, pain, perceived exertion and exercise intensity between different rehabilitative aquatic exercises.DesignCross-sectional.SettingA 25-m indoor swimming pool within a university building.ParticipantsTwenty participants with non-specific CLBP.AssessmentTwenty-six aquatic exercises in shallow water (1.25-m depth). Muscle activity was quantified bilaterally for the erector spinae, multifidus, gluteus maximus and medius, rectus abdominis, and external and internal obliques.Main outcomesMean and peak muscle activity, pain (visual analogue scale), perceived exertion (Borg scale) and exercise intensity (heart rate).ResultsHip abduction/adduction and extension/flexion exercises produced higher activity for gluteal muscles. Variations of squat exercises increased the activity of back extensors. Higher abdominal muscle activity was produced with exercises that made use of buoyancy equipment and included leg and trunk movements while floating on the back, and with some proprioceptive and dynamic lower limb exercises. Pain occurrence and intensity were very low, with 17 exercises being pain free.ConclusionsThis study provides evidence on trunk and gluteal muscle activity, pain, intensity and perceived exertion for people with CLBP performing aquatic exercises. The findings may be useful when prescribing exercises for rehabilitation, as physiotherapists seek to implement progression in effort and muscle activity, variation in exercise type, and may wish to target or avoid particular muscles.Contribution of the Paper• This is the first study to compare trunk or gluteal muscle activity between 26 different aquatic rehabilitative exercises performed by people with CLBP.• Pain occurrence and intensity of aquatic exercises are very low, with most exercises being completely pain free.• The following aquatic exercises are particularly effective in increasing muscle activity: (a) hip abduction/adduction and extension/flexion exercises for gluteus maximus and medius; (b) squat exercises for back extensors (erector spinae and multifidus); and (c) exercises that make use of support buoyancy equipment and include leg movements while floating on the back for abdominals (rectus abdominis, and external and internal obliques)

Using a cognitive architecture to examine what develops

Different theories of development propose alternative mechanisms by which development occurs. Cognitive architectures can be used to examine the influence of each proposed mechanism of development while keeping all other mechanisms constant. An ACT-R computational model that matched adult behavior in solving a 21-block pyramid puzzle was created. The model was modified in three ways that corresponded to mechanisms of development proposed by developmental theories. The results showed that all the modifications (two of capacity and one of strategy choice) could approximate the behavior of 7-year-old children on the task. The strategy-choice modification provided the closest match on the two central measures of task behavior (time taken per layer, r = .99, and construction attempts per layer, r = .73). Modifying cognitive architectures is a fruitful way to compare and test potential developmental mechanisms, and can therefore help in specifying “what develops.

Entanglement and purity of two-mode Gaussian states in noisy channels

We study the evolution of purity, entanglement and total correlations of general two--mode Gaussian states of continuous variable systems in arbitrary uncorrelated Gaussian environments. The time evolution of purity, Von Neumann entropy, logarithmic negativity and mutual information is analyzed for a wide range of initial conditions. In general, we find that a local squeezing of the bath leads to a faster degradation of purity and entanglement, while it can help to preserve the mutual information between the modes.Comment: 10 pages, 8 figure

Abundance and degree of residency of humpback dolphins Sousa plumbea in Mossel Bay, South Africa

Indian Ocean humpback dolphins Sousa plumbea inhabit nearshore waters from South Africa to eastern India. Humpback dolphins are vulnerable to conservation threats due to their naturally small population sizes and use of nearshore habitats, where human activities are highest. We investigated the abundance and residency of this species inhabiting Mossel Bay, South Africa, using photographic mark-recapture. Data were collected during 81 surveys in Mossel Bay between 2011 and 2013. Open population modelling using the POPAN parameterisation produced a ‘super-population’ estimate of 125 individuals (95% CI: 61–260) and within-year estimates of between 33 and 86 individuals (2011: 71 [95% CI: 30–168]; 2012: 33 [15–73], 32 [15–70]; 2013: 46 [20–108]). Although less appropriate, closed capture models were also run for comparison with previous studies in the region and generated similar, but slightly smaller, population estimates within each year. We compared our catalogue with opportunistic data collected from East London, Plettenberg Bay, De Hoop and Gansbaai. The only catalogue matches attained were between Plettenberg Bay (n = 44 identified) and Mossel Bay (n = 67 identified), separated by 140 km. Population exchange was moderate, with nine individuals resighted in multiple years between these two areas. This study supports previous findings of long-range movements for this species and provides a baseline from which to assess future impacts on the population.http://www.tandfonline.com/loi/tams202017-04-30hb201