Barry D. Wilson

The nature and circumstances of tackle injuries in rugby union

This study describes the nature and circumstances of injury occurring in rugby union tackles (33% of 569 injury events) using data from the Rugby Injury and Performance Project (RIPP) and provides supplementary information on the nature of tackles involving injury from analysis of videotape of tackle injury events. The most common tackle injuries in the RIPP data were sprains/strains (41%) followed by haematomas/bruising (26%). The most frequently injured body sites were the head/neck/face (22%) and the knee (17%). The ball carrier and tackler were injured in tackles in similar proportions in both RIPP and New Zealand Rugby Football Union (NZRFU) video tackle incidents. Both players were most often in motion in the tackle at the time of injury with approximately 70% of injuries occurring when the injured player was running or diving/falling to the ground. Tackle injury was most often caused by impact with another player rather than impact with the ground. The use of protective padding may reduce the risk of impact injury. The majority of tackle injuries were associated with stopping tackles to the trunk which were from the front (63%), rather than from the side or behind. Thus consideration should be given to coaching strategies or to rule changes which reduce the likelihood or prohibit front-on tackles.

The New Zealand rugby injury and performance project. III. Anthropometric and physical performance characteristics of players.

OBJECTIVE: To investigate the anthropometric and physical performance characteristics of New Zealand rugby players of different ages and both sexes. METHODS: 356 rugby players (264 male, 92 female) took part in the study during a single season. Playing grade ranged from schoolboys and schoolgirls to senior men and women. Assessment of height, weight, neck circumference, and somatotype was performed before the competitive rugby season. A battery of six physical performance assessments was completed after the anthropometry. Analysis of variance was used to examine differences in these variables between field positions and grades. RESULTS: Significant differences between forwards and backs on anthropometric and physical performance variables were apparent at all grades assessed. In terms of anthropometric characteristics, forwards of a given grade were generally taller, possessed greater body mass, and were more endomorphic and less ectomorphic than backs of the same grade. The backs tended to perform better on physical performance measures than forwards, being more aerobically fit, faster, more agile, and possessing a higher degree of muscular endurance. Differences in anthropometry and physical performance attributes were also apparent between players from the various grades. The players at higher levels were generally larger, and performed better on tests of physical performance than the players at lower levels. These differences were found in both sexes. CONCLUSIONS: The greater body mass of the forwards allows them to obtain greater momentum than the backs when sprinting. The ability to obtain greater momentum is important in the body contact phases of the game. Forwards may compromise their aerobic fitness and speed to some extent in order to maintain a high body mass. The anthropometric and physical performance characteristics of players appear to reflect the demands placed on them by the sport.

Drafting distance in swimming.

PURPOSE This study investigates the effect of the distance separating the lead and draft swimmers on the metabolic and hydrodynamic responses of the draft swimmer. METHODS A nondrafting swim of 4 min at 95% of the best 1500-m pace for 11 swimmers was compared with swimming in a drafting position at four different distances directly behind another swimmer (0, 50, 100, and 150 cm). Swimming performance was assessed by stroke rate and stroke length; the metabolic response by oxygen uptake, heart rate, and blood lactate; and the rating of perceived exertion by the Borg scale. Passive drag was assessed at these drafting distances by passive towing. Then, passive drag was measured in six swimmers towed in six lateral drafting positions, with swimmers separated by approximately 40 cm, and then measured in two positions at the rear of the lead swimmer with a reduced lateral distance between swimmers of 50 and 0 cm. RESULTS Oxygen uptake, heart rate, blood lactate, rating of perceived exertion, and stroke rate were significantly reduced and stroke length was significantly increased in all drafting positions compared with the nondrafting position. For drag, the most advantageous drafting distances were 0 and 50 cm back from the toes of the lead swimmer. Drag was reduced by 21% and 20%, respectively. In lateral drafting, drag was significantly reduced by 6% and 7%, respectively, at 50 and 100 cm back from the hands of the lead swimmer. CONCLUSIONS Swimming behind another swimmer at a distance between 0 and 50 cm back from the toes was the most advantageous, whereas in lateral drafting the optimal distance was 50-100 cm back from the hands of the lead swimmer.

Swimming: Differences in stroke phases, arm‐leg coordination and velocity fluctuation due to event, gender and performance level in breaststroke

Abstract The purpose of this study was to analyse stroke phases, arm‐leg coordination and trunk motion fluctuation during breaststroke in elite male and female 50, 100 and 200m events at the 9th FINA World Swimming Championships, Fukuoka 2001. Four phases of the arm stroke and three phases of the leg kick as well as phases of simultaneous arm and leg propulsion and recovery were identified from video of swimmers’ motions below the surface. The duration of each phase was expressed as a proportion of the whole stroke cycle. Three measures of the arm‐leg coordination, percent simultaneous arm‐leg recovery time (%SRT), percent arm lag time (%ALT) and percent simultaneous arm‐leg propulsion time (%SPT) were calculated. Mean mid‐pool swimming hip velocity (V), stroke rate (SR) and stroke length (SL) were also calculated. In addition, the intra‐cycle hip velocity of the swimmers was obtained by cinematographic analysis. The SR decreased and SL increased significantly as the event distance increased. For the arm‐leg coordination the %ALT, %SPT and %SRT indicated significant differences between event, gender and performance level. In particular, for increasing event distance and for the higher performing swimmer the lower the %SPT and the higher the %SRT. In addition, the range of the intra‐cycle hip velocity fluctuation in the lower performing group was greater than the higher performing group. The non‐propulsive phase seems to be a key factor for better performance. The breaststroke swimmers must avoid rapid deceleration during the non‐propulsive phase by adopting a low resistance posture and stroking technique.

A computational technique to determine the angular momentum of a human body

Abstract A general procedure for determining the angular momentum of a human body is presented. This procedure was used in the analysis of four activities each of which contained an airborne phase. The results were evaluated in terms of repeated determinations of the angular momentum during each airborne phase. It was concluded that the procedure is acceptably accurate for first approximations, that it shows potential for further development and that it is highly versatile.

Protective headgear in rugby union.

SummaryThis article interprets the studies performed on the use of headgear in sport which relate to rugby. The design and testing of helmets and their effective use for protection in sport in general appears to be well documented. This is not the case for the use of protective headgear in rugby. Nevertheless, some conclusions and recommendations are warranted.Protection from the range of impacts that can arise through participation in contact sports does not seem to be attainable by using protective helmets or protective rugby headgear. However, the use of headgear is recommended for protection against lacerations and abrasions and to provide a limited protection from injury caused by impact. Referees should discourage the use of protective headgear, to manipulate an opponent by using the rules to eliminate such behaviour. Coaches, athletes and administrators must be committed to the practice of safe performance skills, for example, by not using the head as an implement and not targeting the headgear of the opposing player.Further research is required to determine the effectiveness of protective headgear in reducing the risk of injury in rugby, whether the use of headgear places a player at a greater risk of injury through altered behaviour and the reasons why players currently choose not to wear headgear.

Effect of Fastskin Suits on Performance, Drag, and Energy Cost of Swimming

PURPOSE To investigate the effect of fastskin suits on 25- to 800-m performances, drag, and energy cost of swimming. METHODS The performances, stroke rate and distance per stroke, were measured for 14 competitive swimmers in a 25-m pool, when wearing a normal suit (N) and when wearing a full-body suit (FB) or a waist-to-ankle suit (L). Passive drag, oxygen uptake, blood lactate, and the perceived exertion were measured in a flume. RESULTS There was a 3.2% +/- 2.4% performance benefit for all subjects over the six distances covered at maximal speed wearing FB and L when compared with N. When wearing L, the gain was significantly lower (1.8% +/- 2.5%, P < 0.01) than when wearing FB compared with N. The exercise perception was significantly lower when wearing FB than N, whereas there was no statistical difference when wearing L. The distance per stroke was significantly higher when wearing FB and L, whereas the differences in stroke rate were not statistically significant. There was a significant reduction in drag when wearing FB and L of 6.2% +/- 7.9% and 4.7% +/- 4.4%, respectively (P < 0.01), whereas the energy cost of swimming was significantly reduced when wearing FB and L by 4.5% +/- 5.4% and 5.5% +/- 3.1%, respectively (P < 0.01). However, the differences between FB and L were not statistically significant for drag and oxygen uptake. CONCLUSION FB and L significantly reduced passive drag, and this was associated with a decreased energy cost of submaximal swimming and an increased distance per stroke, at the same stroke rates, and reduced freestyle performance time.

Estimating subject-specific body segment parameters using a 3-dimensional modeller program

The estimation of body segment properties is important in the biomechanical analysis of movement. Current subject-specific estimation methods however can be expensive and time-consuming, while other methods do not adequately take into account individual or group variability. We describe a simple procedure for estimating subject-specific geometric properties, independent of joint centres. The method requires only a small number of anthropometric measurements and digital images of the segment or subject, a 3-dimensional modeller program and simple mathematical calculations to estimate segment volumes and centroids. Assuming that the segment is of uniform density, its mass and moment of inertia can also be derived. Future work should include generating segment density profiles for particular populations, to increase the accuracy of the method, and comparing the accuracy of the results obtained with those produced by other techniques.

Prediction of fluid forces acting on a hand model in unsteady flow conditions

The aim of this study was to develop a method to predict fluid forces acting on the human hand in unsteady flow swimming conditions. A mechanical system consisting of a pulley and chain mechanism and load cell was constructed to rotate a hand model in fluid flows. To measure the angular displacement of the hand model a potentiometer was attached to the axis of the rotation. The hand model was then fixed at various angles about the longitudinal axis of the hand model and rotated at different flow velocities in a swimming flume for 258 different trials to approximate a swimmers stroke in unsteady flow conditions. Pressures were taken from 12 transducers embedded in the hand model at a sampling frequency of 200Hz. The resultant fluid force acting on the hand model was then determined on the basis of the kinetic and kinematic data taken from the mechanical system at the frequency of 200Hz. A stepwise regression analysis was applied to acquire higher order polynomial equations that predict the fluid force acting on the accelerating hand model from the 12 pressure values. The root mean square (RMS) difference between the resultant fluid force measured and that predicted from the single best-fit polynomial equation across all trials was 5N. The method developed in the present study accurately predicted the fluid forces acting on the hand model.

Modification of movement patterns to accomodate to a change in surface compliance in a drop jumping task

Abstract This study investigated changes in kinematics as subjects adapted to a change of surface compliance in a drop jumping task. It was hypothesised that changes in the pattern of centre of gravity acceleration with respect to the surface would be associated with improved performance. Six subjects performed 200 trials on a hard surface and then 190 trials on a compliant (sprung) surface. There was considerable improvement in height achieved (0.12 m to 0.41 m) by subjects during the sprung surface trials. With the exception of one subject, improvement was still occuring towards the end of the 190 trials on the sprung surface. The improvement in height was primarily due to improvements in the velocity of the centre of gravity with respect to the surface at last contact. In general, this was not achieved by increasing the displacement over which the centre of gravity could be accelerated with respect to the surface. The pattern of accelerations relative to the surface changed over the learning period and were directly related to improvement in performance as hypothesised. The Fourier spectra of the relative accelerations changed such that the amplitude of higher frequency harmonics increased with practice. There was a gradual shift in the angular kinematics away from the patterns associated with jumps from the hard surface. In particular, flexion of the ankle, knee, and hip following first contact decreased with increasing trials on the sprung surface.