Changes in muscle activation following balance and technique training and a season of Australian football

OBJECTIVES

Determine if balance and technique training implemented adjunct to 1001 male Australian football players' training influenced the activation/strength of the muscles crossing the knee during pre-planned and unplanned sidestepping.

DESIGN

Randomized Control Trial.

METHODS

Each Australian football player participated in either 28 weeks of balance and technique training or 'sham' training. Twenty-eight Australian football players (balance and technique training, n=12; 'sham' training, n=16) completed biomechanical testing pre-to-post training. Peak knee moments and directed co-contraction ratios in three degrees of freedom, as well as total muscle activation were calculated during pre-planned and unplanned sidestepping.

RESULTS

No significant differences in muscle activation/strength were observed between the 'sham' training and balance and technique training groups. Following a season of Australian football, knee extensor (p=0.023) and semimembranosus (p=0.006) muscle activation increased during both pre-planned sidestepping and unplanned sidestepping. Following a season of Australian football, total muscle activation was 30% lower and peak valgus knee moments 80% greater (p=0.022) during unplanned sidestepping when compared with pre-planned sidestepping.

CONCLUSIONS

When implemented in a community level training environment, balance and technique training was not effective in changing the activation of the muscles crossing the knee during sidestepping. Following a season of Australian football, players are better able to support both frontal and sagittal plane knee moments. When compared to pre-planned sidestepping, Australian football players may be at increased risk of anterior cruciate ligament injury during unplanned sidestepping in the latter half of an Australian football season.

Optimizing whole-body kinematics to minimize valgus knee loading during sidestepping: implications for ACL injury risk

The kinematic mechanisms associated with elevated externally applied valgus knee moments during non-contact sidestepping and subsequent anterior cruciate ligament (ACL) injury risk are not well understood. To address this issue, the residual reduction algorithm (RRA) in OpenSim was used to create nine subject-specific, full-body (37 degrees of freedom) torque-driven simulations of athletic males performing unplanned sidestep (UnSS) sport tasks. The RRA was used again to produce an optimized kinematic solution with reduced peak valgus knee torques during the weight acceptance phase of stance. Pre-to-post kinematic optimization, mean peak valgus knee moments were significantly reduced by 44.2 Nm (p=0.045). Nine of a possible 37 upper and lower body kinematic changes in all three planes of motion were consistently used during the RRA to decrease peak valgus knee moments. The generalized kinematic strategy used by all nine simulations to reduce peak valgus knee moments and subsequent ACL injury risk during UnSS was to redirect the whole-body center of mass medially, towards the desired direction of travel.

Use of field-based tests to identify risk factors for injury to fast bowlers in cricket

OBJECTIVE

To identify risk factors for injury to cricket fast bowlers using field-based tests.

DESIGN

Prospective cohort study.

SETTING

High performance Australian cricket.

PARTICIPANTS

Ninety-one male adolescent and adult fast bowlers (aged 12-33 years).

ASSESSMENT OF RISK FACTORS

A field-based pre-participation screening, consisting of musculoskeletal, fitness and anthropometric assessments and analysis of bowling technique was undertaken. Bowlers were prospectively monitored over the 2003-4 season and bowling workload and injuries were recorded. Logistic regression was used to identify injury risk factors.

MAIN OUTCOME MEASUREMENT

Repetitive microtrauma injury to the trunk, back or lower limb associated with fast bowling.

RESULTS

Two variables were identified as independent predictors of injury in the multivariate logistic regression analysis. Bowlers with hip internal rotation of < or =30 degrees on the leg ipsilateral to the bowling arm were at a significantly reduced risk of injury (OR 0.20, 95% CI 0.06 to 0.73) compared with bowlers with >40 degrees of rotation. Bowlers with an ankle dorsiflexion lunge of 12.1-14.0 cm on the leg contralateral to the bowling arm were at a significantly increased risk (OR 4.03, 95% CI 1.07 to 15.21) than bowlers with a lunge of >14 cm. Bowlers with a lunge of < or =12 cm were also at an increased risk, but not significantly so (OR 1.38, 95% CI 0.40 to 4.84).

CONCLUSIONS

Biomechanical research is needed to investigate how these two intrinsic risk factors increase injury risk so that appropriate interventions can be developed.

Comparison of buoyancy, passive and net active drag forces between Fastskin and standard swimsuits

A cross-sectional comparison between the buoyancy, passive and net active drag force characteristics of full-length, Fastskin swimsuits with that of standard swimsuits was completed with nine Open National level swimmers (5 males and 4 females). Subjects were weighed in a hydrostatic tank and then towed via a mechanical winch on the surface and 0.4 m deep at 1.6, 2.2 and 2.8 m/s. The subjects performed a prone streamlined glide and maximum effort flutter kick at each towing velocity and depth. Hydrostatic weight differences between swimsuit types were not significant (p> 0.05. Fastskin passive drag values were significantly less than normal swimsuits during surface towing at 1.6 and 2.8 m/s: and at 0.4 m deep towing at 1.6, 2.2 and 2.8 m/s. Net active drag force values also were lower for the Fastskin suits when compared with those of normal swimsuits and a significant difference existed for surface towing at all three velocities of 1.6, 2.2 and 2.8 m/s. The full-length, Fastskin swimsuits created less total hydrodynamic resistance than normal swimsuits while providing no additional buoyancy benefits.

An upper limb kinematic model for the examination of cricket bowling: a case study of Mutiah Muralitharan

We show how biomechanics can be used to accurately assess spin-bowling techniques (offspin, legspin and topspin) in cricket, under controlled conditions, when the player is suspected of throwing. A 50 Hz six-camera Vicon Motion Analysis system was used to record the movements of markers strategically placed on the upper limb during each of the above bowling actions. A kinematic model of the upper limb, created using Vicon BodyBuilder software, enabled the movements of the upper arm and forearm to be described during each delivery. Selected physical characteristics of the upper limb were also measured. The present 'no ball' law in cricket with reference to throwing states that 'the arm should not be straightened in the part of the delivery that immediately precedes ball release'. The bowler, Mutiah Muralitharan, was shown to maintain a relatively constant elbow angle in the 0.06 s before ball release. Furthermore, this angle changed little from the time that the upper arm was angled vertically downward until ball release during the three spin-bowling actions.

Back injuries and the fast bowler in cricket

Here, I review research that has investigated the aetiology of injuries experienced by adolescent and adult fast bowlers. Mechanical factors play an important role in the aetiology of degenerative processes and injuries to the lumbar spine. This is particularly so in fast bowling, where a player must absorb vertical and horizontal components of the ground reaction force that are approximately five and two times body weight at front-foot and rear-foot impact, respectively. Attenuated forces are transmitted to the spine through the lower limb, while additional forces at the lumbo-sacral junction are caused by trunk hyperextension, lateral flexion and twisting during the delivery stride. Fast bowlers are classified as side-on, front-on or mixed. The mixed action is categorized by the lower body configuration of the front-on action and the upper body configuration of the side-on technique. This upper body configuration is produced by counter-rotation away from the batsman in the transverse plane about the longitudinal axis of the body of a line through the two shoulders. Counter-rotations of 12-40 degrees during a delivery stride have predicted an increased incidence of lumbar spondylolysis, disc abnormality and muscle injury in fast bowlers. During the delivery stride, the mixed bowling action also shows: more lateral flexion and hyperextension of the lumbar spine at front-foot impact, and a greater range of motion of the trunk over the delivery stride when compared with the side-on and front-on techniques. The pars interarticularis of each vertebra is vulnerable to injury if repetitive flexion, rotation and hyperextension are present in the activity. Fast bowlers should reduce shoulder counter-rotation during the delivery stride to reduce the incidence of back injuries. When a player is required to bowl for extended periods irrespective of technique, overuse is also related to an increased incidence of back injuries and must be avoided.

Net forces during tethered simulation of underwater streamlined gliding and kicking techniques of the freestyle turn

We assessed the net forces created when towing swimmers while gliding and kicking underwater to establish an appropriate speed for initiating underwater kicking, and the most effective gliding position and kicking technique to be applied after a turn. Sixteen experienced male swimmers of similar body shape were towed by a motorized winch and pulley system. A load cell measured net force (propulsive force - drag force) at speeds of 1.6, 1.9, 2.2, 2.5 and 3.1 m x s(-1). At each speed, the swimmers performed a prone streamline glide, a lateral streamline glide, a prone freestyle kick, a prone dolphin kick and a lateral dolphin kick. A two-way repeated-measures analysis of variance revealed significant differences between the gliding and kicking conditions at different speeds. The results demonstrated an optimal range of speeds (1.9 to 2.2 m x s(-1)) at which to begin underwater kicking to prevent energy loss from excessive active drag. No significant differences were found between the prone and lateral streamline glide positions or between the three underwater kicking techniques. Therefore, there appears to be no significant advantage in using one streamlining technique over another or in using one kicking style over another.

Long-axis rotation: the missing link in proximal-to-distal segmental sequencing

Most assessments of segmental sequencing in throwing, striking or kicking have indicated a proximal-to-distal sequencing of end-point linear speeds, joint angular velocities, segment angular velocities and resultant joint moments. However, the role of long-axis rotations has not been adequately quantified and located in the proximal-to-distal sequence. The timing and importance of upper arm internal-external rotation and pronation-supination in the development of racquet head speed have been examined in the tennis serve and squash forehand drive and considered in relation to conventional concepts of proximal-to-distal sequencing. Both long-axis rotations reached their peak angular speeds late in both strokes, typically after shoulder flexion-extension, shoulder abduction-adduction and elbow extension. These results clarify and confirm the importance of upper limb long-axis rotations in the production of racquet head speed. It appears that traditional proximal-to-distal sequencing concepts are inadequate to describe accurately the complexity of the tennis serve or squash forehand drive. It is essential to consider upper arm and forearm longitudinal axis rotations in explaining the mechanics of these movements and in developing coaching emphases, strength training schedules and injury prevention programmes.

Landing in netball: effects of taping and bracing the ankle

OBJECTIVES

To investigate the effect of bracing and taping on selected electromyographic, kinematic, and kinetic variables when landing from a jump.

METHODS

Fifteen netball players performed a jump, so as to land on their dominant limb on a force plate. Electromyographic activity was recorded from the gastrocnemius, tibialis anterior, and peroneus longus muscles. Subjects were also filmed and measures of rearfoot motion were derived.

RESULTS

Significantly less electromyographic activity (p<0.007) was observed from the gastrocnemius and peroneus longus muscle groups when subjects were braced. No other significant electromyographical findings were observed. Peak vertical ground reaction force and time to peak for vertical ground reaction force were not affected by bracing and taping, nor were the rearfoot and Achilles tendon angles at foot strike.

CONCLUSIONS

The effect of bracing and taping on the selected biomechanics variables associated with landing was specifically limited to a reduction in muscle action, particularly for the braced condition. Netball players can be confident that the biomechanics of their landing patterns will not be altered whether they choose to wear a brace or tape their ankle joints.

Measures to prevent cricket injuries: an overview

Cricket is a major international sport, generally played in British Common-wealth nations. Although strictly a non-contact sport, injuries in cricket can result in a number of ways. In high level cricket, overuse injuries are common and related to the physical demands of the sport, particularly in the delivery of the ball. The bowling action involves repetitive twisting, extension and rotation of the trunk at the same time as absorption of large ground reaction forces over a short period of time. These movements, if performed incorrectly or too frequently, can lead to overuse injuries of the back, particularly in elite and high level cricketers. Cross-sectional studies have demonstrated that spinal overuse injuries occur more frequently to cricketers adopting a mixed bowling action than to those who favour a front- or side-on bowling technique. Strategies to ensure that cricketers do not adopt the mixed action or bowl too fast for extended periods can prevent these back injuries. Injuries resulting from impacts, generally from the cricket ball, can also occur and are more common during low level competition or informal participation. Because of the potential severity of these impacts, a range of protective equipment ranging from body padding to gloves and face protectors are now common features of standard cricket equipment. Although a number of measures to prevent cricket injuries have been widely suggested in the literature, there have been very few studies that have formally assessed their effectiveness in preventing injury. Further research is needed to gain a greater understanding of the biomechanics of cricket actions, the mechanisms of resultant injuries and the role of various risk factors in injury causation.

The influence of plyometric training on the freestyle tumble turn

This study examined the effects of a plyometric training program on freestyle tumble turns. Thirty-eight age group swimmers were assigned to a control group which swam 1.5 hours, three times per week for 20 weeks; or an experimental group which supplemented 1.25 hours of swimming with 15 minutes of plyometrics for the same time frame. The same coach conducted all swimming and plyometric sessions to ensure uniformity. Swimming performance was assessed from 50 m time. Freestyle turning performance was measured by 2.5 m round trip time (RTT), 5 m RTT, wall contact time and selected kinematic and kinetic variables associated with the turn. A Plyopower system was also used to test jump height and velocity. Repeated measures, multivariate analysis of variance showed no significant differences between the groups (pre-, mid- and post-intervention) over the period of the study for any swimming, kinetic or plyopower measures. Thus, equal benefits were derived from normal practice time in the water or land based plyometric exercises.

Aetiology and occurrence of diving injuries. A review of diving safety

This paper examines multifaceted aspects of diving entries into water which are the cause of many critical injuries (costed at $A150 million) and therefore have important safety ramifications. Wedge and compression fractures are most commonly found in the cervical area of the spine with off-centre impacts with the pool or sea bottom. Diving-related injuries range from 2.3 in a South African study to 21% of spinal cord injuries in Poland. Alcohol and diving do not mix because of diminished awareness and information processing. Children aged under 13 years suffer fewer cervical injuries (1 to 4%), but complication rates are relatively high for this group. Sports trauma (diving-related in particular) is one of the more prevalent causes of spinal cord injury in children aged 6 to 15 years. The highest incidence occurs among those aged 10 to 14, followed by the group aged 5 to 9 years. This contradicts the common perception that 15-to 19-year-olds comprise the highest risk group. Boys are more frequently injured, and swimming pools are more common as an injury location then is the case with adults. The role played by water depth has been conclusively ascertained; technique, and therefore education, appear to be more important considerations in injury prevention. Although 89% of injuries occur in water < 1.52m, injuries are rare in water of 0.46 to 0.61m. Care with pool design to avoid sudden depth changes and the resultant "spinal wall' is necessary. Minimum depth values for diving vary from 1 to 1.52 m. Velocities and angles of entry are considered to ascertain the body's decelerative capacity upon entry. The scoop, racing start dive has been shown to require at least 1.22 m of water even when practised by trained divers; the risks involved must therefore be weighed against the fact that it may be no faster than more conventional dives. While it may be safe to perform kneeling and crouching dives into shallowers water, standing dives by untrained divers require a greater margin of error. Lack of education is an issue which needs to be addressed and this paper makes recommendations for safety practices such as steering up to the surface, head protection with the arms and only diving when absolutely necessary.

The biomechanics of fast bowling in men's cricket: a review

This review concentrates on synthesizing and analysing the biomechanical research which has been carried out on fast bowling in men's cricket. Specifically, it relates to those elements of the bowling technique which contribute towards a fast ball release, the aerodynamics and technique of swing bowling, and the association between fast bowling and lower back injury. With regard to bowling technique, no firm conclusions are drawn on the relationships between elements of the fast bowling technique and ball release speed. Recommendations for future research in this area include intra-player studies to establish the bowler-specific factors which contribute to fast ball release and features of body segment dynamics. There is general agreement that the phenomenon of differential boundary layer separation is the reason for normal and reverse cricket ball swing. Systematic research to establish the essential aspects of the bowling technique which contribute to successful swing bowling is recommended, along with studies of the behaviour of the ball in games to ascertain the effects of ball asymmetries on ball swing. There is sufficient evidence in the literature to establish a strong link between injury to the lower back and the use of the mixed technique. Recommendations are made for screening and intervention to reduce the use of the mixed technique, and for research into other aspects of injury. Fundamental research to develop biomechanical models of the lower back in fast bowling is strongly recommended.

Safe depths for teaching children to dive

Eight stages commonly used to teach diving were analysed for peak vertical velocity; vertical velocity at and following water impact and at previously recommended minimum water depths; maximum depth reached; and relationship between vertical velocity and maximum depth attained at each stage; for 13 male and 13 female children aged 6-8 years. Comparisons of mean water impact vertical velocities and maximum depths attained revealed significantly lower impact vertical velocities (F[6] = 117.39, p < 0.0001) and maximum depths (F[6] = 36.59, p < 0.0001) when performing the sit dive compared to the reference standing dive. At other stages, subjects travelled faster than the critical head velocities shown to cause adult cervical spine damage when passing through previously recommended minimum water depths.

Thoracolumbar disc degeneration in young fast bowlers in cricket: a follow-up study

OBJECTIVE: To determine the progression of thoracolumbar disc degeneration in young fast bowlers in cricket. DESIGN: Prospective fast bowling technique and MRI follow-up study. BACKGROUND: Previous studies on high-performance young fast bowlers have found that lumbar spine pathology was related to the mixed bowling technique. METHODS: Nineteen young male fast bowlers (mean age 13.6 years) underwent MRI scans to detect the presence of intervertebral disc abnormalities. Subjects were also filmed laterally (200 Hz) and from directly above (100 Hz) whilst bowling two maximum velocity deliveries (session 1). Subjects were tested using an identical methodology 2.7 years later (session 2). RESULTS: At session 1, the incidence of thoracolumbar disc degeneration was 21%; however, at session 2, the incidence significantly (P = 0.008) increased to 58%. Furthermore the increase in the incidence of back pain between session 1 and session 2 was also significant (P = 0.002). The progression of disc degeneration was found to be significantly (P = 0.015) related to the group of fast bowlers who utilized the mixed technique during both session 1 and 2 when compared to those who used this technique during one session only. CONCLUSIONS: Thoracolumbar disc degeneration and back pain increase significantly during the time period examined in this study. Further, bowlers who utilize the mixed bowling technique stand a greater chance of developing degenerative changes of the spine.

The effect of a 12-over spell on fast bowling technique in cricket

Nine members of the Western Australian Cricket Association fast bowling development squad were selected to determine the effects that a 12-over spell would have on fast bowling technique and selected physiological variables. Three high-speed cameras operating at 100 Hz filmed the subjects bowling the 5th and 6th balls of their 1st, 6th, 10th and 12th overs. Blood lactate and heart rate were recorded and the bowlers were shown to work at between 80.3% (1st over) to 84.7% (12th over) of their maximum heart rate during the 12-over bowling spell. Data from the 5th and 6th deliveries from each over were averaged to provide representative data, as no significant differences were evident between these two deliveries for the selected kinematic variables. For all subjects, no significant differences were recorded for the selected kinematic variables throughout the duration of the 12-over spell, indicating that in general fast bowling technique does not change over this length of spell. In addition, there was some evidence of change in technique for the bowlers who used a front-on action, where counter-rotation of the shoulders was found to increase; however, this could only be confirmed by a more comprehensive study.

Do selected kinanthropometric and performance variables predict injuries in female netball players?

The aim of this study was to determine which kinanthropometric and performance variables predict injuries in female netball players. In a prospective study, 72 volunteer grade A netball players (mean age 20.6 +/- 3.6 years, range 15-36 years) were measured for hypermobility, somatotype, static balance, jumping abilities and anaerobic fitness at the University of Western Australia Human Movement Performance Laboratory prior to the start of their 14-week season. Injuries were classified by site, diagnosis and severity, and were monitored throughout the entire season by the same physiotherapist at the Western Australia (WA) Matthews Netball Centre, Perth, Australia. A total of 22 injuries in 22 players were recorded, affecting the ankle joint lateral ligament complex (59%), knee ligaments (18%), back (18%) and Achilles tendon (5%). Injuries were more common among grade A1 players than other grades (54 vs 19%, P < 0.001). Within grade A1 players, the proportion of injuries decreased with age (P < 0.05). Players were more likely to have had an injury if they had better jumping ability, better anaerobic fitness and if they were low on the endomorphy somatotype scale (P < 0.05). After allowing for both jumping ability and endomorphy, there was no longer a significant difference between A1 and non-A1 players in their risk for injury. Young elite players are at a substantially increased risk of injury. This higher risk appears to be associated with--if not a direct consequence of--their being thinner, fitter and having more powerful jumping capabilities. This suggests that injury-prevention programmes should be targeted at elite players, especially the younger ones.

Disc degeneration and the young fast bowler in cricket

Twenty-four male fast bowlers of mean age 13.7 years, who bowled competitively at a school and club level were selected from five Western Australian schools. At the time of the testing all bowlers, who were bowling completely freely, underwent magnetic resonance imaging to detect the presence of intervertebral disc abnormalities. While these radiological data were being analysed, the players were filmed both laterally (200 Hz) and from directly above (100 Hz) as their front foot impacted a force platform during the delivery stride of the fast bowling action. In addition these bowlers performed selected physical capacity tests. The occurrence of abnormal radiological data were then used to group the bowlers (group 1, no abnormal features; group 2, disc degeneration and/or bulging on scan). A Mann-Whitney U rank test was then used to identify any significant differences (P < 0.1) between the groups for all dependent variables. Five of the subjects recorded abnormal magnetic resonance imaging scans of the lumbar spine, while nineteen recorded normal intervertebral discs, normal alignment of the lumbar spine, and no sign of spondylolisthesis. Bowlers who rotated the trunk to realign the shoulders to a more side-on position between back foot impact and front foot impact in the delivery stride were more likely to record abnormal intervertebral disc features.

Stretch shorten cycle performance enhancement through flexibility training

Sixteen experienced male powerlifters served as subjects in a training study designed to examine the effect of flexibility training on: (i) the stiffness of the series elastic components (SEC) of the upper body musculature and (ii) rebound and purely concentric bench press performance. Nine of the subjects participated in two sessions of flexibility training twice per week for 8 wk. Prior to and after the training period the subjects' static flexibility, SEC stiffness, rebound bench press (RBP), and purely concentric bench press (PCBP) performance were recorded. The flexibility training induced a significant reduction in the maximal stiffness of the SEC. Furthermore, the experimental subjects produced significantly more work during the initial concentric portion of the RBP lift, enabling a significantly greater load to be lifted in the post-training testing occasion. The benefits to performance achieved by the experimental group consequent to flexibility training were greater during the RBP lift as compared with the PCBP lift. The control subjects exhibited no change in any variable over the training period. These results implied that the RBP performance enhancement observed consequent to flexibility training was directly caused by a reduction in SEC stiffness, increasing the utilization of elastic strain energy during the RBP lift.

The relationship between stiffness of the musculature and static flexibility: an alternative explanation for the occurrence of muscular injury

The static flexibility of the gleno-humeral joint of fourteen experienced male weight lifters was determined. Further the subjects performed a series of quasistatic muscular actions of the deltoid/pectoralis musculature during which a brief perturbation was applied. The damped oscillations resulting from such a procedure provided data pertaining to the stiffness of each subject's musculature. A significant correlation (r = -0.544, p less than 0.05) between maximal stiffness and static flexibility was observed. This relationship is discussed with reference to the popular belief that flexibility is related to the incidence of muscular injury. It is proposed that the injury-reducing benefits associated with a high degree of flexibility can be effectively explained through the relationship between flexibility and stiffness.

The effect on performance of imposing a delay during a stretch-shorten cycle movement

Twelve experienced male weight lifters of varying ability completed a series of bench press lifts at 95% of maximum. These lifts included a rebound bench press, which was performed without a delay between the downward and upward components of the lift, a bench press performed without a downward phase, and two bench press movements performed with various pause periods imposed between the downward and upward phases of the lift. Force and cinematographic data were collected during each lift. The augmentation to performance derived from prior stretch was observed to decay as a function of the pause duration. This relationship was accurately described (P less than 0.01) by a negative exponential equation with a half-life of 0.85 s. The nature of this decay is discussed with reference to the implications for stretch-shorten cycle movements that are performed with a period of pause between the eccentric and concentric phases and for stretch-shorten cycle research paradigms.

Optimal stiffness of series elastic component in a stretch-shorten cycle activity

Twelve experienced male weight lifters performed a rebound bench press and a purely concentric bench press lift. Data were obtained pertaining to 1) the benefits to concentric motion derived from a prior stretch and 2) the movement frequency adopted during performance of the stretch-shorten cycle (SSC) portion of the rebound bench press lift. The subjects also performed a series of quasi-static muscular actions in a position specific to the bench press movement. A brief perturbation was applied to the bar while these isometric efforts were maintained, and the resulting damped oscillations provided data pertaining to each subject's series elastic component (SEC) stiffness and natural frequency of oscillation. A significant correlation (r = -0.718, P less than 0.01) between maximal SEC stiffness and augmentation to concentric motion derived from prior stretch was observed. Subjects were also observed to perform the SSC portion of the rebound bench press movement to coincide with the natural frequency of oscillation of their SEC. These results are interpreted as demonstrating that the optimal stiffness in a rebound bench press lift was a resonant-compliant SEC.

A biomechanical analysis of the sticking region in the bench press

The performance of ten elite powerlifters were analyzed in a simulated competition environment using three-dimensional cinematography and surface electromyography while bench pressing approximately 80% of maximum, a maximal load, and an unsuccessful supramaximal attempt. The resultant moment arm (from the sagittal and transverse planes) of the weight about the shoulder axis decreased throughout the upward movement of the bar. The resultant moment arm of the weight about the elbow axis decreased throughout the initial portion of the ascent of the bar, recording a minimum value during the sticking region, and subsequently increased throughout the remainder of the ascent of the bar. The electromyograms produced by the prime mover muscles (sternal portion of pectoralis major, anterior deltoid, long head of triceps brachii) achieved maximal activation at the commencement of the ascent phase of the lift and maintained this level essentially unchanged throughout the upward movement of the bar. The sticking region, therefore, did not appear to be caused by an increase in the moment arm of the weight about the shoulder or elbow joints or by a minimization of muscular activity during this region. A possible mechanism which envisages the sticking region as a force-reduced transition phase between a strain energy-assisted acceleration phase and a mechanically advantageous maximum strength region is postulated.

Biomechanics of the serve in tennis. A biomedical perspective

Epidemiological studies have indicated that the serve, arguably the most important facet of the game of tennis, is also the most likely stroke to cause injury, particularly to the elbow and back. A review of the kinematic and kinetic studies on the service action fails to clearly identify the reason(s) for these injuries. Data from these studies does, however, allow possible causes of injury to be postulated. Electromyographic data from the prime mover muscles involved in the serve have shown that muscle action was greater for beginners, whose muscles were active for longer periods than those of advanced players. Ground reaction forces associated with different serving techniques were small compared to those recorded from activities involving running or jumping. The potential to cause injury seems to be related to high internal forces (combination of muscle and joint reaction forces), particularly where these forces are associated with poor technique and high segment accelerations. These situations occur when the racket moves behind the body and the vertebral column is laterally flexed and hyperextended. The pronation of the forearm and the forces associated with the swing to the ball, the impact and the early follow through are also factors that have the potential to cause injury. The action of serving induces strains and pressures upon the body. A sensible approach to the number of serves, particularly when practising (overuse), appropriate physical preparation and a technique that does not introduce excessive forces to selected body parts (misuse) will greatly reduce the potential for injury from this activity.

The penalty throw in water polo: a cinematographic analysis

Three-dimensional (3-D) high-speed cinematography was used to record the penalty throw in water polo by six elite male (M) and six elite female (F) players. The direct linear transformation technique (DLT) was used in the 3-D space reconstruction from 2-D images recorded via laterally placed phase-locked cameras operating at 200 Hz. Five of the twelve subjects lifted the ball from underneath at the start of the throw whilst the remaining subjects opted for a rotation lift. As the ball was brought behind the head the females used very little hip and shoulder rotation compared to the male players so that four of the six female subjects were square on to the target at the rear point. At the completion of the backswing the wrist was flexed to a similar angle (M-162 degrees; F-158 degrees); the elbow angle showed significantly greater flexion for females (85 degrees) than males (107 degrees). During the forward swing, from rear point to release, the wrist joint of the female players flexed from a rear point angle of 158 degrees to 148 degrees at release. The wrist movement for male subjects was different from the females in that it flexed from 162 degrees to 147 degrees, 0.10 s prior to release and then extended to 159 degrees at palmar release before again flexing to 156 degrees at release. The amount of elbow extension during the forward swing was 48 degrees for both groups; however, the females actually released the ball with the forearm vertical (89 degrees) compared to the male forearm angle of 78 degrees. Maximum angular velocity of the wrist and elbow occurred at release for 9 of the 12 subjects. Both the wrist and elbow joints (F-148 degrees; M-156 degrees at wrist and F-126 degrees; M-148 degrees at elbow) demonstrated greater flexion at release in female subjects, compared with males. Maximum linear endpoint velocities for the forearm and hand segments occurred at ball release resulting in mean ball velocities of 19.1 m s-1 and 14.7 m s-1 for male and female subjects respectively.

Biological characteristics of young swimmers, tennis players and non-competitors

One hundred and twelve finalists in the State Swimming Championships aged between seven and twelve years and 65 ranked tennis players of similar age were selected on the basis of their sporting performances. A third group comprised children of similar socio-economic status who only took part in casual sport. The tests which were used in the study were those considered to be important for successful athletic performance. A multifactorial analysis of variance and post-hoc t-tests were applied to the data to determine if any statistical differences were apparent between the three groups. The results demonstrated that no size, body shape, flexibility, strength or lung function differences were evident between the competitors and non-competitors, but that the swimmers and tennis players were superior to the non-competitors in cardiovascular endurance.

A biomechanical evaluation of the role of fatigue in middle-distance running

Eight college level runners were filmed using high speed photography at the 500 m, 1,300 m, 2,100 m and 2,900 m stages of a 3,000 m time trial. Kinematic and spatio-temporal data were obtained through an interfaced digitiser computer system. Mean horizontal velocities of 5.18 m/s, 5.17 m/s, 5.18 m/s and 5.16 m/s indicated that minimal variations occurred from the four stages of the trial. No significant changes in biomechanical data were apparent between the first three stages of the trial; however, changes were evident when Stage 4, the 2,900 m mark, was compared to the earlier sections of the trial. With the development of fatigue stride length decreased while stride rate increased to maintain the constant velocity. There was also a small shift to increase the period of support and correspondingly decrease the period of non-support. The leg was more angled at foot strike, the thigh was less extended at the end of the support phase, and the trunk was carried further forward during the running cycle. Success in middle-distance running requires the athlete to maintain an efficient co-ordinated movement pattern over the entire race. The coach who can identify the changes in movement patterns over a race increases the likelihood of success for his athletes.

Blood pressure and rectal temperature responses of middle-aged sedentary, middle-aged active and "A"-grade competitive male squash players

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