Intra-abdominal pressure increases stiffness of the lumbar spine

Intra-abdominal pressure (IAP) increases during many tasks and has been argued to increase stability and stiffness of the spine. Although several studies have shown a relationship between the IAP increase and spinal stability, it has been impossible to determine whether this augmentation of mechanical support for the spine is due to the increase in IAP or the abdominal muscle activity which contributes to it. The present study determined whether spinal stiffness increased when IAP increased without concurrent activity of the abdominal and back extensor muscles. A sustained increase in IAP was evoked by tetanic stimulation of the phrenic nerves either. unilaterally or bilaterally at 20 Hz (for 5 s) via percutaneous electrodes in three subjects. Spinal stiffness was measured as the force required to displace an indentor over the L4 or L2 spinous process with the subjects lying prone. Stiffness was measured as the slope of the regression line fitted to the linear region of the force-displacement curve. Tetanic stimulation of the diaphragm increased IAP by 27-61% of a maximal voluntary pressure increase and increased the stiffness of the spine by 8-31% of resting levels. The increase in spinal stiffness was positively correlated with the size of the IAP increase. IAP increased stiffness at L2 and L4 level. The results of this:study provide evidence that the stiffness of the lumbar spine is increased when IAP is elevated. (C) 2004 Elsevier Ltd. All rights reserved.

Ergonomic issues in team lifting

In this article we review and critique the current body of scientific knowledge regarding the use of team lifting including: (a) psychophysical studies of team lifting capacity, and (b) studies of manual handling, patient handling, and stretcher carriage performed by lifting teams. The consensus of the research literature is that team-lifting capacity is greater than the lifting capacity of an individual, but that the capacity of lifting teams is less than the summed capacity of individual team members. Further, biomechanical, psychophysical, and physiological stress tends to be reduced compared to the equivalent lifts and transfers performed by individuals. However, the stress associated with team lifting depends on a broad range of individual team member, load, task and environmental factors, which can interact in unexpected ways. Caution is therefore recommended against making broad assumptions regarding the use of team lifting. Future studies are needed to examine how effort and load are distributed among lifting team members, with emphasis on identifying factors that may increase the risk of injury.

The influence of natural body sway on neuromuscular responses to an unpredictable surface translation

Previous research has shown that the postural configuration adopted by a subject, such as active leaning, influences the postural response to an unpredictable support surface translation. While those studies have examined large differences in postural conditions, it is of additional interest to examine the effects of naturally occurring changes in standing posture. Thus, it was hypothesized that the normal postural sway observed during quiet standing would affect the responses to an unpredictable support surface translation. Seventeen young adults stood quietly on a moveable platform and were perturbed in either the forward or backward direction when the location of the center of pressure (COP) was either 1.5 standard deviations anterior or posterior to the mean baseline COP signal. Postural responses, in the form of electromyographic (EMG) latencies and amplitudes, were recorded from lower limb and trunk muscles. When the location of the COP at the time of the translation was in the opposite, as compared to the same, direction as the upcoming translation, there was a significantly earlier onset of the antagonists (10-23%, i.e. 15-45 ms) and a greater EMG amplitude (14-39%) in four of the six recorded muscles. Stepping responses were most frequently observed during trials where the position of the COP was opposite to the direction of the translation. The results support the hypothesis that postural responses to unpredictable support surface translations are influenced by the normal movements of postural sway. The results may help to explain the large variability of postural responses found between past studies.

Proprioceptive neuromuscular facilitation stretching - Mechanisms and clinical implications

Proprioceptive neuromuscular facilitation (PNF) stretching techniques are commonly used in the athletic and clinical environments to enhance both active and passive range of motion (ROM) with a view to optimising motor performance and rehabilitation. PNF stretching is positioned in the literature as the most effective stretching technique when the aim is to increase ROM, particularly in respect to short-term changes in ROM. With due consideration of the heterogeneity across the applied PNF stretching research, a summary of the findings suggests that an 'active' PNF stretching technique achieves the greatest gains in ROM, e.g. utilising a shortening contraction of the opposing muscle to place the target muscle on stretch, followed by a static contraction of the target muscle. The inclusion of a shortening contraction of the opposing muscle appears to have the greatest impact on enhancing ROM. When including a static contraction of the target muscle, this needs to be held for approximately 3 seconds at no more than 20% of a maximum voluntary contraction. The greatest changes in ROM generally occur after the first repetition and in order to achieve more lasting changes in ROM, PNF stretching needs to be performed once or twice per week. The superior changes in ROM that PNF stretching often produces compared with other stretching techniques has traditionally been attributed to autogenic and/or reciprocal inhibition, although the literature does not support this hypothesis. Instead, and in the absence of a biomechanical explanation, the contemporary view proposes that PNF stretching influences the point at which stretch is perceived or tolerated. The mechanism(s) underpinning the change in stretch perception or tolerance are not known, although pain modulation has been suggested.

Batting with occluded vision: An in situ examination of the information pick-up and interceptive skills of high- and low-skilled cricket batsmen

The capability of cricket batsmen of different skill levels to pick-up information from the pre-release movement pattern of the bowler, from pre-bounce ball flight, and from post-bounce ball flight was examined experimentally. Six highly skilled and six low-skilled cricket batsmen batted against three different leg-spin bowlers while wearing liquid crystal spectacles. The spectacles permitted the specific information available to the batsmen on each trial to be manipulated such that vision was either: (i) occluded at a point prior to the point of ball release (thereby only allowing vision of advance information from the bowler's delivery action); (ii) occluded at a point prior to the point of bat[ bounce (thereby permitting the additional vision of pre-bounce ball flight); or (iii) not occluded (thereby permitting the additional vision of post-bounce bat[ flight information). Measurement was made on each trial of both the accuracy of the definitive (forward-backward) foot movements made by the batsmen and their success (or otherwise) in making bat-bat[ contact. The analyses revealed a superior capability of the more skilled players to make use of earlier (pre-bounce) bat[ flight information to guide successful bat-bat[ interception, thus mirroring the greater use of prospective information pick-up by skilled performers observed in other aspects of batting and in other time-constrained performance domains. (c) 2006 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

How do world-class cricket batsmen anticipate a bowler's intention?

Four experiments are reported that examine the ability of cricket batsmen of different skill levels to pick up advance information to anticipate the type and length of balls bowled by swing and spin bowlers. The information available upon which to make the predictive judgements was manipulated through a combination of temporal occlusion of the display and selective occlusion or presentation of putative anticipatory cues. In addition to a capability to pick up advance information from the same cues used by intermediate and low-skilled players, highly skilled players demonstrated the additional, unique capability to pick up advance information from some specific early cues (especially bowling hand and arm cues) to which the less skilled players were not attuned. The acquisition of expert perceptual-motor skill appears to involve not only refinement of information extraction but also progression to the use of earlier, kinematically relevant sources of information.

The effects of sway velocity on the triceps surae H-reflex during quiet standing

We have previously observed a change in the magnitude of the soleus (SOL) and medial gastrocnemius (MG) H-reflexes during different sway positions of quiet standing. The purpose of the present study was to extend the earlier finding by examining whether the SOL and MG H-reflexes are additionally influenced by the velocity of sway, i.e., whether the body is swaying in either the forward or backward direction. Five healthy subjects participated in the study. The mean position of the centre of pressure (COP) in the antero-posterior direction was determined while the subject stood quietly on a force plate for 60 s. In contrast to the earlier study, where the H-reflex was tested at the outermost positions of sway (±6 mm from the baseline mean), the current study elicited a SOL and MG H-reflex as the COP passed through the mean position of sway. This resulted in two sway conditions, where the position of the COP was the same but the sway velocity was different (10 mm s-1 forward and 10 mm s-1 backward). During the forward as compared to the backward velocity condition, there was a 20% and 25% increase in the amplitude of the H-reflex for the SOL and MG muscles, respectively, while the size of their respective background activities were the same. SOL and MG M-waves, as well as the level of background activity from the antagonist (tibialis anterior), were not different between the two sway conditions and thus cannot account for the observed changes to the amplitude of the H-reflexes. It can be concluded from these results that the direction (velocity) of sway has the ability to influence the size of the SOL and MG H-reflexes. The facilitation of the SOL and MG H-reflexes observed while swaying forward may be due to a reduction in presynaptic inhibition or an improvement in Ia synaptic efficacy brought about by changes in muscle length.