Targeted gripping reduces shoulder muscle activity and variability

The purpose of this study was to determine if the effect of visually targeted gripping on shoulder muscle activity was maintained with repeated exposures. Eleven healthy males had eight shoulder muscles monitored via surface electromyography while maintaining shoulder elevation at 90° in the scapular plane with and without a 30% grip force. Three non-gripping trials were followed by 15 gripping trials and another 3 non-gripping control trials. Gripping significantly decreased the activity of the anterior deltoid, trapezius, and latissimus dorsi over the exposure of 15 trials. Gripping also reduced variability in all muscles' activity. The changes in shoulder muscle activity are likely in response to forces being transferred through multi-articular muscles spanning from the forearm to the shoulder. Targeted gripping during shoulder elevation resulted in small but significant decreases in muscle activity and reduced variability which supports previous evidence for increased risk of upper extremity disorders in occupational settings.     

Technical-methodological report: a nomogram for peak leg power output in the vertical jump

Leg power is an important component in assessing both performance-related and health-related fitness. The Lewis equation and nomogram have been used for years to estimate leg power. A recent evaluation of the Lewis equation and further research led to the development of the Sayers equation. This equation provides an estimate of peak leg power, which has greater relevance than average power. Our purpose was to provide a simple and effective nomogram for calculating peak leg power output. The Sayers equation was transformed to an alignment nomogram and evaluated for facility of use and accuracy. The resultant alignment nomogram is easy to use and generates values for peak leg power in the vertical jump, which are well within the precision of the regression equation (r > 0.9999, CV < 0.2%). Interobserver error was less than 0.3% with a correlation of 0.9999. The Keir nomogram provides a simple and effective representation of the Sayers equation for use in both performance-related and health-related fitness assessments.     

Modelling the transition from simple to complex Ca2+oscillations in pancreatic acinar cells

A mathematical model is proposed which systematically investigates complex calcium oscillations in pancreatic acinar cells. This model is based on calcium-induced calcium release via inositol trisphosphate receptors (IPR) and ryanodine receptors (RyR) and includes calcium modulation of inositol (1,4,5) trisphosphate (IP₃) levels through feedback regulation of degradation and production. In our model, the apical and the basal regions are separated by a region containing mitochondria, which is capable of restricting Ca²⁺ responses to the apical region. We were able to reproduce the observed oscillatory patterns, from baseline spikes to sinusoidal oscillations. The model predicts that calcium-dependent production and degradation of IP₃ is a key mechanism for complex calcium oscillations in pancreatic acinar cells. A partial bifurcation analysis is performed which explores the dynamic behaviour of the model in both apical and basal regions.     

The reliability of linear position transducer and force plate measurement of explosive force-time variables during a loaded jump squat in elite athletes

The best method of assessing muscular force qualities during isoinertial stretch shorten cycle lower body movements remains a subject of much debate. This study had 2 purposes: Firstly, to calculate the interday reliability of peak force (PF) measurement and a variety of force-time measures, and, secondly, to compare the reliability of the 2 most common technologies for measuring force during loaded jump squats, the linear position transducer (PT), and the force plate (FP). Twenty-five male elite level rugby union players performed 3 rebound jump squats with a 40-kg external load on 2 occasions 1 week apart. Vertical ground reaction forces (GRFs) were directly measured via an FP, and force was differentiated from position data collected using a PT. From these data, a number of force-time variables were calculated for both the FP and PT. Intraclass correlation coefficient (ICC), coefficient of variation (CV), and percent change in the mean were used as measures of between-session reliability. Additionally, Pearson's product moment correlation coefficients were used to investigate intercorrelations between variables and technologies. Both FP and PT were found to be a reliable means of measuring PF (ICC = 0.88-0.96, CV = 2.3-4.8%), and the relationship between the 2 technologies was very high and high for days 1 and 2, respectively (r = 0.67-0.88). Force-time variables calculated from FP data tended to have greater relative and absolute consistency (ICC = 0.70-0.96, CV = 5.1-51.8%) than those calculated from differentiated PT data (ICC = 0.18-0.95, CV = 7.7-93.6%). Intercorrelations between variables ranged from trivial to practically perfect (r = 0.00-1.00). It was concluded that PF can be measured reliably with both FP and PT technologies, and these measurements are related. A number of force-time values can also be reliably calculated via the use of GRF data. Although some of these force-time variables can be reliably calculated using position data, variation of measurement is generally greater when using position data to calculate force.