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Beatriz H. Thames and Stacey L. Gorniak

When humans adjust their grip to prevent the slipping of objects grasped by the fingertips, the component of their grip force (the force normal to the object surface) generated at the fingertips must be sufficient to generate a tangential frictional force that can prevent slip. 1 This sufficient

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Paula Chaves, Daniela Simões, Maria Paço, Sandra Silva, Francisco Pinho, José Alberto Duarte and Fernando Ribeiro

use, to treat tendon pain such as physical agents, deep friction massage (DFM), counterforce bracing, education and abnormal movement pattern correction, and exercise namely eccentric training. 9 – 11 Regarding DFM, despite the lack of definitive clinical evidence to support its use in the management

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Adriana V. Savescu, Mark L. Latash and Vladimir M. Zatsiorsky

This article proposes a technique to calculate the coefficient of friction for the fingertip– object interface. Twelve subjects (6 males and 6 females) participated in two experiments. During the first experiment (the imposed displacement method), a 3-D force sensor was moved horizontally while the subjects applied a specified normal force (4 N, 8 N, 12 N) on the surface of a sensor covered with different materials (sandpaper, cotton, rayon, polyester, and silk).The normal force and the tangential force (i.e., the force due to the sensor motion) were recorded. The coefficient of frictiond) was calculated as the ratio between the tangential force and the normal force. In the second experiment (the beginning slip method), a small instrumented object was gripped between the index finger and the thumb, held stationary in the air, and then allowed to drop. The weight (200 g, 500 g, and 1,000 g) and the surface (sandpaper, cotton, rayon, polyester, and silk) in contact with the digits varied across trials. The same sensor as in the first experiment was used to record the normal force (in a horizontal direction) and the tangential force (in the vertical direction). The slip force (i.e., the minimal normal force or grip force necessary to prevent slipping) was estimated as the force at the moment when the object just began to slip. The coefficient of friction was calculated as the ratio between the tangential force and the slip force. The results show that (1) the imposed displacement method is reliable; (2) except sandpaper, for all other materials the coefficient of friction did not depend on the normal force; (3) the skin–sandpaper coefficient of friction was the highest µd = 0.96 ± 0.09 (for 4-N normal force) and the skin–rayon rayon coefficient of friction was the smallest µd = 0.36 ± 0.10; (4) no significant difference between the coefficients of friction determined with the imposed displacement method and the beginning slip method was observed. We view the imposed displacement technique as having an advantage as compared with the beginning slip method, which is more cumbersome (e.g., dropped object should be protected from impacts) and prone to subjective errors owing to the uncertainty in determining the instance of the slip initiation (i.e., impeding sliding).

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Athanasios Trampas, Anastasia Mpeneka, Vivian Malliou, George Godolias and Periklis Vlachakis

Context:

Previous studies showed improved dynamic-balance (DB) performance after core-stability (CS) exercises in populations with chronic low back pain. Although clinical massage plus exercise is likely to better enhance analgesia than exercise alone, its efficacy on balance remains unclear.

Objective:

To evaluate the immediate effects of CS exercises plus myofascial trigger-point (MTrP) therapy in comparison with CS exercises alone on DB performance, pressure-pain threshold (PPT), and cross-sectional area of active MTrPs in patients with clinical instability of the lumbar spine and chronic myofascial pain syndrome.

Design:

Randomized, assessor-blind, test–retest.

Setting:

University research laboratory.

Patients:

10 physically active adults (5 men, 5 women).

Main Outcome Measures:

Single-leg DB performance and side-to-side ratios in 2 planes of motion (frontal, sagittal), as well as PPT and cross-sectional area of active MTrPs, were measured using stabilometry, pressure algometry, and real-time ultrasound scanning, respectively.

Interventions:

The 1st group performed CS exercises alone, whereas the same exercise program was applied in the 2nd group plus cross-fiber friction on active MTrPs (3.5 min/MTrP).

Results:

Within-group statistically and clinically significant differences were observed only for group II in PPT. However, group I also exhibited a large effect size with clinically significant changes from baseline on this outcome. Furthermore, patients in group II clinically improved their balance ratios and differed from group I at posttest in sagittal-plane DB performance of the painful side.

Conclusion:

CS exercises immediately increase the PPT of active MTrPs in physically active adults with clinical instability of the lumbar spine and chronic myofascial pain syndrome. When MTrP therapy is added, side-to-side asymmetries in DB are minimized.

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Bart Van Gheluwe and Eric Deporte

Tennis movements are characterized essentially by lateral displacements, thus external load on the lower extremities is created predominantly by friction generated between shoes and playing surfaces. This study analyzed the behavior of frictional forces and torques produced during an open stance forehand using various playing surfaces and different sport shoes. The frictional data were obtained from 12 advanced players returning a tennis ball fired from a ball machine and hitting a large Kistler force plate located at the base line of the tennis court. Using statistical ANOVA techniques, friction was found to be more sensitive to the choice of playing surface than to the choice of tennis shoe. “Fluid” type surfaces displayed the lowest frictional values in most cases. Additionally, comparison of the frictional data collected during the forehand with the measurements from a standardized laboratory test demonstrated that extrapolation of friction results from laboratory to real field conditions may lead to erroneous conclusions.

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Hans Jobse, Ruud Schuurhof, Ferenc Cserep, A. Wim Schreurs and Jos J. de Koning

Portable equipment for active measurements of push-off force and ice friction was developed. The equipment consists of a pair of skates with three measuring elements between the shoe and the skate blade to register force in both fore/aft and normal direction. A portable computer samples the friction force and normal force signals during one or more strokes, calculates the mean coefficient of ice friction, and stores the sampled data in memory. The push-off force and ice friction force were measured. The peak push-off forces reach values of up to 140% of body weight. The magnitude of the coefficient of ice friction varies, depending on the weather conditions and preparatory method, generally between 0.003 and 0.007 when skating the straightaway. During the skating of the curves the coefficient of ice friction is 35% higher, most likely due to the different skating technique in the curves.

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Matthew A. Kilgas, Scott N. Drum, Randall L. Jensen, Kevin C. Phillips and Phillip B. Watts

Rock climbers believe chalk dries the hands of sweat and improves the static coefficient of friction between the hands and the surface of the rock. The purpose of this study was to assess whether chalk affects geometric entropy or muscular activity during rock climbing. Nineteen experienced recreational rock climbers (13 males, 6 females; 173.5 ± 7.0 cm; 67.5 ± 3.4 kg) completed 2 climbing trails with and without chalk. The body position of the climber and muscular activity of the finger flexors was recorded throughout the trial. Following the movement sequence participants hung from a standard climbing hold until they slipped from the climbing structure, while the coefficient of friction and the ratio of the vertical forces on the hands and feet were determined. Although there were no differences in the coefficient of friction (P = .748), geometric entropy (P = .359), the ratio of the vertical forces between the hands and feet (P = .570), or muscular activity (P = .968), participants were able to hang longer after the use of chalk 62.9 ± 36.7 s and 49.3 ± 25.2 s (P = .046). This is advantageous because it may allow for prolonged rests, and more time to plan the next series of climbing moves.

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Geraldine L. Pellecchia, Holly Hamel and Peter Behnke

The purpose of this study was to compare an established protocol of modalities and transverse friction massage (MOD & TFM) with iontophoresis of dexamethasone and lidocaine (IONTO) in the treatment of patients with infrapatellar tendinitis. Thirty cases with infrapatellar tendinitis were randomly assigned to either the MOD & TFM or the IONTO intervention. Subjects still symptomatic after six sessions of intervention received the alternate treatment protocol. Four measures were used to assess patient status: a functional index questionnaire, a visual analog pain scale, a rating of tenderness with palpation of the involved tendon, and the number of step-ups needed to elicit pain. In response to the MOD & TFM intervention, only the number of step-ups performed to elicit pain showed significant improvement. All status measures improved significantly with the IONTO intervention. The results suggest that iontophoresis may be more effective and efficient in decreasing pain, reducing inflammation, and promoting healing in patients with infrapatellar tendinitis.

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Rachel L. Wright, Dan M. Wood and David V.B. James

The aims of the study were to investigate whether starting cadence had an effect on 10-s sprint-performance indices in friction-loaded cycle ergometry and to investigate the influence of method of power determination. In a counterbalanced order, 12 men and 12 women performed three 10-s sprints using a stationary (0 rev/min), moderate (60 rev/min), and high (120 rev/min) starting cadence Calculated performance indices were peak power, cadence at peak power, time to peak power, and work to peak power. When the uncorrected method of power determination was applied, there was a main effect for starting cadence in female participants for peak power (stationary 635 ± 183.7 W, moderate 615.4 ± 168.9 W and high 798.4 ± 120.1 W) and cadence at peak power (89.8 ± 2.3 rev/min, 87.9 ± 21.5 rev/min, and 113.1 ± 12.5 rev/min). For both the uncorrected and directly measured methods of power determination in men and women, there was a main effect for starting cadence for time to peak power and work to peak power. In women, for an uncorrected method of power determination, it can be concluded that starting cadence does affect peak power and cadence at peak power. This effect is, however, negated by a direct-measurement method of power determination. In men and women, for both uncorrected and directly measured methods o power determination, time to peak power and work to peak power were affected by starting cadence. Therefore, a higher-cadence start is unsuitable, particularly when sprint-performance indices are determined from an uncorrected method.

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Steven L. Fischer, Bryan R. Picco, Richard P. Wells and Clark R. Dickerson

Exerting manual forces is critical during occupational performance. Therefore, being able to estimate maximum force capacity is particularly useful for determining how these manual exertion demands relate to available capacity. To facilitate this type of prediction requires a complete understanding of how maximum force capacity is governed biomechanically. This research focused on identifying how factors including joint moment strength, balance and shoe-floor friction affected hand force capacity during pulling, pressing downward and pushing medially. To elucidate potential limiting factors, joint moments were calculated and contrasted with reporte joint strength capacities, the balancing point within the shoe-floor interface was calculated and expresess relative to the area defined by the shoe-floor interface, and the net applied horizontal forces were compare with the available friction. Each of these variables were calculated as participants exerted forces in a series o conditions designed to systematically control or restrict certain factors from limiting hand force capacity. The results demonstrated that hand force capacity, in all tested directions, was affected by the experimental conditions (up to 300%). Concurrently, biomechanical measures reached or surpassed reported criterion threshold inferring specific biomechanical limitations. Downward exertions were limited by elbow strength, wherea pulling exertions were often limited by balance along the anterior-posterior axis. No specific limitations wer identified for medial exertions.