Differences In Peak Force Research Articles

Influence of interfacial bond between rebar and concrete on the lateral resistance of RC columns under different loading rates

The interfacial bond between rebar and concrete is a critical factor that influences the performance of reinforced concrete (RC) structures because it affects the effective force transfer between concrete and rebar and hence the composite actions. In finite element modelling of RC structures, the bond-slip relation between rebar and concrete is generally neglected due to the increased model complexity by considering debonding behaviours. Limited studies show the debonding performance is loading rate dependent, neglecting it in numerical modelling may lead to inaccurate structural response predictions, but there is no systematic investigation of bonding performance on responses of structures under load of different loading rates. The influences of neglecting debonding in structural response analysis are therefore not properly defined yet. In this study, the finite element model was established and validated by the available impact test data. The lateral resistance and damage modes of the column considering and neglecting bond-slip behaviour between rebar and concrete were examined under various loading rates ranging from 50 kN/s to 1.0 × 106 kN/s. It is found that neglecting bond-slip relation in finite element modelling of RC columns leads to underprediction of the peak force and damage. The assumption of perfect bond has a significant influence on predicting the peak force and damage of column under low loading rates, but its influence reduces with the increase in loading rate, especially when the loading rate exceeds 1.0 × 105 kN/s. The maximum relative difference in peak force between considering and neglecting bond-slip at 50 kN/s is 18.63 %. Parametric studies were conducted to investigate the effects of bonding performance on columns of different width, depth, height, and concrete strength. Based on the numerical results, an analytical formula is developed to quantitatively predict the errors in peak force predictions by neglecting debonding between concrete and rebars of RC columns. The results highlight the importance of considering bond-slip in finite element modelling of RC structures subjected to quasi-static and low-rate dynamic loadings, and demonstrate it is reasonable to neglect debonding in structural response analysis under high-rate dynamic loadings.

Changes in isometric mid-thigh pull peak force and symmetry across anterior cruciate ligament reconstruction rehabilitation phases.

Whether functionally relevant strength assessments, such as the isometric mid-thigh pull (IMTP), can be used either bilaterally or unilaterally to evaluate and guide rehabilitation progress in those with anterior cruciate ligament reconstruction (ACLR) is under-researched. This study assessed changes in peak force (PF) and asymmetry across 3 phases for bilateral and unilateral IMTP assessments in patients with ACLR. Peak isometric force from the IMTP was compared to peak torque from isokinetic dynamometry as well as against a cohort of healthy, uninjured individuals. Participants (ACLR, n = 15) completed bilateral and unilateral IMTP assessments at weeks 12 (baseline), 16 (phase 3), and 20 (phase 4) of rehabilitation to evaluate changes in PF and asymmetry. Asymmetry was evaluated using the asymmetry angle. Isometric data from the IMTP were compared to that from an isokinetic dynamometer as well as against a cohort of healthy, uninjured participants (n = 63) allowing for a detailed analysis of limb-specific force production. The PF during the bilateral IMTP increased for both the injured (0.94 N/kg) and uninjured (0.26 N/kg) limbs from baseline to phase 4, whereas the PF of the injured limb increased by 1.5 N/kg during the unilateral IMTP in the same time frame. Asymmetry values systematically reduced by ∼1% and ∼0.5% for the bilateral and unilateral IMTP tests from baseline to phase 4. Significant differences in PF of the injured limb were evident between those with ACLR and healthy controls across all phases (p = 0.022-0.001). The rate of progression in PF capacity was dependent on test type, amounting to 0.1 and 0.2 body weights per week for the bilateral and unilateral IMTP respectively. Small-to-large correlations (r = 0.12-0.88) were evident between IMTP PF and peak torque from the isokinetic dynamometer as well as between asymmetry metrics from both tests. The findings suggest that IMTP PF has potential for monitoring changes in PF and asymmetry during the ACLR rehabilitation progress. Both injured limb and uninjured limb show improvement in force-generating capacity, implying a positive adaptation to rehabilitation protocols. The findings highlight that ACLR is a unilateral injury that requires bilateral rehabilitation.

Upright versus Horizontal Squat Jumps: A comparison of peak force, peak velocity, peak power and muscle activity in male athletes

Sports performance coaches and rehabilitation specialists commonly prescribe explosive squat jumps (SJ) in the upright position to improve lower body power using loads based upon an individual’s one-repetition maximum (1RM) back squat. Recently, using a horizontal leg press to perform SJ has become popular purportedly due to its less technical nature. To date, little research exists comparing upright and horizontal SJ. Therefore, this investigation examined peak force, peak velocity, peak power and muscle activity of upright versus horizontal SJ using loads based upon each condition’s respective 1RM. Twelve males completed two sets of three repetitions of SJ at 20%, 30%, 40%, 50% and 60%1RM. Statistical significance was set to P ≤ 0.05. No significant differences existed between trial 1 and 2 for any measures. Two-way analysis of variance revealed a) no significant difference in peak force between the SJ conditions at any intensity; b) significantly greater peak velocity during upright SJ at all intensities; c); significantly greater peak power during upright SJ at all intensities; and d) no difference in muscle activity between SJ conditions. In conclusion, in a key measure of performance, power output during upright SJ was significantly greater than during horizontal SJ.

Validity and Reliability of a Load Cell Sensor-Based Device for Assessment of the Isometric Mid-Thigh Pull Test.

In recent years, there has been an exponential increase in the number of devices developed to measure or estimate physical exercise. However, before these devices can be used in a practical and research environment, it is necessary to determine their validity and reliability. The purpose of this study is to test the validity and reliability of a load cell sensor-based device (LC) for measuring the peak force (PFr) and the rate of force development (RFD) during the isometric mid-thigh pull (IMTP) test, using a force plate (FP) as the gold standard. Forty-two undergraduate sport science students (male and female) participated in this study. In a single session, they performed three repetitions of the IMTP test, being tested simultaneously with an LC device and a Kistler force platform (FP). The PFr and RFD data were obtained from the force-time curve of the FP and compared with the LC data, provided automatically by the software of the device (Smart Traction device©). The mean difference between the results obtained by the LC device and the gold-standard equipment (FP) was not significantly different (p > 0.05), for both PFr and RFD, which suggests the validity of the ST results. Bland-Altman analysis showed a small mean difference in PFr = 1.69 N, upper bound = 47.88 N, and lower bound = -51.27 N. RFD showed that the mean difference was -5.27 N/s, upper limit = 44.36 N/s, and lower limit = -54.91 N/s. Our results suggest that the LC device can be used in the assessment of the isometric-mid-thigh-pull test as a valid and reliable tool. It is recommended that this device's users consider these research results before putting the ST into clinical practice.

Efficient stress integration algorithm of memory surface model with shrinking rule under plane stress field

Reliable nonlinear finite element analysis (FEA) of steel structures requires a constitutive model capable of predicting the cyclic plasticity of structural steels. Steel structure members are typically composed of multiple thin steel plates. The FEA of such structures has frequently used shell elements to capture the bending deformation and reduce the computational complexity, where its stress state can be regarded as the plane stress field. This study provides a constitutive model with a memory surface under a plane stress field for the cyclic plasticity of structural steels. A noble computationally efficient algorithm for stress integration and consistent tangent operator was proposed, where the constitutive equations were linearized after solving some unknown variables. The proposed model was implemented in the Abaqus FEA code. The residual-force convergence rate of the consistent tangent operator is investigated using a single-shell element under simple boundary conditions, where the consistent tangent operator achieves more than a quadratic convergence. The proposed model was validated by comparing the experimental results and FEA results with the proposed model for thin-walled steel members under cyclic loading. The average difference in peak forces between FEA and experimental results was 11.5 % for the local buckling tests and 8.4 % for the shear buckling tests at most. These results suggest that the proposed model provides an accurate prediction for other thin-walled steel structures under cyclic loading.

Differences in strength, leg lean mass,and lifestyle factors between premenopausal and perimenopausal women.

Menopausal changes coupled with age-related reductions in muscle strength can impact functionality. To evaluate the differences in muscle strength, dominant leg lean mass (DLMleg ), relative protein intake (r_PRO)and physical activity (PA) between premenopausal (PRE) and perimenopausal (PERI) women. Twenty-fourPRE- (age = 39.8 ± 3.3 years; BMI: 25.3 ± 5.0 kg/m2 ) and 24 PERI-women (age = 50.0 ± 3.3 years; BMI: 26.5 ± 5.4 kg/m2 ) participated in leg extensor isometric peak force (PF), DLMleg , r_PROand PA. Independent samples t-tests and one-way analyses of covariance covaried for age and DLMleg were used to compare groups. The PRE group had significantly higher PF (mean difference ± standard error: 57.8 ± 28.0 N; p = 0.045) and DLMleg (0.7 ± 0.3 kg; p = 0.031) when compared to the PERI group. There were no significant differences in r_PRO, or PA between groups (p = 0.173-0.423). When covaried for age and DLMleg , there was no significant difference in PF (p = 0.982 and 0.405, respectively). Age and DLMleg may be important contributors to menopause-phase related differences in strength.

Effect of Cryotherapy Temperature on the Extension Performance of Healthy Adults' Legs.

Simple SummaryThe aim of this study was to investigate the effect of different temperature cryotherapy on leg extension performance. A short period of cold treatment at 0 °C may increase the leg extension ability; however, further lower cold treatment temperatures may cause a decrease in the stretching speed. This may indicate that 0 °C cold therapy for a short period of time is more suitable than −5 °C cold therapy for athletes to recover during the interval within a competition.Cryotherapy as a measurement of sports recovery and treatment has been utilized by more and more athletes and coaches. The aim of this study was to investigate the effect of different temperature cryotherapies on leg extension performance. Thirty-one male participants from a University volunteered to join two different temperature cryotherapies. The peak power and peak force of right leg extension performance of each participant was measured by Keiser, before and after cryotherapy, respectively. The results of this study show that there was a significant difference in peak power (t = −3.203, p value = 0.003) and peak force (t = −4.662, p value = 0) before and after 0 °C cryotherapy. In addition, there was a significant difference in peak force (t = −4.36, p value = 0) before and after −5 °C cryotherapy. Besides, the changing rates of peak power (3.03%) and peak force (11.51%) in the 0 °C group were higher than those of peak power (2.80%), as well as peak force (7.45%), in the −5 °C group. The PF in the 0 °C and −5 °C groups both significantly increased after cryotherapy. Peak power significantly increased after 0 °C cryotherapy, but did not significantly increase after −5 °C cryotherapy. The changing rates of peak power and peak force in the 0 °C group were both higher than the −5 °C group. A short period of cold treatment at 0 °C may increase the leg extension ability. A 0 °C cold therapy for a short period of time is more suitable than a −5 °C one for athletes to recover during the interval within a competition. Athlete and coach could choose an appropriate temperature to help increase performance of physical level and recovery.

The Effect of Rim Preparation, Labral Augmentation, and Labral Reconstruction on the Suction Seal of the Hip

To evaluate the biomechanical properties of the labral suction seal in the native labrum and after rim preparation, labral augmentation, and labral reconstruction. Eight hemi-pelvises were dissected to the level of labrum and mounted for biomechanical testing. Each specimen was tested in axial distraction starting with the native labrum and then sequentially following rim preparation from 12 to 3 o'clock, labral augmentation, and segmental labral reconstruction using the iliotibial band allograft. In each condition, the specimens were compressed to 250 N and then distracted at 10 mm/s with force and displacement continuously recorded. Each test was repeated 3 times, and the mean peak force, displacement at peak force, and work were calculated. Data were reported as a percentage of the intact values to account for sex and size differences. Statistical testing was performed via a repeated-measures analysis of variance with a post hoc Tukey analysis. Peak loads occurred within 2.21 to 3.11 mm of displacement. The mean peak force, displacement at peak force, and work relative to the intact condition were the following: rim preparation (91.1% ± 8.5%, 94.4% ± 14.3%, 93.4% ± 23.5%, respectively), augmentation (66.1% ± 27.6%, 78.2% ± 16.3%, 55.7% ± 30.7%, respectively), and reconstruction (55.6% ± 25.7%, 64.7% ± 31.4%, 38.7% ± 27.2%, respectively). There was no significant difference in peak force following the rim preparation (P= .807), but peak force was significantly decreased after augmentation and reconstruction (P= .010 and P < .001, respectively). There was no significant difference in displacement at peak force following rim preparation or augmentation (P= .936 and P= .125, respectively), but displacement at peak force was significantly decreased after reconstruction (P= .005). The work from the suction seal was significantly less in both augmentation and reconstruction states compared to the intact labrum (P= .004 and P < .001, respectively) and rim preparation (P= .017 and P < .001, respectively). The results show that the suction seal is not significantly changed following rim preparation. Relative to the rim preparation, labral augmentation may re-create the labral suction seal better than labral reconstruction. This study provides a biomechanical basis for surgical decision making and clinical management of patients with labral tears of the hip.

Peak Forces and Force Generating Capacities of Lower Extremity Muscles During Dynamic Tasks in People With and Without Chronic Ankle Instability

ABSTRACT People with chronic ankle instability (CAI) exhibit neuromuscular deficits. However, no study has investigated deficits in forces or force-generating capacities of individual muscles in people with CAI during dynamic tasks. Therefore, the purpose of this study was to estimate and compare peak forces and force-generating capacities of individual muscles during dynamic tasks in people with CAI and healthy controls (CON). Eleven people with CAI and eleven CON performed landing, anticipated cutting, and unanticipated cutting as motion capture, force plate, and electromyography data were recorded. A musculoskeletal model was used to estimate the force and force-generating capacity of lower extremity muscles. People with CAI exhibited greater gluteus maximus force and force-generating capacity than CON during all tasks. In addition, people with CAI exhibited greater force-generating capacity of the vastii muscles than CON during the unanticipated cutting task. These findings suggest that, during dynamic tasks, people with CAI exhibit a neuromuscular control strategy that is characterised by differences in peak forces and force-generating capacities of proximal muscles, which may allow them to compensate for previously described deficits in distal muscles.

Comparing Hip Contact Pressures Between Acetabulum Labral Repair vs. Total Labral Reconstruction

To biomechanically compare the contact area, contact pressures, and peak forces of primary labral repair versus labral reconstruction. A cadaveric study was performed using 8 frozen hemi-pelvises with cam-type deformities (alpha angle >55°) with an intact labrum. Intraarticular pressure maps were produced for each specimen under the following conditions: 1) intact labrum, 2) labral repair, and 3) labral reconstruction using iliotibial band (ITB) allograft. Specimens were examined at neutral, 20° of extension and 60° of flexion to simulate the complete arc of the natural hip range of motion during normal gait on a level surface and during stair climbing. Each specimen was placed in a custom-designed jig in the MTS electromechanical test system to create pressure and area map measurements. In each condition, contact pressure, contact area, and peak force within a region-of-interest (ROI) were obtained. Repeated measures ANOVA was used to identify differences in biomechanical parameters among the three conditions with post-hoc analysis using pairwise comparison with Bonferroni correction to analyze the differences within each condition. Analysis of contact pressures between labral repair and labral reconstruction were normalized to the pressures measured in the intact labrum. Repeated measures ANOVA for contact area in neutral, extension, and flexion demonstrated statistically significant differences between study states (p<0.05). Post-hoc analysis for each consistently demonstrated significantly larger contact areas measured in labral repair specimens compared labral reconstruction specimens. In addition, paired-T test analysis demonstrated significantly higher contact areas (33.3+-7.9 vs 27.4+-6.9; p=0.009) and significantly lower contact pressures (2.5+-0.3 vs 2.7+-0.4; p=0.038) in labral repair specimens compared to labral reconstruction specimens. Finally, there was no statistically significant difference in peak forces measured between specimens (p<0.05 for all). Primary labral repair may result in lower intra-articular hip contact pressures and higher contact area compared to primary complete labral reconstruction.

Isometric Mid-Thigh Pull Performance in Rugby Players: A Systematic Literature Review.

The isometric mid-thigh pull (IMTP) is a multi-joint test of whole-body force production relevant to rugby players. “Rugby AND (mid-thigh pull OR midthigh pull OR mid thigh pull” were searched in PubMed, Sportdiscus, Academic Search Premier, CINAHL Plus with Full Text, and Google Scholar; the final date of search was 24 January 2018. Data extraction from 24 articles included subject characteristics, force data, and IMTP testing procedures. Select ranges of peak forces reported were: Youth: 1162–2374 N; Academy: 1855–3104 N; Professional: 2254–3851 N. Rate of force development (RFD) at 100 and 200 ms ranged from 5521 to 11,892 N and 5403 to 8405 N, respectively, among professional rugby players. Studies’ research design were of moderate quality, but most studies lacked detailed reporting of IMTP procedures. Variability of force characteristics derived from the IMTP within similar populations (e.g., approximately 200% difference in peak force between samples of professional rugby league players) as well as large and unexpected overlaps between dissimilar populations, limit conclusions about force production capabilities relative to playing level, likely due to limitations and lack of standardization of IMTP procedures. Greater uniformity in IMTP testing procedures and reporting is needed. This manuscript provides a guide for reporting needs when presenting results from an IMTP in research.

Utility of a Shortened Isometric Midthigh Pull Protocol for Assessing Rapid Force Production in Athletes.

Suarez, DG, Carroll, KM, Slaton, JA, Rochau, KG, Davis, MW, and Stone, MH. Utility of a shortened isometric midthigh pull protocol for assessing rapid force production in athletes. J Strength Cond Res 36(7): 1819-1825, 2022-The purpose of this investigation was to determine the magnitude of difference, reliability, and relationship to performance of a shortened isometric midthigh pull (IMTP) protocol. Fourteen strength-trained men (age: 26.8 ± 5.0 years, height: 176.3 ± 6.9 cm, body mass: 86.8 ± 13.9 kg, and training age: 8.5 ± 6.9 years) performed 1-second (SHORT) and traditional (TRAD) IMTP protocols during consecutive weeks. Peak force (PF), instantaneous force (90 & 200 ms), rate of force development (RFD) (0-90 ms & 0-200 ms), and impulse (0-90 ms & 0-200 ms) from each protocol were collected. Paired samples t test and Hedge's g were calculated to determine the magnitude of difference in each variable between protocols. Within-session and between-session reliability was assessed with intraclass correlation coefficient, coefficient of variation, and 95% confidence intervals. Static jumps were performed to compare relationships of the IMTP variables from each protocol with jumping performance. There was no statistically significant (p > 0.05) difference in PF between the protocols (p = 0.345; g = -0.07). All early force-time variables were significantly higher in the SHORT protocol (p = <0.001-0.018; g = 0.38-0.79). The SHORT protocol resulted in more reliable RFD measures within-session. Correlations with jumping performance were mostly similar between protocols (r = 0.253-0.660). The SHORT IMTP protocol resulted in comparable PF values and considerably higher early force-time characteristics despite a restrained time to produce force and shorter rest. The SHORT protocol allows for an accurate assessment of rapid force-generating abilities while necessitating shorter collection periods than typical IMTP protocols.

Biomechanical Characteristics of Labral Augmentation Versus Labral Reconstruction in a Hip Cadaver Model

Objectives:An integral component of hip stability is the negative pressure gradient created by the labral suction seal. No prior studies have quantitatively compared the integrity of the suction seal under normal, pathologic, and surgical conditions. The purpose of this study was to evaluate the biomechanical properties of the labral suction seal in the following four scenarios: intact labrum, labral tear, labral augmentation, and labral reconstruction.Methods:Eight fresh-frozen hemi-pelvises without osteoarthritis and with an intact labrum were dissected to the level of labrum and mounted for biomechanical testing. Each specimen was evaluated sequentially under four testing conditions: intact labrum, labral tear, labral augmentation, and labral reconstruction. Following testing of the intact labrum, the specimens were manipulated to create a labral tear from 12- to 3-o’clock. Labral augmentation was then performed with bone anchors and iliotibial band graft after debridement of only the peripheral half of the labral tear. Labral reconstruction was performed last with bone anchors and iliotibial band graft after removing the entire labral tear. In each condition the specimens were placed in the test machine to undergo pure distraction of the joint. First, the femur was compressed with 250 N of force and then distracted at 10 mm/s with force and displacement continuously recorded until the suction seal was disrupted. In each specimen, the tests were repeated for a total of three tests in each of the four conditions, and the average peak force was calculated. Data was normalized to the intact peak force for each specimen to account for gender and size differences. Statistical testing was performed via a repeated measures ANOVA with a post hoc Bonferroni correction for pairwise analysis.Results:Peak loads occurred early in displacement. The average peak force values (mean ± standard deviation) were as follows: intact (137.2 ± 40.7), labral tear (126.3 ± 43.5), labral augmentation (94.7 ± 59.7), labral reconstruction (78.9 ± 51.2). The average normalized peak force values relative to the intact condition were as follows: labral tear (91.1 ± 8.5), augmentation (66.1 ± 27.6), and reconstruction (55.6 ± 25.7). There was no statistically significant difference in peak force relative to the intact labrum for the labral tear (p = 0.34). Relative to the labral tear, there was no significant difference in peak force for the augmentation (p = 0.12), but there was a significant decrease in peak force for the reconstruction (p = 0.03).Conclusion:This model provides a new means of quantitatively evaluating the labral suction seal under various normal, pathologic, and surgical conditions. The results show that relative to the labral tear condition, labral augmentation may recreate the labral suction seal better than labral reconstruction. Clinically, these findings suggest augmentation may improve hip stability over labral reconstruction.Figure 1.

Lumbar Diagnosis and Pressure Difference Variance.

There is no consensus on the correlation between clinical experience and accuracy in diagnosing somatic dysfunctions, which makes it difficult to justify the use of more subjective measures to evaluate this important association. To better understand this relationship, palpatory forces can be observed while diagnosing a somatic dysfunction. To quantify the pressure applied in diagnosing lumbar somatic dysfunction, find a correlation between accuracy of diagnosis and palpation pressure, set the standards for palpation, and develop precise palpatory skills for osteopathic medical students. The palpatory forces were evaluated between participants with varying experience levels (osteopathic medical students and attending physicians from the New York Institute of Technology College of Osteopathic Medicine). Two osteopathic physicians confirmed an L5 somatic dysfunction diagnosis in a volunteer standardized patient (SP), who served as the control. Participants then palpated the lumbar segment of the SP in a prone position with F-Scan System (TekScan) sensors, which recorded the amount of pressure and time used to reach a full diagnosis. Participants (11 osteopathic medical students and 10 attending physicians) who diagnosed an L5 somatic dysfunction consistent with the SP's diagnosis had less of a difference in peak force (mean [SD] difference, 62.50 [325.7] g/cm2) between the contact points (right hand vs left hand). In contrast, participants with a dissimilar L5 diagnosis from the SP's had a mean (SD) difference in peak force of 319.38 (703.1) g/cm2. Similarly, the difference in the mean (SD) force of palpation between the contact points was lower in participants who made the correct diagnosis (16.81 [117.4] g/cm2) vs those who made an incorrect diagnosis (123.92 [210.3] g/cm2). No statistical significance was found between the diagnostic accuracy of the students and physicians (P=.387) or the time taken to reach a diagnosis (P=.199). We observed that using equal pressures in both hands while palpating a lumbar segment correlates to more accurate somatic dysfunction diagnoses.

Assessing the Reliability of Using a Horizontal Leg Press Equipped With a Force Plate to Report on Measures of Positive and Negative Neuromuscular Characteristics.

Ferley, DD and Vukovich, MD. Assessing the reliability of using a horizontal leg press equipped with a force plate to report on measures of positive and negative neuromuscular characteristics. J Strength Cond Res 33(2): 360-371, 2019-Individuals participating in sport or returning from a lower-extremity injury routinely perform assessments of lower-body anaerobic capacity and power to gauge fitness or readiness to return to competition. However, many commonly used assessments lack the specificity of movement and muscle contraction demonstrated in sprinting, jumping, and changing direction. Therefore, this investigation assessed the reliability of a novel lower-body power test called a Plyo Press Power Quotient (3PQ), which involves jumping on a horizontal leg press equipped with a force plate. Thirty participants completed 1 repetition maximum (1RM) strength testing for 1 and 2 legs and a countermovement vertical jump. Two trials of 1- and 2-leg jump tests were performed using 30, 40, 50, and 60% of 1RM for 20 and 30 seconds, respectively. Dependent variables were a variety of positive (concentric) and negative (eccentric) neuromuscular indices. Statistical significance was set to p ≤ 0.05. No significant differences existed between trial 1 and 2 for any measures. One-way analysis of variance between %1RM conditions revealed significant differences in peak force (right; both), average negative power (left; right), average negative work (left; right), rate of power development (both), percent positive and negative fatigue (left; right; both), and velocity of movement (left; right; both). Peak power of all 2-leg jump tests correlated highly with vertical jump (r ≥ 0.89) but was significantly different. We conclude 3PQ testing provides a reliable assessment of anaerobic capacity and power, with the added benefit of easy single-leg comparisons.

Comparison of lower limb segment forces during running on artificial turf and natural grass.

Introduction: Artificial turf, soon after being introduced in the 1980s, became associated with an increased injury incidence in football players. While more recent generations of artificial turf have mitigated the problem, perception of the material is still widely negative. So, the decision to play the 2015 Fe'de'ration Internationale de Football Association Women s World Cup in Canada on artificial turf was met with vocal criticism by many players. One common approach is to assess injury incidence to quantify risk differences in playing surfaces. This, however, does not account for possible confounding variables or chronic injuries. Direct measurement of ground reaction forces is difficult because conventional multicamera-based motion capture and force plate equipment are limited in its use outside of dedicated laboratories.Methods:We describe a method of generating realistic force data by using miniature load cells that are installed directly into the weight-bearing structure of the body.Results:Pilot data show a significant (p<0.01) difference in peak forces on artificial turf (272% of body weight) and natural grass (229% of body weight).Discussion:Invasive surgical procedures were avoided by installing the load cell into the prosthesis of an athlete with lower limb loss. As modern prosthetic devices allow a close approximation of able-bodied kinematics and kinetics, such prosthesis-based data are transferable to a general population.

The effect of impact duration on the axial fracture tolerance of the isolated tibia during automotive and military impacts.

Axial impacts to the lower leg during debilitating events such as frontal automotive collisions and military underbody blasts can cause significant injuries to the tibia. Several studies have conducted axial impact tests to determine the injury limits of the lower leg, mostly focused on automotive intrusions, resulting in an established force criterion for injury assessments. Due to the viscoelastic properties of bone, it remains unclear whether results from automotive experiments can be applied to higher-rate military blasts. Twelve male isolated cadaveric tibias (from six pairs, mean age: 62 ± 8 years) were subjected to axial impact loads using a custom-built pneumatic impactor, with one specimen from each pair tested at velocity and impact durations representative of a military blast condition, and the contralateral under conditions representing an automotive collision. Impacts were applied in increasing levels of intensity (defined using energy levels) until fracture occurred. Fracture risk was influenced by projectile velocity, kinetic energy, impulse, and load rate, and there was a significant difference in peak force (p = 0.023), impulse (p = 0.09), and load rate (p = 0.025) between the automotive and military test conditions causing fracture. A 10% risk of fracture corresponded to an impact force of 9.0kN for the automotive condition and 12.2kN for the military condition. These results suggest that fracture tolerances developed in studies that simulate automotive impacts cannot be directly applied to military impacts of shorter duration. The number of factors identified to predict injury also suggests that fracture is not controlled by a single variable.

Peak Patellofemoral and ACL/PCL Forces While Performing the Forward Lunge Exercise With Varying Techniques

PURPOSE: To compare peak patellofemoral and ACL/PCL forces among varying lunging techniques involving lunging with a long and short stride both on flat ground and up to a 4 inch platform. METHODS: Sixteen male and female subjects (mean bodyweight 678N, 69.1 kg mass; 175.9 cm height; 28.9 years old) using bodyweight only performed a forward lunge with a long stride (shank vertical at bottom position) and a short stride (1/2 the long stride distance) on flat ground and up to a 4 inch platform. Force platform and video data were collected and input into a biomechanical model, and peak patellofemoral and ACL/PCL were calculated as a function of knee angle. A One-Way Repeated measures ANOVA assessed significant differences among lunging techniques (p<0.05). RESULTS: Peak patellofemoral force occurred between 79°-96° knee angles and was significantly greater (p<0.001) with a short stride lunge on flat ground (1668±479N) and up to a 4 inch platform (1553±580N) compared to lunging with a long stride lunge on flat ground (1193±512N) and up to a 4 inch platform (1061±523N), but no significant differences in peak patellofemoral force were found between the two short stride lunges (p=0.99) and between the two long stride lunges (p=0.99). Peak ACL force occurred between 7°-12° knee angles and was not significantly different (p=0.70) among any of the lunging techniques. Peak PCL force occurred between 62°-83° knee angles and was significantly greater (p<0.001) with a long stride lunge on flat ground (554±220N) and up to a 4 inch platform (609±265N) compared to lunging with a long stride lunge on flat ground (402±114N) and up to a 4 inch platform (458±145N), but no significant differences in peak PCL force were found between the two short stride lunges (p=0.99) and between the two long stride lunges (p=.99). CONCLUSIONS: Lunge technique variations did affect peak patellofemoral and cruciate ligament forces. Compared to a long stride lunge, lunging with a short stride, which caused the knees to translate forward approximately 8 cm beyond the knees at bottom lunge position, resulted in greater peak patellofemoral force but less PCL force. Lunging technique variations did not affect peak ACL force. There were no patellofemoral or PCL differences in peak force between the two long stride lunges or between the two short stride lunges.

Jumping From a Chair is a More Sensitive Measure of Power Performance In Older Adults Than Chair Rising

Background/Study Context: The study estimates the reliability of peak velocity and peak power during chair rising and chair jumping tests and their ability to discriminate between different age and physical activity level groups.Methods: Physically active and sedentary individuals (N = 262) of different ages (young: 22.9 ± 2.0 years, range: 21–25 years; older: 63.1 ± 1.8 years, range: 61–65 years) performed, in random order, chair rising and chair jumping tests on a force plate. Randomly selected young subjects performed both tests repeatedly on two different occasions separated by 1 week. From the sitting position with the arms crossed on the chest, they either stand up completely (chair rising test), or jump as high as possible (chair jumping test).Results: The test-retest reliability of peak power and peak velocity during chair rising as well as chair jumping was excellent, with high intraclass correlation coefficients (ICCs; .90–.98) and low standard error of measurement (SEM; 7.0–9.1%). Post hoc analysis revealed significant differences in peak power and peak velocity between the sedentary and physically active young and older subjects. However, greater coefficients of variation for both parameters were found for chair jumping than chair rising (21.1–40.2% vs. 11.0–15.2%). Additionaly, there were moderate correlations of peak power and peak velocity between chair rising and chair jumping (r = .42–.49). There were greater within- and between-group differences in peak force and peak power and a steeper increase in their values during the initial phase of chair jumping than chair rising.Conclusion: Both chair rising and chair jumping tests provide reliable data and are valid indicators of lower body power in young and older adults. However, jumping from a chair is a more sensitive measure of strength and power performance than chair rising.

Cluster Sets: Permitting Greater Mechanical Stress Without Decreasing Relative Velocity.

To determine the effects of intraset rest frequency and training load on muscle time under tension, external work, and external mechanical power output during back-squat protocols with similar changes in velocity. Twelve strength-trained men (26.0 ± 4.2 y, 83.1 ± 8.8 kg, 1.75 ± 0.06 m, 1.88:0.19 one-repetition-maximum [1RM] body mass) performed 3 sets of 12 back squats using 3 different set structures: traditional sets with 60% 1RM (TS), cluster sets of 4 with 75% 1RM (CS4), and cluster sets of 2 with 80% 1RM (CS2). Repeated-measures ANOVAs were used to determine differences in peak force (PF), mean force (MF), peak velocity (PV), mean velocity (MV), peak power (PP), mean power (MP), total work (TW), total time under tension (TUT), percentage mean velocity loss (%MVL), and percentage peak velocity loss (%PVL) between protocols. Compared with TS and CS4, CS2 resulted in greater MF, TW, and TUT in addition to less MV, PV, and MP. Similarly, CS4 resulted in greater MF, TW, and TUT in addition to less MV, PV, and MP than TS did. There were no differences between protocols for %MVL, %PVL, PF, or PP. These data show that the intraset rest provided in CS4 and CS2 allowed for greater external loads than with TS, increasing TW and TUT while resulting in similar PP and %VL. Therefore, cluster-set structures may function as an alternative method to traditional strength- or hypertrophy-oriented training by increasing training load without increasing %VL or decreasing PP.