Reproducibility of velocity-dependent power: before and after lengthening contractions

2011 ◽  
Vol 36 (5) ◽  
pp. 626-633 ◽  
Author(s):  
Geoffrey A. Power ◽  
Brian H. Dalton ◽  
Charles L. Rice ◽  
Anthony A. Vandervoort
Keyword(s):  
Peak Power ◽  
High Reliability ◽  
Similar Amount ◽  
Shortening Velocity ◽  
Lengthening Contractions ◽  
Isokinetic Testing ◽  
Typical Error ◽  
Before And After ◽  
Absolute Reliability ◽  
Ankle Dorsiflexors

The determination of power using isokinetic testing has been shown to be highly reliable. However, isotonic and isokinetic testing involve specific mechanical constraints that likely necessitate different neuromuscular strategies. Therefore, the purpose here was to establish test–retest intrarater reliability (separated by 7 days) of loaded maximal shortening velocity and velocity-dependent power of the ankle dorsiflexors using the isotonic mode of the Biodex dynamometer (i) at baseline and (ii) throughout recovery following 150 high-intensity lengthening contractions. Intraclass correlation coefficients (ICC)2,1 with 95% CIs were used to determine relative reliability, whereas absolute reliability included typical error (TEM) and typical error expressed as a coefficient of variation (TEMCV). Twenty-four young men and women volunteered for the study. Maximal shortening velocity and power were determined with a fixed resistance set at 20% of maximal voluntary isometric contraction across 2 testing sessions separated by 7 days. ICCs were 0.93 and 0.98 for maximal shortening velocity and peak power, respectively. Following the lengthening contractions, ICCs indicated high reliability for maximal shortening velocity and peak power, 0.86 and 0.94, respectively, suggesting that a similar amount of fatigue was incurred on both days. Measures of absolute reliability for maximal shortening velocity and peak power also yielded high reliability. The isotonic mode is highly reliable when testing velocity-dependent power of the ankle dorsiflexors at baseline and following fatiguing lengthening contractions. The high reliability of this measure is encouraging and suggests that the isotonic mode can be used in various settings to track group changes before and after training and following fatigue and lengthening contractions.

Peak power is reduced following lengthening contractions despite a maintenance of shortening velocity

2013 ◽  
Vol 38 (12) ◽  
pp. 1196-1205 ◽  
Author(s):  
Geoffrey A. Power ◽  
Brian H. Dalton ◽  
Charles L. Rice ◽  
Anthony A. Vandervoort
Keyword(s):  
Peak Power ◽  
Recovery Period ◽  
Shortening Velocity ◽  
Lengthening Contractions ◽  
Maximum Voluntary Isometric Contraction ◽  
Relative Contribution ◽  
Rate Of Torque Development ◽  
Isometric Torque ◽  
Torque Development ◽  
Shortening Contractions

Following repetitive lengthening contractions, power (the product of torque and velocity) is impaired during shortening contractions. However, the relative contribution of each component to power loss and the underlying factors are unclear. We investigated neuromuscular properties of the dorsiflexors in 8 males (27 ± 3 years) and 8 females (26 ± 4 years) for a potential sex-related difference before, during, and after 150 unaccustomed maximal lengthening actions. Velocity-dependent power was determined from shortening contractions at 8 levels (1 N·m to 70% of maximum voluntary isometric contraction (MVC)) before, after, and throughout recovery assessed at 0–30 min, 24 h, and 48 h. Immediately following task termination, both sexes displayed similar impairments of 30%, 4%, and 10% in MVC torque, shortening velocity, and overall peak power, respectively (P < 0.05). Peak rate of isometric torque development (RTD) was reduced by 10% in males, but females exhibited a 35% reduction (P < 0.05). Rate of torque development for the MVC remained depressed in both sexes throughout the 30 min recovery period; however, the RTD returned to normal by 24 h in males but did not recover by 48 h in females. Power was reduced preferentially at higher loads (i.e., 60% MVC), with a greater loss in females (65%) than males (45%). For lower loads (<20% MVC), power was impaired minimally (4%–8%; P < 0.05) and recovered within 30 min in both groups. The reduction in maximal angular velocity persisted until 30 min of recovery, and peak power did not recover until 24 h for both sexes. Unaccustomed lengthening contractions decreased power preferentially at higher loads, whereas peak power was reduced minimally owing to maintenance of maximal shortening velocity.

Intersession Reliability of Isokinetic Strength Testing in Knee and Elbow Extension and Flexion Using the BTE PrimusRS

2017 ◽  
Vol 26 (4) ◽  
Author(s):  
Alexander Törpel ◽  
Tim Becker ◽  
Angelina Thiers ◽  
Dennis Hamacher ◽  
Lutz Schega
Keyword(s):  
High Reliability ◽  
Intraclass Correlation ◽  
Young Male ◽  
Peak Torque ◽  
Male Students ◽  
Clinical Settings ◽  
Isokinetic Testing ◽  
Sports Science ◽  
Isokinetic Strength Testing ◽  
Absolute Reliability

Context:The use of isokinetic dynamometers playing an important role in different settings of sports and medicine. Therefore, a high reliability of these devices is required. Objective: The aim of this study was to examine the intersession reliability of the dynamometer BTE PrimusRS regarding to the isolated single-joint exercises extension/flexion of the knee and elbow for isokinetic testing. Design: Intersession reliability. Setting: Clinical settings and sports science. Participants: 16 young male students. Intervention: The testing protocol includes 5 consecutive repetitions (concentric/concentric) at a velocity of 60°/s for the exercises. Main Outcome Measures: Raw data of torque curves were used to determine the peak torque. Reliability was evaluated with the intraclass correlation coefficient (ICC), the limits of agreement (LoA), and the bias and the variability of measurements (V). Results: High ICC values (.954-.991) were found for the used exercises. However, the LoAs yielded up to over 16 Nm and the V yielded up to nearly 9 % in several testing exercises, indicating poor absolute reliability. Conclusion: The BTE PrimusRS shows good to excellent reliability. However, regarding the absolute measures of reliability, the users must decide as experts in their fields whether this reliability is sufficient for their purposes.

Midfoot Function Before and After Total Ankle Arthroplasty

2021 ◽  
pp. 107110072199578
Author(s):  
Frank E. DiLiberto ◽  
Steven L. Haddad ◽  
Steven A. Miller ◽  
Anand M. Vora
Keyword(s):  
Cohort Study ◽  
Prospective Cohort Study ◽  
Prospective Cohort ◽  
Peak Power ◽  
Nonparametric Tests ◽  
Total Ankle Arthroplasty ◽  
Control Group ◽  
Ankle Arthroplasty ◽  
First Metatarsal ◽  
Before And After

Background: Information regarding the effect of total ankle arthroplasty (TAA) on midfoot function is extremely limited. The purpose of this study was to characterize midfoot region motion and power during walking in people before and after TAA. Methods: This was a prospective cohort study of 19 patients with end-stage ankle arthritis who received a TAA and 19 healthy control group participants. A motion capture and force plate system was used to record sagittal and transverse plane first metatarsal and lateral forefoot with respect to hindfoot motion, as well as sagittal plane midfoot region positive and negative peak power during walking. Parametric or nonparametric tests to examine differences and equivalence across time were conducted. Comparisons to examine differences between postoperative TAA group and control group foot function were also performed. Results: Involved-limb midfoot function was not different between the preoperative and 6-month postoperative time point in the TAA group (all P ≥ .17). Equivalence testing revealed similarity in all midfoot function variables across time (all P < .05). Decreased first metatarsal and lateral forefoot motion, as well as positive peak power generation, were noted in the TAA group postoperative involved limb in comparison to the control group (all P ≤ .01). Conclusion: The similarity of midfoot function across time, along with differences in midfoot function in comparison to controls, suggests that TAA does not change midfoot deficits by 6 months postoperation. Level of Evidence: Level II, prospective cohort study.

Impact of COVID-19 Lockdown on Serie A Soccer Players’ Physical Qualities

2021 ◽  
Author(s):  
Ermanno Rampinini ◽  
Federico Donghi ◽  
Marco Martin ◽  
Andrea Bosio ◽  
Marco Riggio ◽  
...  
Keyword(s):  
Aerobic Fitness ◽  
Mixed Models ◽  
Peak Power ◽  
Vertical Jump ◽  
Soccer Players ◽  
Limited Evidence ◽  
Professional Soccer ◽  
Home Based ◽  
Before And After ◽  
Different Seasons

AbstractIn March 2020, the COVID-19 pandemic forced most activities in Italy, including soccer, to cease. During lockdown, players could only train at home, with limited evidence regarding the effect of this period. Therefore, this study aimed to investigate the effect of COVID-19 lockdown on professional soccer players’ physical performance. Aerobic fitness and vertical jump were assessed before and after four periods in two different seasons: COVID-19 lockdown, competitive period before lockdown, competitive period and summer break of the 2016–2017 season. Linear mixed models were used to examine within-period changes and between-period differences in changes observed during COVID-19 lockdown and the three other periods. Within-period changes in aerobic fitness showed a significant improvement following COVID-19 lockdown (p<0.001) and a significant decline during summer break (p<0.001). Between-period differences were significant in the comparison of COVID-19 lockdown with both the competitive 2019–2020 season (p<0.01) and summer break (p<0.001). For the vertical jump, only the between-period comparison revealed significant differences as the changes associated with COVID-19 lockdown were worse than those of the two competitive periods, for both absolute (p<0.05; p<0.001) and relative peak power (p<0.01; p<0.001). Home-based training during lockdown was effective to improve aerobic fitness, although it did not allow players to maintain their competitive period’s power levels.

Force-velocity and force-power properties of single muscle fibers from elite master runners and sedentary men

1996 ◽  
Vol 271 (2) ◽  
pp. C676-C683 ◽  
Author(s):  
J. J. Widrick ◽  
S. W. Trappe ◽  
D. L. Costill ◽  
R. H. Fitts
Keyword(s):  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Power Output ◽  
Peak Power ◽  
Isometric Force ◽  
Peak Force ◽  
Peak Power Output ◽  
Type I ◽  
Shortening Velocity ◽  
Force Velocity

Gastrocnemius muscle fiber bundles were obtained by needle biopsy from five middle-aged sedentary men (SED group) and six age-matched endurance-trained master runners (RUN group). A single chemically permeabilized fiber segment was mounted between a force transducer and a position motor, subjected to a series of isotonic contractions at maximal Ca2+ activation (15 degrees C), and subsequently run on a 5% polyacrylamide gel to determine myosin heavy chain composition. The Hill equation was fit to the data obtained for each individual fiber (r2 > or = 0.98). For the SED group, fiber force-velocity parameters varied (P < 0.05) with fiber myosin heavy chain expression as follows: peak force, no differences: peak tension (force/fiber cross-sectional area), type IIx > type IIa > type I; maximal shortening velocity (Vmax, defined as y-intercept of force-velocity relationship), type IIx = type IIa > type I; a/Pzero (where a is a constant with dimensions of force and Pzero is peak isometric force), type IIx > type IIa > type I. Consequently, type IIx fibers produced twice as much peak power as type IIa fibers, whereas type IIa fibers produced about five times more peak power than type I fibers. RUN type I and IIa fibers were smaller in diameter and produced less peak force than SED type I and IIa fibers. The absolute peak power output of RUN type I and IIa fibers was 13 and 27% less, respectively, than peak power of similarly typed SED fibers. However, type I and IIa Vmax and a/Pzero were not different between the SED and RUN groups, and RUN type I and IIa power deficits disappeared after power was normalized for differences in fiber diameter. Thus the reduced absolute peak power output of the type I and IIa fibers from the master runners was a result of the smaller diameter of these fibers and a corresponding reduction in their peak isometric force production. This impairment in absolute peak power production at the single fiber level may be in part responsible for the reduced in vivo power output previously observed for endurance-trained athletes.

Abstract 199: Hardwiring Institutional Learning Through Team-Based Problem-Solving in a Pediatric Cardiovascular Intensive Care Unit

2012 ◽  
Vol 5 (suppl_1) ◽  
Author(s):  
Eric A Williams ◽  
Lauren Ladwig ◽  
De Ann Nikolai ◽  
Gay Matthews ◽  
Jeanine M Graf
Keyword(s):  
Problem Solving ◽  
Real Time ◽  
Task Force ◽  
High Reliability ◽  
Ease Of Use ◽  
Practice Change ◽  
Frontline Staff ◽  
Pareto Chart ◽  
Exact Test ◽  
Before And After

Introduction: Our purpose was to develop a high reliability system (The SWARM) to empower frontline staff to share information regarding communication and process inefficiencies to rapidly develop solutions. Hypothesis: A systematic process for recognition, evaluation, and transparent feedback would increase the use of problem-solving. Methods: A multidisciplinary team, led by a physician and nurse, developed an email strategy to let frontline staff identify problems in real-time and solve and spread this knowledge throughout the CVICU and Heart Center. Problems submitted were outside the scope of institutional patient safety reporting. Unless immediate attention was required, the SWARM team evaluated entries weekly. Entries were categorized as: 1) Useful information to share with ICU staff; 2) More information needed to be obtained and personnel consulted; or 3) A multidisciplinary task force needed to generate consensus and evidence-based guidelines. Solutions were shared with ICU staff via direct email and a monthly newsletter. After 6 months ICU staff were surveyed with 5 questions regarding awareness, utility, and ease of use of the SWARM process. Staff were resurveyed after re-education and institution of leadership walk-rounds. Rates of SWARM entries before and after re-education were compared using Fisher’s Exact Test for proportions.*p<.05 Results: Of the total 65 SWARM entries, 9% were level 1, 86% were level 2 and 5% were level 3. Entries were categorized into problem types and are shown in the Pareto Chart as percent of total(See Chart). Pre- and post- survey results indicated that staff awareness increased from 70% to 91% and staff understanding of utility increased from 57% to 75%. After re-education, use in CVICU increased by 417% (0.7/week to 2.9/week)*. The increased rate of use of the SWARM system has been sustained for 8 weeks post education. The current rate is 1.8/week. The top two Solutions by category were Re-Education (62%) and Practice Change (17%). Conclusions: A system was developed to better manage quality through real-time awareness of our performance. The formal creation of a standardized context for information sharing has resulted in a significant increase in the performance of problem-solving. This multidisciplinary effort allows for minimizing unnecessary variation in how quality improvement efforts are identified and performed.

A 300°C High Reliability HALT/HAST Screening/Sorting Procedure for Ceramic Capacitors

2018 ◽  
Vol 2018 (HiTEC) ◽  
pp. 000129-000137 ◽  
Author(s):  
Harold L. Snyder
Keyword(s):  
High Reliability ◽  
Stress Test ◽  
Electrical Current ◽  
Accelerated Life Test ◽  
Test Results ◽  
Electrical Model ◽  
Current Leakage ◽  
Ceramic Capacitor ◽  
Ceramic Capacitors ◽  
Before And After

Abstract A highly accelerated life test (HALT) and highly accelerated stress test (HAST) procedure for ceramic capacitors developed by the author in the mid 1980's to early 1990's, and published in 1994, consists of a 400 Volt biased six (6) hour stress sort at 150°C (423K), a methanol current leakage test that located mechanical and structural cracks, a visual inspection at ten times (10×) magnification, and a capacitance and dissipation measurement before and after the test. In over thirty (30) years of use, there has never been a user reported in-circuit failure in industrial, military, and aerospace application at temperatures as high as 500°C (773K). However, reviewing user feedback, two concerns with the original sorting procedure are the stress is performed at 150°C (423K), and the lack of a more detailed ceramic capacitor electrical model. To address the first, the low aging temperature, the stress temperature was increased from 150°C to 300°C, in order to age ceramic solid state crystal mineral phases that may change with temperature. The test results for X7R and NP0/COG multilayer ceramic capacitors (MLCC) at 300°C, are compared to the test results using the original HALT/HAST procedure at 150°C. Differences between X7R/NP0/COG and porcelain capacitors are discussed when applicable. Further, a more detailed ceramic capacitor electrical model that represents the physical and electrical characteristics of the ceramic capacitors is presented, including the electrical current leakage effects with temperature, and the carbonized residue effects from the manufacturing process.

Manufacturability and Reliability Screening of Lower Melting Point, Pb-Free Alloys Containing Bismuth

2015 ◽  
Vol 12 (1) ◽  
pp. 1-28 ◽  
Author(s):  
Joseph M. Juarez ◽  
Polina Snugovsky ◽  
Eva Kosiba ◽  
Zohreh Bagheri ◽  
Subramaniam Suthakaran ◽  
...  
Keyword(s):  
High Reliability ◽  
Temperature Cycling ◽  
Vibration Testing ◽  
Excellent Performance ◽  
Test Conditions ◽  
Surface Finishes ◽  
Before And After ◽  
Microstructure Examination ◽  
Lower Melting Point ◽  
Failure Monitoring

This paper explores the manufacturability and reliability of three Pb-free Bi-containing alloys in comparison with conventional SAC305 and SnPb assemblies. The first alloy included in the study is a Sn-based alloy with 3.4%Ag and 4.8%Bi, which showed promising results in the National Center for Manufacturing Sciences and German Joint projects. The other two alloy variations have reduced Ag content, with and without Cu. BGA and leaded components were assembled on medium-complexity test vehicles using these alloys, as well as SAC305 and SnPb as baseline alloys, for comparison. Test vehicles were manufactured using two board materials, 170°C glass transition temperature (Tg) and 155°C Tg, with three surface finishes: ENIG, ENEPIG, and OSP. The accelerated temperature cycling (ATC) testing was done at −55°C to 125°C with 30-min dwells and 10°C/min ramps, for 3,000 cycles. Detailed microstructure examination before and after ATC testing is described, as is failure analysis. All three experimental alloys showed excellent performance in harsh-environment thermal cycling. Vibration testing at two G-force test conditions with resistance failure monitoring was performed on the daisy-chained components. A detailed description of the technique for the vibration testing using 2 G and 5 G harmonic dwells is provided. The lowest failure rate found at both the 2 G and 5 G levels was for the Cu-containing alloy known as Violet. These results provide data for further statistical analysis leading to the choice of proper combinations of the solder alloys, board materials, and surface finishes for high-reliability applications.

Catchlike-inducing train activation of human muscle during isotonic contractions: burst modulation

1999 ◽  
Vol 87 (5) ◽  
pp. 1758-1767 ◽  
Author(s):  
Samuel C. K. Lee ◽  
Cara N. Becker ◽  
Stuart A. Binder-Macleod
Keyword(s):  
Isometric Contraction ◽  
Peak Power ◽  
Average Power ◽  
Knee Extension ◽  
Human Muscle ◽  
Constant Frequency ◽  
Maximum Voluntary Isometric Contraction ◽  
Before And After ◽  
Isotonic Performance ◽  
Isotonic Contractions

Stimulation trains that exploit the catchlike property [catchlike-inducing trains (CITs)] produce greater forces and rates of rise of force than do constant-frequency trains (CFTs) during isometric contractions and isovelocity movements. This study examined the effect of CITs during isotonic contractions in healthy subjects. Knee extension was electrically elicited against a load of 10% of maximum voluntary isometric contraction. The stimulation intensity was set to produce 20% of maximum voluntary isometric contraction. The muscle was tested before and after fatigue with a 6-pulse CFT and 6-pulse CITs that contained an initial doublet, triplet, or quadruplet. For prefatigue responses, the greatest isotonic performance was produced by CITs with initial doublets. When the muscles were fatigued, triplet CITs were best. CITs produce greater excursion, work, peak power, and average power than do CFTs, because CITs produced more rapid rates of rise of force. Faster rates of rise of force enabled the preload on the muscle to be exceeded earlier during the stimulation train.

Coordinated changes in contractility, energetics, and isomyosins after aortic stenosis

1987 ◽  
Vol 252 (2) ◽  
pp. H275-H282
Author(s):  
Y. Lecarpentier ◽  
L. B. Bugaisky ◽  
D. Chemla ◽  
J. J. Mercadier ◽  
K. Schwartz ◽  
...  
Keyword(s):  
Cardiac Hypertrophy ◽  
Peak Power ◽  
Ventricular Hypertrophy ◽  
Left Ventricular ◽  
Ascending Aorta ◽  
Peak Power Output ◽  
Shortening Velocity ◽  
Old Rats ◽  
Quantitative Changes

To investigate possible alterations of myocardial performance in young rats, cardiac hypertrophy was induced by stenosis of the ascending aorta (AS) in three groups of 25-day-old rats that were compared with three groups of sham-operated controls (C). The cardiac overload duration was 8-10 days, 1 mo, and 2 mo in groups 1, 2, and 3, respectively. Mechanics and energetics were studied in left ventricular papillary muscles, and determination of the V1 and V3 isomyosin pattern was achieved in the same papillary muscle. The majority of quantitative changes concerning the cardiac growth process, contractility, and isomyosin shifts occurred within 8-10 days of stenosis. At this point, the degree of left ventricular hypertrophy relative to C was 53 +/- 6%, whereas maximum unloaded shortening velocity (Vmax) decreased significantly (2.8 +/- 0.1 in C vs. 1.9 +/- 0.1 Lmax/s in AS), peak power output (Emax) decreased (1.8 +/- 0.3 in C vs. 0.6 +/- 0.1 in AS), and the curvature of Hill's hyperbola increased (1.3 +/- 0.4 in C vs. 2.0 +/- 0.7 in AS); moreover, the percent V1 isomyosin decreased significantly (98 +/- 1 in C vs. 51 +/- 3% in AS) and the percent V3 isomyosin increased significantly (2 +/- 1 in C vs. 26 +/- 2% in AS). Beyond 8-10 days of AS, additional changes in cardiac hypertrophy and in mechanical and biochemical parameters were less marked.(ABSTRACT TRUNCATED AT 250 WORDS)

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