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Dean Norris, David Joyce, Jason Siegler, James Clock and Ric Lovell

associated injury risk. 16 – 19 Furthermore, explosive force–time measures collected from the IMTP may have a potential advantage of giving insight into the neural and contractile mechanisms of neuromuscular fatigue, 20 – 22 with early-phase rate of force development (RFD, <75 ms) being predominantly

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Andrés Pérez, Domingo J. Ramos-Campo, Cristian Marín-Pagan, Francisco J. Martínez-Noguera, Linda H. Chung and Pedro E. Alcaraz

statistical analysis. The maximal rate of isometric force development (RFD; N·s −1 ) was determined from the best MVC and was derived as the average slope of the moment–time curve (moment/time) for the time intervals 0 to 50, 0 to 100, 0 to 200 ms relative to the onset of contraction. In addition, RFD peak

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Ty B. Palmer, Jose G. Pineda and Rachel M. Durham

Strength-based performance characteristics, such as peak force (PF) and rate of force development (RFD), are commonly measured to assess functional ability, 1 discriminate between athletes of different performance levels, 2 and monitor neuromuscular performance changes in response to training or

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Talyene G.C. Corrêa, Stephanie V.S. Donato, Kauê C.A. Lima, Ronaldo V. Pereira, Mehmet Uygur and Paulo Barbosa de Freitas

tangential slip force (e.g.,  Crevecoeur, Thonnard, Lefèvre, & Scott, 2016 ; Johansson & Westling, 1988 ). One of the most common outcome variables used to quantify neuromuscular quickness has been the rate of force (or torque) development (RFD). The RFD has been calculated in maximal rapid force generation

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Thomas Dos’Santos, Paul A. Jones, Jonathan Kelly, John J. McMahon, Paul Comfort and Christopher Thomas

Skeletal-muscle function can be evaluated using force-time curves generated during dynamic and isometric activities. Peak force (PF) and peak rate of force development (RFD) are commonly assessed 1 – 5 and have been reported to relate to various athletic performance tasks including baseball

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Martin H. Rose, Annemette Løkkegaard, Stig Sonne-Holm and Bente R. Jensen

We investigated lower-extremity isometric tremor Approximate Entropy (irregularity), torque steadiness and rate of force development (RFD) and their associations to muscle activation strategy during isometric knee extensions in patients with Parkinson’s disease (PD). Thirteen male patients with idiopathic PD and 15 neurologically healthy matched controls performed isometric maximal contractions (extension/flexion) as well as steady submaximal and powerful isometric knee extensions. The patients with PD showed decreased isometric tremor irregularity. Torque steadiness was reduced in PD and the patients had increased muscle coactivation. A markedly lower RFD was found in PD and the decreased RFD correlated with reduced agonist muscle activation. Furthermore, patient RFD correlated with the Movement-Disorder-Society-Unified-Parkinson’s-Disease-Rating-Scale 3 (motor part) scores. We concluded that both knee isometric tremor Approximate Entropy and torque steadiness clearly differentiate between patients with PD and healthy controls. Furthermore, severely compromised RFD was found in patients with PD and was associated with decreased agonist muscle activation.

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Heiner Baur, Alessia Severina Groppa, Regula Limacher and Lorenz Radlinger

Maximum strength and rate of force development (RFD) are 2 important strength characteristics for everyday tasks and athletic performance. Measurements of both parameters must be reliable. Expensive isokinetic devices with isometric modes are often used. The possibility of cost-effective measurements in a practical setting would facilitate quality control. The purpose of this study was to assess the reliability of measurements of maximum isometric strength (Fmax) and RFD on a conventional leg press. Sixteen subjects (23 ± 2 y, 1.68 ± 0.05 m, 59 ± 5 kg) were tested twice within 1 session. After warm-up, subjects performed 2 times 5 trials eliciting maximum voluntary isometric contractions on an instrumented leg press (1- and 2-legged randomized). Fmax (N) and RFD (N/s) were extracted from force-time curves. Reliability was determined for Fmax and RFD by calculating the intraclass correlation coefficient (ICC), the rest-retest variability (TRV), and the bias and limits of agreement. Reliability measures revealed good to excellent ICCs of .80-.93. TRV showed mean differences between measurement sessions of 0.4-6.9%. The systematic error was low compared with the absolute mean values (Fmax 5-6%, RFD 1-4%). The implementation of a force transducer into a conventional leg press provides a viable procedure to assess Fmax and RFD. Both performance parameters can be assessed with good to excellent reliability allowing quality control of interventions.

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Maria Bellumori, Slobodan Jaric and Christopher A. Knight

Physical quickness is less in older adults with implications for fall prevention, movement initiation, and activities of daily living. The purpose was to compare control of rapid contractions in young and older adults within two diverse muscle groups: powerful elbow extensors (EE) and dexterous index finger abductors (IFA). Most-rapid force pulses to a variety of levels were recorded and peak force and rate of force development (RFD) were analyzed with linear regression. The resulting slope represents the dependent variable of interest, the RFD-scaling factor (RFD-SF). RFD-SF of EE and IFA strongly correlated both overall (r = .87, p < .01) and separately in young (r = .60, p < .05) and older (r = .77, p < .01) adults. RFD-SF values were different between muscle groups (F 1,28 = 19.1, p < .001) and also less in elderly (F 1,28 = 32.6, p < .001). We conclude that RFD-SF provides a sensitive assessment of muscle quickness that can be used to evaluate neuromuscular function in aging humans.

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Bradley C. Nindl, William J. Kraemer, Lincoln A. Gotshalk, James O. Marx, Jeff S. Volek, Jill A. Bush, Keijo Häkkinen, Robert U. Newton and Steve J. Fleck

Regional fat distribution (RFD) has been associated with metabolic derangements in populations with obesity. For example, upper body fat patterning is associated with higher levels of free testosterone (FT) and lower levels of sex-hormone binding globulin (SHBG). We sought to determine the extent to which this relationship was true in a healthy (i.e., non-obese) female population and whether RFD influenced androgen responses to resistance exercise. This study examined the effects of RFD on total testosterone (TT), FT, and SHBG responses to an acute resistance exercise test (ARET) among 47 women (22 ± 3 years; 165 ± 6 cm; 62 ± 8 kg; 25 ± 5 %BF; 23 ± 3 BMI). RFD was characterized by 3 separate indices: waist-to-hip ratio (WHR), ratio of upper arm fat to mid-thigh fat assessed with magnetic resonance imaging (MRI ratio), and ratio of subscapular to triceps ratio (SB/TRi ratio). Skinfolds were measured for the triceps, chest, subscapular, mid-axillary, suprailaic, abdomen, and thigh regions. The ARET consisted of 6 sets of 10 RM squats separated by 2-min rest periods. Blood was obtained pre- and post- ARET. TT, FT, and SHBG concentrations were determined by radioimmunoassay. Subjects were divided into tertiles from the indices of RFD, and statistical analyses were performed by an ANOVA with repeated measures (RFD and exercise as main effects). Significant (p < .05) increases following the AHRET were observed for TT (~25%), FT (~25%), and SHBG (4%). With multiple regression analysis, anthropometric measures significantly predicted pre- concentrations of FT, post-concentrations of TT, and pre-concentrations of SHBG. The SB/TRi and MRI ratios but not the WHR, were discriminant for hormonal concentrations among the tertiles. In young, healthy women, resistance exercise can induce transient increases in testosterone, and anthropometric markers of adiposity correlate with testosterone concentrations.

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Bernardo Requena, Jaan Ereline, Helena Gapeyeva and Mati Pääsuke

Context:

The understanding of posttetanic potentiation (PTP) in human muscles induced by percutaneous electrical stimulation (PES) is important for effective application of electrical stimulation in rehabilitation.

Objective:

To examine the effect of 7-second high-frequency (100-Hz) submaximal (25% of maximal voluntary contraction force) direct PES on contractile characteristics of the knee-extensor (KE) muscles.

Design:

Single-group repeated measures.

Setting:

Kinesiology laboratory.

Subjects:

13 healthy men age 18–27 years.

Measurement:

Peak force (PF), maximal rates of force development (RFD) and relaxation (RR) of supramaximal twitch, and PF of doublet and 10-Hz tetanic contractions before and after direct tetanic PES.

Results:

A significant potentiation of twitch, doublet, and 10-Hz tetanic-contraction PF has been observed at 1–5 minutes posttetanic. Twitch RFD and RR were markedly potentiated throughout the 10-minute posttetanic period.

Conclusions:

A brief high-frequency submaximal tetanic PES induces PTP in KE muscles associated with small increase at 1–5 minutes.