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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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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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Kevin M. Carroll, Jake R. Bernards, Caleb D. Bazyler, Christopher B. Taber, Charles A. Stuart, Brad H. DeWeese, Kimitake Sato and Michael H. Stone

Resistance training (RT) has repeatedly shown the capability to enhance physical performance characteristics, such as maximal strength 1 – 4 and rate of force development (RFD). 5 Maximal strength and RFD are critically important for athletes, particularly in strength–power sports. 6 , 7

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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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Lasse Ishøi, Per Aagaard, Mathias F. Nielsen, Kasper B. Thornton, Kasper K. Krommes, Per Hölmich and Kristian Thorborg

reach high force production during a short period of time, defined as the rate of force development, 15 may be a substantial factor for sprint performance. 16 The importance of rate of force development for sprint performance has been highlighted in a previous study observing strong negative

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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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Roger O. Kollock, Bonnie Van Lunen, Stacie I. Ringleb and James Onate

The ability to produce force rapidly and to maintain it is essential to sports performance. Although rapid force production and endurance are indispensable characteristics of optimal health and performance, assessing these qualities of strength is difficult because of clinician time constraints. The purpose of this study was to determine if peak force is a predictor of rate of force production and strength endurance. The results indicated peak force is a predictor of rate of force development, but not strength endurance. Clinicians should assess both maximum strength and endurance to gain a more complete picture of lower extremity strength deficits.

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Michael H. Stone, William A. Sands, Kyle C. Pierce, Michael W. Ramsey and G. Gregory Haff

Purpose:

To assess the effects of manipulating the loading of successive sets of midthigh clean pulls on the potentiation capabilities of 7 international-level US weightlifters (4 men, 3 women).

Methods:

Isometric and dynamic peak-force characteristics were measured with a force plate at 500 Hz. Velocity during dynamic pulls was measured using 2 potentiometers that were suspended from the top of the right and left sides of the testing system and attached to both ends of the bar. Five dynamic-performance trials were used (in the following order) as the potentiation protocol: women at 60, 80, 100, 120, and 80 kg and men at 60, 140, 180, 220, and 140 kg. Trials 2 vs 5 were specifically analyzed to assess potentiation capabilities. Isometric midthigh pulls were assessed for peak force and rate of force development. Dynamic lifts were assessed for peak force (PF), peak velocity (PV), peak power (PP), and rate of force development (RFD).

Results:

Although all values (PF, PV, PP, and RFD) were higher postpotentiation, the only statistically higher value was found for PV (ICCα = .95, P = .011, η2 = .69).

Conclusions:

Results suggest that manipulating set-loading configuration can result in a potentiation effect when heavily loaded sets are followed by a lighter set. This potentiation effect was primarily characterized by an increase in the PV in elite weightlifters.

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Pedro Jiménez-Reyes, Fernando Pareja-Blanco, David Rodríguez-Rosell, Mario C. Marques and Juan José González-Badillo

Purpose:

To determine what variables determine the differences in performance on 2 tests of squat jump (SJ) performed under light load in highly trained athletes using maximal velocity (Vmax) or flight time (FT) as the discriminating factor of SJ performance.

Methods:

Thirty-two participants performed 2 maximal weighted SJs using a force platform synchronized with a linear transducer. Mean force (Fmean), mean and maximal power (Pmean, Pmax), peak force (PF), maximal rate of force development (RFDmax), and time required to attain PF (TPF) and RFDmax (TRFDmax) were analyzed. SJs were divided into 2 segments: from the initiation of force application to PF1 and from the moment after PF1 to Vmax.

Results:

Traditional significance statistics revealed significant differences in the same variables between best and worst SJs using both FT and Vmax. However, to use an approach based on the magnitude of the effect, the best SJ showed greater Pmax (83/17/0%), Pmean (85/15/0%), Fmean (71/29/0%), RFDmax1 (73/27/0%), and PF1 (53/47/0%) and lower TPF2 (0/61/39%) than the worst SJ when Vmax was used to discriminate SJ performance. However, using FT to differentiate SJ performance, no difference was observed between best and worst.

Conclusions:

Although jump height assessed through FT is a valid measure, these results suggest that Vmax is a more sensitive variable than FT to detect differences in loaded-SJ performance.

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

Purpose:

Skeletal-muscle function can be evaluated using force–times curves generated via the isometric midthigh pull (IMTP). Various sampling frequencies (500–1000 Hz) have been used for IMTP assessments; however, no research has investigated the influence of sampling frequency on IMTP kinetics. Therefore, the purpose of this study was to investigate the influence of sampling frequency on kinetic variables during the IMTP, including peak force, time-specific force values (100, 150, and 200 ms), and rate of force development (RFD) at 3 time bands (0–100, 0–150, 0–200 ms).

Methods:

Academy rugby league players (n = 30, age 17.5 ± 1.1 y, height 1.80 ± 0.06 m, mass 85.4 ± 10.3 kg) performed 3 IMTP trials on a force platform sampling at 2000 Hz, which was subsequently down-sampled to 1500, 1000, and 500 Hz for analysis.

Results:

Intraclass correlation coefficients (ICC) and coefficients of variation (CV) demonstrated high within-session reliability for all force and RFD variables across all sampling frequencies (ICC ≥ .80, CV ≤ 10.1%). Repeated-measures analysis of variance revealed no significant differences (P > .05, Cohen d ≤ 0.009) in kinetic variables between sampling frequencies. Overall, high reliability was observed across all sampling frequencies for all kinetic variables, with no significant differences (P > .05) for each kinetic variable across sampling frequencies.

Conclusions:

Practitioners and scientists may consider sampling as low as 500 Hz when measuring peak force, time-specific force values, and RFD at predetermined time bands during the IMTP for accurate and reliable data.