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David Hawkins and Mark Smeulders

The purpose of this study was to determine if the characteristic Hill model, used to describe me force–velocity relationship for isolated tetanically stimulated muscle, could be modified and used to describe me torque–velocity behavior of me hip for maximally and submaximally stimulated hip extensor muscles. Fourteen subjects performed hip extension movements at effort levels of 100%, 70%, and 40% of a maximum isometric effort. A solenoid provided isometric resistance to hip extension. Once the desired effort level was achieved, as indicated by me isometric force, the solenoid released and me hip moved against an opposing elastic resistance equal to 75%, 50%, 25%, and 0% of the specified effort level. An electrogoniometer quantified hip angle. Hip velocity was determined by numerically differentiating the angle data. Torque-velocity-activation (or effort level) data were determined for each trial. Model parameters were determined to give me best fit to the data for each subject. Average parameter values were determined for each gender and for the entire group. The modified Hill-type model, Tm = (Tmax · AK1 · ω)/(K2 · ω + 1), accurately describes me relationship between joint torque (Tm), maximum isometric joint torque (Tmax), joint velocity (ω), and muscle activation level (A) for subject-specific parameters (K1 and K2), but not for parameters averaged across genders or the entire group. Values for Tmax, K1, and K2 ranged from 90 to 385 Nm, 6.1 to 47.9 Nms, and 0.030 to 0.716 s, respectively.

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Keijo Häkkinen, Markku Alen, Mauri Kallinen, Mikel Izquierdo, Kirsi Jokelainen, Helka Lassila, Esko Mälkiä, William J. Kraemer and Robert U. Newton

Forty-two healthy men and women in two age groups (40 and 70 years) were examined for muscle cross-sectional area (CSA), maximal voluntary bilateral isometric force, force-time characteristics, maximal concentric 1 RM. and power performance of the leg extensors in a sitting position, squat jump, and standing long-jump. The results suggested that the decline in maximal strength with increasing age is related to the decline in muscle CSA; however, particularly in older women, the force/CSA ratio may also be lowered. Explosive force seems to decrease with increasing age even more than maximal strength. suggesting that muscle atrophy with aging is greater in fast-twitch fibers. The voluntary activation of the agonist and antagonist muscles seems to vary depending on the type of muscle action and/or velocity and time duration of the action in both age groups but to a greater extent in older people. There appears to be an age-related increase in antagonist co activation. especially in dynamic explosive movements.

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Rebecca L. Krupenevich, William H. Clark, Gregory S. Sawicki and Jason R. Franz

and passive structures spanning the ankle joint and represents an aggregate measure of this interaction. Our research group recently provided empirical evidence that ankle joint quasi-stiffness (1) can be actively regulated through the activation-dependent modulation of soleus length–tension behavior

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Sarah A. Roelker, Elena J. Caruthers, Rachel K. Hall, Nicholas C. Pelz, Ajit M.W. Chaudhari and Robert A. Siston

Musculoskeletal modeling and simulation techniques enable estimates of variables that influence movement, including muscle activations and forces. Many of these variables are not commonly determined in human experiments because of the significant pain and discomfort to the subject with approaches

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Brice T. Cleland and Sheila Schindler-Ivens

There are many examples of altered movement-related brain activation in individuals with poststroke hemiparesis. Changes in the extent, intensity, and location of brain activation have been observed during upper and lower limb movements, in acute and chronic stroke survivors, and before and after

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Panteleimon Ekkekakis, Eric E. Hall and Steven J. Petruzzello

Two studies were conducted to examine the internal consistency and validity of the state anxiety subscale of the State-Trait Anxiety Inventory (SAI) in the context of acute exercise. SAI responses typically found in the exercise literature were replicated. Analysis at the item level revealed divergent response patterns, confounding the total SAI score. During moderate and immediately after vigorous exercise, scores on items referring to cognitive antecedents of anxiety decreased, whereas scores on items assessing perceived activation increased. Indices of internal showed exercise-associated decreases. A principal-components analysis of responses immediately postexercise revealed a multidimensional structure, distinguishing “cognitive” and “activation” items. By failing to discern exercise-induced and anxiety-related increases in activation from anxiety-antecedent appraisals, the SAI exhibits compromised internal consistency and validity in the context of acute exercise.

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Hong-Wen Wu, Cheng-Feng Tsai, Kai-Han Liang and Yi-Wen Chang

. The effect of different squat skills on muscle activation, such as wall squat or single-leg squat, has been examined in previous literatures. Ayotte et al 6 compared the differences of muscle activities of gluteal muscles, biceps femoris, and vastus medialis among wall squat, minisquat, and step

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William H. Clark and Jason R. Franz

Some evidence suggests that muscle stiffness is activation dependent 6 ; however, it remains unclear precisely how the neuromechanical behavior of the triceps surae muscles and series elastic tendon interact to modulate k A , with implications for functional activities such as walking. In walking, k A

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Justin Goins

alignments, and functional abilities essential for normal gait. 2 Decreased activation of the GM and increased activation of hamstrings have been observed clinically in patients with hamstring injuries and low back pain. 1 , 3 – 6 Overactivity of the erector spinae and hamstring muscles, along with

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Junyeon Won, Alfonso J. Alfini, Lauren R. Weiss, James M. Hagberg and J. Carson Smith

). Additionally, exercise training in healthy older adults reduces cortical activation during a semantic memory retrieval task (the famous name recognition task [FNT]). This effect occurred in the absence of changes in performance, suggesting improved neural efficiency during semantic memory retrieval ( Smith et