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Scott A. Conger, Alexander H.K. Montoye, Olivia Anderson, Danielle E. Boss and Jeremy A. Steeves

populations such as individuals who are at risk for falls ( Han & Yang, 2015 ; Levinger et al., 2017 ), patients with cerebral palsy ( Kirk et al., 2016 ), and athletes ( Griffiths et al., 2019 ; Kawamori & Haff, 2004 ) may benefit from faster movement speeds during RT. However, slower RT movement speeds

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Neil A. Doldo, Matthew J. Delmonico, Jason A. Bailey, Brian D. Hand, Matthew C. Kostek, Karma M. Rabon-Stith, Kalapurakkal S. Menon, Joan M. Conway, Craig R. Carignan and Ben F. Hurley

To determine sex and race differences in muscle power per unit of muscle contraction, knee-extensor muscle power normalized for knee-extensor muscle volume was measured in 79 middle-aged and older adults (30 men and 49 women, age range 50–85 years). Results revealed that women displayed a 38% faster peak movement velocity than men and African Americans had a 14% lower peak movement velocity than Whites of a similar age when expressed per unit of involved muscle (p < .001). As expected, men exhibited greater knee-extensor strength and peak power per unit of muscle than women, but women had a faster knee-extension movement velocity per unit of muscle than men at the same relative strength level. Moreover, African Americans had greater knee-extensor muscle volume than Whites but exhibited lower knee-extensor strength and lower movement velocity per unit of muscle when tested at the same relative strength levels.

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Blanka Hejduková, Nasser Hosseini, Bo Johnels, Pall E. Ingvarsson, Goran Steg and Torsten Olsson

During transport of an object using the precision grip with thumb and index finger, a modulation of the grip force is needed in response to the forces evoked by the movement. We measured the grip force (GF) and the load force (LF) in 10 healthy participants moving a 640-g object forward and upward. The task was repeated with various speeds. There were considerable changes with speed of the LF trajectory but not of the GF trajectory. A loss of synergy between GF and LF appeared in fast lifts. This is in contrast to the close coupling between load force and grip force repeatedly demonstrated during simple lifts. We suggest that (a) speed should be considered as an input parameter for movement planning, and (b) regulation of GF and of LF are independent under certain conditions. We discuss whether the grip-load force synergy should be considered a special case rather than a more general principle.

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Brian M. Wood, Herman Pontzer, Jacob A. Harris, Audax Z.P. Mabulla, Marc T. Hamilton, Theodore W. Zderic, Bret A. Beheim and David A. Raichlen

, measures of movement speed and subject height. The influence of these variables is clear under controlled experimental conditions, but their inclusion in a model may not have a major impact on results given the imperfect nature of GPS data. Noise in GPS signals might overshadow any signal of the influence

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Tomoko Aoki, Hayato Tsuda and Hiroshi Kinoshita

, this study demonstrated that finger motor abilities evaluated by rapid tapping declined in older individuals in terms of both movement speed and finger independence. It is presumed that a number of factors collectively contribute to the age-related decline in finger motor function observed in the

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Jonathan P. Norris, Jamie Highton and Craig Twist

between a linear series of cones, with movement speed controlled by an audio signal. Two bouts of 23-minute activity were interspersed with a 20-minute passive recovery period to simulate the mean playing time of elite interchanged rugby league players. 2 Each bout was identical and consisted of 12

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Matthew R. Blair, Nathan Elsworthy, Nancy J. Rehrer, Chris Button and Nicholas D. Gill

patterns across sports. For example, all the investigations show that rugby union referees spend the majority of match time with heart rate (HR) in higher zones (>80%HR max ). 8 In comparison, most of the accumulated distance traveled occurs at lower movement speeds (<2 m·s −1 ). 5 , 18 Therefore, it

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Birgit Larsen, Michael Voigt and Michael J. Grey

The influence of pedaling frequency and crank load on the sensitivity of the soleus short latency stretch reflex (SLR) was examined in nine healthy subjects during pedaling by the use of a custom-built robotic actuator. The SLR decreased successively in downstroke when pedaling frequency increased from 20 to 40 and 60 revolutions per minute at a constant crank load (p = .005). The SLR was unchanged at crank load increases of 2.6 or 5.1 Nm at a constant pedaling frequency (p > .05). Accordingly, it was shown that increased muscle activation level as a consequence of added crank load and increased movement speed does not increase the sensitivity of the soleus SLR.

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Thomas Korff and Jody L. Jensen

When performing skillful movement muscular and nonmuscular forces act in concert to produce a resultant force that complies with the goal of the task. Nonmuscular forces are directly dependent on the anthropometry of the performer. The purpose of this study was to determine the effect of age-related changes in relative anthropometric characteristics between 5 and 10 years of age on muscular power production during pedaling. A secondary purpose was to determine the dependence of this effect on movement speed. A torque-driven model of two-legged pedaling was used to track experimental kinematics and forces obtained from 6 experienced adult cyclists pedaling at 60 and 120 rpm. Relative anthropometric characteristics were modified to simulate pedaling for children of 5, 7.5, and 10 years of age. Analyses of variance revealed that age-related differences in anthropometry did not affect the muscular contribution to crank power (p > .05), while they had a significant effect on the muscular contribution to limb power (p < .05). Adjustments by the proximal muscle groups (muscles spanning the hip and knee joints) were necessary to account for anthropometry-driven changes in nonmuscular power. These effects were independent of movement speed. Our results provide researchers with useful information to interpret age-related differences in muscular power production more accurately.

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Richard A. Preuss and Milos R. Popovic

This study defines the limits of stability in sitting, and quantitatively assesses two measures of postural control relative to these limits. Young, healthy subjects sat, feet unsupported, on an elevated force plate. The limits of stability were determined by a least square fit of an ellipse to the center of pressure (CoP) excursion during maximal leaning in 8 directions. These were highly symmetrical and centered within the base of support. The ellipses had a mean eccentricity of 0.66 (major axis in the sagittal plane) and covered an area approx. 1/3 of the base of support. The CoP was then monitored over 4 min of quiet sitting, during which the postural sway covered an area <0.05% of the limits of stability and was closely centered within the latter. Finally, target-directed trunk movements were performed, in 5 directions, at 4 movement speeds and 3 target distances. Increased target distance and movement speed both decreased the margin of stability (distance between the CoP and the limits of stability), as did movement in the frontal plane, reflecting the eccentricity of the limits of stability. These combined findings support the validity of this quantitative method of defining the limits of stability in sitting, for healthy individuals.