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Alberto Ranavolo, Romildo Don, Angelo Cacchio, Mariano Serrao, Marco Paoloni, Massimiliano Mangone and Valter Santilli

Kinematic and kinetic methods (sacral marker, reconstructed pelvis, segmental analysis, and force platform methods) have been used to calculate the vertical excursion of the center of mass (COM) during movement. In this study we compared the measurement of vertical COM displacement yielded by different methods during able-bodied subjects’ hopping at different frequencies (varying between 1.2 and 3.2 Hz). ANOVA revealed a significant interaction between hopping frequency and method (p < 0.001), showing that increasing hopping frequency reduced the differences between methods. A post hoc analysis revealed a significant difference between all methods at the lowest hopping frequency and between the force platform and both the sacral marker and reconstructed pelvis methods at the intermediate hopping frequencies, with differences ranging from 16 to 67 millimeters (all p < 0.05). Results are discussed in view of each methods’ limits. We conclude that the segmental analysis and force platform methods can be considered to provide the most accurate results for COM vertical excursion during human hopping in a large range of hopping frequency.

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Seung Pil Lee, T. Bettina Cornwell and Kathy Babiak

The objective of this study is to develop an instrument to measure the social impact of sport. While there is a rich literature suggesting and measuring the ways in which sport contributes to society, no broad, encompassing scale has been developed. A measure of this type is useful if sport initiatives are to gain social, political and financial support, especially in the form of corporate sponsorship. The proposed “Social Impact of Sport Scale” includes the dimensions of social capital, collective identities, health literacy, well-being and human capital. In addition to development of a detailed 75 item composite scale stemming largely from past measurement, a shorter set of global measures is also examined. A convenience sample of university students is used in scale development as well as a partial test of the scale in context. Results find support for the detailed scale and for the short global measure instrument. In addition, the partial test of the scale in a context of sport experience relevant to students is reported. The value of the scale in use and areas of future research are discussed.

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Vera L. Talis and Irina A Solopova

We investigated the development of postural reactions induced in standing subjects by Achilles tendon vibration. We compared vibratory reactions in 3 different conditions: normal standing, standing near support, and when the solid support being protracted forward changed the initial posture. Additional support for the back was placed at subject's sacral or shoulder level. In the easy standing condition, the postural vibration reaction consists of progressive backward upper body movement. When the body contacted the additional support on the sacral level during the vibratory reaction, the movement of the upper body continued in most of the subjects. This was accompanied by an increase of pressure on the toes. When the support was applied at the shoulder level, the body motion reversed its direction in half of the subjects. In this case, backward-forward oscillations occurred near the support. The initial change of body-support interaction did not influence the ensuing vibration reaction; namely the reaction was similar to that with the support near to the body at the sacral level. Our data demonstrate that the vibration-induced reaction is not a local reaction limited to one joint, but a complex postural synergy that involves both leg and trunk muscles and integrates the information from touch and pressure afferents of the upper body.

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Karen J. Winegard, Audrey L. Hicks and Anthony A. Vandervoort

The purpose of this study was to assess the reliability of measuring voluntary isometric strength, evoked isometric twitch properties (peak torque, time to peak torque, half-relaxation time), M-wave amplitude, and passive tension in very old adults (73-92 years). Five male and 5 female subjects were tested on two different test occasions that were 1 week apart. Using the intraclass correlation coefficient (ICC) method, the mean reliability coefficient of all measurements on the dorsiflexor (DF) and plantar flexor (PF) muscle groups was .91 ± .05. Similar ICC values were found for DF and PF muscles (.92 ± .04 and .90 ± .05, respectively). Resting PF half-relaxation time was the least reliable measure, with an ICC value of .80, while maximum voluntary strength was the most reliable with ICC values of .98 for DF and .97 for PF. The variation ranged from 0.2 to 12.3%. It was concluded that ankle muscle function (both voluntary and evoked) can be reliably assessed in this very old age group.

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Dennis A. Nowak, Joachim Hermsdörfer, Jens Philipp, Christian Marquardt, Stefan Glasauer and Norbert Mai

We investigated the quality of predictive grip force control during gravity changes induced by parabolic flight maneuvers. During these maneuvers gravity varied: There were 2 periods of hypergravity, in which terrestrial gravity nearly doubled, and a 20-s period of microgravity, during which a manipulated object was virtually weightless. We determined grip and load forces during vertical point-to-point movements of an instrumented object. Point-to-point movements were a combination of static (stationary holding) and dynamic (continuous movements) task conditions, which were separately analyzed in our previous studies. Analysis of the produced grip forces revealed that grip adjustments were closely linked to load force fluctuations under each gravity condition. In particular, grip force maxima coincided closely in time with load force peaks, although these occurred at different phases of the movement depending on the gravity level. However, quantitative analysis of the ratio of maximum grip force to the corresponding load force peak revealed an increased force ratio during microgravity when compared to that during normal and hypergravity, We hypothesize that the impaired precision of force coupling with respect to force magnitude during microgravity results from reduced feedback information about the object's mass during the stationary holding of the object in between each movement. The results indicate that the temporal grip force regulation is highly automatized and stable, whereas economical planning of force magnitude is more flexible and might reflect changes of the external loading condition.

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Sheng Li, Frederic Danion, Mark L. Latash, Zong-Ming Li and Vladimir M. Zatsiorsky

One purpose of the present study was to compare indices of finger coordination during force production by the fingers of the right hand and of the left hand. The other purpose was to study the relation between the phenomena of force deficit during multifinger one-hand tasks and of bilateral force deficit during two-hand tasks. Thirteen healthy right-handed subjects performed maximal voluntary force production tasks with different finger combinations involving fingers of one hand or of both hands together. Fingers of the left hand demonstrated lower peak forces, higher indices of finger enslaving, and similar indices of force deficit. Significant bilateral effects during force production by fingers of both hands acting in parallel were seen only during tasks involving different fingers or finger groups in the two hands (asymmetrical tasks). The bilateral deficit effects were more pronounced in the hand whose fingers generated higher forces. These findings suggest a generalization of an earlier introduced principle of minimization of secondary moments. They also may be interpreted as suggesting that bilateral force deficit is task-specific and may reflect certain optimization principles.

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Sheng Li, Jennifer A. Stevens, Derek G. Kamper and William Z. Rymer

The purpose of this study was to investigate the effect of motor imagery on the premotor time (PMT). Twelve healthy adults performed reaction time movements in response to external visual signals at rest, when holding an object (muscle activation), or performing different background imagined movements (motor imagery). When compared to rest, muscle activation reduced the PMT; imagined finger extension of the right hand and imagined finger flexion of the left hand elongated the PMT; imagined finger flexion of the right hand had no effect on the PMT. This movement-specific effect is interpreted as the sum of the excitatory effect caused by enhanced corticospinal excitability specifically for the primary mover of the imagined movement and an overall inhibition associated with increased task complexity during motor imagery. Our results clearly demonstrate that motor imagery has movement-specific effects on the PMT.

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Winston D. Byblow, Jeffery J. Summers, Andras Semjen, Irina J. Wuyts and Richard G. Carson

Two experiments required right-handed subjects to trace circular trajectories while complying with either a symmetric or asymmetric pattern. In symmetric patterns, circles were traced in a mirror image either inward or outward. In asymmetric patterns, circles were traced in the same direction either clockwise or counterclockwise. Subjects were instructed to trace with spatial accuracy while maintaining a strict temporal relationship to a metronome that scaled movement rates from 1.25 to 3 Hz. The symmetric patterns were more stable than asymmetric patterns; the circularity of trajectories was greater for the dominant side; and there were spontaneous reversals in the direction of circling in the nondominant limb when performing asymmetric patterns. The second experiment examined the same subjects under the instruction of intentionally changing the pattern by reversing the left or right limb circling direction when cued to do so. The degree of interlimb interference was highly asymmetric and contingent on the direction of pattern change. Intentional direction reversals were more expedient and with less disruption to the contralateral limb when asymmetric to symmetric pattern changes were effected through a reversal in the direction of nondominant side. The results are interpreted with reference to evidence that the supplementary motor area mediates descending input to the upper limbs during disparate bimanual actions, but not during symmetric actions.

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Sheng Li, Woo-Hyung Park and Adam Borg

The study investigated squeezing reaction time (RT) in response to a visual cue during rhythmic voluntary breathing at 0.6 Hz paced by a metronome, breath holding, or at rest in 13 healthy subjects. Rhythmic voluntary breathing slowed down RT, only in the expiratory phase with accompanied changes in the length of respiratory phases, while breath-holding reduced RT. The prolonged RT during voluntary expiratory phases and the absence of changes in RT during voluntary inspiratory phases are most likely related to disproportionally increased cognitive demands during the expiratory phase of voluntary breathing. The absence of changes in RT during voluntary inspiration is likely to be compensated by respiratory-motor facilitation mechanisms in this phase. Shortened RT during breath holding is possibly associated with increased attention.

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Asger R. Pedersen, Peter W. Stubbs and Jørgen F. Nielsen

The aim was to challenge the assumptions of standard statistical analyses of average surface electromyography (sEMG) data as a measurement of response magnitudes following the generation of a reflex. The ipsilateral tibial nerve was stimulated at three stimulation intensities and the response sEMG was measured in the contralateral soleus (cSOL) muscle. The magnitude of the cSOL response was measured at a set time window following ipsilateral tibial nerve stimulation. The averaged and trial-by-trial response magnitudes were assessed and compared. The analysis of the averaged and trial-by-trial response revealed significantly different results as the trial-by trial response magnitudes were log-normally distributed with between subject variance heterogeneity violating assumptions of standard statistical analyses. A statistical model has been suggested for the analysis of the responses. By ignoring trial-by-trial response variability and distribution, erroneous results may occur. This may change the interpretation of the results in some studies.