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Ryu Nagahara, Alberto Botter, Enrico Rejc, Masaaki Koido, Takeshi Shimizu, Pierre Samozino and Jean-Benoit Morin

Purpose:

To test the concurrent validity of data from 2 different global positioning system (GPS) units for obtaining mechanical properties during sprint acceleration using a field method recently validated by Samozino et al.

Methods:

Thirty-two athletes performed maximal straight-line sprints, and their running speed was simultaneously measured by GPS units (sampling rate: 20 or 5 Hz) and either a radar or laser device (devices taken as references). Lower-limb mechanical properties of sprint acceleration (theoretical maximal force, theoretical maximal speed, maximal power) were derived from a modeling of the speed–time curves using an exponential function in both measurements. Comparisons of mechanical properties from 20- and 5-Hz GPS units with those from reference devices were performed for 80 and 62 trials, respectively.

Results:

The percentage bias showed a wide range of overestimation or underestimation for both systems (-7.9% to 9.7% and -5.1% to 2.9% for 20- and 5-Hz GPS), while the ranges of its 90% confidence limits for 20-Hz GPS were markedly smaller than those for 5-Hz GPS. These results were supported by the correlation analyses.

Conclusions:

Overall, the concurrent validity for all variables derived from 20-Hz GPS measurements was better than that obtained from the 5-Hz GPS units. However, in the current state of GPS devices’ accuracy for speed–time measurements over a maximal sprint acceleration, it is recommended that radar, laser devices, and timing gates remain the reference methods for implementing the computations of Samozino et al.

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Sergio L. Molina and David F. Stodden

education (S2.H2.L2, p. 34; SHAPE America, 2013 ). Inquiry from Fitts’ initial work also led to the development of impulse-variability (IV) theory ( Schmidt, Zelaznik, Hawkins, Frank, & Quinn, 1979 ), which provides a theoretical framework to describe the relationship between force and force variability

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Xiaogang Hu and Karl M. Newell

The purpose of this study was to investigate the mechanisms contributing to the different scaling functions between force and force variability in continuous and discrete isometric forces. Muscle forces were simulated with the Fuglevand et al. (1993) model of motor unit recruitment and rate coding, and a range of recruitment and firing properties were manipulated. The influence of time-to-peak force on the discrete force variability was also examined. The results revealed that the peak firing rate, the synchrony between motoneurons, and the recruitment range contributed to the different variability functions in continuous and discrete forces. The shorter time-to-peak force led to higher variability in the peak force. The findings show that the model can produce the distinct properties of the force variability scaling functions in continuous and discrete forces. The simulation results provide preliminary insight into the neuromuscular mechanisms of the different force variability functions in continuous and discrete isometric forces.

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Ewald M. Hennig and Mario A. Lafortune

Using data from six male subjects, this study compared ground reaction force and tibial acceleration parameters for running. A bone-mounted triaxial accelerometer and a force platform were employed for data collection. Low peak values were found for the axial acceleration, and a time shift toward the occurrence of the first peak in the vertical force data was present. The time to peak axial acceleration differed significantly from the time to the first force peak, and the peak values of force and acceleration demonstrated only a moderate correlation. However, a high negative correlation was found for the comparison of the peak axial acceleration with the time to peak vertical force. Employing a multiple regression analysis, the peak tibial acceleration could be well estimated using vertical force loading rate and peak horizontal ground reaction force as predictors.

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Jacob J. Sosnoff, Sae Young Jae, Kevin Heffernan and Bo Fernhall

The purpose of the current investigation was to examine the relation between cardioballistic impulse and the fluctuations in continuous isometric force production. Subjects produced isometric force via index finger flexion to constant force targets (0.5, 1 and 2 N) with and without visual feedback while beat to beat blood pressure of their middle finger was recorded. Force fluctuations were quantified using distributional statistics. The association between blood pressure oscillations and fluctuations in force output were quantified with coherence analysis. Overall, it was found that force variability (i.e., SD) increased with force level and removal of visual feedback. Coherence values between blood pressure oscillations and force fluctuations were significant and the greatest in the 8–12 Hz bandwidth. There was no effect of force magnitude on the coupling strength between blood pressure oscillations and force production. This coupling was greater in the visual condition. These data suggest that peripheral alterations in blood pressure are related to fluctuations in isometric force production independent of force level and that this interaction is influenced by visual feedback.

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Caroline W. Stegink Jansen, Bruce R. Niebuhr, Daniel J. Coussirat, Dana Hawthorne, Laura Moreno and Melissa Phillip

This cross-sectional study aimed to assess the impact of age and gender on 4 measures of grip and pinch force of well elderly community dwellers and to provide normative values. The hypotheses were that age and gender affect pinch and grip force and that these 2 factors might interact. Hand strength of 224 seniors 65–92 years old was tested. Grip and pinch force decreased in successively older age groups past 65 years. Men’s grip force exceeded that of women in all age groups. Men’s hand-force decline was steeper than that of women over successive age groups, suggesting that gender differences in force decreased with age. Trends were the same for all 4 types of grip- and pinch-force measurement but were most clearly visible in grip and key-pinch force. Norms were provided for seniors age 65–85+ years in 5-yr increments.

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Muammer Altun

in human movement control, which is fundamental for daily activities, exercise, and sports. 5 Poor proprioception at a joint may result in an increased likelihood of injury. 6 Knee proprioception is mostly evaluated by assessing JPS and force sense (FS). 7 – 10 Some researchers have argued that

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Maury L. Hull, Richard Brewer and David Hawkins

This paper reports on the design, fabrication, and performance evaluation of a new force plate. The force plate is unique in that it can be manufactured “in house” using conventional machine tools for substantially lower cost than commercially available units. To achieve these attributes, the force plate embodies four octagonal strain ring sensing elements that are instrumented with conventional strain gauges. Strain gauge signals are amplified by simple signal conditioning circuits with a low component count. Despite the simplicity of the design, a calibration and accuracy check revealed root mean squared errors of 14 N for the vertical force component and less than 11 N for the horizontal force components.

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Amador García-Ramos and Slobodan Jaric

The linear force–velocity (F–V) relationship is frequently used to evaluate the maximal capacities of active muscles to produce force ( F 0 ), velocity ( V 0 ), and power (P max ) during a variety of tasks (vertical jump, bench press throw [BPT], isokinetic exercises, etc). 1 – 4 The F–V slope (ie

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Timothy J. Suchomel and Christopher J. Sole

The force-production characteristics of 3 weight-lifting derivatives were examined by comparing the force–time curves of each exercise. Sixteen resistance-trained men performed repetitions of the hang power clean (HPC), jump shrug (JS), and hang high pull (HHP) on a force platform at several relative loads. Relative peak force (PFRel), relative impulse (IMPRel), peak rate of force development (PRFD), and time-normalized force–time curves of each exercise were compared. The JS produced greater PFRel than the HPC (P < .001, d = 1.38) and HHP (P < .001, d = 1.14), while there was no difference between the HPC and HHP (P = .338, d = 0.26). Similarly, the JS produced greater IMPRel than the HPC (P < .001, d = 0.52) and HHP (P = .019, d = 0.36). The HHP also produced greater IMPRel than the HPC (P = .040, d = 0.18). Finally, the JS produced greater PRFD than the HPC (P < .001, d = 0.73) and HHP (P = .001, d = 0.47), while there was no difference between the HPC and HHP (P = .192, d = 0.22). The HPC, JS, and HHP force–time profiles were similar during the first 75–80% of the movement; however, the JS produced markedly different force–time characteristics in the final 20–25% of the movement. The JS produced superior force-production characteristics, namely PFRel, IMPRel, and PRFD, as well as a unique force–time profile, compared with the HPC and HHP across several loads.