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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.

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Jefferson W. Streepey, M. Melissa Gross, Bernard J. Martin, Sundravalli Sudarsan and Catherine M. Schiller

The relationship between playing surface and muscle fatigue was examined in 22 male subjects performing a simulated basketball task on a conventional wood floor and less stiff composite floor. Force and electromyographic activity (EMG) were measured during maximum and submaximum (10% of maximum) voluntary contractions of knee extensor and ankle plantarflexor muscles before and after completion of the simulated basketball task. Jump height was evaluated during the task, and perceived fatigue was assessed at the end of the task. Although not all subjects jumped significantly higher on the composite floor compared to the wood floor. competitive basketball players showed a significant improvement in jump height (3.4 cm. 6%) when jumping on the composite floor. Perceived fatigue was significantly lower for the composite floor (21.7%) than the wood floor (30.2%). The objective measures indicated the occurrence of fatigue; however, force and EMG magnitudes obtained during maximum exertions were not sensitive lo floor types. Post-task increase in EMG magnitude indicated a significant fatigue effect for the soleus muscle on the wood floor only. These findings suggest that the composite floor may benefit human performance without increasing fatigue during basketball-related activities.

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Robert W. Meyers, Jon L. Oliver, Michael G. Hughes, Rhodri S. Lloyd and John B. Cronin


The aim of this study was to examine the influence of age and maturation upon magnitude of asymmetry in the force, stiffness and the spatiotemporal determinants of maximal sprint speed in a large cohort of boys.


344 boys between the ages of 11 and 16 years completed an anthropometric assessment and a 35 m sprint test, during which sprint performance was recorded via a ground-level optical measurement system. Maximal sprint velocity, as well as asymmetry in spatiotemporal variables, modeled force and stiffness data were established for each participant. For analysis, participants were grouped into chronological age, maturation and percentile groups.


The range of mean asymmetry across age groups and variables was 2.3–12.6%. The magnitude of asymmetry in all the sprint variables was not significantly different across age and maturation groups (p > .05), except relative leg stiffness (p < .05). No strong relationships between asymmetry in sprint variables and maximal sprint velocity were evident (rs < .39).


These results provide a novel benchmark for the expected magnitude of asymmetry in a large cohort of uninjured boys during maximal sprint performance. Asymmetry in sprint performance is largely unaffected by age or maturation and no strong relationships exist between the magnitude of asymmetry and maximal sprint velocity.

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Travis J. Peterson, Rand R. Wilcox and Jill L. McNitt-Gray

Our aim was to determine how skilled players regulate linear and angular impulse while maintaining balance during the golf swing. Eleven highly-skilled golf players performed swings with a 6-iron and driver. Components contributing to linear and angular impulse generated by the rear and target legs (resultant horizontal reaction force [RFh], RFh-angle, and moment arm) were quantified and compared across the group and within a player (α = .05). Net angular impulse generated by both the rear and target legs was greater for the driver than the 6-iron. Mechanisms used to regulate angular impulse generation between clubs varied across players and required coordination between the legs. Increases in net angular impulse with a driver involved increases in target leg RFh. Rear leg RFh-angle was maintained between clubs whereas target leg RFh became more aligned with the target line. Net linear impulse perpendicular to the target line remained near zero, preserving balance, while net linear impulse along the target line decreased in magnitude. These results indicate that the net angular impulse was regulated between clubs by coordinating force generation of the rear and target legs while sustaining balance throughout the task.

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Lars Janshen, Klaus Mattes and Günter Tidow

In sweep-oar rowers, asymmetrical force production of the legs is a known phenomenon. The purpose of this study was to investigate the muscular activity of the legs that may cause this asymmetry even when oarsmen perform a symmetrical endurance task. Seven male young elite oarsmen performed an all-out 2000-m test on a rowing ergometer. During stroke kinematics, myoelectric activity of six muscles of each leg and pressure distribution under both feet were measured. Data were collected over two 30-s time windows starting 1 and 5 min after the test started. No significant differences were observed between legs and time windows for the range of motion of the hip, knee, and ankle joint as well as for the onset/offset timing of muscles. However, in the drive phase, the knee and hip muscles of the leg on the oar side (inside leg) showed 20–45% (both p < .05) higher activation intensities compared with the leg opposite the oar (outside leg). Corresponding to this, 56–91% (both p < .05) higher mean pressure values under the ball of the inside foot compared with the outside foot indicated an asymmetrical force production of the legs even under kinematically symmetrical working conditions.

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Kathleen Williams, Kathleen Haywood and Ann VanSant

Older adults were tested to clarify findings of an earlier examination of movement responses to shifting task requirements (Williams et al., 1993). Eleven participants (average age = 77 years) were evaluated on form and velocity as they performed overarm throws for force and accuracy. Significant gender and force-accuracy differences occurred for resultant velocity. Although no statistically significant differences occurred for force-accuracy comparisons of movement form, there were trends toward change in most movement components. Additionally, many individuals displayed change in one or more components as they shifted from force to accuracy throws. Results of this study point to the importance of examining developmental status and task requirements simultaneously.

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Alexander W. Hooke, Sohit Karol, Jaebum Park, Yoon Hyuk Kim and Jae Kun Shim

The purpose of this study was to investigate central nervous system (CNS) strategies for controlling multifinger forces during a circle-drawing task. Subjects drew 30 concentric, discontinuous clockwise and counter clockwise circles, at self and experimenter-set paces. The three-dimensional trajectory of the pen’s center of mass and the three-dimensional forces and moments of force at each contact between the hand and the pen were recorded. Uncontrolled Manifold Analysis was used to quantify the synergies between pen-hand contact forces in radial, tangential and vertical directions. Results showed that synergies in the radial and tangential components were significantly stronger than in the vertical component. Synergies in the clockwise direction were significantly stronger than the counterclockwise direction in the radial and vertical components. Pace was found to be insignificant under any condition.

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Joseph P. Stitt and Karl M. Newell

This paper presents the stochastic modeling of isometric force variability in the steady-state time series recorded from the index finger of young adults in the act of attempting to hold different levels of constant force. The isometric force time series were examined by assuming that the stochastic (random) models were linear. System identification techniques were employed to estimate the parameters of each linear model. Once the models were parameterized, the values of the estimated parameters were compared to determine if a single linear time-invariant model was applicable across the entire isometric force range. Although the overall random models were found to be nonlinear functions of the target force level, within a fixed target level, linear modeling provided adequate estimates of the underlying processes thus enabling the use of well-known linear system identification algorithms.