This preliminary study aimed to quantify the magnitude of the peak shoulder distraction force during the bowling action of female cricket fast bowlers. An eight camera Vicon motion analysis system operating at 120 Hz recorded the fast bowling actions of 18 Australian female fast bowlers. A three segment inverse solution model of the bowling arm was used to calculate the shoulder distraction force. A large peak shoulder distraction force was recorded during the early stages of the follow-through of the bowling action. When normalized for body weight, the distraction force was within the range of values reported for baseball and softball pitchers, who are considered to be at high risk of shoulder injury. Therefore, the relative importance of the peak shoulder distraction force in the fast bowling action for the development of shoulder pain in female cricket fast bowlers warrants further investigation.
Max C. Stuelcken, René E.D. Ferdinands, Karen A. Ginn and Peter J. Sinclair
Ryu Nagahara, Alberto Botter, Enrico Rejc, Masaaki Koido, Takeshi Shimizu, Pierre Samozino and Jean-Benoit Morin
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.
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.
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.
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.
Matthew J. Hodgson, David Docherty and E. Paul Zehr
The contractile history of muscle can potentiate electrically evoked force production. A link to voluntary force production, related in part to an increase in reflex excitability, has been suggested.
Our purpose was to quantify the effect of postactivation potentiation on voluntary force production and spinal H-reflex excitability during explosive plantar fexion actions.
Plantar flexor twitch torque, soleus H-reflex amplitudes, and the rate of force development of explosive plantar fexion were measured before and after 4 separate conditioning trials (3 × 5 s maximal contractions).
Twitch torque and rate of force production during voluntary explosive plantar flexion were significantly increased (P < .05) while H-reflex amplitudes remained unchanged. Although twitch torque was significantly higher after conditioning, leading to a small increase in the rate of voluntary force production, this was unrelated to changes in reflex excitability.
We conclude that postactivation potentiation may result in a minor increase in the rate of voluntary isometric force production that is unrelated to neural excitability.
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
Roger J. Paxton, Caitlin Feldman-Kothe, Megan K. Trabert, Leah N. Hitchcock, Raoul F. Reiser II and Brian L. Tracy
The purpose was to determine the effect of peripheral neuropathy (PN) on motor output variability for ankle muscles of older adults, and the relation between ankle motor variability and postural stability in PN patients.
Older adults with (O-PN) and without PN (O), and young adults (Y) underwent assessment of standing postural stability and ankle muscle force steadiness.
O-PN displayed impaired ankle muscle force control and postural stability compared with O and Y groups. For O-PN, the amplitude of plantarflexor force fluctuations was moderately correlated with postural stability under no-vision conditions (r = .54, p = .01).
The correlation of variations in ankle force with postural stability in PN suggests a contribution of ankle muscle dyscontrol to the postural instability that impacts physical function for older adults with PN.
Daniel Cury Ribeiro, Joelly Mahnic de Toledo, Roberto Costa Krug and Jefferson Fagundes Loss
Shoulder injuries are often related to rotator cuff muscles. Although there are various models for muscle force estimation, it is difficult to ensure that the results obtained with such models are reliable. The aim of the current study was to compare two models of muscle force estimation. Eight subjects, seven male and one female (mean age of 24 yr; mean height of 1.83 m), performed five isokinetic maximum concentric contractions of internal and external shoulder rotation. Two models with different algorithms were used. In both, the input data consisted of the measured internal rotation moment. Comparisons were made between the difference and the average results obtained with each model of muscle force estimation. There was reasonable agreement among the results for force between the two models for subscapularis, pectoralis major, and anterior deltoideus muscles results. Conversely, poor correlation was found for the latissimus dorsi, teres major, and middle deltoid. These results suggest that the algorithm structure might have a strong effect on muscle force estimation results.
John H. Challis
This study examined the influence of force plate targeting, via stride length adjustments, on the magnitude and consistency of ground reaction force and segment angle profiles of the stance phase of human running. Seven male subjects (height, 1.77 m ± 0.081; mass, 72.4 kg ± 7.52; age range, 23 to 32 years) were asked to run at a mean velocity of 3.2 m · s–1 under three conditions (normal, short, and long strides). Four trials were completed for each condition. For each trial, the ground reaction forces were measured and the orientations of the foot, shank, and thigh computed. There were no statistically significant differences (p > .05) between the coefficients of variation of ground reaction force and segment angle profiles under the three conditions, so these profiles were produced consistently. Peak active vertical ground reaction forces, their timings, and segment angles at foot off were not significantly different across conditions. In contrast, significant differences between conditions were found for peak vertical impact forces and their timings, and for the three lower limb segment angles at the start of force plate contact. These results have implications for human gait studies, which require subjects to target the force plate. Targeting may be acceptable depending on the variables to be analyzed.
Masato Maeda, Eiji Shamoto, Toshimichi Moriwaki and Haruo Nomura
The present paper presents a new sensor to measure 6 components of force and 2 components of deflection applied to the javelin during the throw. Since the javelin is deflected and vibraled during throwing, measurement of force and deflection applied to the javelin will provide important information for throwers in how to better throw the javelin and to design javelins with better dynamic characteristics. The sensor is designed not to significantly change the static and dynamic characteristics of the javelin. The force sensor performs well in terms of linearity and crosstalk, and the javelin equipped with this sensor has similar characteristics to ordinary javelins. The present paper also presents an example of measurement in the javelin throw.
Gaspare Pavei, Elena Seminati, Jorge L.L. Storniolo and Leonardo A. Peyré-Tartaruga
We compared running mechanics parameters determined from ground reaction force (GRF) measurements with estimated forces obtained from double differentiation of kinematic (K) data from motion analysis in a broad spectrum of running speeds (1.94–5.56 m⋅s–1). Data were collected through a force-instrumented treadmill and compared at different sampling frequencies (900 and 300 Hz for GRF, 300 and 100 Hz for K). Vertical force peak, shape, and impulse were similar between K methods and GRF. Contact time, flight time, and vertical stiffness (kvert) obtained from K showed the same trend as GRF with differences < 5%, whereas leg stiffness (kleg) was not correctly computed by kinematics. The results revealed that the main vertical GRF parameters can be computed by the double differentiation of the body center of mass properly calculated by motion analysis. The present model provides an alternative accessible method for determining temporal and kinetic parameters of running without an instrumented treadmill.
Kathleen Williams, Kathleen Haywood and Ann VanSant
Older adults threw tennis balls for force and accuracy to examine their adaptability to different task demands. Twenty-one (13 women, 8 men) participants were videotaped as they performed five force and five accuracy throws. The developmental level of each throw was determined; resultant ball velocities also were examined. Roberton’s (1977, 1978) movement components were used in the former analysis. The typical pattern of gender differences occurred for both movement component and velocity measures. Men performed at higher levels than women. Only minor force versus accuracy differences were found in the movement patterns used by either men or women; none of these differences were significant. Clear task differences occurred for ball velocities. Men’s forceful throws were faster than those for accuracy; women’s throws did not differ for the two tasks. The generally lower developmental level of women’s throws accounted for gender differences in velocity. Insufficient task differences may explain the lack of clear contrast in movement patterns.