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Iris F. Kimura, LouAnne M. Jefferson, Dawn T. Gulick and R. David Coll

The purpose of this study was to investigate intratester and intertester reliability when using the Chatillon and MicroFet hand-held dynamometers (HHDs) to measure isometric force production of the wrist extensors, elbow flexors, ankle dorsiflexors, and knee extensors. Twelve subjects participated, with each joint tested four times with each HHD. Intratester and intertester intraclass con-elation coefficients were measured for both devices separately and between the devices- Results indicated that the HHDs were more reliable when used by a single examiner who had been properly trained in their use. Reliability of the HHDs appears to be affected by both the magnitude of the force produced by the subject and the examiner's ability to resist the force. There was no correlation between examiner's stature and consistent force production values. Caution should be taken when interpreting data obtained from different testers or different HHDs. The same clinician should use the same HHD for successive tests to yield the most reliable data.

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Karen L. Perell, Robert J. Gregor and A.M. Erika Scremin

The purpose of this sludy was to compare individual pedal reaclion force components following bicycle training with and without effective force feedback in subjects with unilateral cerebrovascular accident (CVA). Eight ambulatory subjects with CVA were studied on a recumbent bicycle equipped with custom-built pedals, which measure normal and tangential components of the load applied to the pedal surface. Comparisons of normal and tangential pedal reaction forces were made following 1 month of bicycle training (3 times/week for 4 weeks) during retention tests performed without feedback. The ratios of involved to contralateral (I/C ratios) force parameters were used to assess symmetry. Subjects were randomly assigned to 2 groups: (a) a feedback group that received visual/verbal feedback regarding effective force patterns, bilaterally, after each trial; and (b) a no-feedback group dial received no feedback. Two critical results were found: (a) tangential pedal forces were significantly more posteriorly directed bilaterally following training across all subjects, but the change was greater for the no-feedback group relative to the feedback group, and (b) effective force feedback training did not demonstrate improvements in the I/C ratios above that of the control group. A more posteriorly applied tangential pedal force may represent increased dorsiflexion and may suggest that bicycle training facilitated ankle control. The cyclical nature of cycling, however, may allow for natural patterns to develop without feedback or may require less frequent use of feedback based on retention test performance.

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Amador García-Ramos, Slobodan Jaric, Paulino Padial and Belén Feriche

This study aimed to (1) evaluate the linearity of the force–velocity relationship, as well as the reliability of maximum force (F 0), maximum velocity (V 0), slope (a), and maximum power (P 0); (2) compare these parameters between the traditional and ballistic bench press (BP); and (3) determine the correlation of F 0 with the directly measured BP 1-repetition maximum (1RM). Thirty-two men randomly performed 2 sessions of traditional BP and 2 sessions of ballistic BP during 2 consecutive weeks. Both the maximum and mean values of force and velocity were recorded when loaded by 20–70% of 1RM. All force–velocity relationships were strongly linear (r > .99). While F 0 and P 0 were highly reliable (ICC: 0.91–0.96, CV: 3.8–5.1%), lower reliability was observed for V 0 and a (ICC: 0.49–0.81, CV: 6.6–11.8%). Trivial differences between exercises were found for F 0 (ES: < 0.2), however the a was higher for the traditional BP (ES: 0.68–0.94), and V 0 (ES: 1.04–1.48) and P 0 (ES: 0.65–0.72) for the ballistic BP. The F 0 strongly correlated with BP 1RM (r: 0.915–0.938). The force–velocity relationship is useful to assess the upper body maximal capabilities to generate force, velocity, and power.

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Pablo Floria, Luis A. Gómez-Landero and Andrew J. Harrison

The purpose of this study was to determine if children exhibit greater variability in center of mass movement and kinetics compared with adults in vertical jumping. Countermovement jumps with arms (CMJA) and without arms (CMJ) performed by 20 female children and 20 female adults were examined using force platform. The data were analyzed using continuous methods to determine differences in variability between groups and between types of jump. Jumping variability was measured by using the average coefficient of variation of the force-, velocity-, displacement-, and rate of force development-time curves across the jump. The analysis indicated that children and adults had similar levels of variability in the CMJ but different levels in the CMJA. In the CMJA, the children had a greater coefficient of variation than adults in force- (20 ± 7% and 12 ± 6%), velocity- (41 ± 14% and 22 ± 9%), displacement- (8 ± 16% and 23 ± 11%) and rate of force development-time (103 ± 46% and 75 ± 42%) curves, as well as in force-velocity relationship (6 ± 2% and 4 ± 2%). The results of analysis suggest that the variability depends on both the level of maturation of the participants as well as the task complexity.

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Christos Papadopoulos, Vasilios I. Kalapotharakos, Georgios Noussios, Konstantinos Meliggas and Evangelia Gantiraga

Objective:

To examine the effect of static stretching on maximal voluntary contraction (MVC) and isometric force-time curve characteristics of leg extensor muscles and EMG activity of rectus femoris (RF), biceps femoris (BF), and gastrocnemius (GA).

Design:

A within subjects experimental design.

Participants:

Ten healthy students were tested after a jogging and a jogging/stretch protocol.

Intervention:

The stretching protocol involved a 10 min jog and seven static stretching exercises.

Main Outcomes:

Measurements included MVC, time achieved to MVC (TMVC), force at 100ms (F100), index of relative force (IRF), index of rate of force development (IRFD), and average integrated EMG activity (AEMG).

Results:

There were slight but no significant changes in MVC (1%), TMVC (4.8%), F100 (7.8%), IRF (1%), and IRFD (3.5%) between measurement. A significant difference (21%; P < 0.05) in AEMG of RF was found.

Conclusions:

The present study indicated that a moderate volume of static stretching did not alter significantly the MVC and the isometric force-time curve characteristics. Neural inhibition, as it is reflected from AEMG of RF, did not alter MVC and isometric force-time curve characteristics.

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Tom G. Welter and Maarten F. Bobbert

We have investigated, in fast movements, the hypothesis that bi-articular muscles are preferentially selected to control me direction of force exerted on the environment, while mono-articular muscles are selected to control both this exerted force direction as well as the movement direction. Fourteen subjects performed ballistic arm movements involving shoulder and elbow rotations in the horizontal plane, either with or without an external force applied at the wrist. Joint torques required to counteract the external force were in the same order of magnitude as those required to overcome the inertial load during movements. EMG was recorded from mono- and bi-articular flexors and extensors of me elbow and shoulder. Signals were rectified and integrated (IREMG) over 100 ms following the first detected activity. MANOVA revealed mat, contrary to the hypothesis, IREMG of bi-articular muscles varied with movement direction just as that of the mono-articular muscles. It was concluded that the present data do not support me hypothesis mentioned above. A second finding was that movement effects on IREMG were much stronger than external force effects. This could not be explained using Hill's force-velocity relationship. It may be an indication that in the initiation of fast movements, IREMG is not only tuned to movement dynamics and muscle contractile properties, but also to me dynamics of the build up of an active state of the muscle.

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Darren G. Burke, Shawn Silver, Laurence E. Holt, Truis Smith-Palmer, Christopher J. Culligan and Philip D. Chilibeck

Dietary supplementation (SUP) has become a significant part of athletic training. Studies indicate that creatine (Cr) can enhance short-duration, high-intensity activities. This study examined the effect of 21 days of low dose Cr SUP (~7.7 g/day) and resistance training on force output, power output, duration of mean peak power output, and total work performed until fatigue. A double-blind protocol was used, where an individual, who was not part of any other aspect of the study, randomly assigned subjects to creatine and placebo groups. Forty-one male university athletes were randomly assigned to either Cr (n= 20) or placebo (n = 21) SUP. On the first and last day of the study, subjects were required to perform concentric bench press movements until exhaustion on an isokinetic dynamometer. The dynamometer was hard-wired to a personal computer, which provided force, velocity, and duration measures. Force and power output until fatigue, were used to determine total work, force-time, and power-time relationships. ANOVA results revealed that the Cr subjects performed more total work until fatigue, experienced significantly greater improvements in peak force and peak power, and maintained elevated mean peak power for a longer period of time. These results indicate that Cr SUP can significantly improve factors associated with short-duration, high-intensity activity.

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Jérémy Rossi, Benjamin Goislard De Monsabert, Eric Berton and Laurent Vigouroux

The objectives of this study were to investigate the effect of handle shape on the grip force distribution in the hand and on the muscle forces during maximal power grip tasks. Eleven subjects maximally grasped 3 handles with different external shapes (circular, elliptic, and double-frustum). A handle dynamometer, equipped with both a force sensor and a pressure map, was used to record the forces exerted at the hand/handle interface. The finger and wrist joint postures were also computed from synchronized kinematic measurement. These processed data were then used as input of a biomechanical hand model to estimate muscle forces. The results showed that handle shape influences the maximal grip force, the grip force distribution, and the finger joint postures. Particularly, we observed that the elliptical shape resulted in a 6.6% lower maximal grip force compared with the circular and double-frustum handle. Concomitantly, the estimated muscle forces also varied significantly according to the handle shape, with up to 48% differences for the flexor digitorum superficialis muscle for example. Interestingly, different muscle coordination strategies were observed depending on the handle shape, therefore suggesting a potential influence of these geometrical characteristics on pathological risks such as tendonitis.

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Danielle P. Formosa, Mark Gregory Leigh Sayers and Brendan Burkett

This study explored and quantified gender differences in passive drag and instantaneous net drag force profile for elite backstroke swimmers (FINA points 938 ± 71). Nine female and ten male backstroke swimmers completed eight maximum speed trials. During the passive drag condition participants were towed at the speed achieved within the maximum effort backstroke swimming trials, while holding a supine stationary streamline position. The remaining trials, swimmers performed their natural swimming stroke, while attached to an assisted towing device. Male participant’s passive (P < .001) and mean net drag force (P < .001) were significantly higher compared with female participants. In addition, there were no significant differences by gender between either the minimum or maximum net drag forces produced during the left and right arm strokes. Instantaneous net drag force profiles demonstrated differences within and between individuals and genders. The swimmers who recorded the fastest speed also recorded the smallest difference in net drag force fluctuations. The instantaneous net drag force profile within elite backstroke swimming provides further insight into stroke technique of this sport.

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Jonathan Sinclair, Sarah J. Hobbs, Paul J. Taylor, Graham Currigan and Andrew Greenhalgh

In running analyses where both kinetic and kinematic information is recorded, participants are required to make foot contact with a force and/or pressure measuring transducer. Problems arise if participants modify their gait patterns to ensure contact with the device. There is currently a paucity of research investigating the influence of different underfoot kinetic measuring devices on 3-dimensional kinematics of running. Fifteen participants ran at 4.0 m/s in four different conditions: over a floor embedded force plate, Footscan, Matscan, and with no device. Three-dimensional angular kinematic parameters were collected using an eight camera motion analysis system. Hip, knee, and ankle joint kinematics were contrasted using repeated-measures ANOVAs. Participants also rated their subjective comfort in striking each of the three force measuring devices. Significant differences from the uninhibited condition were observed using the Footscan and Matscan in all three planes of rotation, whereas participants subjectively rated the force plate significantly more comfortable than either the Footscan/Matscan devices. The findings of the current investigation therefore suggest that the disguised floor embedded force plate offers the most natural running condition. It is recommended that analyses using devices such as the Footscan/Matscan mats overlying the laboratory surface during running should be interpreted with caution.