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Simon Avrillon, Boris Jidovtseff, François Hug and Gaël Guilhem

Purpose:

Muscle strengthening is commonly based on the use of isoinertial loading, whereas variable resistances such as pneumatic loading may be implemented to optimize training stimulus. The purpose of the current study was to determine the effect of the ratio between pneumatic and isoinertial resistance on the force–velocity relationship during ballistic movements.

Methods:

A total of 15 participants performed 2 concentric repetitions of ballistic bench-press movements with intention to throw the bar at 30%, 45%, 60%, 75%, and 90% of the maximal concentric repetition with 5 resistance ratios including 100%, 75%, 50%, 25%, or 0% of pneumatic resistance, the additional load being isoinertial. Force-, velocity-, and power-time patterns were assessed and averaged over the concentric phase to determine the force–velocity and power–velocity relationships for each resistance ratio.

Results:

Each 25% increase in the pneumatic part in the resistance ratio elicited higher movement velocity (+0.11 ± 0.03 m/s from 0% to 80% of the concentric phase) associated with lower force levels (–43.6 ± 15.2 N). Increased isoinertial part in the resistance ratio resulted in higher velocity toward the end of the movement (+0.23 ± 0.01 m/s from 90% to 100%).

Conclusions:

The findings show that the resistance ratio could be modulated to develop the acceleration phase and force toward the end of the concentric phase (pneumatic-oriented resistance). Inversely, isoinertial-oriented resistance should be used to develop maximal force and maximal power. Resistance modality could, therefore, be considered an innovative variable to modulate the training stimulus according to athletic purposes.

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Andrea Biscarini

The author derived the exact analytical expression of the instantaneous joint power in exercises with single-joint, variable-resistance, selectorized strength-training equipment, taking into account all the relevant geometric, kinematic, and dynamic variables of both the movable equipment elements (resistance input lever, cam–pulley system, weight stack) and of the user’s exercising limb. A numerical algorithm was also designed to express, in the presence of a cam, the rectilinear kinematic variables of the weight stack as a function of the rotational kinematic variables of the resistance input lever, and vice versa. Given that information, one can measure the value of the instantaneous and mean joint power exclusively by means of a linear encoder placed on the weight stack or, alternatively, only by the use of an angular encoder placed on the rotational axis of the resistance lever. The results highlight that, for knee extension exercises with leg extension equipment, the real values of both instantaneous and mean joint power may differ by more than 50% in comparison with the values obtained by taking into account only the mass and velocity of the weight stack. These differences are notable not only in explosive exercises, but also whenever considerable joint velocities/accelerations occur within the range of motion.

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Tibor Hortobágyi, Richard G. Israel, Joseph A. Houmard, Kevin F. O'Brien, Robert A. Johns and Jennifer M. Wells

Four methods of assessing body composition were compared in 55 black and 35 white, Division 1, American football players. Percent body fat (%BF) was estimated with hydrostatic weighing at residual volume, corrected for race; seven-site skinfolds (7 SF), corrected for race; bioelectrical impedance analysis (BIA); and near-infrared spectrophotometry (NIR). Percent body fat with HW in blacks (mean = 14.7%) and whites (19.7%) did not differ (P > .05) from %>BF with 7 SF (blacks, 14.7%; whites, 19.0%). In relation to HW, BIA significantly (P < .05) overpredicted (blacks: 20.1%, SEE = 3.2%; whites; 22.3%, SEE = 4.3%) and NiR underpredicted %BF (blacks; 12.6%, SEE = 3.9%; whites; 17.7%, SEE = 3.6%). The contribution of BIA variables (resistance, phase angle, conductance) and NIR optical density to predict %BF was trivial compared to body mass index. It appears that race may not substantially influence %BF prediction by NIR and BIA. It was concluded that when considering the cost and expertise required with NIR and BIA, SF measurements appear to be a superior alternative for rapid and accurate body composition assessment of athletes, independent of race.

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Kevin J. Cole, David L. Costill, Raymond D. Starling, Bret H. Goodpaster, Scott W. Trappe and William J. Fink

The purpose of this investigation was to determine the effect of caffeine ingestion on work output at various levels of perceived exertion during 30 min of isokinetie variable-resistance cycling exercise. Ten subjects completed six trials 1 hr after consuming either 6 mg · kg−1 caffeine (3 trials) or a placebo (3 trials). During each trial the subjects cycled at what they perceived to be a rating of 9 on the Borg rating of perceived exertion scale for the first 10 min, a rating of 12 for the next 10 min, and a rating of 15 for the final 10 min. Total work performed during the caffeine trials averaged 277.8 ± 26.1 kJ, whereas the mean total work during the placebo trials was 246.7 ± 21.5 kJ (p < .05). Blood glycerol and free fatty acid levels increased over time to a significantly greater degree in the caffeine trials than in the placebo trials (p < .05). However, there were no significant differences between conditions in respiratory exchange ratio. These data suggest that caffeine may play an ergogenic role in exercise performance by altering both neural perception of effort and substrate availability.

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Mohamed Abdelmegeed, Everett Lohman, Noha Daher, June Kume and Hasan M. Syed

FlexBar®; Sammons Preston Inc, Chicago, IL) with variable resistances. The patient was in a seated position, with elbow flexed to 90° and forearm rested on the table or on his/her thigh depending on the strength tool he/she is using. For the first week of intervention, patients used a softball and a

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Alasdair Strokosch, Loic Louit, Laurent Seitz, Richard Clarke and Jonathan D. Hughes

often used. 7 , 8 The requirement of such lengthy recovery periods to induce a PAP effect could extend the duration of a training session so that it then becomes impractical to implement. One possible solution to this problem is the use of variable resistance training (VRT) utilizing accommodating

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Alexei Wong and Arturo Figueroa

underwent three supervised exercise sessions per week on nonconsecutive days. Four exercises (leg press, leg extension, leg flexion, and calf raise) were performed on variable-resistance machines (MedX, Ocala, FL). Participants performed two sets of exercises involving 18–22 repetitions of each exercise, to

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INTERNATIONAL SPORT COACHING JOURNAL

DIGEST VOLUME 5, ISSUE #1

Sergio Lara-Bercial, A.J. Rankin-Wright, Jason Tee, Fieke Rongen, Tom Mitchell, Mike Ashford, David Piggott and Kevin Till

period. Findings demonstrated highly variable resistance training practices of adolescent rugby union players. Relationships between resistance training practices and 12 week change in physical performance demonstrated that resistance training volume load completed over the 12 weeks was related to power

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Danny Lum and Tiago M. Barbosa

, and (4) studies that included any modes of strength training (including isotonic, isometric, isokinetic, plyometric, variable resistance, and calisthenics). Studies were excluded for the following reasons: (1) not randomized controlled trials, (2) reported only physiological measures and no

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Richard B. Kreider

specialists are typically responsible for assessing training and conditioning levels and planning all phases of training before and during the competitive season. Table 1 Types of Resistance Training Type Description Accommodating resistance Using bands or chains attached to a bar that adds variable