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Jozo Grgic, Filip Sabol, Sandro Venier, Ivan Mikulic, Nenad Bratkovic, Brad J. Schoenfeld, Craig Pickering, David J. Bishop, Zeljko Pedisic and Pavle Mikulic

can acutely enhance aerobic and muscle endurance, muscle strength, power, jumping height, and exercise speed. 4 , 5 In research studies, caffeine is often administered in moderate to high doses (3–6 mg·kg −1 ), with 6 mg·kg −1 being the most common. 4 There is, however, emerging interest in

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Kensaku Suei, Leslie McGillis, Randy Calvert and Oded Bar-Or

We assess relationships among muscle endurance, strength, and explosiveness in forty-eight 9.6- to 17.0-year-old males divided into 3 maturational groups (Tanner Stages I, II-IV, and V). Peak torque during isometric knee extension and flexion was averaged to reflect strength. Mechanical power in the Sargent vertical jump was taken as explosiveness, and total work in the Wingate test reflected muscle endurance. Correlations (3 groups combined) among the variables, expressed in absolute terms, were r = .82 to .92, but only -.11 to .70 when expressed per body mass or lean thigh size. These correlations were distinctly lower in the Tanner V boys than in the 2 less-mature groups, which may suggest that specialization into discrete muscle performance characteristics does not occur before late puberty.

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Scott C. Forbes, Darren G. Candow, Jonathan P. Little, Charlene Magnus and Philip D. Chilibeck

The purpose of this study was to determine the effects of Red Bull energy drink on Wingate cycle performance and muscle endurance. Healthy young adults (N = 15, 11 men, 4 women, 21 ± 5 y old) participated in a crossover study in which they were randomized to supplement with Red Bull (2 mg/kg body mass of caffeine) or isoenergetic, isovolumetric, noncaffeinated placebo, separated by 7 d. Muscle endurance (bench press) was assessed by the maximum number of repetitions over 3 sets (separated by 1-min rest intervals) at an intensity corresponding to 70% of baseline 1-repetition maximum. Three 30-s Wingate cycling tests (load = 0.075 kp/kg body mass), with 2 min recovery between tests, were used to assess peak and average power output. Red Bull energy drink significantly increased total bench-press repetitions over 3 sets (Red Bull = 34 ± 9 vs. placebo = 32 ± 8, P < 0.05) but had no effect on Wingate peak or average power (Red Bull = 701 ± 124 W vs. placebo = 700 ± 132 W, Red Bull = 479 ± 74 W vs. placebo = 471 ± 74 W, respectively). Red Bull energy drink significantly increased upper body muscle endurance but had no effect on anaerobic peak or average power during repeated Wingate cycling tests in young healthy adults.

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Steven R. Bray, Kathleen A. Martin Ginis and Jennifer Woodgate

Self-regulation consumes a form of strength or energy. The authors investigated aftereffects of self-regulation depletion on muscle-endurance performance in older adults. Participants (N = 61, mean age = 71) were randomized to a self-regulation-depletion or control group and completed 2 muscle-endurance performance tasks involving isometric handgrip squeezing that were separated by a cognitive-depletion task. The depletion group showed greater deterioration of muscle-endurance performance than controls, F(1, 59) = 7.31, p = .009. Results are comparable to those of younger adults in a similar study and support Baumeister et al.’s limited-strength model. Self-regulation may contribute to central-nervous-system fatigue; however, biological processes may allow aging muscle to offset depletion of self-regulatory resources affecting muscle-endurance performance.

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Mark B.A. De Ste Croix, Neil Armstrong and Joanne R. Welsman

The purpose of this study was to examine the reliability of repeated isokinetic knee extension and flexion in young children and to examine sex differences in 30 untrained subjects (16 boys and 14 girls) aged 12.2 ± 0.3 years. Total work and the percentage decline in average torque and work were recorded during 50 repetitions. Intra-class correlation coefficients indicated a strong positive correlation between test 1 and 2 for all parameters ranging from 0.36–0.95. Coefficient of variation data ranged from ± 0% to ± 5.4%. Repeatability coefficients and limits of agreement indicated that the extensors were more reliable than the flexors for both torque and work. There were no significant sex differences in any of the parameters measured. This study suggests that repeated isokinetic muscle actions of the knee, as a function of muscle endurance, can be reliably assessed in young people.

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Jerry L. Mayhew, Sidney Palmer Hill, Melissa D. Thompson, Erin C. Johnson and Lyndsay Wheeler

Purpose:

The purpose of this study was to evaluate the effectiveness of repetitions to fatigue (RTF) using absolute and relative muscle-endurance performances to estimate 1-repetition-maximum (1-RM) bench-press performance in high school male athletes.

Methods:

Members of high school athletic teams (n = 118, age = 16.5 ± 1.1 y, weight = 82.7 ± 18.7 kg) were tested for 1-RM bench press and RTF with an absolute load of 61.4 kg and a relative load that produced 7 to 10 RTF (7- to 10-RM). All participants had completed a minimum of 4 wk of resistance training before measurement.

Results:

All 7- to 10-RM-prediction equations had higher correlations between predicted and actual 1-RM (r > .98) than the 61.4-kg absolute-load equation (r = .95). Despite the high correlations, only 3 of 11 equations produced predicted values that were nonsignificantly different from actual 1-RM. The best 7- to 10-RM equation predicted 65% of the athletes’ performances within ±4.5 kg of their actual 1-RM. The addition of simple anthropometric dimensions did not increase the validity correlations or decrease the prediction errors.

Conclusion:

The 7- to 10-RM method can provide an accurate method of estimating strength levels for adjusting loads in a training program and is more accurate for predicting 1-RM bench press in high school athletes than the 61.4-kg repetition method.

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R. Barry Dale and Tim Ogletree

Column-editor : R. Barry Dale

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Taylor K. Dinyer, M. Travis Byrd, Ashley N. Vesotsky, Pasquale J. Succi and Haley C. Bergstrom

repetition ranges from 20 to 25 repetitions should be used for muscle endurance training. 21 – 23 The CR (56 [11] kg) was 33.9% lower than the ESR 30 (75 [14] kg), although the SDs were similar for the CR (11 kg) and the ESR 30 (14 kg). This likely indicates the CR derived from the 2-parameter, linear

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James W. Youdas, Kady E. Adams, John E. Bertucci, Koel J. Brooks, Meghan M. Nelson and John H. Hollman

Context:

No published studies have compared muscle activation levels simultaneously for the gluteus maximus and medius muscles of stance and moving limbs during standing hip-joint strengthening while using elastic-tubing resistance.

Objective:

To quantify activation levels bilaterally of the gluteus maximus and medius during resisted lower-extremity standing exercises using elastic tubing for the cross-over, reverse cross-over, front-pull, and back-pull exercise conditions.

Design:

Repeated measures.

Setting:

Laboratory.

Participants:

26 active and healthy people, 13 men (25 ± 3 y) and 13 women (24 ± 1 y).

Intervention:

Subjects completed 3 consecutive repetitions of lower-extremity exercises in random order.

Main Outcome Measures:

Surface electromyographic (EMG) signals were normalized to peak activity in the maximum voluntary isometric contraction (MVIC) trial and expressed as a percentage. Magnitudes of EMG recruitment were analyzed with a 2 × 4 repeated-measures ANOVA for each muscle (α = .05).

Results:

For the gluteus maximus an interaction between exercise and limb factor was significant (F 3,75 = 21.5; P < .001). The moving-limb gluteus maximus was activated more than the stance limb's during the back-pull exercise (P < .001), and moving-limb gluteus maximus muscle recruitment was greater for the back-pull exercise than for the cross-over, reverse cross-over, and front-pull exercises (P < .001). For the gluteus medius an interaction between exercise and limb factor was significant (F 3,75 = 3.7; P < .03). Gluteus medius muscle recruitment (% MVIC) was greater in the stance limb than moving limb when performing the front-pull exercise (P < .001). Moving-limb gluteus medius muscle recruitment was greater for the reverse cross-over exercise than for the cross-over, front-pull, and back-pull exercises (P < .001).

Conclusions:

From a clinical standpoint there is no therapeutic benefit to selectively activate the gluteus maximus and gluteus medius muscles on the stance limb by resisting sagittal- and frontal-plane hip movements on the moving limb using resistance supplied by elastic tubing.