RESUMO
The aim of this study was to conduct a comprehensive examination of caffeine's effects on countermovement jump (CMJ) performance. In this randomized, double-blind, crossover study, twenty-two resistance-trained men (age: 28 ± 5 years; height: 183 ± 5 cm; weight: 79 ± 10 kg; habitual caffeine intake: 127 ± 102 mg/day) performed the CMJ test on two occasions, following the ingestion of capsule containing 3 mg/kg of caffeine or placebo (3 mg/kg of dextrose). Fifteen outcomes derived from the force plate during the CMJ test were analyzed. As compared to placebo, there was a significant ergogenic effect of caffeine for peak force, force at eccentric to concentric action transition, time to peak force, peak power, maximum rate of power development, peak velocity, power at peak force, velocity at peak power, velocity at peak force, and vertical jump height. Effect sizes ranged from 0.11 to 0.38, p-values ranged from 0.048 to 0.002. There were no significant differences between caffeine and placebo for mean force, mean power, time to peak power, impulse at 300 ms, and force at peak power. This study shows that caffeine ingestion impacts a wide array of outcomes derived from the force plate during the CMJ test, not only jump height. From a practical perspective, the findings suggest that: (1) individuals interested in acute increases in CMJ performance may consider caffeine supplementation; and, (2) caffeine intake should be standardized before CMJ testing.
RESUMO
The aim of this systematic review was to explore the test-retest reliability of isometric mid-thigh pull maximum strength assessment. We searched through five databases to find studies that examined the test-retest reliability of peak force in the isometric mid-thigh pull exercise. From each included study, we extracted intra-class correlation coefficients (ICC) and/or coefficient of variation (CV). The methodological quality of the included studies was evaluated using the COSMIN checklist. A total of 16 good-to-excellent quality studies were included in the review. When considering results from all included studies, ICCs ranged from 0.73 to 0.99 (median ICC = 0.96), where 78% of ICCs were ≥ 0.90, and 98% of ICCs were ≥ 0.75. The range of reported CVs was from 0.7% to 11.1% (median CV = 4.9%), where 58% of CVs were ≤ 5%. Reliability was also good-to-excellent for both relative and absolute peak force and for both bilateral and unilateral isometric mid-thigh pull tests. The majority of studies did not find significant differences between testing sessions. It can be concluded that the isometric mid-thigh pull maximum strength assessment has good-to-excellent test-retest reliability. The isometric mid-thigh pull maximum strength assessment can be used as a reliable test in sports practice and for research purposes.
RESUMO
BACKGROUND: The test-retest reliability of the one-repetition maximum (1RM) test varies across different studies. Given the inconsistent findings, it is unclear what the true reliability of the 1RM test is, and to what extent it is affected by measurement-related factors, such as exercise selection for the test, the number of familiarization trials and resistance training experience. OBJECTIVES: The aim of this paper was to review studies that investigated the reliability of the 1RM test of muscular strength and summarize their findings. METHODS: The PRISMA guidelines were followed for this systematic review. Searches for studies were conducted through eight databases. Studies that investigated test-retest reliability of the 1RM test and presented intra-class correlation coefficient (ICC) and/or coefficient of variation (CV) were included. The COSMIN checklist was used for the assessment of the methodological quality of the included studies. RESULTS: After reviewing 1024 search records, 32 studies (pooled n = 1595) on test-retest reliability of 1RM assessment were found. All the studies were of moderate or excellent methodological quality. Test-retest ICCs ranged from 0.64 to 0.99 (median ICC = 0.97), where 92% of ICCs were ≥ 0.90, and 97% of ICCs were ≥ 0.80. The CVs ranged from 0.5 to 12.1% (median CV = 4.2%). ICCs were generally high (≥ 0.90), and most CVs were low (< 10%) for 1RM tests: (1) among those without and for those with some resistance training experience, (2) conducted with or without familiarization sessions, (3) with single-joint or multi-joint exercises, (4) for upper- and lower-body strength assessment, (5) among females and males, and (6) among young to middle-aged adults and among older adults. Most studies did not find systematic changes in test results between the trials. CONCLUSIONS: Based on the results of this review, it can be concluded that the 1RM test generally has good to excellent test-retest reliability, regardless of resistance training experience, number of familiarization sessions, exercise selection, part of the body assessed (upper vs. lower body), and sex or age of participants. Researchers and practitioners, therefore, can use the 1RM test as a reliable test of muscular strength.