Μια αρκετα ενδιαφερουσα μελετη που βγηκε πριν λιγες μερες στην οποια εγινε συγκριση 2 πολυ γνωστων προεξασκητικων με placebo!!

Το ενα ηταν το pre-jym και το αλλο το carbon prep (χωρις καφεινη αυτο).

Το συμπερασμα της μελετης ηταν πως σε συγκριση με placebo, καφεινουχα και μη-καφεινουχα προεξασκητικα απετυχαν να βελτιωσουν την παραγωγη δυναμης σε θετικες και αρνητικες κινησεις.

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Effects of two pre-workout supplements on concentric and eccentric force production during lower body resistance exercise in males and females: a counterbalanced, double-blind, placebo-controlled trial
Grant M. TinsleyEmail author, Matthew A. Hamm, Amy K. Hurtado, Austin G. Cross, Jose G. Pineda, Austin Y. Martin, Victor A. Uribe and Ty B. Palmer
Journal of the International Society of Sports Nutrition201714:46


Background
Pre-workout supplements purportedly enhance feelings of energy, reduce fatigue and improve exercise performance. The purpose of this study was to examine the performance effects of caffeinated and non-caffeinated multi-ingredient pre-workout supplements.


Methods
In a counterbalanced, double-blind, placebo-controlled design, eccentric and concentric force production during lower body resistance exercise on a mechanized squat device were assessed after supplement ingestion. Repetitions-in-reserve/RPE and subjective feelings of energy, focus and fatigue were also examined. Twenty-one resistance-trained adults (12 F, 9 M) completed three conditions in random order: caffeinated supplement, non-caffeinated supplement and placebo. Subjects were not informed of the presence of a placebo condition. Thirty minutes after supplement ingestion, a 3-repetition maximum test and 5 sets of 6 repetitions were completed using the squat device. Each repetition involved 4-s eccentric and concentric phases, and the force signal throughout each repetition was sampled from a load cell contained within the squat device. The scaled and filtered force signals were analyzed using customized software. Repeated measures analysis of variance and appropriate follow-up analyses were utilized to compare dependent variables, and relevant effect sizes (d) were calculated.


Results
Supplement or placebo ingestion led to similar subjective responses (p?>?0.05). Energy (+8 to 44%; d?=?0.3 to 0.8) and focus (+8 to 25%; d?=?0.3 to 0.5) were acutely increased by supplement or placebo ingestion and decreased as the exercise session progressed. Fatigue was acutely decreased by supplement or placebo ingestion (?7 to 38%; d?=??0.1 to ?0.6) and increased as the exercise session progressed. Eccentric and concentric forces were unimproved by supplementation during the exercise sets for both sexes. In the non-caffeinated supplement condition only, maximal eccentric force production was lower during sets 3 to 5, as compared to set 1 (p?<?0.05). Effect size data indicated that both the caffeinated and non-caffeinated supplements may contribute to small increases in concentric force production in males (+5 to 20%, d?=?0.2 to 0.4 relative to placebo), but not females.


Conclusions
As compared to placebo, caffeinated and non-caffeinated multi-ingredient pre-workout supplements failed to improve concentric and eccentric force production. In males, effect size data indicate a possible small benefit of supplementation on concentric force production, although this was not statistically significant. When resistance-trained subjects were unaware of the presence of a placebo, resistance exercise performance was similar regardless of whether a placebo or multi-ingredient supplement was ingested.

Ολο το κειμενο: https://jissn.biomedcentral.com/arti...970-017-0203-x