The main finding of the study was that CAF supplementation has a significant effect on TUT [s], with no significant changes in the number of performed REP [n]. The ingestion of CAF led to a significant decrease in TUT during the explosive bench press exercise between the CAF group (G
CAF) and the placebo group (G
PLA). To date, no scientific study has analyzed the effect of caffeine on TUT. Despite significant differences in TUT between G
PLA and G
CAF, it was not related to the number of performed REP. The evaluations showed no statistical significance in REP (G
CAF 16.6 ± 1.56 vs G
PLA 15.9 ± 1.69). This is inconsistent with previous findings [
33,
35,
60,
61]. Duncan et al. [
34] demonstrated an increase in exercise volume using an external load of 60%1RM, following the use of 5 mg of CAF/kg/b.m. In the next years, Duncan et al. [
33,
60] also confirmed a significant effect of CAF intake on the number of performed REP, exercise volume and increase in muscle activity. The results of our study are partially consistent with those published by Goldstein et al. [
18], who failed to find the effect of CAF supplementation on the number of performed REP. A similar pattern was observed in a study by Williams et al. [
14], Green et al. [
35], Astorino et al. [
37], Richardson and Clarke [
62]. However, one should stress that most studies that have analyzed the effect of CAF intake on exercise volume, both those that have demonstrated a significant effect on exercise capacity [
33,
34,
37,
60,
63] and those which did not confirm such effects [
14,
62], evaluated exercise volume using the number of REP or tonnage. No previous studies have taken into account movement tempo and TUT, during resistance exercises. According to Wilk et al. [
44] TUT is a more accurate and credible indicator of work performed compared to the number of performed REP. These findings were also confirmed in our study, which showed a significant decline in TUT between the G
CAF and G
CON groups (13,68 ± 1346 vs 15,33 ± 1698 s) with no significant changes in the number of REP. The TUT determines how long the resistance effort lasts regardless of the number of REP performed. A decreased values of TUT in the CAF group may have resulted from the increased muscle tension generated during the movement in the CAF group. CAF leads to higher activation of motor units [
33] and higher MVIC [
20,
32]. Increased muscle activation can lead to a higher energy demand during exercise, thus leading to a faster depletion of energy substrates in muscle cells [
21], which may partially explain a decline in TUT in the G
CAF group. However, the effect of increased muscle tension following CAF intake did not modify the power generated during the CON phase of the movement. The experiment did not demonstrate significant changes in P
MEAN, P
MAX and V
MEAN, V
MAX, despite a significant shortening of TUT in the G
CAF group. The lack of significant differences in P and V indicates that the decline in TUT in the G
CAF group is not related to the level of generated power and velocity in the CON phase of the movement. Importantly, the experiment showed a significant increase in velocity but only in the ECC phase of the movement (VE
MEAN). A significant increase in ECC velocity (G
CAF 0.690 ± 0.08 ms vs G
PLA 0.609 ± 0.05 ms) with a presumable increase in muscle tension in G
CAF can partially explain the decline in TUT. Cole et al. [
64] and other authors suggested that caffeine impacts mechanoreceptors feedback, such as the Golgi apparatus and class III/IV muscle afferents [
64‐
66]. Caffeine may alter feedforward information and may alter how information from either feedforward/feedbackward mechanism is processed centrally [
67]. Despite the increase in velocity of the ECC movement, it did not lead to significant changes in velocity and power generated during the CON phase of the movement. Cronin et al. [
68] demonstrated that muscle power generated during the CON movement depends on the effective use of the stretch-shortening cycle (SSC). The SSC cycle leads to the release of the energy stored in the ECC phase in order to maximize power generated during the CON phase. The same author [
68] demonstrated that performing an ECC contraction before the CON phase impacts the generated power compared to performing only the concentric phase of the movement. A faster tempo of the entire movement cycle without a pause between the ECC and CON phases increases activation and more effective utilization of the SSC cycle [
69]. However, to date, it remains unclear whether the efficiency of SSC depends on the velocity in the ECC phase and whether the SSC is susceptible to CAF supplementation. Although in this study VE
MEAN was higher in G
CAF (0.690 ± 0.08 ms vs 0.609 ± 0.05 ms), this change did not lead to a more effective use of the energy accumulated for explosive performance of the CON phase. Therefore, it can be speculated that the change in VE
MEAN and CAF intake do not lead to a more effective use of the SSC cycle. No increase in both mean (V
MEAN; P
MEAN) and maximal (V
MAX; P
MAX) values of CON movement with declining TUT questions the validity of CAF intake before high-intensity anaerobic exercise with a duration of between ten and twenty seconds. A limitation of the present study pertains to the lack of assessments related to CAF intolerance in the tested athletes. However it should be noted that before and during the experiment no study participant reported any side effects from ingesting caffeine.