Experimental protocol
Experimental protocol was shown on Fig. Experimental protocol.On the day before the first formal experiment, the participants' dietary intake was recorded, and they were asked to replicate the same diet before the next experiment. Participants were also instructed to avoid consuming caffeinated foods for 24 h before the formal experiment and to refrain from excessive exercise training for 72 h.On the day of the experiment, the participants arrived at the laboratory in the afternoon, following their regular training schedule. After a 5-min warm-up on a bicycle ergometer, they chewed either food-grade caffeinated chewing gum (200 mg per serving) or a placebo gum for 5 min. After a 10-min rest period, participants performed a set of 6 repetitions and 5 sets of Romanian Deadlift (RDL) exercises using the non-gravity-dependent flywheel inertial device (K-Box 4, Exxentric®, Stockholm, Sweden). There was a 3-min rest period between sets. The Exxentric kMeter (© Exxentric AB, Sweden), connected to its application via Bluetooth, was used in each RDL test to record average power (W), average force (N), peak concentric power (W), peak eccentric power (W) and total work (KJ). This device had been used in other studies and had demonstrated good reliability and validity in measuring various performance indicatorsAfter completion of the first experiment, participants had a 7-day rest and washout period before proceeding to the next set of experiments. All trials were completed within one month, followed by analysis of the experimental results.