Background: Acetaminophen (also known as Tylenol or Paracetamol) is a very popular drug, that requires no prescription and is usually used as analgesic and antipyretic. A considerable number of previous studies show that acetaminophen has no effects that could alter exercise capacity or performance. On the other hand, there are studies sustaining that exercise performance can be improved with acetaminophen through a reduction in perceived pain, and also a reduction of the body heat produced by the muscle contraction. Purpose: The aim of our study was to check if acetaminophen influences reaction speed and power of the lower limbs muscles. Participants and method: For this study we recruited twenty-nine males, aged between 19 and 28 years old. We had two testing sessions for each participant, in the same day (the baseline evaluation, and the second evaluation at half an hour after acetaminophen ingestion). The evaluation sequence was: Body composition evaluation, acoustic-visual reaction test for one leg (left and right), Squad jump on one leg (5 jumps on each foot) and Stiffness test (7 jumps on each foot). Results: Acetaminophen has no significant influence on visual and acoustic reaction time of left or right leg. The Squat Jump test revealeda significant increase of explosive power on left leg (from 10.19±1.66 to 10.61±1.66 W/Kg, p=0.03) and right leg (10.16±1.59 W/Kg to 10.62±1.84 W/Kg, p=0.02). Another significant result of our study is the increase of reactive power (obtained during the Stiffness test) after the acetaminophen ingestion (from 16.35±4.86 to 17.53±3.79 W/Kg on left leg and from 15.92±4.2 to 17.04±4.26 W/Kg on right leg). Conclusions: Acetaminophen ingestion does not influence visual or acoustic reaction time but can improve the exercise performance through an increase in both explosive and reactive power of lower limbs.
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