Caffeine, Resistance Exercise and EMG

Effect of Acute Caffeine Intake on Muscle Electrical Activity and Muscular Strength, Power, and Endurance Performance

Introduction: Several studies have evaluated and confirmed the ergogenic effects of acute caffeine intake on sports performance. However, some studies suggest that this effect predominantly occurs in large muscle groups, potentially due to increased skeletal muscle electrical activity.

Objectives: This study aims to evaluate the acute effects of caffeine intake on strength, power, muscle endurance, and muscle electrical activity in young adults. It will also analyze the influence of circadian rhythms (morning vs. afternoon) on exercise performance (bench press vs. squat).

Methods: Twelve healthy, physically active participants will be recruited for the study. Using a triple-blind, crossover, randomized, and controlled design, participants will ingest either caffeine (3 mg/kg body mass) or a placebo (maltodextrin, 3 mg/kg) 60 minutes before the trial. Muscular strength, power, and endurance performance will then be assessed through 1RM tests, and at 25%, 50%, 75%, and 90% of 1RM, along with muscle endurance tests at 65% of 1RM, for both squat and bench press exercises. EMG will be used to measure skeletal muscle electrical activity during the tests. The experimental sessions will be conducted in the morning (8:00 am to 10:00 am) and the afternoon (4:30 pm to 6:30 pm).

Inclusion Criteria:

• Age between 18 and 35 years.
• Body Mass Index (BMI) < 25 kg/m².
• Resistance-trained individuals (more than 2 years of structured training).
• Healthy men and women without neurological, cardiometabolic, immunological, or physical conditions that prevent them from exercising.
• Participants must be able to perform the tests described in the following section.

Exclusion Criteria:

• History of neuromuscular diseases, heart disease, or conditions that may affect liver or muscle metabolism.
• Use of drugs, stimulants, or sports supplements that could interfere with the dietary supplement used in the study.
• Sedentary habits (less than 150 minutes/week of moderate exercise).
• Having undergone prolonged periods of physical inactivity in the 6 months prior to the study.
• Engaging in strenuous exercise within 48 hours prior to the tests.
• Failure to replicate the same food intake on both experimental days.
• Consumption of caffeine or any other stimulant after 6 pm on the day before the tests, to avoid headaches, discomfort, or lethargy in regular caffeine consumers.