The Underlying Mechanisms From Exercise-induced Muscle Damage on Force Loss

A within participant, repeated measures experimental design will be used such that each participant will serve as his/her own control. Caffeine and placebo will be administered in a double-blind, counterbalanced manner. Caffeine and placebo (white flour) pills will be prepared by Kerri Tiedman or Jackie Straughn at the Doctors Park Pharmacy using an analytical balance. Anhydrous caffeine or white flour will be placed into opaque capsules. The pills will be placed into envelopes by Chris Black. He will then use a computer generated random number table to assign caffeine or placebo pills for each testing session in a counter-balanced fashion. The participant's identification number, as well as session number will be placed on the envelope. A spreadsheet containing only the participants' numbers and the testing condition will be kept by Chris Black until the study is complete. Jessica, Robby, Alex, Josh, and Jamie the research assistants, who will be blinded to the contents of the envelopes, will administer the pills to the participants and collect data from the participants. This will ensure the blinding of the researchers to the condition during data collection. Following the completion of data collection the spreadsheet will be given to all the above stated research assistants and the blinding will be broken for data analysis.

Total time commitment for the study will be approximately 10 hours over the course of 14 days. Three familiarization session and 5 testing sessions will be completed.

Test Day 1: - Potential participants will report to the sensory and muscle function lab for a 30 minute session involving the following:

D1.1 Written and verbal description of the experiment and all procedures will be given, and any questions will be answered. Informed consent will be completed.

D1.2 A physical activity readiness questionnaire (PAR-Q) will be completed (identifies contraindications to exercise.D1.3 A questionnaire screening for the potential adverse reactions to caffeine, current medication and supplements as well as an increased risk of rhabdomyolysis use will be competed. D1.4 Seated, resting blood pressure will be assessed in the right brachial artery. D1.5 Potential participants deemed eligible for the study will be asked to orally state to the researchers what they will be expected to do in the study and explain the risks and benefits of the study to confirm they understand the procedures, time commitment, freedom to withdraw, and risk and benefits of study participation. D1.6 Next, participants will practice the procedure for determining maximal voluntary isometric strength (MVC) of the plantar flexor muscle group. Participants will be seated in a specially designed chair with their hip at an angle of 90 degrees. A series of 3 maximal, all-out isometric contractions (contractions against a stationary object where the muscle does not shorten or lengthen) will be performed. Each contraction will last approximately 3 seconds. Participants will be given verbal encouragement throughout the contraction. Muscle activation (the amount or percentage of total muscle mass of the plantar flexors the person is able to use during a contraction) during the isometric contractions will be assessed using the interpolated-twitch technique (ITT). This technique involves applying an electrical current to the muscle via stimulation of the tibial motor axon (nerve) while it is contracting to determine if the muscle is able to generate any additional force, above and beyond what the participant can generate on their own. The force from this stimulation is compared to the force generated in a relaxed, non-contracting muscle to determine the percentage of the muscle the participant can active during a contraction. To perform the ITT stimulating electrodes are placed proximal to the patella and behind the knee over the tibial nerve. Participants will receive a brief (10 milliseconds) high intensity stimulation of the muscle during each contraction, and at 4 and 6 seconds following each contraction (while the muscle is relaxed). The MVC as well as the ITT will be determined in both the right and left calf.