Effects of MusclePharm Assault Black on spinal excitability and postactivation potentiation

Caffeine, as contained in AssaultTM, has been shown to increase acute muscle performance, and may do so partially through altering lower motorneuron function. Therefore the purpose of this study is to examine the neural contribution to increases in muscle performance as a result of supplementing with AssaultTM. In this repeated-measures crossover study approximately 15-20 persons, ages 20-35, will ingest either AssaultTM or a placebo 20 minutes prior to testing. The two intra-subject testing sessions will be separated by 4-7 days. Testing will consist of being electrically stimulated at the tibial nerve at increasing intensities to obtain an H-M wave recruitment curve of the lateral gastrocnemius, from which Hmax (the maximum peak-to-peak EMG response of the H-wave) and Mmax (the maximum peak-to-peak EMG response of the M-wave) will be determined. Subsequently, subjects will perform a 10 second maximum voluntary isometric contraction (MVIC) of the plantarflexors. Thereafter stimulations at the intensities that elicited Hmax and Mmax +20% will be given at specific time points for a 20 minute time period to observe the time course of potentiation from the MVIC. Dependent variables include the Hmax/Mmax ratio from the H-M wave recruitment curve, as well as this ratio and forces at select time points of stimulation during the 20 minutes following the MVIC. We hypothesize that AssaultTM will result in a larger H-wave EMG amplitude from the recruitment curve than the placebo, reflecting a greater degree of spinal excitability. We also hypothesize that AssaultTM will result in more and longer lasting potentiation (Hmax/Mmax ratio and force increases) from the MVIC than the placebo. A paired t-test will be performed between conditions for the initial H-M ratio. A two-way repeated measures ANOVA will be performed on each of the time-series variables during the 20 minutes of testing post-MVIC (Hmax/Mmax ratio and force). Statistical significance will be set at p