Resistive exercise is used in the assessment of musculoskeletal health, performance, training interventions, and population differences (i.e., gender, age, training status). There is a need to determine the amount of familiarization required to stabilize performance prior to testing. Fifteen males completed a familiarization session consisting of 3 blocks of 5 maximal isometric dorsiflexion contractions, followed by a retention test (an additional block of 5 contractions) performed 3 days later. Mean force and surface electromyography (sEMG) from both the agonist and antagonist muscles were collected. A variance ratio, representing the stability between trials, was calculated for each of the 4 blocks of 5 contractions for both force and sEMG. The variance ratio for both force and agonist sEMG decreased significantly within the first 10 trials and remained stable during the retention test. The variance ratio for antagonist sEMG was stable across the 3 blocks of familiarization and significantly decreased during the retention test. The magnitude variables all remained stable across the 3 familiarization blocks. However, an 11% increase in mean force was seen during the retention test while both agonist and antagonist sEMG remained stable. Although slight changes occurred in the magnitude variables during the retention test, the stabilization of the force and agonist sEMG variance ratios suggest that familiarization to the task was achieved within the first 10 contractions and was sustained over a 3-day period.

The return of force to initial values, rather than a persistent decrement was a result of several mechanisms operating simultaneously. The sEMG data indicate an increase in conduction velocity, while an increase in peak RFD suggests contraction-induced facilitation of ATPase pump activity. However, alterations in muscle coordination were observed as a reduction in antagonist co-activity.