April 7, 2015
Lara A. Green, Justin J. Parro, David A. Gabriel
Electromyographic Kinesiology Laboratory, Faculty of Applied Health Sciences, Brock University, St. Catharines, ON L2S 3A1, Canada
Resistive exercise is used in the assessment of musculoskeletal health, performance, training interventions, and population differences (i.e., gender, age, training status). When performing a specific exercise task, there is a period of time where the individual learns how to coordinate the task, while psychologically and physically acclimating to the testing/training environment. There is a need to determine the amount of familiarization required to stabilize performance before collecting data related to the investigation of resistive exercise, so that changes can be attributed to the experimental manipulation, rather than a learning/acclimatization effect.
Fifteen males completed an initial testing session (familiarization) where they were introduced to the testing room and equipment, and performed the required task. During this familiarization session participants performed a total of 15 contractions (3 blocks of 5 contractions). A retention test (an additional block of 5 contractions) was performed 3 days later to assess how much of the skill was preserved. The task was maximal isometric dorsiflexion. Participants were required to dorsiflex so that the top of the foot compressed against an immobile padded metal bar, without extending the toes.
The same type of electrodes placed on the chest to monitor the electric activity of the heart, can also be placed on the skin to measure the electrical activity of the muscle to assess neural activation during a contraction. Force and electrical activity of agonist (tibialis anterior) and antagonist (soleus) muscles, were monitored concurrently. The variability of force and muscle electrical activity was calculated for each block of five trials, to determine reproducibility of how participants performed the resistive exercise task. A variance ratio compares multiple contractions on a point-by-point basis to calculate how similar in shape and magnitude they are. A variance ratio of 0 would mean that the five traces within a block were identical, therefore, a lower variance ratio is better. Stability in a variance ratio across blocks indicates that a participant has become consistent in their task performance.
The variance ratios for both force and electrical activity of the agonist muscle, decreased significantly within the first 10 trials and remained stable thereafter, including the retention test. The variance ratio for the antagonist muscle electrical was stable across the 3 blocks of familiarization but decreased significantly during the retention test. Mean force and muscle electrical activity remained stable across the three familiarization blocks. Although slight increase in mean force was observed during the retention test, the stabilization of the variance ratios for force and agonist muscle activity suggest that familiarization to the task was achieved within the first 10 contractions and was sustained over a 3-day period.
This information is important for professionals in the areas of physical activity, health, and fitness. Proper familiarization is needed to account for the learning effect, which can influence both pre-test and post-test assessments of strength. While the results indicate at least 10 trials are required for maximal isometric strength assessment, the number may be higher for more complex tasks. The variance ratio can be a valuable tool to ensure that task performance has stabilized prior to data collection for a resistive exercise study, regardless of the task complexity.
Green LA, Parro JJ, Gabriel DA. Quantifying the familiarization period for maximal resistive exercise. Applied Physiology, Nutrition, and Metabolism 2014; 39(3), 275-281.
If you intend citing any information in this article, please consult the original article and cite that source. This summary was written for the Canadian Society for Exercise Physiology and it has been reviewed by the CSEP Knowledge Translation Committee.