Comparison Of Biceps Brachii Activation During An Isometric Curl Using Offset Loads

PURPOSE: The purpose of this study was to evaluate the difference in biceps brachii electromyographic (EMG) activity using two offset loads during an isometric bicep curl in healthy individuals. METHODS: Participants performed three isometric bicep curls at 90 degrees of elbow flexion with neutral, medial, and lateral offset loads. This was accomplished using weighted dumbbells which included an evenly-loaded 10 pound dumbbell (5 pounds on each side) and a medially and laterally offset dumbbell (7.5 pounds and 2.5 pounds on each side with the term “medially offset” describing the condition where the 7.5 pound weight was situated on the medial side of the dumbbell when placed in the participant’s supinated hand). The order of the testing was randomly assigned. The isometric bicep curl was performed standing against the wall while maintaining 90 degrees of elbow flexion and full forearm supination. Each participant performed 3 repetitions for 5 seconds for each condition. Surface EMG activity was recorded from the biceps brachii muscle during the isometric contraction and peak muscle activity was recorded for each trial. The average of the three trials was used for data analysis. RESULTS: The biceps brachii in the dominant arm of 20 asymptomatic participants (11 females; mean age = 24.6 years, SD = 2.5; mean BMI = 25.4 kg/m2, SD = 3.1) was assessed. Peak EMG activity of the biceps brachii during a medial offset load (1590 μV ± 707 μV) was significantly greater when compared to neutral (449 μV ± 237 μV) (mean difference = 1141 μV; p < 0.001) and lateral offset (336 μV ± 135 μV) (mean difference = 1255 μV; p < 0.001). When normalizing the peak EMG values to the neutral grip peak EMG value, the medial offset resulted in a mean 392% increase while the lateral offset resulted in a mean 17% decrease in biceps brachii activation. CONCLUSIONS: The results indicate significantly greater activation of the biceps brachii with a medial offset load when compared to a lateral offset and neutral load. A lateral offset load showed a decrease in biceps brachii activity compared to a neutral load. This knowledge leads to a better understanding of the effects of utilizing different offset grips for a supinated curl and may support the use of offset loading as a more effective method of general resistance training for the biceps brachii in the healthy population.