Date of Award


Document Type

Scholarly Project

Degree Name

Doctor of Physical Therapy (DPT)


Physical Therapy

First Advisor

Schawnn Decker


Abdominal Muscles; Muscle Contraction


Purpose: The purpose of this study was to determine the effect of a hamstring contraction on the abdominal musculature during a standard crunch. Studies in the past have looked at abdominal and core strengthening, exercise equipment, and exercise techniques and their effect on abdominal electromyography (EMG). Few published studies have looked at the effect on the abdominals during a modified crunch, which is a hamstring contraction during a standard crunch.

Methods: Participants (n=30) for this study were between the ages of 18 and 60 with no history of acute or chronic back pain or major abdominal surgery. EMG was used to record the activity of four muscle groups including the: upper rectus abdominus (URA), lower rectus abdominus (LRA), external obliques (EO), and the biceps femoris during a standard crunch and also during a modified crunch. Data analysis compared EMG output to each participant's individual maximal voluntary contraction (MVC) for each muscle group analyzed.

Results: There was a significant (p<0.05) increase in the average mean difference in the LRA of + 26.89% and EO of +46.3% in EMG activity during the modified crunch. URA displayed an increase of +2.25%; however, it was not found to be statistically significant.

Discussion: In this study there was an increase in abdominal EMG output for the modified crunch; however, other factors that need to be considered include: the effects of gender, age, previous abdominal training, influence of pathologies, and other musculature involvement.