Differences in Abdominal Muscle Thickness, Strength, and Endurance in Persons Who Are Runners, Active, and Inactive.

Background: Core musculature is important for efficiency during activities including running. Both abdominal muscle strength and endurance contribute to this efficiency. The purpose of this study is to determine what differences and relationships exist in abdominal muscle thickness, strength, and endurance among persons who are runners, active, and inactive.

Hypothesis: Persons in the running group would show significantly greater abdominal muscle thickness, muscle strength, and muscle endurance compared with those in the nonrunning groups.

Study design: Quantitative cohort design.

Level of evidence: Level 2b.

Methods: A total of 78 subjects aged 18 to 27 years were divided into 3 groups: runners, active, and inactive. Assessment included abdominal muscle thickness via diagnostic ultrasound (Mindray North America), strength using a static Isotrack dynamometer (JTech Medical), and abdominal muscle endurance using a side plank. Statistical analysis using analysis of variance, t tests, and Pearson's correlation coefficients and partial correlations was performed using SPSS Version 26 with a significance level of P < 0.05.

Results: Significantly greater muscle thickness of internal obliques (IOs) at rest and during contraction was found in the running group compared with the active group, the active group compared with the inactive group, and the running group compared with the inactive group. There were no statistically significant differences in overall strength measured by dynamometry among the 3 groups. Plank time was significantly greater for the running group compared with the other 2 groups. Male participants were greater in all areas: strength, plank time as a measure of muscle endurance, and muscle thickness. Body mass index was significantly correlated with resting thickness, muscle endurance, and muscle strength.

Conclusion: Persons who run, are active, and are inactive use their abdominal muscles differently. Runners have thicker IOs and better abdominal muscle endurance than the other 2 groups. Focusing on endurance training of the obliques may be beneficial for persons who run.

Clinical relevance: This research could contribute to developing core training programs to ensure runners target the correct abdominal muscles with the best type of training.