Gastrocnemius Muscle Contraction and Its Role in Orthostatic Anti-Gravity Adjustment – The Effects of Body Mass Index

Abstract

BACKGROUND: Obesity is a global concern with severe detrimental health and economic effect. Body mass index (BMI) is an inexpensive, non-invasive indicator for different diseases, and associated with abnormal weight. AIM: The aim of the study was to investigate the relationship between BMI and the contraction of gastrocnemius muscle (GM) and its possible role in peripheral muscle pump activity and pathogenesis of orthostatic intolerance. METHODS: One hundred and four volunteers (63 women and 41 men, mean age 39 ± 14 years) were divided into three subgroups according to their BMI values (with normal weight, overweight, and obesity). Changes in the transverse diameter and pennation angle of GM at rest and during maximal active plantar flexion (MAPF) were measured with multimodal ultrasound imaging. An active orthostatic test was performed and changes in systemic blood pressure and heart rate in supine position and active standing on the 1st, 5th, and 10th min were monitored. The results were statistically processed with alternative, variational, and correlational analysis. RESULTS: Patients with abnormal BMI were significantly older and had higher anthropometrical parameters compared to the subgroup with normal weight. They showed a significantly larger diameter and pennation angles at rest and during maximal active plantar flexion of GM bilaterally, which was more pronounced for the dominant right leg. However, the amount of changes in the GM diameter and pennation angles was similar in the different subgroups. CONCLUSION: The study showed that BMI affects predominantly the initial values of GM parameters at rest and MAPF without influence on its antigravity contractility associated with active straightening.