Effect of Abdominal Weight Training on Diaphragm Thickening Fraction and Respiratory Muscle Strength in Healthy People: A Quasi-Experimental Study

Introduction Abdominal weight training (AWT) is a simple technique that applies external resistance to the diaphragm during breathing by placing weights on the abdomen. Although it is an accessible method for respiratory muscle training, its physiological effects remain unclear. This quasi-experimental study in healthy young adults evaluated the immediate and four-week effects of AWT on diaphragm thickening fraction (DTF) and maximal inspiratory pressure (MIP). Methods A quasi-experimental study was conducted with 26 healthy participants allocated to either an AWT group or a control group. The AWT group performed diaphragmatic breathing with abdominal weights for four weeks, while the control group performed unloaded diaphragmatic breathing. DTF was assessed under different weight conditions to examine immediate effects, and both DTF and MIP were measured on days 0, 14, and 28 to evaluate longitudinal effects using mixed-effects models. Results No significant immediate effect of abdominal loading on DTF was observed (β = 0.15; 95% confidence interval: -3.81 to 4.10; <i>p</i> = 0.94), with DTF decreasing under the 5-kg load condition. Over the four-week intervention, no significant group × time interaction was found for DTF (β = -0.13; 95%CI: -0.51-0.26; <i>p</i> = 0.53) or MIP (β = -0.00; 95%CI: -0.17-0.17; <i>p</i> = 0.99). However, both groups showed modest increases in DTF and MIP over time. Conclusion AWT did not significantly improve DTF or respiratory muscle strength compared to unloaded diaphragmatic breathing in healthy young adults. These findings suggest that AWT, in its current form, may have limited utility, and optimization of training parameters is necessary before broader application. Key limitations include a small sample, non-random allocation, and a short four-week period; longer, optimized trials are warranted.