The diaphragm, crucial for breathing and regulating the autonomic nervous system, is often only partially utilized, which can increase cardiac stress and blood pressure. Proper diaphragmatic breathing can improve lung function, reduce stress, and enhance blood pressure and circulation. This breathing technique can also increase abdominal muscle strength and core stability during resistance exercises. The aim of this study was to examine the impact of diaphragmatic breathing on the performance of the back squat in individuals with and without experience in this technique. The effects on horizontal bar displacement, execution speed, force, muscle strength, and subjective safety and recovery speed were analyzed. Hypotheses suggested that diaphragmatic breathing could improve all these aspects. Twenty-one participants took part, and video analysis software was used to quantify performance parameters. Results showed that diaphragmatic breathing significantly improved performance at loads of 60% and 80% of 1RM (p < 0.05). Participants reported improved stability and greater safety during squat execution, especially at higher loads. Additionally, diaphragmatic breathing reduces negative bar displacement, improving postural control and reducing the risk of injury. This study highlights the benefits of diaphragmatic breathing in resistance training, though further research is needed to confirm long-term effects and applicability across different populations.