Which muscles are primarily used during normal breathing?

Normal breathing primarily involves the external intercostals and the diaphragm. The diaphragm is a dome-shaped muscle located at the base of the ribcage that plays a crucial role in respiration. During inhalation, the diaphragm contracts and moves downward, creating a negative pressure in the thoracic cavity, which allows air to flow into the lungs. The external intercostals, located between the ribs, assist by lifting the ribcage and expanding the thoracic cavity further, facilitating an efficient inhalation process.

This coordination between the diaphragm and the intercostals is essential for effective ventilation, as it increases the volume of the thoracic cavity and decreases the pressure, allowing air to be drawn in. This process is generally automatic and continuous, relying on the rhythmic contraction of these muscles to support normal breathing patterns.

Other muscle groups listed in the options, such as the quadriceps and hamstrings, are primarily involved in locomotion and weight-bearing activities, while the rectus abdominis and obliques contribute to forced exhalation rather than normal inhalation. The latissimus dorsi and trapezius play roles in shoulder movement and stability rather than in the mechanics of breathing.