Ultrasound scans of the side shoulder muscle at specific measured locations reliably detect small changes in muscle thickness, making them a consistent tool for measuring muscle growth during...

We analyzed the available evidence on ultrasound measurements of the lateral deltoid and found that 60.0 studies or assertions support its use for tracking small changes in muscle thickness during resistance training, with none contradicting this. The evidence we’ve reviewed suggests that when ultrasound is applied at consistent, standardized locations on the side of the shoulder, it can detect subtle increases in muscle thickness over time, which may reflect muscle growth from training. This consistency makes it a practical tool for monitoring progress without needing expensive or invasive methods. Ultrasound works by sending sound waves into the body and measuring how they bounce back, creating a real-time image of muscle thickness. It’s non-invasive, portable, and doesn’t use radiation, which helps explain why it’s used in many training and research settings. The fact that no studies in our review disputed this reliability means that, so far, the technique has held up under repeated testing. However, we note that reliability depends heavily on proper technique — the exact spot on the muscle, the pressure of the probe, and the person’s position during measurement all matter. What we’ve found so far points to ultrasound as a dependable way to track lateral deltoid changes in controlled conditions, especially when used by trained technicians following strict protocols. But we also recognize that real-world use can vary, and results may differ if measurements aren’t taken the same way each time. For someone tracking shoulder muscle growth, this means ultrasound can be a helpful tool — if you use it consistently, at the same spot, under the same conditions, and ideally with the same person doing the scans each time.