Ultrasound scans taken at two specific points along the upper arm reliably measure the thickness of the lateral deltoid muscle, making them suitable for tracking muscle changes in resistance training...

We analyzed the available evidence on ultrasound measurements of lateral deltoid thickness and found that 60.0 assertions support its reliability for tracking muscle changes in resistance training studies, with no assertions contradicting this use. The evidence we’ve reviewed suggests that when ultrasound scans are taken at two specific points along the upper arm, they consistently capture changes in the thickness of the lateral deltoid muscle. This means researchers can use this method to monitor how the muscle responds to training over time without needing invasive procedures or expensive imaging like MRI. 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 relatively low-cost compared to other imaging tools. The two specific points mentioned in the evidence are likely standardized locations that help ensure measurements are taken the same way each time, reducing error. Because no studies have challenged this approach, the current evidence leans toward ultrasound being a practical and repeatable tool for this purpose in training research. However, we note that this analysis is based only on the assertions provided, and we have not reviewed the original study methods or participant details. While the number of supporting assertions is high, we cannot say whether these were conducted across diverse populations, different training programs, or over long periods. For someone designing or interpreting a resistance training study, this suggests ultrasound may be a trustworthy way to track lateral deltoid changes — as long as the same technique and measurement points are used every time.