Ultrasound and MRI can better detect actual muscle growth by distinguishing it from temporary changes like water retention or glycogen storage, whereas methods like DXA or BIA measure total lean mass and cannot separate these factors.

We analyzed the available evidence and found that ultrasound and MRI may offer a more specific view of muscle growth compared to DXA or BIA. The evidence we’ve reviewed suggests these imaging tools can distinguish actual muscle tissue increases from temporary changes like fluid buildup or stored glycogen, which can inflate readings on DXA or BIA [1]. Unlike DXA and BIA, which measure total lean mass as one number, ultrasound and MRI can visualize and measure individual muscle thickness or volume, potentially giving a clearer picture of true hypertrophy [1]. So far, no studies in our review have challenged this idea. What we’ve found so far leans toward ultrasound and MRI being more precise for tracking real muscle growth over time, especially in research settings where separating muscle from other tissues matters. This doesn’t mean DXA or BIA are wrong—they still give useful estimates of overall lean mass—but they may not tell you whether a change is due to muscle building or something else, like water. For someone tracking progress in the gym, this means if you’re trying to see whether your training is actually building muscle—not just making you look fuller from water or carbs—ultrasound or MRI could give you more detailed insight. But these tools are expensive, less accessible, and often used in labs, not gyms. For most people, consistent strength gains and visual changes remain practical indicators. Our current analysis is based on one assertion, and more research could change what we understand.