What 12 Weeks of Strength Training Shows on a Scan

Consider a hypothetical 45 year old who starts lifting three days a week. After a month her lifts are clearly heavier, but the scale has not moved and she wonders whether anything is happening. Something is. It just is not visible on a bathroom scale.

Weeks 1 to 4: the nervous system first

Early strength gains come mostly from the nervous system. Your brain learns to recruit more muscle fibers at once and to coordinate the muscles involved in a lift. That is why someone can add weight to a lift every week at the start without much change in muscle size.

Training also increases the glycogen and water stored in muscle, and the repair process after each session holds fluid for a few days. On an InBody scan, which estimates lean mass from body water, this can show up as a small early rise in lean mass, part tissue and part water. We do not read too much into the first month.

Weeks 4 to 12: real tissue

With consistent training and enough protein, actual muscle protein starts to accumulate. Studies of adults new to strength training commonly show lean mass gains of a few pounds over 10 to 12 weeks, with smaller gains in older adults. Fat mass often drops modestly at the same time, especially if calories are near maintenance or a little below.

The scale can stay flat through all of this. A pound and a half of muscle gained and a pound and a half of fat lost reads as zero on a scale. On a body composition scan it reads as exactly what it is.

What to look for on an InBody

• Lean mass by segment. Arms, legs and trunk are reported separately, so you can see whether the program is building the areas it targets.
• Body fat mass and percentage. Percentage can fall even when fat mass changes little, because lean mass went up.
• Visceral fat level. Training and better eating habits tend to move this in the right direction.

Getting a fair comparison

Because InBody is sensitive to hydration, food and recent exercise, a scan the morning after a hard leg day can overstate lean mass. We scan under the same conditions each time: same time of day, before eating, and not right after training. Monthly is the right rhythm. It gives the body enough time for a change larger than the day to day noise.

Protein matters through all 12 weeks. We set it at about 1 gram per pound of lean body mass per day, spread across 3 to 4 meals of 30 to 50 grams. Training gives the signal and protein supplies the material.

If you have started lifting and want to see what it is actually doing, that is the kind of thing we measure. You can pick your time right after you buy.

Book an InBody scan at HYBRD Health ($39)

This article is educational and is not medical advice.