When young men did leg extensions with a slow upward motion and drank a protein shake right after, their fast-twitch muscle fibers got noticeably bigger—but this didn’t happen if they did the slow downward motion or drank sugar water instead.

The slow-twitch muscle fibers got bigger no matter what kind of workout or drink the men used—whether they lifted slowly up or down, or drank protein or sugar water.

After drinking whey protein shakes every day for a week, older women’s muscles kept building up new protein even on days they didn’t exercise—collagen protein didn’t do this at all.

When older women drink whey protein shakes, their muscles start repairing and growing faster—especially if they also do leg exercises—while collagen protein shakes don’t do much unless they exercise, and even then, it’s much weaker.

For middle-aged men doing strength training, whey protein and this collagen supplement have similar effects on muscle gain and fat loss.