The comparison was against nothing, not against a protein shake
Ten trained men drank 5.6 g of branched-chain amino acids after leg exercise, and biopsies showed muscle protein being built 22 percent faster than on placebo.
What the study found
BCAAs alone raised muscle protein synthesis by 22 percent
The measurement was taken inside the muscle itself. Ten trained men drank 5.6 g of branched-chain amino acids after leg exercise, and biopsies over the next four hours showed protein being built 22 percent faster than on placebo. Whether that beats a protein shake is a separate question.
The caveat · Protein estimate from other studies
Ten men, one four-hour window, and all of them already trained. The comparator was placebo, so this shows branched-chain amino acids beat nothing rather than that they match protein. The authors put the rise at roughly half what intact protein produces in similar designs, which this study never measured directly.