Primary Research
Effects of Essential Amino Acid Supplementation on Musculotendinous Recovery Following Eccentric Plantar Flexor Exercise: A Randomized Controlled Trial
Does taking essential amino acids around a muscle damaging workout reduce soreness?
Does it help the muscle swelling from that workout resolve faster?
Does it change how the tendon responds?
ANSWERS: YES, MODESTLY. YES. NO.
This is our own study. Researchers at the University of Tampa Human Performance Laboratory, led by Ecaterina (Katie) Vasenina, PhD, CISSN, randomized 36 recreationally active young men into three groups: 10 g of essential amino acids (OptimalAmino®), 10 g of a taste matched maltodextrin placebo, or no supplement. The two supplemented groups performed an eccentric plantar flexor protocol (4 sets of 50 single leg eccentric calf raises plus one set to failure) designed to produce exercise induced muscle damage. Supplements were taken 30 minutes before and immediately after the exercise bout, then before and after each lab visit over the next two days, with a final dose before the 72 hour measurement. The study was double blinded.
Recovery was tracked before exercise, immediately after, and at 24, 48, and 72 hours using perceived soreness (Numeric Pain Rating Scale, 0 to 100), pressure pain threshold, calf muscle thickness and Achilles tendon thickness by ultrasound, and calf circumference.
Soreness. The exercise protocol produced classic delayed onset muscle soreness in both exercise groups. The difference showed up at 24 hours, which is when DOMS normally builds toward its peak. Worst pain ratings at 24 hours were 31.4 in the EAA group versus 64.6 in the placebo group, which the authors describe as "approximately 51% lower in the EAA group compared with placebo." Current pain was about 50% lower and average pain about 48% lower at the same time point. By 48 and 72 hours soreness was elevated in both groups with no significant difference between them, so the authors characterize the effect as modest and concentrated in the early recovery window.
Muscle swelling. Calf muscle thickness measured by ultrasound increased after exercise in both groups. In the EAA group it was no longer different from baseline by 72 hours (p = 0.062). In the placebo group it stayed elevated at every time point through 72 hours, roughly 25% above its pre exercise value, and was significantly greater than the non exercising control group at 48 and 72 hours. The condition by time interaction was significant (p < 0.001) with a partial eta squared of 0.463, a large effect. The authors write that this pattern "may suggest an accelerated recovery of exercise-induced swelling in the EAA group," while noting that the EAA and placebo groups were not significantly different from each other at the earlier time points.
Tendon and other measures. Achilles tendon thickness dipped immediately after exercise in all exercise participants, which the authors attribute to normal fluid shifts under load rather than damage, and EAAs did not change that response. Pressure pain threshold and calf circumference also did not differ between groups. Circumference is a blunter instrument than ultrasound, which likely explains why it missed the swelling difference the ultrasound picked up.
The authors' conclusion: "EAA supplementation modestly reduced soreness and was associated with faster recovery of muscle swelling but did not influence tendon morphology within 72 hours."
Limitations worth knowing. The participants were young, recreationally active men only. Follow up stopped at 72 hours. The study did not include a strength or performance test, so it cannot say whether the exercise impaired function or whether EAAs protected it. Because the placebo was maltodextrin rather than protein, the study compares EAAs to no amino acids at all, not to whole protein.
FYI, the dose used in this study is one serving of OptimalAmino (10 g of EAAs, 19.64% leucine) taken before and after the workout, with servings continued through the following days of recovery.
Principal Investigator Katie Vasenina presented the findings on June 17, 2026 at the International Society of Sports Nutrition's 23rd Annual Conference in Ft. Lauderdale, Florida. The study is published open access in the peer reviewed Journal of the International Society of Sports Nutrition (2026).
Read the full-text here: https://doi.org/10.1080/15502783.2026.2726619
For how this fits with the broader recovery literature, see our Science Hub article The Real Science of Recovery.
Journal of the International Society of Sports Nutrition 2026 23:1, 2726619. doi:10.1080/15502783.2026.2726619