Leucic acid (also known as DL-alpha-Hydroxy-isocaproic acid, alpha-hydroxyisocaproic acid or HICA) is an end product of leucine metabolism (leucine metabolite) claimed to be an anti-catabolic substance with anabolic properties. Besides that common claims also include muscle and strength support, increased recovery from workouts, and reduced muscle soreness.
Leucic Acid (HICA) and Protein Synthesis / Protein Degradation
In both animal  and isolated muscles [2,3], branched chain amino acids together or leucine alone (and some of its metabolites) were reported to promote protein synthesis and inhibit protein breakdown. No other plasma amino acid shows such effects in muscle tissues. Scientists from Pennsylvania State University College of Medicine  hypothesized that diet containing 5% alpha-hydroxyisocaproic acid (leucic acid) will slow the loss and/or improve recovery of muscle mass in response to disuse (immobilization-induced atrophy). Results of this study reported that leucic acid does not slow the loss of muscle produced by disuse, but it does speed recovery at least in part by maintaining an increased rate of protein synthesis. In another experiment where alpha-ketoisocaproic acid (leucine metabolite) decreased protein degradation, alpha-hydroxyisocaproic acid (leucic acid) had no influence on this process .
A study conducted by inventors of HICA patent  reported beneficial effects of 3 times a day HICA supplementation. Results showed significantly improved body weight (p < 0.005) with increased lean mass (p < 0.05) and unchanged fat mass. Muscle strength and running velocity did not differ between placebo and HICA supplemented group. Author also mentioned their unpublished pilot study in 10 national top wrestlers where similar dose (0.496 g three times per day) of HICA significantly increased total lean soft tissue mass. According to authors the most important finding of this pilot study was that wrestlers did not suffer from DOMS symptoms (or markedly less) when using HICA.
That is also the only human evidence of HICA effectiveness. It seems to be moderately effective in reducing muscle soreness and increasing muscle mass (probably by increased protein synthesis) but there is currently not enough evidence. There is also not enough evidence about optimal dose.
Are There Any Side Effects From Leucic Acid Ingestion?
Mero et al.  found no changes in blood pressure and heart rate after HICA ingestion suggesting that its use is safe.
(Other common names: Leucate, DL-Leucate, a-Hydroxyisocaproate, a-Hydroxyisocaproic acid, 2-Hydroxyisocaproate, 2-Hydroxyisohexanoate, 2-Hydroxyisohexanoic acid, Leucinic acid, 2-Hydroxy-4-methylpentanoic acid)
- Goldberg, A. L., and St. John, A. C. Annu. Rev. Biochem 45, (1976): 747-803.
Chua, Balvin, Daniel L. Siehl, and Howard E. Morgan. “Effect of leucine and metabolites of branched chain amino acids on protein turnover in heart.” Journal of Biological Chemistry 254.17 (1979): 8358-8362.
Chua, B. H., Daniel L. Siehl, and Howard E. Morgan. “A role for leucine in regulation of protein turnover in working rat hearts.” American Journal of Physiology-Endocrinology And Metabolism 239.6 (1980): E510-E514.
Lang, Charles H., et al. “Chronic alpha-hydroxyisocaproic acid treatment improves muscle recovery after immobilization-induced atrophy.” American Journal of Physiology-Endocrinology And Metabolism (2013).
Tischler, M. E., M. Desautels, and A. L. Goldberg. “Does leucine, leucyl-tRNA, or some metabolite of leucine regulate protein synthesis and degradation in skeletal and cardiac muscle?.” Journal of Biological Chemistry 257.4 (1982): 1613-1621.
Mero, Antti A., et al. “Effects of alfa-hydroxy-isocaproic acid on body composition, DOMS and performance in athletes.” Journal of the International Society of Sports Nutrition 7.1 (2010): 1.