Yes, we (Biotest) are looking into aspartic acid among other things. Here is the link to the human study:
Also, 40% may not seem like a big increase, but when timed properly it may help upregulate androgen receptors. For example:
J Steroid Biochem Mol Biol. 2009 Apr;114(3-5):195-9. Epub 2009 Feb 21.
Elevated endogenous testosterone concentrations potentiate muscle androgen receptor responses to resistance exercise.
Spiering BA, Kraemer WJ, Vingren JL, Ratamess NA, Anderson JM, Armstrong LE, Nindl BC, Volek JS, HÃ¤kkinen K, Maresh CM.
Department of Kinesiology, University of Connecticut, 2095 Hillside Road, Storrs, CT 06269, USA.
The purpose of this study was to determine the influence of endogenous circulating testosterone (T) on muscle androgen receptor (AR) responses to acute resistance exercise (RE). Six healthy men (26+/-4 years; 176+/-5 cm; 75.8+/-11.4 kg) performed a knee extension exercise protocol on two occasions separated by 1-3 weeks. Rest preceded one trial (i.e., control [CON] trial) and a high-volume upper-body RE protocol designed to increase circulating T preceded the other trial (i.e., high T [HT] trial). Serial blood samples were obtained throughout each trial to determine circulating T concentrations. Biopsies of the vastus lateralis were obtained pre-RE (REST), 10-min post-RE (+10), and 180-min post-RE (+180) to determine muscle AR content. Circulating T concentrations remained stable during CON. Alternately, HT significantly (p< or =0.05) increased T concentrations above resting values (+16%). Testosterone area-under-the-time curve during HT exceeded CON by 14%. AR content remained stable from REST to +10 in both trials. Compared to the corresponding +10 value, muscle AR content at +180 tended to decrease during CON (-33%; p=0.10) but remained stable during HT (+40%; p=0.17). Muscle AR content at +180 during the HT trial exceeded the corresponding CON value. In conclusion, acute elevations in circulating T potentiated muscle AR content following RE.
Over time, I would expect an effect like that to improve training adaptations.