Layne Norton includes oral L Carnitine L Tartrate in his recovery supplement and this is the write up, and his citations, that he includes on his webpage
"L-carnitine L-tartrate (LCLT) is a dietary supplement containing the levo-enantiomers of carnitine and tartrate (1). LCLT supplementation may improve workout performance, but it has also demonstrated the ability to enhance recovery (4). LCLT has been shown to improve blood flow and the delivery of oxygen to muscle tissue during and after exercise (2). Additionally, LCLT may reduce muscle soreness (3,5), increase androgen receptor density in muscle cells (6) and increase lean body mass in the elderly (7)
1. National Center for Biotechnology Information, U.S. National Library of Medicine. L-Carnitine L-Tartrate (Concept Id: C1337234) - Medgen - NCBI. [online] Available at: <**broken link removed**> [Accessed 8 July 2020].
2. Kraemer, WJ, Volek, JS, Spiering, BA, and Vingren, JL. L-Carnitine supplementation: a new paradigm for its role in exercise. Chemical Monthly 136: 1383-1390, 2005.
3. Spiering BA, Kraemer WJ, Vingren JL, Hatfield DL, al e. Responses of criterion variables to different supplemental doses of l-carnitine l-tartrate. Journal of Strength and Conditioning Research. 2007;21(1):259-64.
4. Kraemer, WJ, Volek, JS, French, DN, Rubin, MR, Sharman, MJ, Gómez, AL, Ratamess, NA, Newton, RU, Jemiolo, B, Craig, BW, and Häkkinen, K. The effects of L-carnitine L-tartrate supplementation on hormonal responses to resistance exercise and recovery J. Strength Cond. Res. 17:455-462. 2003.
5. Parandak K, Arazi H, Khoshkhahesh F, Nakhostin-Roohi B. The effect of two-week L-carnitine supplementation on exercise -induced oxidative stress and muscle damage. Asian J Sports Med. 2014 Jun;5(2):123-8.
6. Kraemer WJ, Spiering BA, Volek JS, Ratamess NA, Sharman MJ, Rubin MR, French DN, Silvestre R, Hatfield DL, Van Heest JL, Vingren JL, Judelson DA, Deschenes MR, Maresh CM. Androgenic responses to resistance exercise: effects of feeding and L-carnitine. Med Sci Sports Exerc. 2006 Jul;38(7):1288-96.
7. Pistone G, Marino A, Leotta C, Dell’Arte S, Finocchiaro G, Malaguarnera M. Levocarnitine administration in elderly subjects with rapid muscle fatigue: effect on body composition, lipid profile and fatigue. Drugs Aging. 2003;20(10):761-7.