Effects of d-aspartic acid on testosterone and training outcomes in a resistance trained population : findings from an acute dosing study, and a three-month training study

Previous research has demonstrated the effectiveness of the supplement d-aspartic acid to increase testosterone levels in infertile men. With this supplement readily available on the market, supplement companies are capitalising on the purported benefits to improve the resistance training goals of strength and hypertrophy. There is a requirement for more research to fully elucidate these claims within the context of a resistance trained population, and investigate the proposed mechanisms of action. Thus the effectiveness of the supplement d-aspartic acid to improve resistance training gains in resistance-trained men was studied throughout this thesis. This was achieved by 1) observing changes in testosterone over a 2-week dosing study and 2) investigate any testosterone-mediated improvements in strength, power, hypertrophy and neural adaptation over a three-month training study. A secondary objective was to clarify if any relationship exists between gonadal hormones and training related outcomes. Study 1 investigated three dosages: placebo, three grams and six grams of d-aspartic acid, taken daily throughout a two-week combined supplementation and training protocol. No changes in hormones were detected in the three-gram group. Participants within the six-gram group experienced significant reductions in both total testosterone and free testosterone. This reduction suggested that the higher dosage of d-aspartic acid was affecting negative feedback mechanisms within the hypothalamic-pituitary-gonadal axis or potentially over accumulating within the testes, causing disruption to testosterone production. As this was the first study to implement a higher dose of six grams per day, it was unknown what may occur if this dosage was consumed over a longer timeframe. It was important to explore the effects of this dosage further within the context of a long-term training study. Study 2 implemented a 12-week periodised training protocol combined with six grams daily d-aspartic acid supplementation. The d-aspartic group experienced a reduction in estradiol, with no observed change in testosterone. Additionally, supplementation caused an increase in the early rate of force development within the quadriceps muscle. Peripheral neural adaptation of the gastrocnemius muscle was observed in the placebo group, but not in the d-aspartic group. Both groups increased hypertrophy and, strength within the quadriceps and calf muscles to a similar extent. No relationships were observed between testosterone change and hypertrophy or isometric strength change. A positive relationship was observed in change scores between estradiol and h-reflex recruitment gain of the soleus and gastrocnemius muscles. A negative relationship was observed between estradiol and the neural excitability of the soleus muscle, at the level of the motoneuron. Both relationships suggested that reduced levels of estradiol may be negatively impacting spinal plasticity within the calf muscles. The long-term supplementation of d-aspartic, even at the higher dosage of six grams, had no positive influence on testosterone levels in resistance trained men. The reduction observed in estradiol, while not affecting strength or hypertrophy, may have disrupted improvement in calf spinal excitability within this population. This thesis supports and expands upon the current d-aspartic acid literature in resistance trained men. Results suggest that supplementation is ineffective at increasing testosterone levels, and has no ability to yield greater improvements in strength or hypertrophy from 12 weeks of resistance training. D-aspartic acid appears to have some interesting effects on neural adaptation and rate of force development that warrant further investigation to determine if it is a viable supplement for the improvement of quadriceps power

Alien Registration- Melville, Charles W. (Houlton, Aroostook County)

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Topography Changes during Bedform Development

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv