The role of nitric oxide in cardiovascular health has been well described in literature. The effect of nitric oxide on exercise performance, however, has not been clearly elucidated. During a 5 week progressive strength training program, volunteers were given a supplement containing 1 g arginine and 1 g ornithine, or a placebo, each day. The results suggest that the combination of arginine and ornithine taken in conjunction with a high intensity strength training program can significantly increase muscle strength and lean body mass [21
]. Campbell et al [22
] observed that arginine and α-ketoglutarate positively influenced 1 RM bench press and Wingate peak power performance in trained adult men. Arginine was also reported to improve peak power significantly in non-athlete men [23
]. Conversely, a number of studies have failed to identify any beneficial effect of arginine supplementation. Liu et al [24
] investigated the effect of three day supplementation of 6 gram of arginine on performance in intermittent exercise in well-trained male college judo athletes and found the supplementation had no effect on performance. Similarly, it has been shown that supplementation of arginine aspartate for 14 days prior to marathon run did not affect the subsequent performance in trained runners [25
In the present study, we demonstrated a statistically increase of 16.7% in AT after one week of supplementation with L-arginine and antioxidants. The observed increase in AT was further validated by the increase of 22.51 watts of power output at AT. Based on our data, the supplementation group increased their power output at threshold. Therefore, these physiological changes should be associated with prolonged exercise and a higher work rate due to arginine and antioxidant supplementation. These data obtained were also remarkable in that every subject in the supplemented group demonstrated increases in anaerobic threshold, while none of the subjects in the placebo group demonstrated any increase.
Youthful, healthy, athletic individuals generally have a healthier NO system, compared with aging, unhealthy, sedentary individuals [9
]. In humans, exercise capacity declines with advancing age and many individuals lose the inclination to participate in regular physical activity. In healthy adults, arginine can be synthesized in sufficient quantities to meet most normal physiological demands with the rate of de novo synthesis remaining unaffected by several days of an arginine free diet [26
]. Our study subjects had an average age >55 years, while other studies included young athletes [24
]. This difference may explain the significant improvement on AT in our study.
As in other studies [26
] we did not see an increase in VO2max
, which is defined as the highest value of minute ventilation attained and measured during incremental exercise despite the increase in anaerobic threshold. A possible reason for this lack of increase could be the fact that VO2max
, as its name implies, is also a maximum effort measurement and, therefore, is effort dependent. By contrast, anaerobic threshold is a more sensitive test to measure changes in exercise performance because it is a submaximal exercise measure that is not effort-dependent. In a recent review in Journal of Applied Physiology [28
], Saltin stated that VO2max
is limited by cardiac output. With the current study design, we would not expect to see an increase in VO2max
because there is no reason for the cardiac output to increase in these athletes.
It is unclear whether the increase in AT that we observed in this study was due to L-arginine alone, or a combination of the nutrients. Pre-treatment with vitamins C and E has been shown to block vascular dysfunction caused by a high-fat and high-sugar diet [29
]. L-arginine, vitamin C, and vitamin E promote a healthy cardiovascular system by supporting enhanced NO production [15
]. NO formation is further increased by the recycling effect of L-citrulline to L-arginine and the fact that L-citrulline is taken up into cells by a mechanism independent of that for arginine [30
This study was performed in trained athletes who were without any cardiovascular problems. The role of L-arginine supplementation in cardiac patients remains controversial. Furthermore, it is also unclear if arginine supplementation in the sedentary population can have the same results. Further research will be needed to assess the interaction of these factors and to determine the effects of prolonged administration of arginine and antioxidants on exercise performance.