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Informations sur les Sciences de l'Entraînement Sportif

Sports Performance and Antioxidants

by A. Manolova | 17 April 2019

antioxidant, vitamin C, ascorbic acid, VO2MAX, endurnace, reactive oxygen species, free radical, sport, performance, life, stress, recovery, expectancy

Any physical activity stresses the body. The level of this stress depends mainly on the intensity and duration of the activity. In the body, metabolic stress results in the production of reactive oxygen species (free radicals, for example). It is a natural physiological phenomenon that is related to the normal metabolism of oxygen. To defend against attacks caused by these reactive oxygen species (ROS), the body has different systems that can fight at the cellular level. But when the ability of the body to fight oxidative stress is exceeded by the production of ROS, the cellular structures (even DNA) can be damaged. However, regular stimulation of ROS through physical exercise can stimulate the expression of certain genes and stimulate endogenous antioxidant systems, which in the long run can have beneficial effects in the prevention of certain chronic diseases (cancer, cardiovascular diseases, for example).

As we have already discussed in several previously published articles on the site, VO2MAX is one of the best indicators of overall cardiovascular fitness and one of the best predictors of mortality risk. The higher it is, the lower the risk of all cause mortality. Thanks to frequent stimuli, metabolic and cardiovascular systems gain in efficiency and ultimately improve VO2MAX. Of the metabolic improvements, the mitochondrial content (ie, the number of mitochondria) is one of the most important factors. Mitochondrial biogenesis is triggered mainly by PGC-1α, a protein encoded by the PPARGC1A gene. However, PGC-1α is stimulated among others by the ROS. So, does it make sense to supplement antioxidant when our goal is to increase one's cardiovascular endurance ?

The Study

In an attempt to answer this question, a team of Spanish researchers has studied the impact of vitamin C supplementation on the improvement of VO2MAX and endurance capacity during several weeks of training in cardiovascular endurance in men and in rats.

For this study, 14 sedentary men (VO2MAX < 43 ml/kg/min) participated in the 8-week study. They were randomly divided into two groups : a training group without supplementation (n = 9) and a training group with supplementation of 1 gram of vitamin C each day at 9h00 (n = 5). Before and after the 8 weeks of the protocol, all participants evaluated their VO2MAX on a cyclo-ergometer during a maximal effort test and performed a blood test. Then, 3 times a week during the 8 weeks, the participants performed a 40-minute session at a constant pace between 10:00 and 11:00. The starting intensity was 65% VO2MAX, with a 5% increment every two weeks until reaching 80% VO2MAX.

For the animal part, the researchers used 36 Wistar adult male rats which they divided into different groups and which they had done between 3 and 6 weeks of training (5 times a week), with or without Vitamin C supplementation (dose corresponding to 4 times that administered to men). Once the experiment was complete, the rats were killed and muscle and blood tests were performed.

Results & Analyzes

In both men and rats, vitamin C supplementation significantly increased plasma concentrations of ascorbic acid. No changes were observed in the non-supplemented groups.

The main results of this study show that the administration of vitamin C attenuates the effects of training in men and rats. Concerning VO2MAX, in men, the group that did not supplement with vitamin C improved its VO2MAX by 22% (from 38.2 to 46.6 ml/kg/min) while the vitamin C supplemented group did not improved only by 10.8% (from 41.2 to 45.6 ml/kg/min). For rats, the finding was the same, the group without vitamin C improved by 17% while the group with vitamin C only 4.7%. Regarding the endurance capacity (exercise time to exhaustion) measured in rats, those who were supplemented with vitamin C increased from 101.2 to 128 minutes (ie, + 26.5%) while those who did not take vitamin C increased from 99.2 to 284.3 minutes (ie, + 186.7%).

ROS formed during exercise significantly increased the concentrations of 2 antioxidant enzymes (Mn-SOD and GPx) in skeletal muscle. However, this adaptation was non-existent for the groups of rats supplemented with vitamin C. In addition, the muscle concentrations of PGC-1α significantly increased after training for groups of rats that were not supplemented with vitamin C (Fig. 1). These results are confirmed by concentrations of cytochrome C, a marker of mitochondrial content in muscle. Concentrations increased in trained rats, but not in untrained rats and those supplemented with vitamin C.

Figure 1. PGC-1α concentration in untrained, trained and trained and supplemented in vitamin C rats. *Significatively différent from untrained groupe (p<0.05).

Practical Applications

It is important to take into account that reactive oxygen species (ROS) are not systematically harmful to cells. Their production in response to exercise is useful for adapting muscle cells by modulating gene expression. In addition, the body naturally produces antioxidants in response to this secretion of ROS. The ingestion of vitamin C inhibits these processes and subsequent adaptations which result in an attenuation of the metabolic and cardiovascular response to training.

As with other recovery-related phenomena (such as inflammation), it is important to distinguish between acute and chronic. Chronic stress that could be due to a poor ability to recover from too intense training and/or a bad lifestyle (alcohol, tobacco, etc.) and/or a social environment that is too stressful can lead to ROS too high that will negatively affect health (cell, DNA, etc.). It is therefore important to be informed and supplement (or be advised to) intelligently without succumbing to the marketing sirens. The relevance of a supplement in relation to its real needs and its practice, its dosage and the timing of taking are all parameters to consider before using it.

References

  1. Gomez-Cabrera M-C, Domenech E, Romagnoli M, Arduini A, Borras C, Pallardo FV, Sastre J and Vina J. Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance. Am J Clin Nutr 87 : 142-149, 2008.

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