Physical activity is becoming more and more common in the population. Some physical activities require an adapted pace of life or diet. Some people are turning to natural food supplements. Tea is in the mouths of some athletes, but does it really improve sports performance ?
Physiologically, the practice of a physical activity will use our muscles. The ones we are interested in are called striated skeletal muscles. These are muscles that can be contracted by will. These muscles are connected to our bones by tendons, fibrous structures whose health is important for movement.
However, having a lot of muscles would be too simple to be effective! Muscle needs energy to function. One molecule allows this: ATP. ATP is obtained by the degradation of sugars and lipids: this is the oxidative metabolism. This metabolism is active in an "aerobic" condition, i.e. in the presence of oxygen. During effort, the respiratory frequency will increase to facilitate the entry of oxygen. The heart rate will accelerate to increase blood flow to the muscles and to speed up the delivery of nutrients and oxygen. Muscle blood vessels will dilate to optimize blood flow.
During long duration and/or high intensity efforts, oxidative metabolism generates waste products and can be limited by the lack of oxygen/blood flow/nutrients. These wastes can be free radicals, oxidative molecules that will damage muscle fibers (inflammation, death of myocytes or muscle cells, etc). They can also be metabolic products such as lactic acid, which causes muscle soreness when it is in excess in the bloodstream (acidosis). With a less active metabolism, the accumulation of damage to the muscles and the appearance of aches and pains, physical effort is more laborious and one is less efficient.
Breaking down lipids and oxidizing molecules = better performance ?
Among the studies on tea and sports, it is therefore not surprising to see that what is most studied is the antioxidant effect of tea to prevent the appearance of oxidizing molecules during effort and the improvement of the oxidative metabolism of lipids. In an American study of young sprinters, blood tests after drinking green tea extracts for 4 weeks revealed a decrease in the concentration of the main oxidizing molecules appearing during intense efforts. On the other hand, the study did not correlate this reduction in the production of oxidizing molecules with an improvement in the speed or resistance of the sprinters.
Da Silva et al. monitored muscle recovery after physical exercise and consumption of green tea extracts. This 15-day follow-up was carried out in young people, with regular physical activity of about 30 minutes several times a week. It would seem that the blood tests show a decrease in muscle damage by the decrease of oxidizing molecules. On the other hand, the study showed that the tea extracts did not decrease the muscular fatigue of the participants which was caused by the exercises. However, black tea extracts seem to decrease muscle fatigue after 24 and 48 hours of physical exercise while decreasing oxidative stress for young volunteers with regular physical activity (at least 3 times a week).
I could continue to list a good number of publications on the reduction of oxidative stress markers such as these soccer players who ingested pure green tea polyphenols, but these studies have, for the most part, not correlated an improvement in metabolism and a limitation of oxidation to better physical performance.
One may then wonder what beneficial effects for sport have been observed?
The power of muscles, tendons and tea ?
In a randomized Japanese study on 30 non-sporting people, Aizawa et al. demonstrated that theaflavines and catechins injected daily for 8 weeks modified the distribution of body weight. The percentage of subcutaneous fat decreased (5%) and the proportion of skeletal muscle increased (1 to 3% depending on the dose). It should be noted, however, that while these altered proportions were observed, there were no physical tests performed to see whether or not the physical practice of the participants was improved by the pure polyphenols injected.
The increase in leg muscle mass was also found in a 2012 Japanese study on daily catechin intake and walking (twice a week) of women over 75 years old with sarcopenia. This increase in leg muscle mass was associated with a very slightly higher walking speed than in patients not consuming catechins . A very recent study has also shown that bringing muscle cells into contact with green tea extracts could induce the formation of skeletal muscle fibers.
If the proportion of skeletal muscle fibers can condition an effort, healthy tendons are also required. A study in rats with or without tendinitis in the Achilles tendon (heel) showed that green tea extracts could reduce the activity of molecules responsible for inflammation and fragility of tendons in case of tendinitis. While this is not direct evidence of the strengthening of tendons by tea, it can be assumed that tea could have a protective effect on tendons limiting the aggravation of trauma that occurs during effort.
It has been found that the effects of tea on striated skeletal muscles and tendons are present but extremely modest. There is still the concern to correlate improved performance and tissue modifications.
So, where would it all fit?
And dust, you'll take ...
In health research, it is also important to look at the doses and products used in the different studies. What we see in the different studies of tea and sports is that researchers most often use pure powdered polyphenols and powdered tea extracts.
However, a tea infusion will not necessarily contain the full amount of polyphenols present in the leaf. Indeed, the preparation of tea conditions the diffusion of these molecules in water (temperature, duration of infusion, type of water, etc). Moreover, in the organism, it is not said that the absorption of natural polyphenols from the leaf is as good as that of pure polyphenols in powder form.
In the different studies, the levels of pure polyphenols and tea extract powder are extremely high, on average 400 to 600mg / dose. However, in my article on the molecular composition of tea, if I compile the articles I have selected, the total concentration of polyphenols is usually less than 100 mg/g of leaf. If one takes into account the limitations that I stated earlier, not sure to arrive at these doses with the morning mug alone! Worse, some publications on tea and sports have been based on pure catechins. In a tea leaf, the catechin level rarely exceeds 10 mg / g of leaves. It's quite simply a large carafe that should be drunk!
Unfortunately for sports and tea addicts, it is not so obvious to say that tea would improve our physical performance:
- Use of pure extracts in powder form that are highly concentrated compared to the reality of the infused leaf.
- tenuous correlation between muscle/metabolism effects and physical performance
- Too great a disparity of disciplines (sprinting, resistance, etc) and preliminary physical conditions (elderly already weakened, sports liability, etc) in the scientific literature.
The number of unknowns accumulates too many to be able to conclude the benefits of tea on our physical practices. It should be noted, however, that the research is young (a jump in the number of publications is surely at the beginning of 2010!) and that it has the merit of being carried out in most cases with volunteers.
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