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protein-intake pattern, overuse injury

Protein-intake pattern & overuse injury - What protein-intake pattern might best boost recovery after overuse injury?

In light of the findings discussed in the previous article (‘Do questions about muscle soreness hold the key to quicker recoveries?’), in which protein-degradation rate waited patiently to peak until three days following muscular overuse, you might expect that the key time to ingest extra protein in hopes of preserving muscle contractile-protein content would be about three days after a severe bout of exercise. After all, why not take in extra protein when the muscles need it most – when they are breaking down protein at the highest rate? And since muscle contractile-protein content has little effect on the loss of strength observed for the first three days after overuse, why make a special point of taking on additional protein during that time period?

That is sensible and logical thinking, but in fact there is evidence that extra protein taken immediately after strenuous exercise is more important than extra protein ingested later. For example, in a study carried out at the Vanderbilt University Medical Center in Nashville, Tennessee, exercisers trained for a total of 60 minutes and then took in 10 grams of protein, eight grams of carbohydrate, and three grams of fat – either immediately after the exercise or three hours later. A key part of the story was that carbohydrate uptake by the leg muscles and whole-body carbohydrate utilisation were stimulated threefold and 44%, respectively, when the nutrients were taken right after exercise, as opposed to three hours later. Those are good things, because leg-muscle carb uptake can restore glycogen to leg muscles which are glycogen-depleted following prolonged exercise, and whole-body carb metabolism can provide energy for physiological recovery processes (“Postexercise Nutrient Intake Timing in Humans Is Critical to Recovery of Leg Glucose and Protein Homeostasis,” Am J Physiol Endocrinol Metab, Vol. 280(6), pp. E982-993, 2001).

“It is important to initiate protein intake very soon after exercise because such protein consumption can kick-start protein synthesis in the muscles”

What about the protein story, though? As it turned out, muscles achieved a net gain of essential and non-essential amino acids, the building blocks of muscle proteins, when the nutrients were taken on board right after exercise; when the nutritional supplement was utilised three hours later, there was a net protein loss in leg muscles. Although the supplement did not curb actual protein breakdown when it was consumed right after exercise, it did boost protein synthesis, elevating leg-muscle-phenylalanine-protein synthesis threefold, compared with waiting to eat (phenylalanine is a key amino acid utilised to create muscle protein). As the researchers concluded, it is important to initiate protein intake very soon after exercise, because such protein consumption can kick-start protein synthesis in the muscles which have been heavily involved in the exertion.

Admittedly, the degradation process is fairly limited immediately after overuse exercise (remember that it doesn’t reach a peak until after three days or so), but the basic idea is that you want to balance the already initiated breakdown process with as much protein synthesis as you can. In theory, the inevitable low point for muscle-contractile protein (reached after about seven to 14 days) will then be a higher low point, and the returns to normal of both strength and muscle protein will thus be quicker.

Those sceptical of the idea that quick protein intake after strenuous exercise might help recovery point out that the blood itself is fairly rich in amino acids, and that this source of amino acids could be adequate to get the muscles going on the road to protein synthesis again. However, in another study carried out at Vanderbilt University, researchers asked five female and five male cyclists to train for 60 minutes at about 75% of maximal heart rate on three different occasions. Immediately after exercise on each occasion, the cyclists consumed – in random order – one of the following three concoctions:

  1. 10 grams of protein, eight grams of carbohydrate, and three grams of fat,
  2. 0 grams of protein, eight grams of carbohydrate, and three grams of fat, or
  3. A placebo with no protein, carbohydrate, or fat.

And what happened?

When the 10 grams of protein were included in the post-exercise nutriment, plasma amino-acid levels shot up by 33%, leg-muscle extraction of phenylalanine from the blood soared fourfold, and leg-muscle protein synthesis exploded sixfold. In contrast, the two formulations with no protein (nos. 2 & 3 above) produced a net release of amino acids by leg muscles and a net loss of protein from the legs (“Postexercise Protein Intake Enhances Whole-Body and Leg Protein Accretion in Humans,” Medicine and Science in Sports and Exercise, Vol. 34(5), pp. 828-837, 2002). Ingesting protein right after exertion seems to make a major difference with regard to protein synthesis.

So far, we have looked at two examples of endurance exercise, so it’s reasonable to ask if the same situation prevails following strength training. In a recent investigation, scientists at the University of Texas Medical Branch in Galveston followed three female and three male resistance trainers after they engaged in a heavy bout of strength training. In one case the subjects consumed one litre of a mixed amino-acid (40-gram) solution right after exercise, in another they drank 40 grams of essential amino acids in solution, and in a final case they drank a placebo beverage with no amino acids (“Postexercise Net Protein Synthesis in Human Muscle from Orally Administered Amino Acids,” American Journal of Physiology, Vol. 276 (4 Pt. 1), pp. E628-634, 1999). Net muscle protein balance was negative with the placebo but strongly positive when the two amino-acid drinks were utilised. Interestingly enough, there was no significant difference in net protein uptake between the essential-amino-acid drink and the mixed beverage.

Now hear this

Although immediately after strenuous exercise seems to be a great time to ingest protein as part of an attempt to limit the ravages of overuse, there is actually a better time: shortly before exercise begins! In a unique study, also carried out at the University of Texas Medical Branch in Galveston, subjects participated in two trials in random order. In one case they consumed an essential-amino-acid-carbohydrate supplement immediately before exercise; in the other, they took in the same supplement – but immediately after their exertion.

Blood and muscle phenylalanine concentrations were increased by about 130% after drink consumption in both cases. Amino-acid delivery to the leg muscles increased during exercise and remained high for two hours after exercise in both situations. However, total delivery of amino acids (amino-acid concentration times blood flow) was significantly greater when the amino-acid beverage was swallowed before exercise, compared with after, and this was true both during exercise and in the first hour after exercise. In fact, phenylalanine uptake by the leg muscles was about two-and-a-half times greater when the amino supplement was taken before exertion (“Timing of Amino Acid-Carbohydrate Ingestion Alters Anabolic Response of Muscle to Resistance Exercise,” Am J Physiol Endocrinol Metab, Vol. 281(2), pp. E197-206, 2001).

Thus, although traditional wisdom calls for taking in protein right after exercise in order to enhance protein synthesis, the best time of all for athletes to take amino acids may be shortly before they exercise. Of course, the best overall strategy for limiting the loss of muscle contractile protein associated with overuse injury may be to ingest protein shortly before exercising – and then immediately afterwards, too (this could well be even better than merely taking in protein beforehand). One concern, though, is the effect such pre-exercise protein consumption might have on gastric well-being during exercise. It is imperative that an athlete try out various pre-exercise protein-intake patterns before attempting to process protein just in advance of a critical workout or major competition. The optimal amount of protein to take in before and after exercise is not known, and would certainly depend on body size, but amounts in the 25- to 40-gram range would not seem to be unreasonable.

“If you’re an athlete who trains strenuously, what should your daily protein intake be if you want to optimise muscular protein synthesis?”

Remember, though, that the periods just before and right after strenuous exertion are just small parts of the overall muscle-recovery time frame associated with overuse. During the rest of that time frame, it is also imperative that protein intake be adequate. The key question is: if you’re an athlete who trains strenuously, what should your daily protein intake be if you want to optimise muscular protein synthesis?

That is not an easy question to answer, because each individual – and thus each athlete – has unique energy and protein requirements (“Energy Needs of Athletes,” Canadian Journal of Applied Physiology, Vol. 26, Suppl: S202-219, 2001). As a result, the values reported in the scientific literature for the minimum recommended protein intake for non-athletic adults have an incredibly wide range of 0.39 to 1.09 grams per kilogram of body weight (“Protein and Amino Acid Requirements of Adults: Current Controversies,” Canadian Journal of Applied Physiology, Vol. 26, (Suppl: S130-140, 2001). Basically, the current, reasonable belief is that athletes engaged in regular, strenuous training may need about 1.6 to 1.8 grams of protein per kilogram of body weight per day (“Beyond the Zone: Protein Needs of Active Individuals,” Journal of the American College of Nutrition, Vol. 19 (5 Suppl): 513S-521S, 2000). Caveats are that athletes prone to overuse injury might need more than this, and you should be aware that many questions about optimal protein intake for athletes need to be resolved. Total energy intake, carbohydrate availability, exercise intensity, duration, and type, protein quality, training history, gender, age, and the timing of protein intake can all have an effect on protein requirements, so it is a very complex area.

The good news

As long as you have a fairly typical western diet and you are not deliberately restricting your food intake in the belief that “thinner is better”, your protein intake is probably fairly good. If you weigh 60 kilograms (132 pounds), for example, a protein-intake level of 1.7 grams per kilogram would have you shooting for 102 total grams of protein per day, which could be met merely by taking on three ounces of meat (21 grams protein), three ounces of fish (21 grams), one glass of milk (8 grams), one cup of oatmeal (6), two cups of rice (18), three cups of mixed vegetables (15), and two ounces of cheese (14). A strapping 80-kilo (176-pound) athlete would only need 34 additional grams of protein, which could come from one and one-half extra cups of rice (13 grams) and an extra three-ounce slab of fish (21). Obtaining adequate protein to clamp down on contractile protein loss is not that difficult.

The bottom line? To keep your muscle contractile protein levels up to par and reduce the risk of long bouts of reduced muscular strength associated with overuse, train smart, take in protein before and after you exercise, and make sure your diet habitually contains adequate amounts of protein.

Jim Bledsoe

protein-intake pattern, overuse injury