Muscle Growth and mTOR
There's an acronym that's been shimmying its way into a lot of articles about weightlifting lately. It's mTOR, and unless you're a biochemist, the concept of it probably makes you appreciate how even really intelligent dogs can't seem to understand how the TV occasionally makes a doorbell noise.
You might have read that mTOR stands for the "mammalian target of rapamycin" and you wonder exactly which varmint this rapamycin dude is trying to plug with his bow and arrow and why.
Your confusion is well founded, but suffice it to say, mTOR is just another alphabet soup chemical, a "protein kinase" to be specific. It's hugely important, though, in that it's a regulator of cell metabolism.
Sometimes you want more mTOR and sometimes you want less. If you're a lifter, you generally want more, especially during and after workouts, because mTOR also controls protein synthesis and the more protein you synthesize, the more muscle you can grow.
Several things kick mTOR into action, including hormones, growth factors, protein intake, and mechanical loading, i.e., weight lifting. Certain substances also kick mTOR into high gear, especially when combined with mechanical loading. Prominent among these substances is phosphatidic acid or PA for short.
PA is the source of a lot of enthusiasm in the biochemical world, so much that it's spawned a lot of studies on how it affects weight lifting, practically all of which were consolidated into a review paper that was recently published in the journal Nutrition & Metabolism.
- The first study, conducted by Hoffman JR et al., recruited 16 resistance-trained men. They either ingested 750 mg. of PA or placebo over the course of 8 weeks while participating in a 4-day per week split routine. The team found a likely benefit from PA in increasing 1-RM (the most weight they could lift for 1 rep) squat and lean body mass (LBM).
- Joy JM et al. did a study similar to the one above, using a split group of 28 men who followed a 3-day per week undulating resistance program for 8 weeks. The big difference was that in this study, the participants were given 450 mg. of PA 30 minutes before their workout and another 300 mg. immediately post workout. The PA group gained a significantly greater amount of muscle (2.4 kilos, or 5.29 pounds) than the placebo group.
- Gonzalez AM et al. studied the effects of 750 mg. of PA on 15 resistance trained men following a 3-day per week resistance training program. Unlike the other studies, Gonzalez didn't find a difference between the placebo group and the PA group in muscle thickness of the rectus femoris, vastus lateralis, biceps brachii, or triceps brachii muscles. Neither did he find differences in 1RM squat, deadlift, or bench press between groups.
This was the one outlier in the PA studies, but Gonzalez and his team 'fessed up to several potential problems, things like lack of exercise supervision, possible poor dietary adherence, imperfect exercise selection for assessing maximal strength, the design of the exercise program, methods of assessing changes in muscle architecture, body composition, and training status of the participants.
- Andre TL et al. decided to test the effects of lower dosages of PA. They rounded up 28 men and divided them into three groups, one group receiving 250 mg. per day, one group receiving 375 mg. a day, and another group of suckers that got placebo, or zilch. Despite using lower doses of PA, the team found a likely positive effect on lean body mass and cross-sectional area of the rectus femoris muscle in the thigh in both the 250 mg. per day and the 375 mg. per day groups.
- Escalante G et al. recruited 18 strength-trained males and randomly assigned them to a PA group or a placebo group. The men trained 3 times a week for 8 weeks using an undulating resistance program. This study differed, however, in that the PA was combined with specific vitamins and amino acids (or metabolites of amino acids). The supplement-taking group gained a significant amount of lean body mass, along with increasing their 1-RM bench press and 1-RM leg press (compared to the placebo group).
It's pretty clear that PA helps regulate mTOR, and when you add resistance training to the mix, you up-regulate muscle protein synthesis. PA might also play a role in slowing down muscle protein breakdown, in addition to possibly helping fight catabolic conditions like cachexia (the muscle wasting associated with disease).
But, as scientists love to say, further study is needed. Regardless, it looks like PA might be a "useful strategy" for increasing muscle mass and strength when combined with resistance training.
Based on the studies, it looks like taking 750 mg. of phosphatidic acid one hour before training is the best strategy.