What is better? Low weight HIT or high weight HIT?

By Shephen Shocki, Alki X Gym trainer.

This HIT (High Intensity Training) study was performed by Canadian researchers, looking to show the differences in muscle protein synthesis (an indicator of muscle growth), as well as a few other indicators of muscle growth. They used healthy college aged men and had them perform either light weight exercise (low load, high volume) to failure or heavy weight exercise (high load, low volume) to failure. They also had a group match the amount of work they did to the heavy group, which means that they calculated the amount of work done (repetitions X load) in the heavy group and then had the work-matched group (WM) perform a higher number of reps with a lighter weight until they had reached the same level of work, just without muscle failure. While that group did see increases in muscle protein synthesis, they weren’t anywhere near the levels seen in the other two groups so I won’t be talking about the WM much.

In a nut shell, the study showed that working until failure produced a greater increase in all metrics when compared to the non-failure group. So that’s good for X Gymers, because this shows that our style causes more muscle protein synthesis, which means more muscle toning. Interestingly, in the heavy group, muscle protein synthesis was the highest initially, but when you looked at 24 hours after the exercise, the light weight group was the only one who sustained their elevated levels. So while going really heavy gives you more benefit initially, those levels aren’t sustained. Whereas in the light weight group, levels remained elevated at 24 hours and probably stayed elevated for longer than that, seeing as how MYO synthesis was still elevated 199% at 24 hours post exercise!

Side note: they differentiate between two kinds of protein synthesis: myofibrillar (MYO) vs. sarcoplasmic (SARC). MYO protein synthesis is the creation of new contractile fibers (actin and myosin), which means you are getting an increase in tone as well as strength. SARC is more characteristic of fluid being pulled into the muscles, which results in an increase in tone but not necessarily strength.

Because both the light and heavy groups reached failure, they both saw big increases in protein synthesis, but what explains the difference between the two groups? The authors attributed it to the total volume of the work done. The lightweight group did ~ 92 reps, and the heavy group did ~19. This shows pretty clearly that heavy weights/low reps is not the most effective way to tone muscle, but that light weight high volume (so either high number of reps or a high time under load, as is the case with X Gym style training) is more effective. While the heavier load did produce greater increases in certain metrics they were never sustained, and the lightweight group ultimately saw a greater increase when time is factored in. This is especially true with the X Gym style, which takes even less time than the style of workout used in this study.

So how does this apply to us? Well, considering our style of training would fall into the low load, high volume group I would say it applies quite a bit. Mainly this is a great tool to explain to clients exactly why it is that our style works so well. You could say that the evidence supports that high volume training to failure results in the greatest increases in protein synthesis, which means the greatest increases in tone and strength. You can explain that the muscle failure gives you the bulk of the benefit, but the lightweight and high load we use adds additional benefits.

Side note: One of the things the authors point to as far as the additional benefits go is the fact that this style of training causes the muscle to be worked in a state where there is not a lot of blood flow to the muscle. (This is called occlusion training; you limit the blow flow to an area and work it under a low intensity. Studies have shown that even just walking on a treadmill with a belt around your leg will result in significant increases in muscle protein synthesis.) When you contract a muscle, it pinches the blood vessels that are feeding blood to it, and you get occlusion. X Gym style workouts are more or less just one huge contraction, so you are occluding blood flow to that area the entire time. When you relax the muscle blood rushes back in, which can result in a light headed feeling, or "head rush," which many X Gymers comment on, clearly showing this beneficial training style at work.

The only issue I have with this study is the size. 15 participants divided into three groups means you only have 5 men in each group, which is tiny. Nearly all of their findings were statistically significant (p < .05), but I still think to show real significance, they would need to do another study with more subjects. One thing these authors point out that I absolutely loved, was that they said while all these things are interesting and show important correlations, at this point that is all they are: correlations. Correlation is not causation and the two should never be confused. Quote of the day: “… acute scientific studies simply supply the framework on which to build future training studies upon to directly test if a cause-and-effect relationship does in fact exist.”