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2) Time Under Tension: If a high intramuscular tension represents an uppercut, a long time under tension is kinda' like hitting your opponent 60-80 times in a round. The more often you hit your adversary, the more potential damage you can cause.
If a set lasts longer, the time spent causing muscle damage is more important and thus can lead to more growth stimulation. The problem is that there's an inverse relationship between the magnitude of the tension and the time that it can be sustained: if you shoot for a very long set, you won't be able to do the set under a lot of tension.
So while you might spend a lot of seconds working at causing muscle damage, you're actually not causing a lot of damage per second. You can bitch-slap an opponent a thousand times, but it won't knock him out! Just like with tension — increasing the time under tension of a set will lead to more growth stimulation, but only if the tension level stays relatively high.
3) Blood Vessel Occlusion, Metabolite Accumulation, Hormonal Output: You might have heard of "kaatsu" or tourniquet training. It's a training method that relies on lifting light weights (20-30% of your maximum for 15-30 reps) while wearing a special cuff that's tightened up around the proximal end of a limb to restrict blood flow to the muscle.
Studies have shown that despite the light weights being used, the muscle growth response is as big as lifting heavy weights (80% and more). The reason is the blood occlusion, which has been shown to create a deprived oxygen state (since blood flow to the muscle is limited, so is oxygen transport). This leads to an accumulation of lactate which increases the production of both hGH (growth hormone) and IGF-1 (Takareda et al. 2000).
The lack of oxygen (hypoxic state) and increase in acidity has also been shown to increase the recruitment of fast-twitch muscle fibers (Shinohara and Moritani, 1992). In fact, oxygen restriction to the muscle increases fast-twitch recruitment, firing rate, and spike amplitude (Yasuda, 2005).
Finally, exercise with restricted oxygen/blood entry in the trained muscle also leads to the production of Reactive Oxygen Species (ROS), which increase muscle satellite cell activation and proliferation (two key phenomenon involved in the muscle growth process).
The good news is that you don't have to use kaatsu training (which can be risky) to create this oxygen/blood flow restriction to the muscle. Sustained muscle tension (as in never allowing a muscle to relax during a set) can make muscle hypoxic even without external occlusion (Bonde-Peteron et al. 1975, Mitchell et al. 1980).
A recent study compared several training protocols' effects on oxygen levels during the execution of an exercise. With kaatsu training, oxygen levels were at around 22% of the rested/normal state, compared to 32-35% for normal, heavy training — a difference that can explain the efficacy of kaatsu training.
However, they also found that performing sets without blocking blood flow, but using a 303 tempo and never allowing the muscles to relax during the set (always flexing as hard as possible during every inch of every rep) with 50-60% of the maximum performed to failure, led to oxygen levels of 23-24%. Lactate, hGH, and IGF-1 levels were also the same as with kaatsu training.
The moral of the story is that constant tension exercises can build size and strength despite using relatively light weights and even if muscle damage is fairly low. However, if the muscle is allowed to relax during the set, oxygen and blood will flow into the muscle and you won't reach optimal benefits.
So, we could say that muscle growth can be stimulated by:
1. Heavy lifting (4-6 reps), which promotes a high rate of mechanical damage/protein degradation.
2. Relatively high reps (up to 12-15 for the upper body and 15-20 for the lower body), which promote a high mechanical degradation due to the combination of moderate time under tension and intramuscular tension magnitude.
3. Constant tension sets. To do these properly, you must flex the target muscle hard during every inch of every rep. You can never allow the muscle to relax. This means no rest between reps either. This method is best kept for isolation exercises.
Hvad mener I om dette..? Fyr jeres holdninger og indtryk af..?
Interessant imo og noget jeg må eksperimentere med ved de næste træninger.. Specielt omkring iso-øvelser..







