Hypertrophy Mechanisms [3/3]: Metabolic Stress - Training Strategies and Techniques [Part 2/2]


Training strategies

1. Repetition schemes
Moderate repetition schemes rely heavily on anaerobic glycolysis (1,2). This results in a significant buildup of metabolites. Buildup of these metabolites has been shown to have a significant impact on anabolic processes (1,3). There may be a maximum threshold for tension-induced hypertrophy, above which metabolic factors become more important than additional increases in load (1).



Moderate repetition ranges also maximize acute cellular hydration. During moderate rep training, the veins taking blood out of working muscles are compressed while arteries continue to deliver blood into the working muscles. This creates an increased concentration of intramuscular blood plasma. The buildup of fluid in the interstitial spaces causes an extracellular pressure gradient, known as the ‘‘pump’’ (1). This is augmented by the accumulation of metabolic byproducts, which function as osmolytes, drawing fluid into the cell (1,4).

2. Muscular failure

Training to failure is hypothesized to activate a greater number of MUs (5).

Henneman’s size principle (of motor unit activation) states that motor units are recruited in an orderly fashion from smallest to largest with increasing requirement for force generation (6,7). If a submaximal (below 1RM), contraction is sustained motor units that were initially recruited fatigue, thus producing less force or cease firing completely, and need the recruitment of additional motor units (8). This provides an additional stimulus for hypertrophy (9).

It follows that as the repetitions are repeated or as the set progresses to the point of failure, near maximal motor unit recruitment to sustain muscle tension is achieved (10).

3. Intensity

Lower loads (30% RM) lifted to failure result in similar hypertrophy as heavy loads (80% RM) lifted to failure (at least in recreationally active subjects) (11). Lifting lighter loads, so long as fatigue is induced, leads to roughly equivalent hypertrophy and strength gains (11,12,13,14,15).

Also, lighter loads lifted to the point of failure result in a similar amount of muscle fiber activation compared with heavier loads, and both fiber types are stimulated to a roughly equivalent extent (11,16).

4. Time under tension

Time under tension has been shown to stimulate optimal growth (17). The time under tension during lower repetition sets appears to be suboptimal for hypertrophy.

Increased time under tension may enhance the potential for microtrauma and fatigueability. This would seem to have greatest applicability for hypertrophy of slow-twitch fibers, which have greater endurance capacity than fast-twitch fibers and thus would benefit by increased time under tension (1).

5. Rest Interval

Short rest intervals (30s) tend to generate significant metabolic stress leading to metabolite buildup, which enhance anabolic processes (1,18), however this compromises mechanical tension. Moderate rest intervals (60s) appear to provide a satisfactory compromise between long and short rest periods for maximizing the muscle hypertrophy (1).

Moderate rest (60s) induces greater hypoxia, heightening the potential for increased muscular growth (1,19). Moderate rest also is associated with a greater metabolic buildup, spiking anabolic hormonal concentrations after exercise (1,20).

Training techniques

1. Drop sets

Drop sets involve performing a set to muscular failure and then immediately reducing the load for another set (21). Multiple drops can be done in this fashion. The more multiple drops the greater the fatigue for the whole muscle will be (22) and the greater the metabolic stress for slow twitch fibers. Note that fast twitch fibers (for a giving load) are all involved when failure is reached. Drops sets allow for an increased time under tension, more metabolic stress and ischemia.

2. Ascending sets

This is sort of the opposite of drop sets. Rather than dropping the weight each time, the weight is increased every time as the repetitions decrease (12+10+8+6 reps).

Ascending sets might be beneficial to delay their fatigue response (rapid with low reps) and allow them to build up lactate until muscular failure where they are maximally recruited (size-principle). Slow-twitch fibers will get optimally stimulated as well anyway with long periods under tension.

3. Supersets

Supersets are 2 exercises or more performed in succession without rest (21,27). Supersets can performed for the same muscle, or for opposing muscles such as in an agonist-antagonist paired set (APS) training.  Because there’s practically no rest between sets, this may increase muscular fatigue and metabolic stress (28), the same as with drop sets with moderate to high repetitions. Supersets should have be done to failure (every exercise).

4. Blood flow restriction

Occlusion training causes blood flow restriction and involves obstructing blood flow to the veins, but not the arteries so that they continue to deliver blood to the limb (25,26). In other words, blood gets in but struggles to get out. This is done using knee wraps for the legs, and wrist wraps for the arms (25).

Blood flow should not be completely restricted, it should be restricted at about 50-70%. A scale of perceived pressure should be used, for example from 1-10 (10-100%). During BFR, muscle cells reach become so full of fluid that they have to grow or die (29). BFR increase muscle cell swelling, the low oxygen level and accumulation of blood increase fast-twitch muscle fiber recruitment (26,29,30,31) and increase blood lactic acid levels 2 which stimulate protein synthesis (32).

Shorter rest periods (30 seconds) are optimal (32). Interestingly, the concentric action is more important than the eccentric action (33), which is the opposite of traditional training where the eccentric causes more damage and increased protein synthesis. This is because high forces can be generated at a relatively low metabolic cost in eccentric contractions compared to either isometric or concentric contractions (34).

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