How-to: Metabolic Stress
TL; DR Version:
1) The ability to generate mechanical tension still has the greatest impact on muscle gain.
2) Metabolic stress is a second method of generating mechanical tension using longer sets with more moderate weights.
3) The accumulation of metabolic stress chips-away at the active muscle fibres ability to keep working – thus approaching failure.
4) Generating mechanical tension through metabolic stress (repetition-induced fatigue) is an effective complimentary tool to stimulate muscle growth in absence of load-induced muscle fatigue.
While metabolic stress is likely one of the most recognizable feelings in resistance training, the localized muscle burn associated with a challenging set of exercise should actually be more of a strategic tool than most realize.
Mechanical tension (the totality of stress experienced by the working muscle fibres during a resistance training set or session) is the primary driving force in long term muscle gain. Other sources of muscle building stimuli (metabolic stress and muscle damage) may contribute some independent benefits, but as referenced from the previous blog, ultimately, they contribute more to an intensification effect and generation of mechanical tension in absence of the ability to optimally mind-muscle connect or to continue lifting weights on the heavier side of the loading spectrum.
To shed some light on metabolic stress, let’s define some terms.
Metabolism is the umbrella term used to describe the biological building or breaking down of energy molecules or tissues within the body. Anabolism is the building of molecules of tissues, and catabolism is the breakdown of molecules or tissue. In reference to metabolic stress, each time a muscle contracts it demands energy to complete that action. The body has several means of delivering the necessary energy to complete muscle contractions, two of which are extremely fast (to match the speed-of-energy demand of resistance training), whereas the final is more sustainable to provide energy in more relaxed environments (rest) or aerobic cardiovascular training (think long-distance running).
One of these fast energy delivery systems breaks down the sugars found in our muscle. This is a very rapid process that has a trade-off for how quickly it can provide energy for instantly required action (muscle contraction), by also creating unwanted biproducts that accumulate over the duration of an exercise set or session. These biproducts are slowly shuttled away and recycled by the body, but in the short term (say an exercise set), accumulate within the working muscle. As the set duration progresses, eventually the amount of metabolic biproducts of energy production accumulate to the point where it actually inhibits those muscle fibres from continuing to contribute to the set. Thus, metabolic “stress” or accumulation serves as another method of creating a challenge to the muscle capable of triggering it to grow upon recovery.
Now, there are drawbacks to centering entire workouts around generating metabolic stress. While it is an effective method of intensifying exercises to create mechanical tension (as referenced in previous blogs, when metabolic stress inhibits active muscle fibres – other fibres must take on more workload), there is a finite amount of weight that can be lifted to get a muscle working long enough to enter this metabolically stressful state. We must sacrifice the total weight we’re lifting per exercise in order to be able to perform enough repetitions to demand the sugars be broken down to provide energy to the working muscle.
Usually what this looks like is four sets of 8 to 12 or sometimes even more repetitions (in the case of something like an extended or drop set). This amount of work (and in all reality, pain tolerance), can get quite mentally fatiguing. In a similar way to the hard work demanded of a trainee to genuinely approach the mechanical tension required to optimize muscle growth using higher weights, we also must be mentally engaged enough to withstand higher volumes of exercise with more intra-set pain in order to get the muscle to the point of adaptable challenge. Therefore, it requires an intelligently chosen amount of metabolic stress and pure load-induced mechanical tension exercises that can help optimize muscle building, and also, training session economy.
This is an important concept because load-induced training has a higher capacity for simultaneously increasing a trainee’s strength while building muscle. Load-induced mechanical tension (especially once the mind-muscle connection has been refined) help raise the ceiling of possible loading for all exercise stimuli (mechanical tension, metabolic stress, and muscle damage). When a metabolically stressful set produces muscle failure, it could be that there was a chip-away effect on the active muscle fibres as opposed to a genuine full system failure. Enough fibres may have been inhibited by the metabolic stress accumulation such that the remaining available fibres may not have been sufficient to lift the weight. This is in contrast to a load-induced mechanical tension set approaching failure due to a much higher percentage of the muscle fibres failing at once. We will dig into this at a later date.
Tying these concepts together, an effective muscle building workout likely has some combination of exercises that prioritize weight-centric mechanical tension induced sets taken close to failure and others that prioritize approaching muscular failure via metabolic stress. An entire workout emphasizing only one style of exercise may also be effective, but in the long term, might not be the most optimal.
Best,
Eric