Read on to find out all about metabolic stress and discover how it can be used to achieve muscle hypertrophy.
Mechanical tension and muscle damage, along with metabolic stress, are the three ways to achieve muscle hypertrophy. Mechanical tension and muscle damage can be achieved by applying progressive overload in the form of increased weight or by performing more reps for the same weight over a period of time to target growth in the size of muscles, also called hypertrophy.
Since it is not always possible to keep increasing the weight on the bar to achieve progressive overload, the technique of metabolic stress comes into the picture. Metabolic stress technique relies on the “pump” one achieves after a resistance training session to elicit a hypertrophic stimulus.
How does Metabolic Stress work?
Metabolic stress works on the principle of metabolite accumulation inside the muscle cells after a high rep set is performed one after the other, with lower rest periods than usual. Inside the cell, carbohydrates, proteins, and fats serve as potential energy sources. The chemical energy stored in these macronutrients is released as they are broken down into simpler units and the kinetic energy released is used to fuel the processes inside the cell, also referred to as metabolism.
Metabolic stress during resistance training is the stress placed on the muscle from the metabolites of these compounds. It is a physiological process that occurs during resistance training as a response to low energy levels inside the cell that leads to metabolite accumulation [1]. Metabolites such as lactate, inorganic phosphate, intramuscular phosphocreatine, and ions of hydrogen are formed during a bout of resistance training which accumulate inside the cells as we tend to perform set after set with higher repetitions and lower rest period.
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The difference between Metabolic Stress and Fatigue
Fatigue is induced as a result of working at higher intensities of load with lesser reps and longer rest periods. It is the reduction in the ability to produce voluntary force. This reduction in the force-producing ability can be central (the central nervous system is affected) or it can be locally, also called peripheral fatigue, which is the reduction in the force-producing ability of individual muscle fibers.
Central nervous system fatigue can occur either due to a reduction in the size of the signal sent to the brain or the spinal cord or because of an increase in afferent feedback that subsequently reduces motor neuron ability. Many factors can contribute to peripheral fatigue, namely a decrease in the sensitivity of actin-myosin filaments to calcium, or a reduction in the production of calcium ions from the sarcoplasmic reticulum.
It was earlier believed that lactate production during anaerobic glycolysis was the primary reason for causing metabolic stress. However, other theories have been proposed which credit the activation of different types of muscle fibers due to metabolic stress as the driver of hypertrophy.
Signs of Metabolic Stress
One of the most common signs of metabolic stress is the pump that is achieved as a result of working out at a higher intensity effort with shorter rest periods.
How is Metabolic Stress measured?
The pump induced after performing exercises with low to moderate intensity weights and little rest period results in metabolite accumulation in the target muscle, which eventually leads to metabolic stress. As such, there is no definite quantitative way to measure metabolic stress.
How does Metabolic Stress cause Hypertrophy?
Metabolic stress causes hypertrophy by primarily causing fatigue which is accomplished by an accumulation of metabolites in the muscle fiber. The metabolic stress placed on the muscle fiber starts a series of anabolic signaling cascades which has a similar effect as mechanical tension on muscle hypertrophy.
Earlier, it was believed that lengthening contractions produce similar muscle growth output as shortening contractions. However, long-duration static contractions are known to produce greater muscle growth than the same volume (and time under tension) less fatiguing, short-duration static contractions with a rest period in between.
Later, it was concluded that metabolic stress contributes primarily to hypertrophy. It was shown that typical bodybuilding programs, consisting of many sets and moderate load with less rest period, were more suited to build muscle mass optimally as compared to high load training protocols as done in the powerlifting style of training.
Metabolic stress is known to cause an increased motor unit recruitment, systemic hormone release, muscle cytokine (myokine) release, an increase in the number of reactive oxygen species, and finally an increase in cell swelling.
How does metabolic stress affect nutrition status?
Metabolic stress training relies on inducing a metabolite accumulation which, in turn, leads to a pump. There are various supplements that can be used to achieve a greater pump in the muscles. Supplements like L-arginine, Citrulline malate, etc can be used as a pre-workout. These supplements work as vasodilators and increase blood flow as well as oxygen supply to the muscles.
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Metabolic Stress Training
Different training methodologies can be used to cause metabolic stress and as a result, maximize hypertrophy. Following methods can be used to apply metabolic stress.
Time Under Tension (TUT)
Time Under Tension, or more specifically Time under Effective Tension, is the amount of time a muscle is under stress. The basic principle of time under tension training is that the reps have to be effectively slowed down in the eccentric part. The idea is to fatigue type 2 muscle fibers and cause a build-up of metabolites so that type 1 muscle fibers are recruited. The TUT technique can specifically be utilized for isolation movements like the chest fly, lateral raises, etc to get the most out of it.
Supersets/Trisets/Giant Sets
Supersets, trisets, and giant sets are effective intensity techniques that can be used to amp up the intensity of a set and take the set closer to failure. These are advanced techniques and should only be used by intermediate or advanced lifters who are trying to maximize their gains as these can affect recovery and hence, the performance of an individual.
A superset is when two sets of different exercises, for e.g. one set of bench presses, followed by one set of lat pulldowns, are performed with little to minimal rest. The exercises can be of the same body part, e.g. chest fly followed by bench press, or an antagonistic superset wherein one set of each exercise of an opposite muscle group is performed, e.g. one set of bicep curls followed by tricep extension.
A triset involves the use of three exercises performed back to back, for example, a set of overhead dumbbell presses, followed by a set of lateral raises, followed by a set of rear delt flyes, before taking a break. The triset is repeated 3-5 times depending on the volume the lifter is trying to target for the targeted muscle group.
The giant set is similar to the triset, the only difference being in the number of exercises that are clubbed together to be performed back to back without taking any break. These usually incorporate sets of 4-6 exercises, performed consecutively with little to minimal rest period.
All these training methods help in increasing the training intensity and training density (more volume of work done in less time frame) and cause metabolite accumulation in the targeted muscles.
Drop Sets
Drop sets are a very commonly used intensity technique, made popular by bodybuilders from the 1970s, also referred to as the golden era of bodybuilding. To put it simply, a drop set involves taking a set to failure with a given weight and then reducing the weight without taking any rest and continuing to do the reps until failure is achieved again. To amp up the intensity, a double drop set can also be used, where the weight is dropped again after reaching failure on the first drop set.
Occlusion Sets/ Blood Flow Restriction Technique
This method to increase intensity involves wrapping a band around the limbs or legs. This technique is especially useful when training with lighter loads. It stops the venous return of blood flow from the muscle and not the arterial blood flow to the muscles. When you do this, it will cause the blood to pool in the target muscle. It targets the fast-twitch muscle fibers, which have the biggest potential for growth. BFR training restricts blood flow to the muscles, pre-fatigues the slow-twitch muscle fibers, and forces the fast-twitch muscle fibers to come into play, even at loads that are as less as 20-30% of one-rep max.
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Author: Shobhan Ojha
References:
- de Freitas, M. C., Gerosa-Neto, J., Zanchi, N. E., Lira, F. S., & Rossi, F. E. (2017). Role of metabolic stress for enhancing muscle adaptations: Practical applications. World journal of methodology, 7(2), 46–54. https://doi.org/10.5662/wjm.v7.i2.46
