When most people think of increasing tension, they think about adding more weight. There are several ways to increase tension by changing many training variables. Changing load (i.e., weight), proximity to failure, frequency, exercise selection, range of motion, technical execution of the exercise, and rest periods can all influence the potency of the exercise stimulus achieved with any given number of sets.


  •      Muscle hypertrophy can increase in size (diameter) or increase in length.
  •       High muscular tension, sufficient time exposure to that tension, and sufficient effort increase muscle growth.
  •       Repetitions should be completed through a full range of motion


Research gave an update on mechanisms related to muscle hypertrophy and future research:

  •       Mechano-transduction (Tension placed on the muscle is “sensed” resulting in a chemical signal to create an anabolic response). High level of evidence to unravel mechanisms of muscle growth.
  •       Resistance Exercise Acute Increases in Anabolic Hormones (i.e., GH, IGF-1, and Testosterone)- low level of evidence for acute anabolic hormones contributing to muscle hypertrophy.
  •       Muscle Damage- Low level of evidence that muscle damage contributes to muscle hypertrophy.
  •       Metabolites- Increased levels of lactate, hydrogen ions, etc.- low level of evidence that metabolic stress contributes to muscle hypertrophy. [17]


A summary review of the mechanisms of muscle growth [18]:

Load and Intensity:

Heavy and light weight protocols can increase muscle growth equally. Mechanical stress performed to concentric muscular failure, regardless of the weight, results in full muscle fiber activation. Loads between 30 and 90% can increase muscle growth. Heavy weights are needed to maximize strength development.

Types of Contractions:

There is no superiority in emphasizing eccentric contractions over concentric contractions for increasing muscle growth. Both contraction types are equally important for increasing muscle growth.

Number of Repetitions:

The muscle does not have an internal counting mechanism for repetitions. Repetitions can be low with high-intensity exercise (i.e., 5 reps at 80% of a 1-RM) and high with low-intensity exercise (25 reps at 30% of a 1-RM) and increase muscle growth similarly when taken to failure. If sets are taken to complete failure, muscle growth will be similar regardless of repetitions. Various higher repetitions ranges should be utilized to elicit metabolic stress on the muscle.

Repetition Duration:  

A wide range of repetitions can be used to elicit muscle hypertrophy between .5 to 8 seconds. The recruitment of full muscle fiber activation when performing sets to failure stimulates muscle hypertrophy rather than repetition duration.

Number of Sets: Increases in sets can increase muscle growth up to a certain point; more sets can decrease muscle growth. Volume has an inverted U response, with sets increasing muscle growth up to a certain point and, after that, diminishing returns.

Rest Periods Between Sets:

Shorter rest periods reduce total training volume. Shorter rest periods reduce muscle tension but increase metabolic stress, which may be a contributing factor to muscle growth. Total volume seems to be the driving factor for muscle growth rather than rest periods between sets when examining the research.


Frequency has little impact on strength or muscle hypertrophy. Training volume is the determining factor. It is recommended that 48 hours of recovery before an exercise is re-trained for recovery and optimal increases in muscle protein synthesis.

Training to Failure:  

The lighter the weight, the more important it is to train to failure. Training to muscular failure ensures an effective stimulus has occurred. Heavier weight can be used while stopping short of failure and still result in equal muscle growth as training to failure.

Range of Motion:  

A full range of motion should be used for inducing muscle hypertrophy compared to a partial range of motion. A partial range of motion in the lengthened position may be as effective as a full range of motion. People with joint/muscle issues may benefit from a partial range of motion to induce hypertrophy and be used as an effective rehabilitation program.

hypertrophy vs strength the mechanisms strength vs hypertrophy how to get buff progressive overload workout plan myofibrillar hypertrophy 3 factors of hypertrophy building muscle vs strength how to maximize hypertrophy


The primary mechanism in which muscles grow is tension.[1] In the late 60s, researcher Alfred Goldberg, a Harvard Professor of Cell Biology, had an interest in muscle growth and protein synthesis and breakdown. In experiments with rats, he quickly realized that their muscles grew rapidly due to tension overload. Tension is such a powerful promoter of muscle growth that they could do many things to see if they could blunt muscle growth from occurring.

The researchers removed the rat’s pituitary gland to prevent the production of Growth Hormone (GH) and Insulin-Like Growth Factor-1 (IGF-1, which stimulates muscle growth). They also castrated the rats to inhibit testosterone production, removed their thyroid, and withheld food. Despite these punishments, the rats experienced muscle growth when tension was applied to the muscle.

According to Dr. Goldberg, in his research, he stated,

““Maximal tension development leads to increases in muscle hypertrophy. Unlike normal developmental growth, work-induced hypertrophy can be induced in hypophysectomized (rats that can’t produce GH) or diabetic animals (which produce no insulin—an anabolic hormone). This process, thus, appears independent of growth hormone and insulin, as well as testosterone and thyroid hormones. Hypertrophy can also be induced in fasting animals, in which there is generalized muscle wasting. Thus, muscular activity takes precedence over endocrine influences on muscle size.”

— Dr. Goldberg

Muscle Stretch and Muscle Hypertrophy

Besides tension, muscle stretch is a potent stimulus for muscle growth. Animal studies in which a muscle is on chronic stretch results in muscle growth. Stretching a muscle with tension overload results in more muscle growth than tension overload alone. For example, in a review of the animal studies that looked at mechanisms of muscle growth:

·      Stretching + tension overload=20.95% increase in muscle growth.

·      Exercise alone=11.59% increase in muscle growth.

The author concluded that “It appears that hyperplasia (increases in muscle fiber number) muscle cell in animals is greatest when certain types of mechanical overload, particularly stretch, are applied.”[3]

Combining these two principles results in two specific increases in muscle growth. Tension overload increases the muscle’s size, whereas stretching (eccentric contractions) muscle results in an increase in the muscle’s length.[4]

Thus, concentric and eccentric contractions produce unique adaptations in muscles that are separate from each other. Scientists are now experimenting with what is called accentuated eccentric contractions in which the muscle eccentric component is overloaded.


Twenty-eight men participated in a 10-week leg strength-training program twice per week to investigate how the combination of tension overload and muscle stretching affects the growth of muscle fascicle length. The researchers assigned one group to the traditional strength group, which used the same external load for both eccentric and concentric phases throughout the program, while another group was assigned to the accentuated eccentric loading group.

The accentuated eccentric loading group performed strength training with an additional load during the eccentric phase of each repetition (+ 40% greater than the concentric phase). The accentuated eccentric loading group combined two powerful stimuli: tension overload with stretch. Despite both groups using the same training volume, only the accentuated eccentric loading group showed significant increases in fascicle length after the training period (vastus lateralis: ~14% increase, vastus medialis: ~19% increase).


These findings suggest that higher load eccentric training evokes greater fascicle length increases than lower load concentric training.[5] Other contributing factors that may contribute to eccentric exercise’s greater gains in muscle mass from accentuated eccentric loading are increased androgen receptors, IGF-1, and several myogenic regulatory factors (myoD, myogenin, MYF5, MRF4, HGF, and myostatin).[6] This re-emphasizes the importance of tension overload for maximal increases in muscle hypertrophy.

hypertrophy vs strength the mechanisms strength vs hypertrophy how to get buff progressive overload workout plan myofibrillar hypertrophy 3 factors of hypertrophy building muscle vs strength how to maximize hypertrophy

“Tension overload increases the muscle’s size, whereas stretching muscle results in an increase in the muscle’s length.”


Resistance exercise leads to a cascade of events that increase muscle protein synthesis. Several training variables that impact muscle growth are:

  •       High muscular tension (training with sufficiently heavy weight).
  •       Sufficient time exposure to that tension (training with enough sets/reps and/or frequencies).
  •       Sufficient effort (sets should be taken close to the proximity of muscular failure).
  •       Range of Motion (training at stretched muscle length)

To maximize muscle growth, you need a combination of all four. Other variables contributing to muscle growth are metabolic stress and muscle damage, but these are debatable.[7]

Metabolic stress and muscle damage: Do they contribute to Muscle Hypertrophy?

Metabolic stress and muscle damage may contribute to muscle growth, but muscle tension is the king. You may wonder how big a factor tension is for muscle growth; well, if you ever had a cast on for several weeks, you would see how fast a muscle will atrophy. No tension equals no muscle growth. If you go from an active lifestyle to a sedentary lifestyle, muscle loss occurs. Researchers found that if a healthy subject went from an active lifestyle of 13,054 steps per day to a sedentary lifestyle of 1,192 steps, the loss of activity resulted in decreased protein synthesis by 27% and an increase in the muscle suppressing hormone myostatin.[8]

Muscle disuse results in “anabolic resistance,” accompanied by reductions in muscle protein synthesis. This means the anabolic action in muscle is lower. As little as 2 weeks of reduced walking reduces protein synthesis, with rates declining ~13–26% from baseline.[9] For building muscle, “USE IT OR LOSE IT!”

“Low loads (i.e., ≤ 60% of 1RM) provoke higher levels of metabolic stress, but they do not lead more muscle hypertrophy than higher loads (i.e., > 60% of 1RM). It has been suggested that the effect of metabolic stress triggering muscle hypertrophy is mainly related with the increased motor units recruitment provoked by muscle fatigue to maintain the mechanical forces when a set is close to failure. ”

— (Dankel et al. 2017). (18)


Human skeletal muscle consists of three types of muscle fibers: Type I fibers, Type IIX, and Type IIA.


Type I fibers are also known as slow-twitch fibers. These fibers have high aerobic capacity and are used for muscle endurance training, such as endurance competitors like marathoners and triathletes. They are characterized by low force/power/speed production, high endurance, and fatigue resistant. Type I fibers have the least potential for muscle growth. There is evidence of fiber-type transitions that occur with specific training modalities. Researchers investigated the effects of 13 weeks of marathon training on fiber type shifts in novice runners. Leg muscle Type I fiber composition increased by 8%, suggesting muscle fiber transitions to a more aerobic-based capacity with specific training modalities.[10]


Type IIX fibers are characterized by high force/power/speed production and low endurance. They are called fast-twitch fibers and have a greater capacity for muscle growth. The fiber profile of Type IIX shifts towards Type IIA fibers when people use bodybuilding protocols and other anaerobic-based exercises such as sprinting. Type IIX, fast-twitch fibers drive explosive power when doing 1RM or sets of low, heavy repetitions when weightlifting. A study in subjects trained with fast, explosive isokinetic eccentric resistance training for ten weeks found a decrease in Type I fibers (53.8% to 39.1%), with a simultaneous increase in the percentage of type IIX fibers (5.8 to 12.9%).[11]


Type IIA fibers combine Type I and Type IIX fibers, resulting in a hybrid fiber type that exhibits fast contraction velocity and higher resistance to fatigue than Type IIX fibers. Bodybuilding style routines and other anaerobic sports that require a high anaerobic capacity most commonly increase the presence of Type IIA fibers.Researchers discovered that sprint training for 8 weeks increased the proportion of Type IIA fibers in the legs from 31.2% to 46.8%, while simultaneously reducing the percentage of Type I fibers from 50% to 43% and Type IIX fibers from 18.8% to 10.5% [12]

hypertrophy vs strength the mechanisms strength vs hypertrophy how to get buff progressive overload workout plan myofibrillar hypertrophy 3 factors of hypertrophy building muscle vs strength how to maximize hypertrophy



Break down repetitions further into three components: the concentric phase (lift the weight), the isometric phase (contract the muscle without joint movement), and the eccentric phase (lower the weight).

If you use the leg extension, start the lift with a concentric phase where you lift the weight. Pause the weight in the middle of the movement during the isometric phase, and finally, lower the weight during the eccentric phase.

Contraction Type and Muscle Hypertrophy

Contracting (concentric) and stretching (eccentric) muscles are crucial for muscle growth. Contrary to belief, isometric training (no movement) can increase muscle growth.[13] Isometric exercise places tension on the muscle, but the active contracting and stretching of muscle results in superior muscle growth. It’s not uncommon to see people in the gym lifting a weight with no control; however, it’s important to understand that tension and tension duration on the muscle are much more important than the weight. This means that a maximal lift lasting a few seconds will be inferior to muscle growth using a lower weight but more tension on a muscle over a longer time.

Researchers found that when subjects trained with 75% of a maximal voluntary contraction, sustained muscle contractions in the leg extension (contracted the legs explosively for 1 sec, but held the contraction for 3 seconds) resulted in more than a 3-fold greater increase in muscle growth than explosive contractions (contracting as hard and as fast as possible).[14]

This shows that muscle growth depends not only on the weight but also on loading duration (i.e., time). This simple study is a good analogy for muscle growth responses between powerlifting and bodybuilding protocols. Powerlifting protocols use peak tension for a short time frame, whereas bodybuilding protocols result in greater sustained tension for a more prolonged period.

Isometric Contractions and Muscle Hypertrophy

Isometric exercise places tension on the muscle, but no active stretch will result in lesser muscle growth than actively contracting the muscle.[15] By actively stretching and contracting the muscle, you expose different muscle fibers to a wide variety of external stressors. As mentioned previously, each contraction (i.e., concentric and eccentric) causes a different type of muscle growth. Hence, both are equally important.

One study found that lifters who did not pause (i.e., eliminated the isometric contraction pause between contractions) between concentric and eccentric contractions had similar increases in muscle growth to those who paused for one second in the isometric position between contractions.[16] This is not to say that isometric contractions are unnecessary, just of lesser importance than concentric and eccentric contractions for muscle growth.


If you compare the muscle size of bodybuilders to pure-strength athletes, there is a noticeable muscle size difference. Bodybuilders train with less weight but use more sets and reps, resulting in more tension on the muscle over time. In contrast, powerlifters train with very heavy weight, which results in greater peak tension but less total tension over time.

The biggest misconception among lifters is that only heavy weight can increase muscle growth. If heavy weights were the best way to generate muscle growth, doing maximal weights with singles and doubles would produce maximum muscle growth, but this is not the best way because the tension on the muscle is very brief because of the low number of reps. The tension must be of sufficient duration and progressively increased over time to stimulate muscle growth. Increasing volume (i.e., total workload) is especially important for advanced lifters to increase muscle growth, whether by adding more weight or more sets/reps.

“Muscle fiber recruitment is not enough to produce hypertrophy. For example of a 1RM set fully recruits muscles when it is performed, yet no hypertrophy occurs. To provoke skeletal muscle hypertrophy, muscle fibers not only have to be recruited but they also have to reach certain levels of force and fatigue, which is commonly reached going close to failure and performing multiple training sets.”

— Dankelet al. 2017 [18]


When most people think of increasing tension, they think about adding more weight. There are several ways to increase tension by changing many training variables. Changing load (i.e., weight), proximity to failure, frequency, exercise selection, range of motion, technical execution of the exercise, and rest periods can all influence the potency of the exercise stimulus achieved with any given number of sets.

1-RM Training

Exercise intensity or % of a person’s 1 Repetition Maximum (maximum weight a person can lift once) and volume (sets and repetitions) share an inverse relationship. Increasing one variable will come at the cost of the other. When the volume (sets and reps) goes up, intensity (weight) must go down and vice versa.

As resistance exercise intensity (expressed as a percentage of 1RM) increases, the difficulty of the exercise also increases in high-intensity exercise compared to moderate and low-intensity exercise. This holds true even when taking similar rest periods, despite the decrease in repetitions and total workload.

Fatigue prevents the ability to train at higher intensities if additional sets are added. Training intensities cause fatigue to increase, and higher-intensity exercise requires longer recovery periods.  Dr. Mike Israetel has coined the term “high stimulus-to-fatigue ratio” for muscle growth.

When excess fatigue accumulates over a period in your workouts, it is a good sign to back off. Adding reps, sets, and volume too fast can cause sub-optimal muscle growth because of accumulated stress and fatigue too quickly.



[1] Brad J. Schoenfeld, “The Mechanisms of Muscle Hypertrophy and Their Application to Resistance Training,” Journal of Strength and Conditioning Research 24, no. 10 (October 2010): 2857–72.

[2] Alfred L. Goldberg et al., “Mechanism of Work-Induced Hypertrophy of Skeletal Muscle:,” Medicine and Science in Sports and Exercise 7, no. 4 (1975): 248.

[3] George Kelley, “Mechanical Overload and Skeletal Muscle Fiber Hyperplasia: A Meta-Analysis,” Journal of Applied Physiology 81, no. 4 (October 1, 1996): 1584–88.

[4] Kent W. Jorgenson, Stuart M. Phillips, and Troy A. Hornberger, “Identifying the Structural Adaptations That Drive the Mechanical Load-Induced Growth of Skeletal Muscle: A Scoping Review,” Cells 9, no. 7 (July 2020): 1658.

[5] Simon Walker et al., “Increased Fascicle Length but Not Patellar Tendon Stiffness after Accentuated Eccentric-Load Strength Training in Already-Trained Men,” European Journal of Applied Physiology 120, no. 11 (November 1, 2020): 2371–82.

[6] John P. Wagle et al., “Accentuated Eccentric Loading for Training and Performance: A Review,” Sports Medicine 47, no. 12 (December 2017): 2473–95.

[7] Henning Wackerhage et al., “Stimuli and Sensors That Initiate Skeletal Muscle Hypertrophy Following Resistance Exercise.,” Journal of Applied Physiology (Bethesda, Md. : 1985) 126, no. 1 (January 1, 2019): 30–43.


[8] Brandon J. Shad et al., “One Week of Step Reduction Lowers Myofibrillar Protein Synthesis Rates in Young Men,” Medicine and Science in Sports and Exercise 51, no. 10 (October 2019): 2125–34.

[9]Leigh Breen et al., “Two Weeks of Reduced Activity Decreases Leg Lean Mass and Induces ‘Anabolic Resistance’ of Myofibrillar Protein Synthesis in Healthy Elderly,” The Journal of Clinical Endocrinology and Metabolism 98, no. 6 (June 2013): 2604–12

[10] N. Luden et al., “Skeletal Muscle Plasticity with Marathon Training in Novice Runners,” Scandinavian Journal of Medicine & Science in Sports 22, no. 5 (2012): 662–70.

[11] D. Paddon-Jones et al., “Adaptation to Chronic Eccentric Exercise in Humans: The Influence of Contraction Velocity,” European Journal of Applied Physiology 85, no. 5 (September 2001): 466–71.

[12]J. L. Andersen, H. Klitgaard, and B. Saltin, “Myosin Heavy Chain Isoforms in Single Fibres from m. Vastus Lateralis of Sprinters: Influence of Training,” Acta Physiologica Scandinavica 151, no. 2 (1994): 135–42.

[13] Dustin J. Oranchuk et al., “Isometric Training and Long-Term Adaptations: Effects of Muscle Length, Intensity, and Intent: A Systematic Review,” Scandinavian Journal of Medicine & Science in Sports 29, no. 4 (April 2019): 484–503.

[14]Thomas G. Balshaw et al., “Training-Specific Functional, Neural, and Hypertrophic Adaptations to Explosive vs. Sustained-Contraction Strength Training,” Journal of Applied Physiology (Bethesda, Md.: 1985) 120, no. 11 (June 1, 2016): 1364–73


[15] Rodrigo Vanerson Passos Neves et al., “Dynamic, Not Isometric Resistance Training Improves Muscle Inflammation, Oxidative Stress and Hypertrophy in Rats,” Frontiers in Physiology 10 (January 22, 2019): 4.

[16] Michiya Tanimoto and Naokata Ishii, “Effects of Low-Intensity Resistance Exercise with Slow Movement and Tonic Force Generation on Muscular Function in Young Men,” Journal of Applied Physiology (Bethesda, Md.: 1985) 100, no. 4 (April 2006): 1150–57.

[16]Lim, C., Nunes, E. A., Currier, B. S., Mcleod, J. C., Thomas, A., & Phillips, S. M. (2022). An Evidence-based Narrative Review of Mechanisms of Resistance Exercise-induced Human Skeletal Muscle Hypertrophy. Medicine and science in sports and exercise.

[17]Viecelli, C., & Aguayo, D. (2022). May the Force and Mass Be With You-Evidence-Based Contribution of Mechano-Biological Descriptors of Resistance Exercise. Frontiers in physiology, 12, 686119.

[18] Dankel, S. J., Mattocks, K. T., Jessee, M. B., Buckner, S. L., Mouser, J. G., & Loenneke, J. P. (2017). Do metabolites that are produced during resistance exercise enhance muscle hypertrophy?. European journal of applied physiology, 117(11), 2125–2135.

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