Hypertrophy Mechanisms [2/3]: Muscle Damage, Training Strategies and Techniques [Part 2/2]

Stretch overload, hypertrophy and hyperplasia

Hypertrophy involves the enlargement of contractile elements (1). Hyperplasia on the other hand results in an increase in the number of fibers.

Increasing muscular density is very painful. However if significant damage is inflicted the number of fibers can actually increase. As noted, eccentric actions cause the most damage, but there’s another method such as stretch overload. 

Stretch induced overload is when a certain load stretches a muscle, either intermittently, progressively, or chronically. These methods typically produce more sarcomeres in series (elongation). It’s also strongly associated with hyperplasia (2,3,4,5). This is usually studied in animal models. 

1. Intermittent stretch

The intermittent stretch consists of stretching the muscle with the same weight. Stretch periods lasted for 24h in animal models, with 2 or 3 days or rest days in between for recovery. This method produce muscle fiber hypertrophy without fiber hyperplasia (6).  Part of the mass increase is due to increases in muscle length. In one study muscle length increased 26.1% in intermittently stretched muscle (6).

2. Progressive stretch

Progressive stretch overload of skeletal muscle results in hypertrophy before hyperplasia (7,8).

In progressive overload the load is increased every workout, with 2 to 3 days of rest days in between for recovery (7). Again, stretch periods of 24h each. The adaptive response to progressive stretch overload involve an initial fiber hypertrophy – that is increase and peak in cross sectional area and length - followed by hyperplasia (7). Muscle fibers may attain a critical size before the onset of fiber hyperplasia. If fibers enlarge to a critical size and are subjected to further stress they undergo a splitting process, the parent fiber gives rise to two or more daughter fibers (7).

This method produced 142% increase in cross-sectional area (in 16 days of stretch muscles); 50% increase in muscle length; 318% increase in muscle mass (after 28 days of stretch). All of these results exceed any reported in the literature.

3. Chronic stretch

Chronic stretch overload results in hyperplasia before hypertrophy (9). Chronic stretch does not allow for a recovery or rest interval and therefore results in significant muscle fiber injury (6,10). Hence, the initial fiber hyperplasia in the chronically stretched model may be an injury-related phenomenon (6).


1. Heavy negatives

Heavy negatives (supramaximal loaded eccentric actions) is the performance of eccentric contractions at a weight greater than concentric 1RM. This technique usually requires a spotter to help raise the weight.

A muscle is not fully fatigued during concentric training (11), therefore the use of heavy negatives is recommended for an additional hypertrophic stimulus.

2. Assisted Negatives

This technique involves performing regular repetitions while a spotter applies pressure on the negative portion of the rep. Using a load above 1RM isn’t always necessary, the point is doing more total eccentric work than concentric, for any number of reps, for example 70% concentric RM and 90% eccentric.

3. Emphasizing the Negative 

Taking 3-5 seconds to lower the weight may allow a lifter to induce a maximum amount of damage. Emphasizing the negative may increase the micro tears in your muscles and release more satellite cells.

4. Forced Negatives

After concentric failure there’s still more work, failure is not achieved concentrically. After concentric failure a spotter can assist on the positive rep while finishing eccentric reps until failure.

5. Loaded stretches

Putting the muscle at the most stretched position and using a load to stretch. This should be with a moderate weight for at least 30s, perhaps at the end of a set. Several approaches are possible: using one stretch after failure in every set, intraset-stretches (instead of rest interval), descending or ascending. Note that the stretching protocol eliciting more gains was the progressive stretch, in which the weight is increased every workout, but can also be increased every set.


Eccentrics, especially supramaximal eccentric contractions produce:

1. The most muscle damage
2. More protein synthesis
3. More hypertrophy
4. More strength
5. More growth factors
6. More satellite cells

Should be performed above with a load above 1RM (in the case of overload eccentrics), with a tempo between 1-3 seconds, and must be used in moderation (risk of muscle fiber death).

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Also read:


1. Vierck, J, O’Reilly, B, Hossner, K, Antonio, J,Byrne, K, Bucci, L, and Dodson, M. Satellite cell regulation following myotrauma caused by resistance exercise. Cell Biol Int 24: 263–272, 2000.
2. Tsika R: The Muscular System: The Control of Muscle Mass. In: ACSM's Advanced Exercise Physiology. Edited by Tipton C. Baltimore, MD: Lippincott Williams& Wilkins; 2006: 161-177.
3. Siu Pm AS: Age-related apoptotic responses to stretch-induced hypertrophy in quail slow-tonic skeletal muscle. American Journal of Cell Physiology 2005, 285(5):C1105-1113.
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5. Paul A. RN: Different modes of hypertrophy in skeletal muscle fibers. TheJ ournal of Cell Biology 2002, 156(4):751-760.
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8. Progressive overload of the anterior latissimus dorsi of the adult quail produces muscle fiber hypertrophy before fiber hyperplasia. Physiologist 35: 196, 1992
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