What is the fiber type of different muscle groups?

Training in line with the muscle fiber type of body parts could be useful for maximizing hypertrophy. However, for too long, information about muscle fiber types has been promoted based on references to single studies and hearsay. In this article, Chris Beardsley reviews the literature regarding muscle fiber types for the main upper and lower body muscles.

What is the background?

What are muscle fiber types?

Muscle fibers can be classified in various ways. All current methods are dependent upon the assumption that limiting factor for the speed at which cross-bridge cycling can occur is the speed at which the ATPase of the myosin head can hydrolyze ATP to power the process. The three ways are:

Myosin ATPase histochemical staining – this process differentiates between individual muscle fibers on the basis of their staining intensities. These staining intensities differ between muscle fibers as a result of differences in pH sensitivity. The differences indirectly provide relative information between muscle fibers about the speed at which ATP hydrolysis occurs, although the staining procedure does not directly measure the speed of hydrolysis (Scott, 2001). The main three myosin ATPase staining results are referred to as muscle fiber types I, IIA, and IIX (or historically IIB), respectively. Interim fiber types are identified where staining types between the main classes are observed.

MHC isoform identification – this process involves differentiating between individual muscle fibers in the basis of the different myosin heavy chain isoforms. The MHCs contain the site that serves as the ATPase, which is how identifying the MHC isoform is relevant for the speed of ATP hydrolysis. Each muscle fiber can contain more than one MHC isoform. Thus, although there are only three isoforms expressed in human skeletal muscle, there are many more hybrid muscle fiber types comprising muscle fibers with several different isoforms in the same muscle fiber (Scott, 2001). The main three myosin isoforms are most correctly referred to as MHCI, MHCIIa, and MHCIIx (or MHCIIb historically).

Biochemical identification of metabolic enzymes – this process combines information derived from myosin ATPase histochemistry with histochemistry of certain enzymes that are involved in energy metabolism. In such cases, the myosin ATPase fiber typing is used to classify muscle fibers into either type I or type I. Analysis of enzymes is then performed in order to provide information about the metabolic pathways. This leads to describing the muscle fibers as either aerobic/oxidative or anaerobic/glycolytic and ultimately three different fiber types: fast-twitch glycolytic, fast-twitch oxidative, and slow-twitch oxidative (Scott, 2001).

In many circles, the three different methods are taken as producing similar outputs that can be compared across studies. While this has been found to be acceptable for certain muscle fiber types and between certain typing methods (most obviously in respect of type I muscle fibers and between MHC and myosin ATPase), it is certainly not valid across the board and we must bear this in mind when reviewing the literature.

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Why are muscle fiber types relevant?

Type II muscle fibers have greater growth potential than type I muscle fibers. This has led most experts to recommend focusing on type II muscle fiber types in resistance-training for hypertrophy. However, as Ogborn (2014) has explained, type I muscle fibers can also be developed in order to maximize the overall increase in size of a muscle. Thus, hypertrophy programs should be structured with both muscle fiber types in mind.

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How can different muscle fiber types be developed?

Type I (often also called slow twitch) fibers are highly resistant to fatigue and therefore probably respond best to sets of higher repetitions. On the other hand, type II (often also called fast twitch) fibers fatigue quickly and probably respond best to high-load, low-repetition sets. Mixtures of type I and type II muscle fibers will probably need a combined approach, perhaps through a combination of high repetitions and others to low repetitions.

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Why is the muscle fiber type of individual muscles useful?

As we will see in the following analysis, some muscles contain a greater proportion of type I muscle fibers while others contain a higher proportion of type II muscle fibers. Where a muscle does contain a higher proportion of type I muscle fibers, it seems probable (although it remains to be shown in long-term trials), that training with sets of higher repetitions to muscular failure might well lead to superior muscle growth, at least in the short-term. Similarly, where a muscle contains a higher proportion of type II muscle fibers, it seems probable that training with high-load, low-repetition sets might well lead to superior muscle growth, at least in the short-term.

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What are the muscle fiber types of the lower body muscles?

The studies in the tables below have explored the muscle fiber types of the lower body musculature:

Screen Shot 2014-09-05 at 14.36.51In summary, the hamstrings and gluteus maximus comprise a mixed-to-slow muscle fiber type. The soleus is predominantly slow twitch. The gastrocnemius possesses a mixed-to-slow muscle fiber type. The mixed-to-slow fiber type gastrocnemius is a two-joint muscle while the very-slow twitch soleus is only a single-joint muscle. By sitting down to perform plantar flexion, the gastrocnemius enters active insufficiency and the soleus is primarily recruited. In contrast, during standing exercises, the gastrocnemius is more involved. So seated plantar flexion exercises may benefit most from a focus on type I muscle fibers.

Lower body muscle fiber typesThe individual quadriceps range from mixed-to-slow through to fast twitch. The rectus femoris is a two-joint muscle and this is fast twitch. Thus, multi-joint knee extension exercises may benefit more from a focus on type II muscle fibers than single-joint knee extension exercises.

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What are the muscle fiber types of the upper body muscles?

The studies in the tables below have explored the muscle fiber types of the upper body musculature:

Upper body muscle fiber typesThe shoulders are mixed-to-slow twitch muscle fibers, while the biceps, triceps and pectorals are mixed-fast twitch. Most studies have reported that the latissimus dorsi is almost perfectly balanced between slow and fast twitch muscle fibers. A more recent investigation cast doubt upon this using a new method. Future research may therefore find that there is a greater proportion of fast twitch fibers. However, this remains to be seen.

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What do we know about these studies?

If you’re curious about the methodology used in the studies cited above (i.e. whether the researchers used histochemical analysis or immunohistochemical methods, and whether they took biopsies from living subjects or samples from cadavers) or if you simply just want the references, here are the details and links. They’re in alphabetical order:

Baker and Hardy (1989) took muscle samples from the latissimus dorsi by needle biopsy, at rest, before and after a high-intensity exercise training canoe-specific training program, performed 3 times per week for 9 weeks.

Dahmane (2000) explored the histochemical properties of several muscles in two groups of 15 men aged 17 – 40 years using the histochemical analysis of myosin ATPase. The muscles investigated included the biceps brachii, triceps brachii, flexor digitorum superficialis, extensor digitorum, biceps femoris, tibialis anterior and gastrocnemius. They also tested a tensiomyographic, non-invasive measurement technique.

Dahmane (2005) investigated fiber type distribution in 9 limb muscles with histochemical methods in two groups of 15 men aged 17 – 40 years at different depths (superficial and deep).

Dahmane (2006) measured muscle fiber type proportions in samples of the biceps femoris in sedentary young men using the standard histochemical analysis of myosin ATPase as well as the MHC isoform expression test using immunohistochemical analysis.

Edgerton (1975) explored the muscle fiber types of the gastrocnemius, soleus, vastus lateralis and intermedius in 32 humans by autopsy within 25 hours of death. The samples were examined using histochemical analysis of myosin ATPase.

Garrett (1984) explored the muscle fiber type composition of the human hamstring muscles using histochemical analysis of myosin ATPase of necropsy specimens taken from seven locations in the hamstring.

Gouzi (2013) systematically reviewed the studies providing data on fiber type proportion of the vastus lateralis of the quadriceps in healthy subjects aged >40 years old. The methods used in the underlying studies differed and included both histochemical analysis of myosin ATPase and immunohistochemical analysis of MHC isoforms.

Hards (1990) examined the muscle fiber type of internal intercostal, external intercostal, and latissimus dorsi muscle biopsies in 68 patients who were having a thoracotomy using myosin ATPase.

Humphrey (1982) performed an investigation into the muscle fiber composition of the deltoid muscle of elite British slalom kayak competitors for a thesis at the University College of North Wales.

Jennekens (1971) gathered data regarding the distribution of muscle fiber types in 5 human limb muscles using necropsy material from 8 previously normal subjects aged from 8 – 42 years, who died suddenly as a result of trauma or acute illness. The muscles explored included the deltoid, biceps brachii, rectus femoris, gastrocnemius and extensor digitorum brevis. The researchers used histochemical analysis of myosin ATPase to assess muscle fiber type.

Keh-Evans (2010) investigated the contractile, histochemical and biochemical properties of the triceps surae were compared in 13 aerobically-trained male subjects aged 63 – 76 years.

Johnson (1973) also gathered data on the distribution of muscle fiber types in 36 human muscles using necropsy material from 50 sites of 6 previously normal male autopsy subjects aged from 17 – 30 years. The researchers used histochemical analysis of myosin ATPase to assess muscle fiber type.

MacDougall (1984) took muscle biopsies and estimated muscle fiber numbers in vivo in biceps brachii in 5 elite male bodybuilders, 7 intermediate caliber bodybuilders, and 13 age-matched controls. The researchers used histochemical analysis of myosin ATPase to assess muscle fiber type.

Mavidis (2007) took muscle biopsies of the deltoid muscles of Greek professional male tennis players. Myosin ATPase histochemistry and MHC composition analysis were performed on the samples.

Nygaard (1982) investigated the muscle fiber type at nine sites of the brachial biceps and the lateral vastus at autopsy from 5 elderly subjects.

Pierrynowski (1985) evaluated hamstring muscle fiber type in order to develop a musculoskeletal model.

Schantz (1983) took muscle biopsies were taken from the vastus lateralis and triceps brachii and used histochemical analysis of myosin ATPase to assess muscle fiber type.

S̆irca (1980) assessed muscle fiber type of the gluteus maximus, gluteus medius and tensor fasciae latae in patients with osteoarthritis of the hip as well as in autopsy material.

Srinivasan (2007) performed a study of the muscle fiber type composition of 14 muscles spanning the glenohumeral joint. They took material from 4 male cadavers (mean age 50 years) within 24 hours of death and performed histochemical analysis of myosin ATPase to assess muscle fiber type.

Tesch (1983) took muscle biopsies from the mid-portion of deltoid muscles of 7 male wheelchair basketball athletes, 8 high caliber kayak paddlers, 8 wrestlers, and 8 mountain ranger soldiers. performed They used histochemical analysis of myosin ATPase to assess muscle fiber type.

Travnik (1995) took cross-sections from autopsied muscles from 9 healthy men, aged 18 – 44 years, who had died suddenly. They used histochemical analysis of myosin ATPase to assess muscle fiber type.

N.B. This list is not exhaustive in all respects. In particular, if you go digging, you may come across a number of other studies that have explored muscle fiber types in either the vastus lateralis or the gastrocnemius. Unlike other parts of the body, these muscles have been analysed in many investigations. While muscle fiber type does vary, the prevailing trend (as reported in review papers) is for the fiber type in the vastus lateralis to be mixed (around 50%). While the gastrocnemius has not yet been subjected to a review, it does seem to display a mixed-to-slow twitch fiber type.

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What are the practical implications?

For the lower body

The hamstrings and gluteus maximus comprise a mixed-to-slow muscle fiber type. Hip extension exercises, as well as knee flexion exercises, may benefit from being performed with a combined approach with an emphasis on higher repetitions to muscular failure.

The soleus is predominantly slow twitch. The gastrocnemius possesses a mixed-to-slow muscle fiber type. Since sitting preferentially loads the soleus, seated calf raises may benefit from being performed exclusively with higher repetitions to muscular failure, while those performed standing may also benefit from a minor amount of high-load training.

The individual quadriceps range from mixed-to-slow through to fast twitch muscle fiber types. The rectus femoris is a two-joint muscle and is fast twitch. Thus, multi-joint knee extension exercises like squats may be best performed for high-load, low-repetition sets while single-joint knee extension exercises may benefit from a combined approach to loading.

For the upper body

The shoulders are mixed-to-slow twitch muscle fibers, suggesting that they may benefit from being subjected to a combined approach with an emphasis on higher repetitions to muscular failure.

The biceps, triceps and pectorals are all mixed-fast twitch, suggesting that they should be best trained with a combined approach with an emphasis on high-load, low-repetition sets.

The latissimus dorsi is almost perfectly balanced between slow and fast twitch muscle fibers, suggesting that it should be best trained with a combined approach.

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Which type of periodization is best for power?

There is good support in the literature for using periodization during resistance-training for optimising strength gains. Periodization may also be useful for hypertrophy, although the evidence is much weaker. But what about periodization for maximizing gains in muscular power? In this article, Chris Beardsley (@SandCResearch) reviews the literature.

What is the background?

What do we know about periodization?

For the full details of how periodization affects gains in strength and size, please see the previous articles. The very short versions are as follows:

Is periodization better than no periodization for strength gains? The current available evidence suggests that periodizing resistance-training is more effective than not periodizing resistance-training for increasing strength. However, the design of most trials makes it difficult to assess what aspect of periodization is responsible for that improvement. It could be the simple variability in the program or it could be the structure.

Which periodization type is best for strength gains? The current evidence is somewhat conflicting regarding the best type of periodization for strength gains. However, there is some support for non-linear (e.g. daily undulating) being better than linear and reverse linear. There is some support for linear being better than reverse linear. There is also some support for block periodization being better than linear and non-linear. Overall, block and non-linear periodization look like the best options for strength gains.

Is periodization better than no periodization for size gains? The current available evidence assessing whether periodizing resistance-training is more effective than not periodizing resistance-training for increasing size is very limited. There is a slight indication that periodization may be superior but more research is needed.

Which periodization type is best for size gains? The current evidence is both limited and conflicting regarding the best type of periodization for size gains. However, there is some support for non-linear (e.g. daily undulating) being better than linear. There is some support for linear being better than reverse linear. Overall, non-linear periodization looks like the best option but it is almost too difficult to tell at present.

In summary, periodization seems to be effective for increasing strength (and probably also size). Non-linear (e.g. daily undulating) and block periodization models look like the best overall options. When you consider that it is notoriously difficult to get any individual training variable to produce reliable differences in long-term trials because of the inter-individual differences, it is remarkable that something so simple as moving your training loads and volumes around in time should have such a marked effect.

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What are the selection criteria?

For this review, studies have been selected that met the following inclusion and exclusion criteria:

They compared two or more long-term resistance-training programs, where at least one of the groups followed a commonly-used periodization model.

The groups following each program predominantly used the same exercises for similar or equal training volumes.

The preferred outcome variable was power output but given the paucity of studies, other outcome measures were also accepted, including jumping and throwing performance, and bar velocity.

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Does periodization increase gains in power?

The following studies compared the effects of a periodized training program against a non-periodized control training program on gains in muscular power or related outcome measures, such as jumping or throwing performance, or bar speed. The table below summarizes the results:

Periodization power

Moraes (2013) compared a non-periodized resistance-training program and a daily undulating resistance-training program, on strength gains in 38 untrained adolescents over a 12-week period. Before and after the intervention, the researchers measured countermovement jump height and standing long jump distance. The subjects trained 3 days per week. The non-periodized group performed of 3 sets of 10 – 12RM while the daily undulating group performed 3 sets of different relative loads on each of the 3 sessions per week but the total volume of each training programs was similar. The researchers found that neither the non-periodized resistance-training program nor the daily undulating resistance-training program training significantly improved either countermovement jump height (4.7% vs. 5.3%) and standing long jump distance (1.9% vs. 2.2%) and there were no significant difference between groups.

Baker (1994) explored the effects of manipulating volume and relative load on strength and power gains in 22 experienced male athletes. Before and after a 12-week program, the researchers tested countermovement vertical jump height. The subjects trained 3 days per week for 12 weeks using either a non-periodized control mode, a linear periodization model, or a non-linear (weekly undulating) periodization model. Training volume and relative load were the same for all groups. The researchers found that the linear and non-linear (weekly undulating) groups improved countermovement vertical jump height significantly (by 9.3%, 3.8% and 10.2%) but there were no significant differences between groups.

Stowers (1983) compared the effects of 2 non-periodized and 1 periodized resistance-training program on strength gains over a 7-week intervention in which the untrained college-aged male subjects trained 3 times per week. Before and after the intervention, the researcher measured 1RM bench press and parallel back squat. One non-periodized group trained using a low volume (1 x 10RM), the second non-periodized group trained using a high volume (3 x 10RM), and the periodized group trained using 3 different blocks, comprising 2 weeks at 5 x 10RM, 2 weeks at 3 x 5RM, and 2 weeks using 3 x 3RM. The researchers found that the periodized group increased vertical jump height by more than the low volume and high volume groups (5.1cm vs. 0.2cm and 0.7cm).

Stone (1981) compared the effects of a non-periodized and a periodized resistance-training program on strength gains over a 6-week intervention in which untrained college-aged male subjects trained 3 times per week. Before and after the intervention, the researcher measured vertical jump height and power. The non-periodized group trained using 3 x 6RM and the periodized group trained in blocks as follows: 3 weeks of 5 x 10RM, 1 week of 5 x 5RM, 1 week of 3 x 3RM, and 1 week of 2 x 2RM. The researchers found that the periodized group displayed significantly better gains in vertical jump power but not height than the non-periodized group.

In summary, there is limited evidence that periodized resistance-training programs lead to superior gains in power or power-related measures compared to non-periodized resistance-training programs in either trained or untrained populations.

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Linear vs. non-linear periodization?

The following studies compared the effects of linear and non-linear (i.e. either daily or weekly undulating) periodization models on gains in power output or proxies for power output (e.g. jumping height or distance, throwing velocity, bar speed). The table below summarizes the findings:

Periodization power

Franchini (2014) compared the effects of linear and non-linear (daily undulating) periodized resistance-training on strength gains in 13 adult male judo athletes over an 8-week training program. Before and after the intervention, the researchers measured standing long jump performance. However, performance in the standing long jump did not improve at all in either group.

Kok (2009) compared linear and non-linear (daily undulating) periodization on strength changes in 20 untrained women with matched total workload and relative load. Before and after the 9-week intervention, the researchers measured squat jump power output and bench press throw power output. The subjects trained 3 days per week. The researchers found that average power outputs and heights all increased in both groups over time but there were no significant differences in any measure between groups. Squat jump power increased similarly in the linear and non-linear groups by 10.4% and 9.5%, respectively. Bench press throw power increased similarly in the linear and non-linear groups by 11.1% and 13.8%, respectively. Squat jump height increased marginally more in the linear than the non-linear group, at 28.0% and 21.5%, respectively. Bench press throw height also increased marginally more in the linear than the non-linear group, 56.4% and 44.8%, respectively.

Baker (1994) explored the effects of manipulating volume and relative load on strength and power gains in 22 experienced male athletes. Before and after a 12-week program, the researchers tested countermovement vertical jump height. The subjects trained 3 days per week for 12 weeks using either a non-periodized control mode, a linear periodization model, or a non-linear (weekly undulating) periodization model. Training volume and relative load were the same for all groups. The researchers found that the linear and non-linear (weekly undulating) groups improved countermovement vertical jump height significantly (by 9.3%, 3.8% and 10.2%) but there were no significant differences between groups.

In summary, the literature is very conflicting regarding whether linear or non-linear methods of periodization are better for increasing muscular power output.

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Linear vs. block periodization?

The following study compared the effects of linear and block periodization models gains in power output or proxies for power output (e.g. jumping height or distance, throwing velocity, bar speed). The table below summarizes the findings:

Periodization power

Bartolomei (2014) compared block and linear periodization models in 24 strength and power athletes with resistance-training experience over a 15-week period. The subjects trained 4 times per week. The training programs comprised the same exercises and the same volume. The subjects performing block periodization displayed superior improvement in bench press power output (9.6% vs. 3.2%) but the differences in squat jump height (4.2% vs. 1.6%) and countermovement jump height (2.6% vs. 2.8%) were not significant.

In summary, the literature is very limited in comparing linear and block periodization. Since one study found that block periodization was superior, we might infer that block periodization is probably better than linear periodization but clearly further research is needed before we can be certain about this conclusion.

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Non-linear vs. block periodization?

The following studies compared the effects of non-linear and block periodization models on gains in power output or proxies for power output (e.g. jumping height or distance, throwing velocity, bar speed). The table below summarizes the findings:

Periodization power

Hartmann (2009) compared the effects of block-style strength-power periodization and non-linear (daily undulating) periodization models on strength gains in the bench press in male sport students with resistance-training experience. The subjects trained for 14 weeks, 3 days per week. The researchers found that while 1RM bench press increased in both groups, there was no significant difference between groups. They found that block and non-linear groups both significantly increased bench press throw maximum velocity by 7.6% and 6.1%, respectively but there was no significant difference between groups.

In summary, the literature is very limited in comparing non-linear and block periodization, particularly as the only measure was a proxy for power output and power was not measured directly. Further research is needed before we can make any statement with confidence.

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What are the practical implications?

There is some limited evidence that periodization may improve gains in muscular power in comparison with a non-periodized workout program.

There is no strong evidence to support preferentially using linear, non-linear, or block periodization when structuring a resistance-training plan for increasing muscular power output. Therefore, other concerns may be of greater importance when structuring training plans.

Which type of periodization is best for hypertrophy?

Periodization is commonly-used in resistance-training for maximizing hypertrophy. But which periodized training programs are best for increasing muscular size? In this article, Chris Beardsley analyses the long-term trials to find out.

What is the background?

What is periodization and why is it important?

Previously in this series of reviews, I’ve looked at whether periodization leads to greater strength gains and which type of periodization is best for strength gains. In the background sections to those reviews, I’ve explained what periodization is, why it is thought to be important, what types of periodization exist, and what problems we encounter when investigating the effectiveness of the different models.

However, while strength gains and hypertrophy are related, they are certainly not the same thing. So in this review, I’ve explored whether a periodized program is better than a non-periodized program for increasing muscular size, as well as which periodized program is best for muscular hypertrophy. As you might expect, the literature is much more limited than the body of research about strength gains, simply because it’s a lot harder and more time-consuming to measure changes in muscular size than it is to run a 1RM test.

What were the selection criteria?

For this review, studies have been selected where they compared two or more resistance-training programs either where at least two of the programs followed a commonly-used (but different) periodization model, or where there was a periodization model and a non-periodized control group. As before, studies were sought that used the same exercises and used equal or near equal training volumes. Outcome measures were rejected where muscular hypertrophy was measured using arm or thigh circumference as these were considered to be too easily affected by alterations in fat mass.

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Periodization vs. no periodization?

The following studies assessed the effects of periodization for increasing muscular size. The table presents the brief summary:

Periodization hypertrophy

Monteiro (2009) compared changes in lean body mass between non-periodized, linear periodized and non-linear periodized resistance-training models in 27 strength-trained males over a 12-week intervention. The researchers found that none of the groups increased lean body mass significantly. Increases in each of the non-periodized, linear periodized and non-linear periodized groups were -3.0%, 1.2% and 0.3%, respectively.

Baker (1994) explored the effects of manipulating volume and relative load on strength and power gains in 22 experienced male athletes. Before and after a 12-week program, the researchers tested lean body mass. The subjects trained 3 days per week for 12 weeks using either a linear periodization model, a non-linear (undulating) periodization model, or a non-periodized control model. Training volume and relative load were the same for all groups. The researchers found that lean body mass improved significantly in the control, linear and non-linear groups (3.2%, 2.8% and 3.4%) but there were no significant differences between the three groups.

Stone (1981) compared the effects of a non-periodized and a periodized resistance-training program on strength gains over a 6-week intervention in which college-aged male subjects trained 3 times per week. Before and after the intervention, the researcher measured lean body mass. The non-periodized group trained using 3 x 6RM and the periodized group trained in blocks as follows: 3 weeks of 5 x 10RM, 1 week of 5 x 5RM, 1 week of 3 x 3RM, and 1 week of 2 x 2RM. The researchers found that the periodized group displayed significantly greater lean body mass gains than the non-periodized group.

In summary, the evidence is not strong in indicating that a periodized program is superior to a non-periodized program for hypertrophy. However, since there is good evidence that that a periodized program is superior to a non-periodized program for strength gains and since superior strength is helpful for hypertrophy, this is a reason to periodize resistance-training programs even where muscular size is the only goal.

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Linear vs. non-linear periodization?

The following studies compared the effects of non-linear and linear periodization for increasing muscular size. The table below summarizes the results:

Periodization hypertrophy

Simão (2012) compared non-linear (daily undulating) and linear periodized resistance-training on muscle thickness using an ultrasound technique in 30 untrained men. The non-linear program varied bi-weekly in weeks 1 – 6 and on a daily undulating basis in weeks 7 – 12. The linear program changed every 4 weeks. After the intervention, the researchers found significant differences in biceps and triceps muscle thickness between the non-linear periodized group and the control but not between the linear periodized group and the control.

De Lima (2012) compared the effects of muscular endurance training with light loads (15 – 30 repetitions) using either linear or non-linear (daily undulating) periodized resistance-training in 28 sedentary women aged 20 – 35 years over a 12-week intervention. The researchers found that both groups displayed significant increases in lean body mass but there were no significant differences between groups. The linear group increased lean body mass by 2.2kg (4.7%) while the non-linear group increased lean body mass by 1.6kg (3.5%).

Monteiro (2009) compared changes in lean body mass between non-periodized, linear periodized and non-linear periodized resistance-training models in 27 strength-trained males over a 12-week intervention. The researchers found that none of the groups increased lean body mass significantly. Increases in each of the non-periodized, linear periodized and non-linear periodized groups were -3.0%, 1.2% and 0.3%, respectively.

Prestes (2009) compared the effects of linear and daily undulating periodized resistance-training on maximal strength in 40 males with >1 year of resistance-training experience. Before and after the 12-week intervention, the researchers measured lean body mass. The researchers found that neither groups displayed any significant increase in lean body mass as a result of the program and there were no significant differences between the groups. They did not report the exact changes.

Kok (2009) compared linear and non-linear (daily undulating) periodization on strength changes in 20 untrained women with matched total workload and relative load. Before and after the 9-week intervention, the researchers measured muscle cross-sectional area. The researchers found that both groups significantly improved rectus femoris muscle cross-sectional area with no differences between groups. However, the increase in the linear group (8.7%) was non-significantly less than the increase in the non-linear group (14.8%) at the end of the intervention.

Baker (1994) explored the effects of manipulating volume and relative load on strength and power gains in 22 experienced male athletes. Before and after a 12-week program, the researchers tested lean body mass. The subjects trained 3 days per week for 12 weeks using either a linear periodization model, a non-linear (undulating) periodization model, or a non-periodized control model. Training volume and relative load were the same for all groups. The researchers found that lean body mass improved significantly in each group but there were no significant differences between groups.

In summary, there is no strong evidence to support preferentially using either linear or non-linear periodization for enhancing muscular hypertrophy. There is a slight trend in favor of non-linear periodization. This mirrors the literature in respect of strength, which includes significant results in favor of both linear and non-linear periodization protocols.

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Linear vs. reverse linear periodization?

The following studies compared the effects of linear and reverse linear periodization for increasing muscular size. Periodization hypertrophy

Prestes (2009) compared the effects of linear periodization and reverse linear periodization in women aged 20 – 35 years with >6 months of resistance-training experience over a 12-week period. Linear periodization started with 12 – 14RM and finished with loads of 4 – 6RM, while reverse linear periodization began with 4 – 6RM and finished with 12 – 14RM. For all exercises, the subjects performed 3 sets and they trained 3 days per week. Before and after the intervention, the researchers measured fat-free mass. The researchers found that only the linear periodized group displayed a significant increase in fat-free mass.

In summary, the very limited evidence suggests that linear periodization is superior to non-linear periodization for increasing muscular size. However, further research is needed before we can make confident statements, given the limited nature of the literature.

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How can we summarize these findings?

The evidence is weak that a periodized program is superior to a non-periodized program for increasing muscular hypertrophy. However, since there is good evidence that that a periodized program is superior to a non-periodized program for increasing muscular strength, this is one reason to periodize resistance-training programs even where muscular size is the only goal.

There is no strong evidence to support preferentially using either linear or non-linear periodization for enhancing muscular hypertrophy. This mirrors the literature in respect of strength, which is more extensive and includes significant results in favor of both linear and non-linear periodization protocols. Very limited evidence suggests that linear periodization is superior to non-linear periodization for increasing muscular size. However, further research is needed before we can make confident statements, given the limited nature of the literature.

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What are the practical implications?

Although the evidence is relatively weak that a periodized program is superior to a non-periodized program for hypertrophy, the evidence is much better for using a periodized program to maximize strength gains. Since strength is helpful for hypertrophy, this is a reason to periodize resistance-training programs even where muscular size is the only goal.

Since there is no strong evidence to support any particular periodization model for muscular hypertrophy, trainees should make use of whatever scheme is best for them for practical reasons.

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