A common theme of thought among the bodybuilding population is the need to not just train the muscles to a point of fatigue but to annihilate them and leave the gym with the muscles worked being barely able to function. Among this hardcore group, it is considered a badge of pride to be unable to comb your hair the day after training your arms or falling down the stairs in a heap of jelly due to the inability to walk after a tough session of squats. Leaving aside the need for masochism which exists in many, the prime reason for this suffering is undoubtedly due to the belief that the more damage is inflicted on the muscles during training, the greater the subsequent muscle growth experienced. This article will test this belief exploring the data in this regard and then also provide some practical guidelines for hypertrophy.
What happens during a workout?
We have to start by looking at what happens to muscle tissue when training in the gym. A lot of research in this area over the years has conclusively demonstrated that strenuous resistance training will cause muscle damage whose degree is dependent on previous practice of the exercise, training volume, intensity and frequency (1, 2, 3). The degree of damage to muscle tissue also depends on the type of exercise conducted with eccentric exercise being associated with higher levels of muscle damage compared to regular concentric exercise or isometric exercise (4). This reflects what most bodybuilders would experience and indeed explains why many training authorities encourage slow eccentric motions when training. In addition exercise which primarily activates the fast twitch muscle fibres are more likely to lead to greater muscle soreness (5), something which helps explain why ballistic movements with relatively low resistance such as plyometrics or sprint training can cause significant muscle soreness even in relatively experienced subjects.
In the short term, the effects of exercise induced muscle damage on the body leads to increased pain, stiffness, a reduction in muscle flexibility as well as a reduction in performance. This tends to ease over time as trainees become more accustomed to performing a particular exercise and their muscles and connective tissue become less sensitive to the external stimulus imposed by resistance exercise. At this point, many proponents of the need to feel sore after training will argue that exercises should be switched or greater use of intensity techniques should be adopted to help ensure the body is never allowed to adapt and become less resistant to exercise induced muscle damage. We will explore the evidence next.
Mechanisms for how muscle damage could cause growth
A number of theoretical factors could help drive the benefits for muscle growth from causing muscle damage including:
Anabolic Signalling via Inflammatory Factors Satellite Cell Differentiation
IGF-1 Signalling
Cellular Swelling
These were highlighted by Brad Schoenfeld (6) in a recent paper which examined the issue of muscle damage and its effects on hypertrophy.
Schoenfeld conducted a meta review of studies designed to induce a significant degree of muscle damage to measure the effect on hypertrophy gains. The results were inconclusive with no study showing a statistically significant effect on muscle growth of treatments designed to induce muscle damage. However, limitations such as using untrained subjects, failure to match training durations between groups (7) and failure to perform longer trials makes it difficult to reach any firm conclusions.
Roig et.al (8) tested one of the theories beloved of those who argue in favour of heavy eccentric training, namely that it can lead to greater muscle growth as a consequence of the greater damage eccentric contractions can produce. Roig’s group evaluated a number of studies which showed that eccentric exercise led to both greater strength as well as greater muscle mass increases compared to concentric exercise.
In spite of this, Schoenfeld points out other studies which show that concentric exercise may be superior (9) to eccentric exercise as well as highlighting studies showing no benefit to muscle gain of performing eccentric exercise (10). There are inevitably some inconsistencies between different studies but the majority of research to date shows that eccentric exercise is positively correlated with greater muscle gain compared to concentric or isometric exercise.
If we choose to accept the notion that eccentric actions promote greater damage and are associated with greater muscle mass gains, is it logical to deduce that it is the muscle damage itself that promotes the hypertrophy gains?
It has been argued that muscle damage in itself is not a factor in promoting muscle growth. This camp correctly point out that muscle damage produced during strenuous aerobic exercise, or during contact sports is anything but ideal for promoting muscle gains. At the other end of the scale there exists a lot of research supporting the benefits of low intensity training techniques such as occlusion training (using pressure cuffs to minimise the escape of blood from working muscles) for building muscle despite the relatively low levels of muscle damage they induce compared to traditional high intensity training featuring heavy eccentrics. Finally, the fact that the body adapts to any training plan (repeated bout effect) means that muscle damage should be less in trained athletes compared to novices meaning it should not be seen as necessary for muscle growth.
These arguments are countered by those stressing the fact that the repeated bout effect never totally eliminates muscle soreness with even advanced trainees still experiencing muscle trauma. While it is less than what a novice would experience, these trainees are still able to make muscle gains even if not at the same rate at which novices do. The fact that novices gain faster than advanced trainees is highlighted by some as being due to the greater muscle damage they experience, making muscle damage a key goal for advanced athletes to try to replicate the greater muscle gains seen in beginners. Importantly, the fact that the repeated bout effect only attenuates the decline in muscle damage rather than eliminating it, is provided as a casus belli for seeking muscle damage as an end unto itself.
What of the argument that muscle damage experienced during aerobic training such as downhill running is not associated with muscle growth?
While it is true that aerobic training can lead to muscle damage with an absence of muscle gains, this story fails to take into account the fact that aerobic and resistance exercise have different outcomes mediated by an entirely separate set of genes and cellular signalling pathways. Specifically, aerobic training induces changes enhancing mitochondria production, greater oxidative capacity, and reduction in protein synthesis while resistance training promotes muscle growth via entirely different pathways. As such, to state that muscle damage from aerobic work is not sufficient to produce muscle growth rather misses the point, which is that damage is not sufficient to produce muscle growth without an accompanying resistance exercise training model.
How else would hypertrophy be explained?
Although there is some research suggesting that eccentric exercise is associated with greater stress imposed on the muscle compared to concentric actions (11), EMG testing by Grabbiner et.al (12) showed that in spite of this, trainees were unable to generate the same peak force during eccentric compared to concentric actions so that the concentric actions imposed greater mechanical stress on muscles.
The fact that a mass of studies over the years show the superiority of relatively lower intensities in the 65-85% range compared to more heavier loading regimes shows that when looking at the end result most people crave, namely greater hypertrophy, a lower lifting intensity is preferable. The theory that eccentric exercise’s superiority is due to higher force output via heavier loads is thus questionable at this point.
Guidelines for Hypertrophy
Based on the research there does exist a theoretical basis for a role for muscle damage causing a greater gain in muscle growth via the effect of muscle damage on anabolic signalling, inflammatory cell processes and activation of satellite cells. What is not clear, as Schoenfeld’s paper points out, is the extent to which there is a cause and effect relationship between muscle damage and muscle growth and whether or not there is a minimum or maximum threshold of damage necessary to both induce greater hypertrophy gains and where further damage can have an inhibitory effect on muscle growth.
Based on research showing that muscle hypertrophy is better achieved by sticking to moderate intensity levels it could be argued that avoiding excessive muscle damage does indeed lead to better outcomes for muscle growth. Potentially, by overusing heavy weights, using excessive volumes without the work capacity to handle them, and employing techniques designed to specifically induce maximal damage such as loaded heavy eccentrics or forced reps, bodybuilders may potentially be causing too much damage leading to impaired performance and recovery. In addition, the toll this type of training has on the central nervous system means that strength can decline for a considerable period of time after very strenuous workouts which, by forcing a reduction in load, will lead to difficulty in gaining muscle mass.
On the other hand we need to recognise that the adaptive response to workouts seen in highly trained subjects means that they may well have a problem with not incurring enough muscle damage during their training sessions compared to untrained subjects of whom much of the research to date has been conducted. As muscle tissue becomes resistant to the effects of training sessions it means that advanced trainees may need to perform more volumes than untrained subjects to prevent stagnation. Empirically this has much support, with elite athletes across all sports performing far greater work than beginners or intermediates.
In the future we hope to see research which can help answer the question of what is an optimum degree of muscle damage and the extent to which this is affected by training experience. Until then we offer the following guidelines on training volume, intensity and frequency of workouts.
Untrained Subjects – Low volume and low frequency of workouts. Typically focus on weights below 70% of 1RM and train with maybe 2-3 sets per body part with 2-3 weights sessions weekly.
Intermediates (1-3 years experience) – Increase intensity of the average set and can do slightly more sets but should avoid any intensity techniques.
Advanced (3-5 years) – Employ heavier weights in the 75-85% range to elicit optimal hypertrophy and can perform more volume than intermediates with frequency increased per body part subject to individual recovery. Can incorporate occasional use of intensity techniques to induce muscle damage. It would be best to test this out on one body part at a time. The focus should be on progressive overload still and building volume up, not on trying to be sore the next day.
Elite (High strength and muscle mass levels) – The focus should remain on progressive overload but weight increases become difficult at this level so instead it is suggested you focus on gradually increasing volume and frequency rather than concentrating on load as the only variable. Can perform more work than other groups but to advance they will need to do so due to the inherent difficulty in gaining muscle in experienced athletes. Should consider advanced techniques not suitable for others such as occlusion training and use of resistance bands.
What happens during a workout?
We have to start by looking at what happens to muscle tissue when training in the gym. A lot of research in this area over the years has conclusively demonstrated that strenuous resistance training will cause muscle damage whose degree is dependent on previous practice of the exercise, training volume, intensity and frequency (1, 2, 3). The degree of damage to muscle tissue also depends on the type of exercise conducted with eccentric exercise being associated with higher levels of muscle damage compared to regular concentric exercise or isometric exercise (4). This reflects what most bodybuilders would experience and indeed explains why many training authorities encourage slow eccentric motions when training. In addition exercise which primarily activates the fast twitch muscle fibres are more likely to lead to greater muscle soreness (5), something which helps explain why ballistic movements with relatively low resistance such as plyometrics or sprint training can cause significant muscle soreness even in relatively experienced subjects.
In the short term, the effects of exercise induced muscle damage on the body leads to increased pain, stiffness, a reduction in muscle flexibility as well as a reduction in performance. This tends to ease over time as trainees become more accustomed to performing a particular exercise and their muscles and connective tissue become less sensitive to the external stimulus imposed by resistance exercise. At this point, many proponents of the need to feel sore after training will argue that exercises should be switched or greater use of intensity techniques should be adopted to help ensure the body is never allowed to adapt and become less resistant to exercise induced muscle damage. We will explore the evidence next.
Mechanisms for how muscle damage could cause growth
A number of theoretical factors could help drive the benefits for muscle growth from causing muscle damage including:
Anabolic Signalling via Inflammatory Factors Satellite Cell Differentiation
IGF-1 Signalling
Cellular Swelling
These were highlighted by Brad Schoenfeld (6) in a recent paper which examined the issue of muscle damage and its effects on hypertrophy.
Schoenfeld conducted a meta review of studies designed to induce a significant degree of muscle damage to measure the effect on hypertrophy gains. The results were inconclusive with no study showing a statistically significant effect on muscle growth of treatments designed to induce muscle damage. However, limitations such as using untrained subjects, failure to match training durations between groups (7) and failure to perform longer trials makes it difficult to reach any firm conclusions.
Roig et.al (8) tested one of the theories beloved of those who argue in favour of heavy eccentric training, namely that it can lead to greater muscle growth as a consequence of the greater damage eccentric contractions can produce. Roig’s group evaluated a number of studies which showed that eccentric exercise led to both greater strength as well as greater muscle mass increases compared to concentric exercise.
In spite of this, Schoenfeld points out other studies which show that concentric exercise may be superior (9) to eccentric exercise as well as highlighting studies showing no benefit to muscle gain of performing eccentric exercise (10). There are inevitably some inconsistencies between different studies but the majority of research to date shows that eccentric exercise is positively correlated with greater muscle gain compared to concentric or isometric exercise.
If we choose to accept the notion that eccentric actions promote greater damage and are associated with greater muscle mass gains, is it logical to deduce that it is the muscle damage itself that promotes the hypertrophy gains?
It has been argued that muscle damage in itself is not a factor in promoting muscle growth. This camp correctly point out that muscle damage produced during strenuous aerobic exercise, or during contact sports is anything but ideal for promoting muscle gains. At the other end of the scale there exists a lot of research supporting the benefits of low intensity training techniques such as occlusion training (using pressure cuffs to minimise the escape of blood from working muscles) for building muscle despite the relatively low levels of muscle damage they induce compared to traditional high intensity training featuring heavy eccentrics. Finally, the fact that the body adapts to any training plan (repeated bout effect) means that muscle damage should be less in trained athletes compared to novices meaning it should not be seen as necessary for muscle growth.
These arguments are countered by those stressing the fact that the repeated bout effect never totally eliminates muscle soreness with even advanced trainees still experiencing muscle trauma. While it is less than what a novice would experience, these trainees are still able to make muscle gains even if not at the same rate at which novices do. The fact that novices gain faster than advanced trainees is highlighted by some as being due to the greater muscle damage they experience, making muscle damage a key goal for advanced athletes to try to replicate the greater muscle gains seen in beginners. Importantly, the fact that the repeated bout effect only attenuates the decline in muscle damage rather than eliminating it, is provided as a casus belli for seeking muscle damage as an end unto itself.
What of the argument that muscle damage experienced during aerobic training such as downhill running is not associated with muscle growth?
While it is true that aerobic training can lead to muscle damage with an absence of muscle gains, this story fails to take into account the fact that aerobic and resistance exercise have different outcomes mediated by an entirely separate set of genes and cellular signalling pathways. Specifically, aerobic training induces changes enhancing mitochondria production, greater oxidative capacity, and reduction in protein synthesis while resistance training promotes muscle growth via entirely different pathways. As such, to state that muscle damage from aerobic work is not sufficient to produce muscle growth rather misses the point, which is that damage is not sufficient to produce muscle growth without an accompanying resistance exercise training model.
How else would hypertrophy be explained?
Although there is some research suggesting that eccentric exercise is associated with greater stress imposed on the muscle compared to concentric actions (11), EMG testing by Grabbiner et.al (12) showed that in spite of this, trainees were unable to generate the same peak force during eccentric compared to concentric actions so that the concentric actions imposed greater mechanical stress on muscles.
The fact that a mass of studies over the years show the superiority of relatively lower intensities in the 65-85% range compared to more heavier loading regimes shows that when looking at the end result most people crave, namely greater hypertrophy, a lower lifting intensity is preferable. The theory that eccentric exercise’s superiority is due to higher force output via heavier loads is thus questionable at this point.
Guidelines for Hypertrophy
Based on the research there does exist a theoretical basis for a role for muscle damage causing a greater gain in muscle growth via the effect of muscle damage on anabolic signalling, inflammatory cell processes and activation of satellite cells. What is not clear, as Schoenfeld’s paper points out, is the extent to which there is a cause and effect relationship between muscle damage and muscle growth and whether or not there is a minimum or maximum threshold of damage necessary to both induce greater hypertrophy gains and where further damage can have an inhibitory effect on muscle growth.
Based on research showing that muscle hypertrophy is better achieved by sticking to moderate intensity levels it could be argued that avoiding excessive muscle damage does indeed lead to better outcomes for muscle growth. Potentially, by overusing heavy weights, using excessive volumes without the work capacity to handle them, and employing techniques designed to specifically induce maximal damage such as loaded heavy eccentrics or forced reps, bodybuilders may potentially be causing too much damage leading to impaired performance and recovery. In addition, the toll this type of training has on the central nervous system means that strength can decline for a considerable period of time after very strenuous workouts which, by forcing a reduction in load, will lead to difficulty in gaining muscle mass.
On the other hand we need to recognise that the adaptive response to workouts seen in highly trained subjects means that they may well have a problem with not incurring enough muscle damage during their training sessions compared to untrained subjects of whom much of the research to date has been conducted. As muscle tissue becomes resistant to the effects of training sessions it means that advanced trainees may need to perform more volumes than untrained subjects to prevent stagnation. Empirically this has much support, with elite athletes across all sports performing far greater work than beginners or intermediates.
In the future we hope to see research which can help answer the question of what is an optimum degree of muscle damage and the extent to which this is affected by training experience. Until then we offer the following guidelines on training volume, intensity and frequency of workouts.
Untrained Subjects – Low volume and low frequency of workouts. Typically focus on weights below 70% of 1RM and train with maybe 2-3 sets per body part with 2-3 weights sessions weekly.
Intermediates (1-3 years experience) – Increase intensity of the average set and can do slightly more sets but should avoid any intensity techniques.
Advanced (3-5 years) – Employ heavier weights in the 75-85% range to elicit optimal hypertrophy and can perform more volume than intermediates with frequency increased per body part subject to individual recovery. Can incorporate occasional use of intensity techniques to induce muscle damage. It would be best to test this out on one body part at a time. The focus should be on progressive overload still and building volume up, not on trying to be sore the next day.
Elite (High strength and muscle mass levels) – The focus should remain on progressive overload but weight increases become difficult at this level so instead it is suggested you focus on gradually increasing volume and frequency rather than concentrating on load as the only variable. Can perform more work than other groups but to advance they will need to do so due to the inherent difficulty in gaining muscle in experienced athletes. Should consider advanced techniques not suitable for others such as occlusion training and use of resistance bands.