Maintaining sufficient levels of skeletal muscle mass is associated with health and longevity (1). Additionally, skeletal muscle aids in movement and glucose disposal (2). Furthermore, increasing skeletal muscle mass has been shown to improve athletic performance and is a common goal for bodybuilders (3). Thus, individuals are constantly striving to find novel and effective approaches for maximizing muscle growth. The research is clear, resistance exercise in combination with nutrition are the most effective interventions to induce muscle growth. However, the exact approach to maximize muscle growth through resistance exercise and nutrition is often lost with the abundance of information available in today’s society. Therefore, the purpose of this article will be to review some basic principles and provide you with easy to digest research backed tips for maximizing muscle growth!
Mechanisms of muscle hypertrophy
Muscle growth is regulated by the net balance between muscle protein synthesis (MPS) and muscle protein breakdown (MPB). MPS is controlled by the mechanistic target of rapamycin (MTOR). Resistance exercise stimulates MTOR and when repeated over time increased MPS and leads to muscle growth. Additionally, amino acids from protein can also stimulate MPS, the most effective amino acid being leucine (4).
How does resistance exercise lead to muscle growth? Initially, researchers proposed that there were three mechanisms involved muscle growth; mechanical tension, muscle damage and metabolic stress (5). Mechanical tension results when skeletal muscle meets resistance and is required to produce force. It has been suggested that this tension disturbs the integrity of the skeletal muscle leading to cellular responses which stimulate MTOR. The relationship between mechanical tension and muscle growth is best evidenced by increases in growth under periods of loading and decreases in muscle mass (atrophy) during periods of unloading. Resistance exercise may also result in muscle damage. It was previously suggested that muscle damage leads to the release of various growth factors which may increase satellite cell activation and support muscle growth. However, it appears that muscle hypertrophy can occur independent of muscle damage. Furthermore, metabolites (lactate, creatine, inorganic phosphate) are accumulated during resistance exercise and it was previously thought that these metabolites played a significant role in muscle growth. While, each of these metabolites have indirectly been associated with stimulating muscle growth, muscle growth has also been demonstrated independent of metabolic stress. Thus, recent reviews suggest that mechanical tension may be the most influential mechanism for muscle growth (6).
However, just understanding that mechanical tension stimulates muscle growth does not give us all of the tools to maximize muscle growth. Practitioners need to have a brief understanding of how to maximize resistance exercise prescription through the proper programming of acute training variables. The most important acute training variables include volume load, intensity, rest interval length, training frequency and exercise selection.
Manipulating the acute training variables
Volume load can be thought of as the total amount of work performed and appears to be the most important training variable regarding muscle hypertrophy (7). Volume can be calculated via Sets X reps X load. Previous research has demonstrated a dose response relationship between volume load and muscle growth. Meaning the more volume performed the greater the muscle growth. In a recent meta-analysis Schoenfeld et al, (2017) demonstrated 10 sets per week resulted in greater muscle growth compared to 1-5 and 5-9 sets per week. It is also important to mention that there is a lack of research assessing the effects of greater volume loads on muscle growth (I.e >10 sets per muscle group per week) and resistance trained individuals often report training with greater volumes (8). However, a threshold likely exists where too much volume will hinder recovery and negatively affect muscular growth. Thus, to maximize muscle growth it is important to individualize volume load prescription. Start by tracking your current training volume and gradually increase on a weekly basis to ensure progressive overload. It is also important to address that high-volume periods of training should be interspersed with low volume training periods to facilitate recovery and prevent injury (9).
Training Intensity is the amount of weight being lifted and is typically prescribed based off of a percentage of an individual’s one repetitions maximum (1RM), or repetition maximum zones (I.e 8-10RM). It was previously thought that muscle growth occurs with moderate loads of 55-75% 1RM or 8-10RM (10). However, what the research has shown us is that muscle growth can occur at a wide variety of loads ranging from 30%-80% (11). Again, what is critical is the total volume load of a given training session. Therefore, you can choose to perform lighter weights to failure or moderate to heavier weights for less repetitions. Often evidence-based practitioners will prescribe training sessions with heavier loads 6-10RM to focus more on mechanical tension and other sessions with lighter loads 12-30RM to focus more on metabolic stress. Feel free to switch up the intensity and remember to keep your total volume load in mind.
Rest interval length is another interesting training variable. While, previous research has shown that shorter rest interval lengths (30-60 seconds) between sets may maximize the metabolic and hormonal response (12). Recent literature has demonstrated that the acute rise of hormones like testosterone post exercise may not have a significant impact on muscular adaptations (13). Moreover, short rest intervals may not allow for as much recovery and actually reduce volume load (14)! Thus, practitioners are now recommending longer rest intervals (90-120 seconds) in order to maximize the training volume for a given session. This does not go to say that anyone who implements short rest intervals is wrong and killing their gains! If you would like to target metabolic stress and implement short rest intervals every now and then that’s fine. However, for the most part you should emphasize longer rest intervals to facilitate recovery between sets.
Training frequency is a training variable that has been the focus of a lot of research as of late. In 2012, data was presented at a national conference demonstrating that training a muscle group 6x per week resulted in greater strength gains compared to 3x. This created a buzz in the industry and led to the “training frequency” hype (15). The rationale was simple, resistance training increases MPS. For novice lifters MPS may be elevated for 24-48 hours post training. However, in trained individuals MPS is only elevated for roughly 4 hours post training (16). Thus, it was logical to believe that training a muscle group more frequently would increase time in MPS and result in greater strength and hypertrophy gains. Simple enough right? Unfortunately, while this data was presented by a respectable research group the findings were never published in a peer reviewed journal. Moreover, since then an abundance of research has been done comparing training muscle groups 1-6x per week under volume equated conditions (which is key) (17). The current body of literature suggest that there is no benefit to training 6x per week compared to 3x per week and 2x per week may offer a small benefit compared to 1x (17,18). However, volume load is still king. These researchers do point out that increasing training frequency may be an effective way to increase training volume which may have important considerations.
Exercise selection is the last piece to the puzzle for training variables. For muscular growth it is recommended that you perform both full body compound movements and single joint accessory exercises. Full body compound exercises like the back squat, bench press and deadlift exercise activate large muscle groups. However, to fully maximize muscle growth it is recommended to train a muscle at varying lengths. This can be achieved through performing multiple exercises for a given muscle group (I.e. flat bench, incline bench, chest fly’s, dips). Exercise order goes hand in hand with exercise selection. Typically, it is recommended to start your training session with full body compound movements and then progress into accessory exercises (19).
Optimizing your nutrition for muscle growth
Whether you are a fan of the ketogenic diet, Mediterranean diet, paleo or traditional western diet in order to increase muscle mass you need to be in a calorie surplus (20). While, the debate between carbohydrates and fats will seemingly go on forever the importance of protein for muscle growth is not up for debate. Evidence suggest that in order to maximize muscle growth from resistance training daily protein intakes should range from 1.6-2.2 g/kg (4). Protein timing has been another area of concern for researchers. While, initial evidence demonstrated that timing your protein pre and post workout may improve training adaptations. Recent reviews suggest that the effect of “nutrient timing” may not be as important as once thought (21). However, it is still recommended to space out your protein servings (20-30grams) throughout the day. As leucine is the most effective amino acid for stimulating muscle growth protein sources with high leucine content should be sought after such as whey, beef, and egg. While it was once believed that the body could not utilize >25g of protein per sitting. Recent research has suggested that after a full body workouts 40g of protein increased MPS to a greater extent compared to 20g (22). Thus, following demanding workouts greater boluses of protein may be warranted. Additionally, consuming a large protein bolus before bed may decrease muscle protein breakdown during the overnight fast and facilitate recovery (23).
Lastly, there has been a lot of concern over high protein diets negatively affecting kidney function, however, a recent meta-analysis demonstrated that high protein diets do not negatively affect kidney function (24)! In conclusion, follow whichever diet that suits your life style the most. If you want to maximize muscle growth, then you need to be in a calorie surplus. Consider creating this surplus with protein and space the protein throughout the day!
Wrapping it up!
- Skeletal muscle serves a variety of functions throughout the human body
- Resistance training and nutrition are the most effective way to increase muscle growth
- Mechanical tension is likely the strongest mechanism responsible for muscle growth
- Volume load is the most important resistance training variable for muscle growth
- Muscle growth can occur at a wide variety of repetition ranges (switch it up!)
- Longer rest interval lengths may allow for greater volume loads
- Training each muscle group 1-2x per week is enough (volume is king)
- A calorie surplus is necessary to support muscle growth
- To maximize muscle growth aim to consume 1.6-2.2 g/kg of protein per day
- Consume proteins with a high leucine content (2.2-2.7g) spaced throughout the day
- A large protein bolus before bed may decrease muscle protein break down.
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