Skeletal Muscle Adaptations
Written by Ben Bunting: BA, PGCert. (Sport & Exercise Nutrition) // British Army Physical Training Instructor // S&C Coach.
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Welcome to the world of muscle hypertrophy, where the art of sculpting a strong and chiselled physique is backed by science.
If you've ever wondered how to maximise your gains and supercharge your muscle growth, you're in the right place.
In this article, we'll dive into the science behind muscle hypertrophy and explore how increasing resistance training volume can unlock your body's full potential.
By understanding the mechanisms at play and applying the principles of progressive overload, you'll be able to take your workouts to new heights and achieve the muscle gains you've always dreamed of.
Resistance training (also called weight or strength training) is an integral part of any health and fitness routine.
Resistance training entails two neurological elements that govern muscle force: motor unit recruitment and rate coding.
Understanding the Science Behind Muscle Growth
Hypertrophy training involves increasing muscle size. This workout style typically targets those seeking larger muscles and may include exercises like bicep curls and deadlifts.
While some pursue hypertrophy training for health benefits, others use weightlifting to improve body image or simply look better.
Whatever the motivation for a training session, understanding the science behind weightlifting is critical to maximise results and reach maximum muscle-growth potential.
Muscle protein synthesis is one of the key mechanisms involved in hypertrophy training, thickening existing muscle fibers to increase overall muscle size and increasing overall mass.
Hypertrophy training works better for those seeking to increase mass rather than build new fibres, as that would take longer to produce results.
Other factors contribute to hypertrophy in skeletal muscle, beyond muscle protein synthesis, such as cell hypoxia, metabolites and hormones.
Resistance exercise causes temporary cell hypoxia due to compression of muscle tissue; this increases lactate concentration and growth hormone production, both of which signal muscle protein synthesis while also quelling myostatin's inhibitory effects on growth.
Other factors that contribute to muscle hypertrophy include eating a high-protein diet and lifting heavy loads.
Studies have also demonstrated that increasing repetitions during workouts is linked with greater increases in muscle mass and strength.
However, not all studies found the same results; some found discordant increases between size and strength gains, likely because different muscle components react differently to certain stimuli, such as myofibrils, sarcoplasm with organelles inside it, and the ECM around muscles.
Factors that Contribute to Muscle Hypertrophy
Compounding factors contribute to muscle hypertrophy, including genetics, nutrition, hormones, and training variables.
While genetics and hormones are largely outside our control, we can manipulate nutrition and training variables to optimise muscle growth.
In addition to nutrition, training variables such as intensity, volume, and frequency also contribute to muscle growth.
How Increasing Resistance Training Volume Can Maximise Gains
Resistance training volume refers to the total amount of work performed during a training session.
It is typically calculated by multiplying the number of sets, reps, and weight lifted. Increasing resistance training volume can effectively maximise muscle gains.
Research shows that higher training volumes can lead to greater muscle hypertrophy than lower volumes.
This is because higher volumes provide a greater stimulus for muscle growth and increase the metabolic stress placed on the muscles.
Additionally, higher volumes can enhance muscle fibre recruitment, leading to greater gains.
However, increase training volume gradually and progressively.
Jumping from a low volume to a high volume too quickly can increase the risk of overtraining and injury. It's recommended to increase volume by adding additional sets or reps over time, allowing your body to adapt and recover.
Different Methods to Increase Resistance Training Volume
Several strategies can help you increase resistance training volume and maximise gains. Here are a few effective methods:
1. Increase the number of sets: Adding an extra set or two to your workouts can significantly increase the total volume of training. Gradually increase the number of sets for each exercise over time.
2. Increase the number of reps: Instead of stopping at a certain number of reps, push yourself to perform a few more. Increasing reps per set increases total workload and can lead to greater muscle growth.
3. Reduce rest periods: Shortening the rest periods between sets can help increase the metabolic stress placed on the muscles. This can be especially effective for hypertrophy-focused training.
4. Incorporate supersets or drop sets: Supersets involve performing two exercises back-to-back with minimal rest in between. Drop sets, on the other hand, involve gradually reducing the weight after reaching muscle fatigue. Both methods can increase training volume and stimulate muscle growth.
Remember, the key is to gradually increase the resistance training volume over time to allow for proper adaptation and recovery.
Hyperplasia
Skeletal muscle serves as the protein storehouse of our bodies, essential for locomotion, eating, respiration and glucose/lipid homeostasis. Therefore, its loss is considered an early warning signal of metabolic disorders and even mortality.
Hyperplasia occurs when cells within an organ or tissue proliferate and increase in number, expanding that organ or tissue's size.
It is a natural adaptation and can be caused by physiological stressors like lifting an 11-pound bag of potatoes or disease processes like cancer.
Exercise overload increases functional demands on skeletal muscles; they produce more proteins (myofilaments) to generate force while also expanding and growing larger in cross-sectional area; this phenomenon is known as skeletal muscle hypertrophy.
Resistance training has been shown to increase muscle protein synthesis via both the AMPK and mTOR signalling pathways, with muscle growth taking place through both processes in tandem.
Notably, these divergent signalling pathways that influence growth or atrophy don't always work against one another; instead, they interact through a complex interplay of hormones like insulin, IGF-1, TGFβ, IGF-2, FOXO3, YAP or myostatin to produce results that benefit muscular health and myostatin production.
HGF (Hepatocyte Growth Factor) is one such cytokine released after exercise, with its primary role being to stimulate skeletal muscle hypertrophy.
HGF works by activating mTOR, which then phosphorylates its target protein FOXO, inhibiting it and increasing protein synthesis.
Studies show that resistance training increases protein synthesis, leading to an increase in conversion from Type IIb fibres to Type IIa fibres, likely because Type IIa fibres have greater oxidative capacity than Type IIb fibres.
This transition may be an adaptation to resistance training's metabolic stressors; using weights which allow you to train to failure is key here!
Strength
Muscles trained consistently to resist a given load become stronger over time through hypertrophy.
This process takes time, as muscle cells must adjust to new stress. Many people get discouraged when their strength gains plateau.
However, this should be seen as a positive sign, and you should increase either the intensity or volume of your workouts, or use different resistance training equipment such as dumbbells, barbells, powerbands, kettlebells, or your own bodyweight to break through it.
Strengthening your muscles can improve your quality of life as you age by helping prevent sarcopenia (age-related muscle loss) and reducing osteoporosis risk.
Resistance training can also provide great benefit to those suffering from certain chronic health conditions, including type 2 diabetes.
Regular resistance training as part of their exercise routine can help control blood sugar and help manage its fluctuations more effectively, contributing to better control.
Although high-intensity resistance training workouts will certainly increase your heart rate, they tend to burn significantly fewer calories than cardiovascular exercises such as running, cycling, or aerobics because they target muscle and are more sedentary than other forms of exercise.
Women typically burn between 50-100 cals per 10 minutes of strength training, depending on the type of exercise, the amount of resistance used, and the level of exertion.
Toning exercises like sit-ups, squats, and leg raises tend to burn around 53 calories every 10 minutes, while moderate strength training with weights produces about 66 calories, and suspension training burns 99 Calories every 10 minutes.
Gaining muscle is not only good for maintaining a healthy metabolism and appearance - it can even extend your life!
A study published in Frontiers in Physiology demonstrated this point; those who participated regularly in resistance training were less likely to die early than those who didn't, perhaps due to improved bone strength as well as better balance and stability, which become essential components as you age.
Endurance
Endurance training involves isotonic contractions of large muscle groups over multiple sessions (typical examples include running, swimming, and cycling in summer sports; cross-country skiing or speed skating in winter sports).
Endurance exercise increases oxygen uptake capacity and shifts the lactate threshold higher through changes in skeletal muscle metabolism, including increased mitochondrial biogenesis and capillary density, higher oxidative enzyme levels, and a shift from fast-twitch to slow-twitch fibre types over time.
Endurance exercise increases soluble glucose in skeletal muscle by raising expression and activity of glycogen synthase, increasing carbohydrate turnover rates and improving glucose uptake during fatigue onset.
Furthermore, endurance training decreases permeability to calcium ions, further improving calcium use as an activator of ATP synthesis.
Endurance exercise improves one's ability to maintain a higher velocity or average power output over time (performance velocity/power).
This is primarily due to an increase in slow-twitch fibres, which generate more mechanical work from equal energy input.
Increased mitochondrial concentration makes these fibres more efficient at producing ATP via aerobic metabolism.
Studies show that metabolic adaptations to endurance training in older adults remain unchanged over time, providing increased insulin-stimulated skeletal muscle glucose oxidation.
Yet the exact mechanisms remain enigmatic.
Recently, researchers have shown that resistance training with low glycogen availability can increase acute signalling processes that promote mitochondrial biogenesis more than the same exercise with ample glycogen.
This approach can also significantly enhance skeletal muscle responses to resistance training in terms of hypertrophy and strength gains.
Furthermore, this improvement in muscle signalling appears independent of any systemic adaptations, suggesting that glycogen depletion effects depend mainly on local signalling mechanisms.
Conclusion
Skeletal muscles adapt quickly to various physical activities and exercise training programs, with changes depending on factors such as activity patterns, age, and fibre type composition.
Exercise training produces one major adaptation: increased mitochondrial content within trained muscle fibres.
This increased capacity for aerobic energy provision allows trained muscles to better utilise blood glucose and fatty acids, resulting in smaller disruptions of homeostasis during exercise sessions of any intensity level.
To perform sustained exercise tasks, muscle cells must be supplied with glucose and fatty acids from within each fibre as well as oxygen from outside (either via blood flow or diffusion from red cells in capillaries).
The mechanisms controlling energy provision are intricate; they involve many cellular and biochemical processes, and endurance exercise training can induce muscular adaptations that affect these processes, improving performance after several weeks or months of intense training.
In addition to structural and metabolic adaptations, exercise also alters skeletal muscle contractile properties; slow-twitch fibres' contractile characteristics depend on the balance between glycolytic and oxidative potential.
Skeletal muscle contractility has been linked to metabolic diseases such as insulin resistance and type 2 diabetes, where an increase in glycolytic type IIx skeletal muscle fibres has been shown to correlate with an increase in glycolysis-sensitive type IIb fibres (formerly misclassified as type IIx).
Studies indicate that exercise-activated AMP-activated protein kinase (AMPK), an enzyme activated by physical exercise, facilitates biogenesis of new mitochondria as well as increased muscle fibre glycolysis after exercise training.
