Why Crossfit Athletes Build So Much Muscle
The average, recreational Crossfitter typically has a good amount of muscle with a low amount of body fat compared to the average person while a professional Crossfit athlete has enough muscle to rival the physique of a bodybuilder.
So, with no specific muscle-specific training splits how do Crossfit athletes continue to build so much muscle while a majority of their workouts are predominantly cardio based with lighter weights?
There are 3 reasons why (backed by science) below.
1) VOLUME
High reps at sub-maximal weights have been shown to be one of the most important factors for muscle growth.
“Resistance training (RT) is the primary exercise intervention for increasing muscle mass in humans. It is theorized that the volume of training performed in a RT bout—herein determined by the formula: repetitions /×/ sets (1)—plays a significant role in chronic muscular adaptations such as muscle size and strength (2). As compared with single-set routines, acute studies indicate that performing multiple sets augments the phosphorylation of p70S6 kinase and muscle protein synthesis (MPS), suggesting that higher volumes of training are warranted for maximizing the hypertrophic response.“
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6303131/
The volume of repetitions, or “rep volume,” in CrossFit is a significant factor contributing to muscle gain, and this is due to several physiological mechanisms:
1. Mechanical Tension and Muscle Hypertrophy:
High rep volume in CrossFit workouts exposes muscles to prolonged mechanical tension. This tension is a critical factor in muscle hypertrophy, which is the growth and increase of the size of muscle cells.
By performing a high number of repetitions, CrossFit athletes maintain their muscles under tension for extended periods, leading to greater muscle fiber recruitment and growth.
2. Metabolic Stress:
CrossFit’s high rep volume contributes to metabolic stress, another key driver of muscle hypertrophy. Metabolic stress occurs when muscles are worked to fatigue, leading to the accumulation of metabolites like lactate, hydrogen ions, and creatine.
This accumulation is thought to contribute to an anabolic environment that promotes muscle growth through various mechanisms, including hormone release and cellular swelling.
3. Muscle Damage and Repair:
The repeated muscle contractions with high rep volume cause microscopic damage to muscle fibers, which then need to repair and rebuild.
This process of muscle damage and subsequent repair is a natural response that leads to muscle strengthening and growth over time, as the muscle adapts to handle the workload more efficiently.
4. Time Under Tension (TUT):
High rep volume naturally increases the time under tension for the muscles during a workout. Time under tension is a concept in resistance training that refers to how long a muscle is under strain during a set.
A higher TUT has been associated with increased muscle hypertrophy because it can enhance the muscle’s response to growth stimuli.
5. Endurance and Resistance Adaptation:
CrossFit workouts often blend muscular endurance with resistance training.
The high rep volume improves muscular endurance, while the resistance element (using body weight, barbells, kettlebells, etc.) ensures that the muscles are still working against a significant load.
This combination can lead to both sarcoplasmic hypertrophy (increase in muscle glycogen storage) and myofibrillar hypertrophy (increase in muscle fiber size).
6. Hormonal Response:
High-volume training has been shown to increase the body’s production of anabolic hormones such as growth hormone and testosterone, which are vital for muscle growth.
The body’s hormonal response to the stress of high rep volume can thus further enhance muscle hypertrophy.
7. Improved Muscle Fiber Recruitment:
Performing a high volume of reps can lead to improved muscle fiber recruitment.
Initially, the body uses more Type I muscle fibers (slow-twitch), but as these fibers become fatigued, the body recruits Type II muscle fibers (fast-twitch) to maintain performance.
Fast-twitch fibers have a higher potential for growth, and their increased recruitment can lead to greater gains in muscle size.
Related: How CrossFit Increases Testosterone
2) FAILURE
Muscle growth occurs when subjects do sets until failure, regardless of weight.
A 2012 study has shown that completing 3 sets to failure performed with either 30% or 80% of your 1RM has lead to more muscle growth than 1 set to failure done with 80% of your 1RM.
Meaning, more sets done to failure leads to more muscle, regardless of weight used.
Performing workout sets to failure—that is, continuing an exercise set until you can’t complete another repetition with proper form—can stimulate muscle growth for several reasons:
Muscle Fiber Recruitment: When you lift weights to the point of failure, your body recruits as many muscle fibers as possible to handle the load. This process targets both slow-twitch (endurance) and fast-twitch (strength and size) muscle fibers, leading to more comprehensive muscle development.
Mechanical Tension: Lifting weights creates mechanical tension in your muscles, one of the primary factors in muscle growth. When you lift to failure, this tension is maximized.
Metabolic Stress: Working out to failure also creates metabolic stress by causing a buildup of byproducts like lactate in your muscles. This “pump” sensation is associated with anabolic (muscle-building) processes.
Muscle Damage: Intense workouts cause microscopic damage to muscle fibers. While it might sound harmful, this damage is actually a catalyst for muscle growth. Your body repairs these damaged fibers through a cellular process where it fuses muscle fibers together to form new muscle protein strands (myofibrils). These repaired myofibrils increase in thickness and number to create muscle hypertrophy (growth).
Hormonal Responses: Training to failure can lead to a greater acute hormonal response, including an increase in testosterone and growth hormone, both of which are conducive to muscle growth.
During a Crossfit workout the typical athlete will push themselves to get the fastest time possible and in pursuit of that goal they will often get very close to failure on a certain movement. Doing this on a consistent basis leads to consistent muscle growth.
3) CONSTANTLY VARIED WORKOUTS, MOVEMENTS, TRAINING DAYS
First, what is the “repeated bout effect“?
Repeated Bout Effect: The repeated bout effect refers to the adaptation whereby a single bout of eccentric exercise protects against muscle damage from subsequent eccentric bouts.
Muscle is built when you have created tears in the muscle (damage) through resistance training and subsequently repair and fill those tears with nutrients in order for them to grow.
When you consistently repeat the same workout with the same amount of weight your body protects against muscle damage as best as it can, limiting your growth.
In Crossfit no day is ever the same. You may do squats 2 days in a row, you may have cardio paired up with heavy strict press followed by swimming the next day, etc.
Because Crossfit training is designed to have you prepared for anything you may encounter your routine will never be the same, and because of this your body will always be forced to adapt to new stimuli.
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FAQ on Muscle Building in CrossFit Athletes
Q1: Why do CrossFit athletes often have more muscle mass compared to athletes from other sports? A1: CrossFit athletes engage in a training regimen that combines strength training with high-intensity functional movements. This approach not only improves cardiovascular endurance but also places significant stress on the muscles, leading to hypertrophy, which is the increase in muscle size. The varied movements in CrossFit target all major muscle groups, often leading to more balanced muscle development.
Q2: How does the intensity of CrossFit workouts contribute to muscle gain? A2: The high intensity of CrossFit workouts leads to a substantial metabolic response, which includes the release of growth hormones like testosterone and IGF-1. These hormones are crucial for muscle repair and growth. Additionally, the intensity can lead to muscle fatigue, which is a key driver for muscle adaptation and growth.
Q3: Does the variety of exercises in CrossFit affect how muscles are built? A3: Yes, the variety of exercises in CrossFit workouts prevents muscle adaptation to a single movement pattern, which can occur in more repetitive training routines. This constant variation challenges muscles in new ways with each workout, promoting continuous muscle growth and reducing the risk of plateaus.
Q4: Are CrossFit workouts enough for building muscle, or do athletes need additional strength training? A4: While CrossFit workouts typically include elements of strength training, some athletes may incorporate additional targeted strength work to address specific goals or weaknesses. However, for many individuals, the compound movements and lifting sequences in CrossFit provide a sufficient stimulus for muscle growth.
Q5: How important is nutrition in the muscle-building process for CrossFit athletes? A5: Nutrition is critical for muscle building in CrossFit athletes. Adequate protein intake is essential for muscle repair and growth, while carbohydrates are important for fueling the high-intensity workouts that stimulate muscle hypertrophy. Additionally, healthy fats are necessary for hormone production and overall recovery. CrossFit athletes must ensure they are consuming enough calories to support their energy expenditure and facilitate muscle gain.
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