Chris and Paul discuss a model for predicting muscle growth, emphasizing the need to understand research outcomes. They explore training variables and their impact on hypertrophy, including rep ranges, rest periods, and metabolite clearance. The relationship between mechanical tension, volume, and muscle growth is examined, along with the concept of stimulating reps. The hosts discuss exercise order and contrast different models, while debunking the volume model for predicting muscle growth. They delve into the relationship between muscle growth and tension, neuro-mechanical matching, and the entire body of research on muscle growth. The optimal timing for combining cardio and strength training is explored, along with factors for muscle growth and muscle growth in different regions of the pecs. The chapter also discusses isometric ankle plantar flexion strength and the use of the stimulating reps model in predicting muscle growth.
The stimulating reps model suggests that the number of stimulating reps, involving high motor unit recruitment and mechanical tension, determines hypertrophy stimulus.
Increasing sets in a workout does not proportionally increase hypertrophy gains, as additional sets can result in more fatigue and muscle damage without significant increases in stimulating reps.
Fatigue mechanisms, including metabolite accumulation and muscular damage, increase with additional sets, leading to reduced motor unit recruitment and tension.
Exercise order can impact workout performance due to CNS fatigue caused by earlier sets, reducing recruitment and tension in later sets.
The three-part model struggles to explain certain training variables like exercise order and volume, while the stimulating reps model offers a simpler and more comprehensive explanation.
Deep dives
The stimulating reps model explains the effects of rep range
The stimulating reps model suggests that the number of stimulating reps, which involves high motor unit recruitment and mechanical tension, determines the hypertrophy stimulus. Different rep ranges produce similar hypertrophy when trained to failure. This contradicts the three-part model, which suggests that different rep ranges lead to different hypertrophy outcomes due to metabolic stress, muscle damage, and mechanical tension. The stimulating reps model provides a clearer explanation, as rep ranges and short rest periods can reduce motor unit recruitment and tension, leading to diminishing returns in hypertrophy.
The diminishing returns of increasing volume
Increasing the number of sets in a workout does not lead to proportionally higher hypertrophy gains. The stimulating reps model predicts this diminishing return, as additional sets can result in more fatigue and muscle damage without significant increases in stimulating reps. The three-part model fails to explain the diminishing returns, as it does not account for the reduction in recruitment and tension over multiple sets. Research supports the idea that volume plateaus around six sets per muscle group per session, where further sets provide minimal additional hypertrophy stimulus.
The impact of fatigue on volume
Fatigue plays a key role in the decreasing returns of volume. Fatigue mechanisms, including metabolite accumulation and muscular damage, increase with additional sets, leading to reduced motor unit recruitment and tension. The stimulating reps model accurately predicts this decrease in stimulating reps, while the three-part model fails to provide a clear explanation. Understanding the diminishing returns of volume helps optimize training and target the most effective sets for hypertrophy.
The Stimulating Reps Model and Exercise Order
The stimulating reps model explains how exercise order can impact workout performance. As we do more exercises in a workout, the later exercises are typically less stimulating due to CNS fatigue caused by earlier sets. The model attributes this fatigue to the production of myokines in the muscle, which is detected by the brain, leading to reduced recruitment and tension in later sets. The stimulating reps model provides a clear explanation for the exercise order effect without needing additional complex explanations.
The Limitations of the Three-Part Model
The three-part model, which considers mechanical tension, metabolic stress, and muscle damage, struggles to explain certain training variables like exercise order and volume. It cannot accurately predict the effects of different exercise orders or explain the hypertrophic response to varying volumes. Additionally, the model's assumption that more muscle damage always leads to more hypertrophy is contradicted by the existence of volume plateaus. The stimulating reps model, on the other hand, offers a simpler and more comprehensive explanation for training variables.
The Role of Neuro-Mechanical Matching
Neuro-mechanical matching plays a crucial role in muscle recruitment and tension during exercise. The stimulating reps model emphasizes the importance of tension derived from muscle length tension and force-velocity relationships. It explains that tension is influenced by sarcomere length, which differs in different muscle groups. Studies indicate that stretch positions and certain exercises yield more hypertrophy in certain muscle groups, while others show no such effect. The stimulating reps model provides a prediction based on physiological concepts, making it a more effective tool for understanding muscle-specific responses.
The Impact of Concurrent Exercise on Hypertrophy
Concurrent aerobic exercise can impede hypertrophy caused by strength training, particularly when performed immediately before or in high volumes. The stimulating reps model explains that aerobic exercise induces muscle damage, leading to an inflammatory response and subsequent CNS fatigue, reducing recruitment and tension in the trained muscles. To minimize interference, it is advisable to separate aerobic exercise from strength training sessions, either by doing it on non-training days or at least a few hours apart. The timing and intensity of the concurrent exercise are crucial factors in determining their impact on hypertrophy.
The Need for Moment Arm Studies on Transverse Plane Movements
There is a need for research studies that focus on moment arm data for movements in the transverse plane, specifically for the pecs and interior delts, rear delts, and traps. Understanding the leverages and muscle activations within these regions during transverse plane movements could have significant implications for training program design and optimization.
The Challenges with Understanding Calf Muscles
The calves present a unique challenge in the context of the stimulating reps model. While the model explains most training variables effectively, the calves do not fit neatly within its framework. Specifically, studies on the calves have shown conflicting results in terms of fascicle length increases and tension in the stretched position. Further research, particularly studies measuring fast-twitch increases during strength training, is needed to gain insights into the functioning of the calves and how they respond to different training stimuli.
