Fitness experts Milo, Greg, and Pak discuss stretch-mediated hypertrophy, from animal to human studies, implementing lengthened training into workout routines, comparing results with resistance training, and answering audience questions. They explore the impact of longer muscle links on growth, stretching interventions, and the importance of muscle length in achieving hypertrophy. The podcast provides valuable insights on muscle growth strategies and challenges misconceptions in the fitness industry.
Human studies on stretch-mediated hypertrophy show smaller effects due to lower stretching intensity and duration compared to animal studies.
Muscle fibers can grow longitudinally or radially through the addition of sarcomeres, influenced by different types of mechanical loading and training.
Training at longer muscle lengths leads to twice as much muscle growth compared to training at shorter muscle lengths.
Stretching interventions with higher intensities and longer durations are crucial for significant changes in fascicle length and pinnation angle.
Research suggests that observed muscle growth from training at longer muscle lengths is not solely due to stretch stimuli, indicating other influencing factors.
Deep dives
Stretch Mediated Hypertrophy Concept
Stretch mediated hypertrophy refers to muscle growth speculated to be induced through stretching interventions. Studies suggest that muscles can experience hypertrophy even without active contraction, as demonstrated in experiments on denervated muscles in animals. The term originated in animal studies involving prolonged stretching with significant weight loads. Notably, while animal studies show substantial hypertrophy and hyperplasia, human studies present smaller effects due to lower stretching intensity and duration. This raises questions about the generalizability of research findings to human resistance training.
Muscle Fiber Growth Mechanism
Muscle fibers can grow longitudinally or radially, with longitudinal hypertrophy increasing the length of the muscle fiber and radial hypertrophy increasing its diameter. This growth occurs through the addition of sarcomeres either in series or parallel. Studies have shown that hypertrophy mechanisms can differ based on the type of training or mechanical loading, emphasizing stretching and lengthening for longitudinal hypertrophy, potentially influenced by eccentric contractions.
Human Response to Stretching Interventions
Human studies on stretching interventions indicate varied responses in muscle size changes. Review papers highlight differences between animal and human responses due to lower stretching intensities and durations in human studies. While some human studies show significant muscle growth, others find no significant improvements. Notably, the lower intensity and duration of stretching interventions in humans result in smaller effect sizes for hypertrophy compared to animal studies.
Muscle Size Adaptations to Training at Different Muscle Lengths
Training at longer muscle lengths led to twice as much growth compared to training at shorter muscle lengths. The study compared training at 30-65 degrees of knee flexion (short muscle lengths) to training at 65-100 degrees of knee flexion (long muscle lengths). The longer muscle length training group showed approximately twice the muscle growth of the shorter muscle length group, showcasing the impact of training through longer muscle lengths on muscle hypertrophy.
Fascicle Length and Angle Changes in Response to Different Stretching Interventions
Stretching interventions with higher intensities and longer durations were found to be essential for significant changes in fascicle length and pinnation angle. Increased fascicle length was observed when stretching interventions lasted over an hour and a half per week, with higher intensity stretching leading to more pronounced effects. On the other hand, pinnation angle changes favored shorter durations of stretching interventions. The study highlighted the importance of both intensity and duration in inducing changes in fascicle length and angle.
Analysis of Stretch-Mediated Hypertrophy
The research findings indicated that the observed muscle growth from training at longer muscle lengths was not solely mediated by stretch. While longer muscle length training resulted in additional muscle growth compared to shorter muscle lengths, the magnitude of stretch induced by this training was insufficient to independently cause significant hypertrophy. The study suggested that the effects observed were likely due to factors beyond stretch stimuli, as the duration and intensity of the stretching stimulus fell short of what is required to solely mediate muscle hypertrophy.
Training Through Longer Muscle Lengths and its Impact on Hypertrophy
Training through longer muscle lengths, even without inducing a deep stretch sensation, has shown to lead to more growth compared to training at shorter muscle lengths. Research indicates that the benefits of lengthened training are not dependent on feeling a stretch during the exercise. Studies have demonstrated that muscle growth tends to be larger with training at longer muscle lengths, regardless of the perceived stretch during the movement.
Stretch-Mediated Hypertrophy and Different Types of Resistance Training
The concept of stretch-mediated hypertrophy has been scrutinized, with evidence suggesting that factors beyond stretch influence muscle growth. Studies comparing lengthened training to shortened training have shown that training at longer muscle lengths results in greater longitudinal hypertrophy and even notable radial hypertrophy. Different types of resistance training, such as eccentric, concentric, and isometric contractions, may preferentially target fast-twitch fiber growth or changes in pination angle, emphasizing the need for a varied training approach to stimulate diverse hypertrophy outcomes.
Effectiveness of Implementing Lengthened Partial Repetitions
Lengthened and partial repetitions have shown effectiveness in promoting muscle gains, with considerations for standardized ranges of motion using joint angles. Implementing lengthened partials after full-range sets or as lengthened supersets has been found to be beneficial. Studies indicate significant hypertrophy gains from lengthened partials, even after reaching a point of volitional failure, particularly in movements biased towards the lengthened position.
Duration and Sustainability of Fast-Twitch Fiber Length Adaptations
The sustainability of fast-twitch fiber length adaptations from lengthened training remains a topic of discussion. Research suggests that initial gains in fast-twitch fiber length peak early in training and then may exhibit diminishing returns over time. However, evidence from studies with trained individuals contradicts the notion that fast-twitch fiber length adaptations cease altogether after a specific period. There is ongoing debate regarding the long-term sustainability and extent of these adaptations, with the need for further research in trained populations to clarify these outcomes.
In this episode, Milo, Greg, and Pak sit down to discuss the concept of stretch-mediated hypertrophy, from the foundational animal studies, to human stretching studies, to present day hype around stretch-mediated hypertrophy and lengthened partials. They also discuss how they're currently implementing lengthened training into their workout routines.
TIME STAMPS
Note: The full list of sources and notes can be found on the episode page on strongerbyscience.com/podcast-episode-132 here
00:00:00 - Intro and Plugs
00:11:33 - Stretch-mediated hypertrophy and hyperplasia in animals
00:44:59 - Stretch-mediated hypertrophy in humans/how muscle fibers grow
00:56:08 - Impact of stretching interventions on hypertrophy in humans
01:44:28 - Results vs lengthened resistance training
02:11:08 - Recap/takeaways from resistance training literature
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