Rethinking Muscle Growth: Does the Stretch Truly Reign Supreme?
For years, the fitness community has been captivated by a single idea: maximizing muscle growth hinges on emphasizing the stretch phase of an exercise. This belief, fueled by numerous studies, suggested that stretching muscles more intensely during workouts could lead to significantly greater gains. However, a groundbreaking, comprehensive study has challenged this long-held notion, revealing that the ‘stretch obsession’ might be largely overblown for many muscle groups. The research, which involved custom-built machines and advanced MRI technology, aimed to definitively answer whether focusing on the stretch, or the squeeze (peak contraction), is more effective for building muscle.
The Science Behind the Stretch Hype
The concept of stretching muscles for growth isn’t new. Research dating back to the 1970s, including experiments on chickens where stretching their lat muscles led to a 170% increase in size, hinted at its potential. Subsequent human studies demonstrated that extreme loaded stretching, applied to muscles like the chest and calves, could yield growth comparable to traditional strength training. Further investigations compared exercises that placed muscles like the triceps and quadriceps into a deeper stretch versus those that didn’t, consistently finding superior growth in the muscles subjected to a greater stretch.
These findings led to the popularization of ‘stretch-focused training,’ where exercises were modified to maximize tension in the stretched position. The theory proposed that challenging muscles most in their lengthened state was the key to unlocking superior hypertrophy. However, as the current study’s researchers delved deeper, they identified significant gaps in the existing evidence:
- Limited Muscle Scope: Most prior studies focused on easily accessible muscles like the biceps, quads, and calves, which may respond differently to stretching than other muscle groups.
- Confounding Variables: Many studies compared entirely different exercises (e.g., preacher curls vs. incline curls), making it difficult to isolate whether observed growth differences were due to the stretch itself or other factors like stability or range of motion limitations.
- Measurement Limitations: The common use of ultrasound for measuring muscle growth provides only a partial view (thickness at one point) and can be less accurate for certain muscles or for detecting uneven growth patterns.
A Rigorous New Study: Filling the Gaps
To address these limitations, a dedicated research team, including prominent figures like Dr. Brett Contreras (known as ‘The Glute Guy’) and Dr. Kassm Hansen, designed an ambitious study. The primary goal was to compare the effects of emphasizing the stretch versus the squeeze on muscle growth across various muscle groups, including the chest, glutes, side delts, and rear delts – muscles less commonly studied in this context. Crucially, the study employed Magnetic Resonance Imaging (MRI), the gold standard for precise, three-dimensional muscle volume measurement, at a significant cost of approximately $1,000 per hour.
The innovative aspect of the study involved using custom-designed machines that allowed for a direct comparison within the same individual. Each participant’s body was split, with one side performing exercises emphasizing the stretch and the other side performing the same exercises but emphasizing the squeeze. This ‘within-subjects’ design, where each person acts as their own control, significantly increases the statistical power of the findings, making it more robust than a larger study with separate groups.
The machines allowed for the resistance profile of exercises like pec flies, lateral raises, and hip extensions to be altered with a simple knob. This meant the *only* variable differing between the two sides of the body was whether the exercise was made hardest in the stretched position (bottom of the movement) or the contracted position (top of the movement), while maintaining a full range of motion and tension throughout.
The Surprising Results: Stretch vs. Squeeze
After a year of research and extensive MRI analysis, the results were striking: for the chest, side delts, rear delts, and glutes, there was no significant difference in muscle growth between the stretch-focused and squeeze-focused training groups. Both sides of the participants’ bodies exhibited similar increases in muscle volume over the 10-week study period, with an average growth of around 20%.
This finding directly challenged the prevailing belief that maximizing tension in the stretched position is universally superior for hypertrophy. The study’s lead researcher, Adam Jones, spent over 200 hours analyzing the MRI data, meticulously measuring every muscle. The high adherence rate (97%) further solidified the reliability of these results.
Understanding the Nuances: When Does Stretch Matter?
While the study found no difference in growth for the tested muscles when resistance profiles were manipulated, it did highlight important nuances regarding the ‘stretch’ concept:
- Degree of Stretch: Certain muscles, particularly bi-articular muscles (those crossing two joints) like the hamstrings, quads, and triceps, are structurally capable of greater elongation. Research consistently shows that exercises effectively stretching these specific muscles can promote faster growth.
- Full Range of Motion: The study reinforced the importance of a full range of motion. Both the ‘stretch’ and ‘squeeze’ groups performed complete movements, ensuring tension was present in the stretched position. Failing to achieve a sufficient range of motion, thereby neglecting the stretch, can indeed limit gains.
- Resistance Profile: The core finding is that for muscles like the chest, glutes, and deltoids, making an exercise *harder* specifically in the stretched position (via resistance profile changes) does not appear to yield additional growth compared to making it harder in the squeeze, provided a full range of motion and some tension in the stretch is maintained.
A separate, recently published study comparing cable lateral raises (often harder in the stretch) to dumbbell lateral raises (often harder in the squeeze) also found similar shoulder growth, supporting these conclusions.
Who Does This Apply To? Limitations and Takeaways
It’s important to note that this study primarily used untrained individuals. While beginners tend to grow from most stimuli, the findings suggest that the specific emphasis on the resistance profile in the stretch might not be as critical as previously thought, even for novices. For highly trained individuals, introducing new stimuli, whether stretch-focused or otherwise, can often spark growth due to the novelty effect.
The researchers also pointed out that certain muscles, like the calves, might still be exceptions, with some evidence suggesting they respond exceptionally well to training in the stretch, even with partial range of motion. The lats are another muscle group where more data is needed.
Key Health Takeaways
- Focus on Full Range of Motion: Ensure you are moving through a complete range of motion in your exercises to effectively stimulate muscles, especially those that benefit from a deep stretch.
- Stretch Emphasis Not Universally Superior: For muscles like the chest, glutes, and deltoids, making an exercise hardest in the stretch phase does not appear to offer superior growth compared to making it hardest in the squeeze, as long as a full range of motion is used.
- Bi-articular Muscles May Benefit More: Muscles that cross two joints (e.g., hamstrings, quads, triceps) may still see greater benefits from exercises that emphasize their stretched position.
- Exercise Variety is Key: A wide variety of exercises, including those that emphasize the squeeze and those that offer a good stretch, can all be effective for muscle growth when performed with proper form, progressive overload, and consistency.
- Prioritize Fundamentals: Training hard, ensuring adequate volume, controlling the weight, and maintaining consistency remain the most critical factors for muscle building, more so than hyper-focusing on the stretch.
Conclusion: Flexibility in Training
The findings of this extensive study suggest that the fitness community can afford to be more flexible in its approach to exercise selection. Rather than fixating on optimizing every movement for the stretch, individuals can focus on fundamental principles: training hard, using a full range of motion, and progressively overloading their muscles. This allows for greater freedom in choosing exercises that are enjoyable, accessible, or suitable for injury rehabilitation, without necessarily sacrificing growth potential.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional or certified personal trainer before making any changes to your exercise routine or diet.
Source: The Muscle Building Myth Everyone Fell For (NEW Study) (YouTube)
