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[@RenaissancePeriodization] Isometrics Can Build As Much Muscle As Full ROM Training!? (new study)

· 6 min read
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@RenaissancePeriodization - "Isometrics Can Build As Much Muscle As Full ROM Training!? (new study)"

Link: https://youtu.be/SN0M5PF_UuE

Short Summary​

Recent research suggests isometric exercises at lengthened muscle positions can produce muscle growth comparable to dynamic contractions, challenging previous assumptions. While isometrics have practical downsides (difficulty gauging failure, potential for nervous system fatigue), they can be incorporated effectively using pauses during reps and as finishers, and a balanced approach incorporating eccentric, concentric, and isometric contractions is likely optimal for maximizing muscle growth.

Key Quotes​

Here are five direct quotes from the YouTube video transcript that I found to be particularly insightful:

  1. "So while it was never valid to say that isometrics don't grow muscle, it seemed valid at the time tentatively to say they grew less muscle than dynamic contraction. But is that still true?" (This highlights the evolving understanding of isometrics in muscle growth.)

  2. "As of today, as of 2025, 2026, it's unwise to say confidently that isometrics are a waste of time or don't work as well. And it's better to say that at least at the lengthened positions in a deep stretch, isometrics might cause robust growth and be a valuable tool in training." (This represents a significant shift in perspective regarding isometrics and provides a specific condition for their effectiveness.)

  3. "With eccentric training, you use less. So your nervous system gets less tired, but your muscles get just as much growth, if not even a little more. with isometric training use a ton of nervous system drive." (This points to a key difference in neurological fatigue between eccentric and isometric training.)

  4. "Eccentric contractions grow more muscle in series, which means they actually make your muscle belly a little bit longer. Longer, fuller muscles are 100% the thing that you want in bodybuilding and in physique." (This explains the importance of eccentric contractions in achieving a desired aesthetic.)

  5. "I want to trend you guys into the direction of using all three contraction types in your training...because there's decent reason to believe this is tentative but probabilistic that you can get more overall growth doing all three types regularly than just focusing on one or the other." (This advocates for a balanced approach to training, incorporating all three contraction types, and suggests a potentially synergistic effect.)

Detailed Summary​

Okay, here's a detailed bullet-point summary of the YouTube video transcript:

I. Introduction: Isometrics are back on the menu?

  • The video re-evaluates the role of isometrics in muscle growth, challenging the older view that they are inferior to dynamic contractions (concentric and eccentric).
  • Introduces a new study and promises actionable training advice.

II. The New Study: Long muscle length isometric vs. Full ROM isotonic training

  • Study Title: "The effects of long muscle length isometric versus full range of motion isotonic training on regional quadriceps hypertrophy in resistance trained individuals."
  • Authors: Star-studded cast featuring Varovich, Zanjer, Wolf, Androlakis Karakis (Dr. Pack), Brad Schoenfeld, and Pav Mikulich
  • Study Design:
    • 23 participants trained both quads, 2x/week for 6 weeks.
    • Within-subject design: one leg trained with full range of motion leg extensions (dynamic/isotonic), the other with isometric contractions at a lengthened muscle position.
    • Isometric group pressed against a fixed plate in a stretched position.
  • Key Finding: Both isometric and dynamic training resulted in approximately the same overall quad growth.
    • Notes some regional differences, but deemed them too speculative to draw firm conclusions.

III. Changing Perspective on Isometrics

  • Old View: Isometrics were considered inferior for muscle growth due to earlier research (mainly on rodents and some human studies) showing less growth compared to dynamic contractions.
  • New Evidence: A growing body of research (last 5-10 years) shows that isometric training, particularly at lengthened muscle positions, can cause robust muscle growth, comparable to dynamic training.
  • Rat study speculation: The failure of some rat studies to show growth from isometrics may be because the muscles were in a shortened position.
  • Current Recommendation: It's now incorrect to dismiss isometrics as ineffective. Lengthened-position isometrics can be a valuable tool for muscle growth.

IV. Downsides of Isometrics

  • Difficulty gauging failure: Hard to determine when you've reached true failure in an isometric contraction, unlike dynamic movements where bar speed slows or movement stops.
  • High Neurological Demand: Isometrics require a large amount of nervous system drive, potentially leading to more fatigue than dynamic training set for set. This fatigue can accumulate and negatively impact long-term training sustainability.
  • Uneven Muscle Growth: Isometrics may not grow the whole muscle as evenly as dynamic contractions. Shortened-position isometrics may favor the proximal end of the muscle fiber, lengthened positions the distal end. Mid-range isometrics mainly grow the middle.
  • Limited Transfer to Dynamic Abilities: Isometric strength gains don't transfer as well to dynamic movements and real-world activities compared to dynamic training.

V. Implementing Isometrics Effectively

  • Paused Reps: Incorporate pauses under load, especially in the stretched position of exercises (e.g., leg press, bench press, dead hang pull-ups). This provides isometric tension and increases safety.
  • Isometric Finishers: After completing dynamic reps on the last set (or last set of the last exercise), hold an isometric contraction in the stretched position for a set duration.
    • Example: Machine chest press with a hold just above the bottom of the stretch.
  • Two/Thirds Squats with Isometric Hold: Two/thirds squats, from bottom to 2/3 up, until failure. Then hold the bottom position in a just below parallel isometric hold for as long as possible.

VI. The Importance of Using All Three Contraction Types

  • Argues against focusing on a single contraction type at the exclusion of others.
  • Three Contraction Types: Eccentric (lowering), Isometric (holding), Concentric (lifting).
  • Each contraction type stimulates muscle hypertrophy through different mechanisms.
  • Referenced 2017 Franchi paper for skeletal muscle remodeling: morphological, molecular and metabolic adaptations to eccentric versus concentric loading.
  • Eccentric Contractions:
    • Tend to grow muscle in series (lengthening the muscle belly).
    • Can bias growth in the distal portions of the muscle (leading to better aesthetics).
  • Concentric Contractions:
    • Tend to grow muscle widthwise.
    • Tend to bias growth in the middle of the muscle belly.
  • Combining Eccentric and Concentric: Leads to fuller, longer, and thicker muscles with better overall shape (quad sweep, bubble shoulders, hanging triceps).
  • Isometric Integration: Given evidence of isometric growth, integrate these as well.

VII. Conclusion

  • Emphasizes that using all three contraction types (eccentric, isometric, concentric) is likely the best approach for maximizing muscle growth.
  • Suggests varying the emphasis on each contraction type in different training mesocycles.
  • Encourages listeners not to look for one single "magic bullet" answer, but to embrace a multifaceted approach.