Lengthened Bias Training: What’s the Hype?

In the bodybuilding community, lengthened bias training has become the hottest topic in 2025. From Instagram reels showcasing deep-range chest flies and incline curls, to respected researchers highlighting the hypertrophic benefits of loading muscles in the stretched position. The “lengthened bias” trend has quickly moved from a niche curiosity to a mainstream programming principle.

At its core, this concept is simple: if you stretch a muscle under load at longer muscle lengths you may see superior gains in muscle size compared to training it in a more shortened position. Influencers, coaches, and evidence-based educators alike have begun emphasising the strategic use of lengthened-biased exercises like Romanian deadlifts, incline dumbbell curls, and overhead triceps extensions. The results? Anecdotal reports of new found growth and in some cases, complete program overhauls to load the stretch & maximise its benefits.

But as with all trends in fitness, hype needs to be balanced with science. While the research is promising, the story is far from black and white. Not all studies find that training at long muscle lengths leads to superior growth. In fact, emerging evidence suggests that the effects may depend on factors such as training status, muscle group, exercise selection & anatomical structure.

Moreover, this trend has led to some conceptual confusion. Many have begun using the term “stretch-mediated hypertrophy” interchangeably with training at long muscle lengths. While they sound similar & have an overlap in mechanism, they are not the same thing. Understanding their contrast is critical if we want to use these ideas effectively and accurately in program design.

Within this article I aim to unpack some research and nuance behind lengthened-biased training & explore what the science really say & how we can apply it in practice. We’ll also tackle some recent findings; like the work from Martin Refalo on quad hypertrophy, that may challenge this one-size-fits-all narrative.

And like in most cases, we’ll land where most good training advice does: in the middle. Because while long-length training might offer unique advantages, we’re not ready to throw out our preacher curls and lying leg curls just yet.

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The Mix Up: Stretch-Mediated vs. Lengthened-Bias Training

As with many concepts in exercise science, the terminology surrounding training at long muscle lengths has become a bit tangled. The term “stretch-mediated hypertrophy” is often used casually to describe the hypertrophic benefits of performing movements where the force vs length curve biases the stretch position (e.g. flat DB chest fly or a RDL); or through joint manipulation, increases ROM beyond its standard variant (think DB bicep curl with elbows by your side vs the shoulder in extension e.g. Incline DB bicep curl). However, from a physiological and research-based standpoint, this use of the term is technically incorrect.

Stretch-Mediated Hypertrophy (SMH): What It Really Means

Stretch-mediated hypertrophy refers specifically to muscle growth that is triggered by a passive or sustained mechanical stretch, often in the absence of an active contraction. The concept first gained traction in the famous animal bird study, where hanging weights from wings for prolonged periods resulted in enormous increases in muscle mass, even when the muscles weren’t actively contracting.

In more recent human research, SMH typically shows up in studies where muscles are subjected to long-duration loaded stretching, sometimes for 30 to 60 minutes per day. These protocols often result in modest increases in muscle size and fascicle length. This is especially apparent for muscles such as the calves, hamstrings & chest. As you can imagine this style of training requires substantial time & consistency, alongside obvious discomfort!

SMH is a distinct form of hypertrophy because its primary driver is passive mechanical tension, not the active contraction and metabolic stress that encompasses traditional isotonic resistance training.

Lengthened-Bias Training: Different but Related

In contrast, training at long muscle lengths refers to standard resistance training performed in positions where the target muscle is more stretched. Another example of this would be the bottom position of an overhead triceps extension or the fully lengthened position of a RDL. These exercises produce active tension in a lengthened state, combining both eccentric stress and stretch-based mechanical loading.

Most Importantly, these exercises are not “stretch-mediated” in a pure sense. They are still driven by active muscle contraction under load. However, because the muscle is under high tension while elongated, the total mechanical tension (active + passive) is increased. That’s what likely drives the superior hypertrophic response seen in many studies.

In short:

• Stretch-mediated hypertrophy = hypertrophy from passive, sustained stretch, often without contraction (e.g., long-duration static stretching).

• Lengthened-bias training = hypertrophy from a loaded contraction in a stretched position, like incline curls or deep squats.

There is some overlap in mechanism but fundamentally they’re not the same. Confusing the two risks misapplying research findings or overhyping mechanisms that don’t apply to typical bodybuilding training.

I have to credit Chris Beardsley for his fantastic article “What is stretch-mediated hypertrophy and how does it work?” This is a fantastic read for those who want a deeper dive into the mechanistic differences between SMH & lengthened-bias training.

Ultimately understanding the differences between each helps us to more accurately interpret the research and ultimately design better programs.

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Long-Length Training: What the Research Says

Over the past decade, a growing body of research has explored how training at a longer muscle length affects hypertrophy. In some cases, training solely in the stretched position often lead to greater hypertrophy compared to a shortened length. Interesting, there are even studies that show lengthened bias training to be superior when compared to full range of motion (ROM).

Key Studies and Findings

Let’s start with some highlights from the research:

• Isometric Training at Long vs. Short Muscle Lengths: A 2023 systematic review and meta-analysis looked at over 25 studies on isometric training. It found that isometric holds performed in a lengthened position produced nearly three times more muscle growth than isometric holds in a shortened position. This was true across multiple muscle groups and training durations. Despite being static contractions, the stretch-induced tension in the lengthened position provided a significantly stronger hypertrophic signal.

• Dynamic Training with ROM Manipulation: Dynamic studies show similar patterns. A 2021 study compared partial squats in the bottom half of the ROM (deep position) to squats in the top half (near lockout). The deep squats produced significantly greater quadriceps hypertrophy, especially in the distal region of the muscle. Other studies in biceps and triceps show that exercises like incline curls and overhead extensions, which load the muscle at a long length, outperform their shortened-position counterparts in terms of muscle gain.

• Calf Training & Stretch Bias: In perhaps the most dramatic example, a 2022 study compared seated calf raises performed through either the full range of motion, the top half, or the bottom half (stretched position). The bottom-half group saw about 15% greater growth in the gastrocnemius compared to full ROM, and nearly triple the gains of the top-half group. This emphasised just how powerful the stimulus from a lengthened stretch stimulus can be, particularly in muscles like the calves that are notoriously known to be stubborn for growth.

These findings have led many coaches and researchers to speculate that the stretch position is where the “magic” happens. Mechanistically, it makes sense: when a muscle is lengthened under load, it experiences a combination of:

• High active tension (from the contraction)

• Passive tension (from the elongation of elastic structures like titin and fascia)

• Eccentric stress (from resisting lengthening during movement)

This trio appears to be a very powerful combination for mechanical tension & thus stimulation of protein synthesis. The result? Potentially greater hypertrophy, especially at the distal ends of the muscle, where stretch tension is the greatest.

Fascicle Length and Architectural Changes

Another interesting adaptation from long-length training is an increase in muscle fascicle length which describes the length of individual muscle fibres. This implies sarcomerogenesis in series, or the addition of contractile units end-to-end, essentially making the fibres longer. This can enhance not only hypertrophy but also strength through longer ranges of motion, and potentially even injury resilience in certain muscles (e.g. hamstrings).

In contrast, training at shorter muscle lengths tends to emphasise muscle thickness (cross-sectional area) in the mid-belly of the muscle. So in theory, training at long lengths might build not just bigger muscles, but longer and fuller ones too.

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Sounds Great, But Not So Fast! Context & Limitations

For all the excitement surrounding lengthened-bias training, it’s important to acknowledge that not all research tells the same story. While many studies show superior hypertrophy at long muscle lengths, others reveal more nuanced or even contradictory results. That’s why it’s important to keep an open mind when interpreting research.

The Larsen’s Quadriceps Study

One of the most relevant recent examples is a study led by Stian Larsen (2025), which investigated how full vs. partial range of motion in the leg press affects quadriceps hypertrophy, with quadriceps thickness assessed at the proximal, central & distal regions of the mid and lateral thigh.

What was great about this study is that it was an in-participant design, where each limb of a participant was divided:

• One limb was trained with a fixed & shortened ROM between 5-100° of knee flexion

• The other limb was trained within the participants individualised maximum knee ROM. In theory, emphasising a more lengthened position for the quadriceps musculature

The results? Similar hypertrophy for the quadriceps femoris regardless of knee flexion ROM. These findings reiterate that a more lengthened bias training style may not apply to every movement & muscle. The researchers put forth some interesting hypotheses regarding the lack of increased hypertrophy with greater ROM training.

Firstly, lack of additional benefits from greater knee flexion might be related to knee extensor sarcomere lengths potentially exceeding the optimal range for force production beyond 90-100° of knee flexion. Secondly, greater ROM from the full range leg press may have compromised stability due to the greater demands for ankle dorsiflexion,  thus impacting mechanical tension up the kinetic chain.

From a programming perspective, this could be highly relevant as it reinforces that there are additional considerations when determining if an individual would benefit from a more lengthened biased position, particularly if stability is compromised.

Not All Muscles Respond Equally

Another important caveat is that certain muscles seem more responsive to lengthened-biased training than others.

• Calves and hamstrings have consistently shown strong hypertrophic responses when trained at long lengths. This may be due to their architecture (long fascicles), their role in postural control, or simply their resistance to growth through traditional training.

• In contrast, muscles like the biceps, triceps, and even parts of the quadriceps don’t always demonstrate the same degree of benefit from stretch-biased loading. In some cases, full ROM training is just as effective, or the stretch component offers only marginal improvements.

Additionally, some muscles may not tolerate aggressive lengthened loading. A muscle that comes to mind is the psoas (hip flexors) which would be especially difficult to load under a lengthened position for individuals with lower back discomfort & mobility restrictions. Overemphasis on lengthened loading in these areas can lead to joint irritation or soft tissue strain if not carefully managed.

Training Status Likely Matters

One more layer of nuance: novice athletes tend to benefit the most from lengthened-biased training.

Early studies suggest that the stretch stimulus offers a strong novel signal to untrained muscles, resulting in rapid fascicle remodelling and size increases. But as lifters become more trained and their muscles adapt to mechanical stress, the relative benefit of training at long lengths may diminish.

In trained populations, there is an aspect of diminishing returns where it becomes more difficult to stimulate hypertrophy & while long-length training may still offer an edge, it’s unlikely to be a silver bullet. This underscores the importance of not overhyping one training variable as universally superior, especially for experienced lifters.

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Practical Implications: Do We Ditch Preacher and Leg Curls?

Given the enthusiasm around long-length training, it’s tempting to ask: should we abandon short-range exercises entirely? Should we stop doing preacher curls, lying leg curls, cable crossovers from above shoulder height, or any movement that emphasises the contracted (shortened) position of a muscle?

My personal opinion is no.

While training at long muscle lengths may offer hypertrophic advantages in many scenarios, exercises that challenge the muscle in its shortened range still bring important value to a well-rounded program.

1. Mind-Muscle Connection and Mechanical Advantage

Exercises performed at shorter muscle lengths often allow for a stronger peak contraction and a more focused mind-muscle connection. This can enhance motor unit recruitment and internal cueing, especially for athletes struggling to feel or activate a target muscle.

Think of the sensation at the top of a preacher curl or a glute kickback. These positions can reinforce muscle control and movement pattern quality, which is particularly valuable for newer lifters or those rehabbing from injury.

2. Load Management and Joint Stress

Stretch-biased movements often require working in deep joint angles, which means more passive tension on tendons, connective tissue, and stabilisers. This can be beneficial, but adds additional fatigue is not managed well with volume manipulation & ample recovery i.e. quality sleep & nutrition.

In contrast, exercises at short muscle lengths generally allow for more joint-friendly loading, especially for athletes with shoulder, elbow, or knee issues. They can also be used for high-rep metabolic work, isolation finishers, or deload strategies when reducing joint stress is a priority.

3. Training Variety and Adaptation

Muscles adapt best when exposed to a variety of stimuli. That includes different joint angles, contraction types, and muscle lengths. Biasing one range to the exclusion of others may lead to plateaus or imbalances over time.

Instead, think in terms of emphasis, not exclusion. For example:

• Prioritise long-length movements as your primary drivers of hypertrophy.

• Use shorter bias exercises to compliment them. Either to fill in regional gaps, drive metabolic stress, or support recovery.

A program that includes both incline curls and preacher curls, or RDLs and hip thrusts may provide a more complete & balanced stimulus.

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The Conclusion: The Answer is in the Grey

The popularity of lengthened-bias training isn’t without merit. The research is compelling: training muscles at longer lengths tends to produce greater mechanical tension and in many cases, superior hypertrophy outcomes compared to training at shorter lengths. For certain muscles it might be the missing link for growth that many lifters could benefit from.

For Intelligent Bodybuilding, the key is understanding why it works, and how to apply it in order to maximise progress.

Too often in the fitness industry, new findings are taken as replacement rather than refinement. What starts as a useful insight quickly becomes a black-and-white dichotomy: “stretch = good, short = bad.” This kind of thinking leads people to become dismissive in pursuit of a silver bullet that may not actually exist.

The truth is more balanced.

• Stretch-mediated hypertrophy – in its pure form, is not the same thing as training with long muscle lengths.

• Lengthened-position training – is effective & often more so than training in short ranges, but it’s not inherently superior in every context, for every muscle, or for every athlete.

• Shortened-position training still matters – particularly for regional hypertrophy, joint-friendly loading, and motor control.

So no, we’re not ready to throw away our preacher curls and lying leg curls.

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References

Behrens, M., Mau-Moeller, A., & Bruhn, S. (2017). Effect of chronic stretch training on muscle performance and muscle architecture in humans. Journal of Applied Physiology, 123(2), 350-358. https://doi.org/10.1152/japplphysiol.00104.2017

Evangelidis, P. E., Massey, G. J., Pain, M. T., & Folland, J. P. (2019). Strength and hypertrophic adaptations following isometric training at different muscle lengths. Scandinavian Journal of Medicine & Science in Sports, 29(5), 773-785. https://doi.org/10.1111/sms.13403

Gonzalez, A. M., & Hoffman, J. R. (2013). Chapter 6: Hypertrophy-specific training. In NSCA’s Guide to Program Design (pp. 91-118). Human Kinetics.

Lamas, L. L., Nosaka, K., & Libardi, C. A. (2023). Effects of strength training performed at different muscle lengths on muscle size and strength: A systematic review and meta-analysis. Scandinavian Journal of Medicine & Science in Sports, 33(3), 314-330. https://doi.org/10.1111/sms.14306

Maeo, S., Yamamoto, M., Kanehisa, H., & Nosaka, K. (2021). Influence of range of motion on muscle hypertrophy in resistance training: A systematic review and meta-analysis. Sports Medicine, 51, 1183-1195. https://doi.org/10.1007/s40279-020-01363-8

Massey, G. J., Evangelidis, P. E., & Folland, J. P. (2021). Training at long muscle lengths optimizes the site-specificity of muscle hypertrophy. European Journal of Applied Physiology, 121, 2657-2671. https://doi.org/10.1007/s00421-021-04750-5

Wolfe, R. R. (2006). The underappreciated role of muscle in health and disease. The American Journal of Clinical Nutrition, 84(3), 475-482. https://doi.org/10.1093/ajcn/84.3.475

Wolf, M., & Schoenfeld, B. J. (2023). Training at long muscle lengths: A new frontier in resistance training hypertrophy? Strength & Conditioning Journal. https://doi.org/10.1519/SSC.0000000000000731