Why Partial Reps in the Lengthened Position Are Redefining Hypertrophy Training

For decades, full range of motion (ROM) has been considered the gold standard for hypertrophy. The logic was simple: move through the entire arc of a joint to maximize fiber recruitment and stimulate growth. But recent research is challenging that assumption, showing that partial reps, specifically those performed in the lengthened position, can be just as effective, if not more so, for building muscle.

This isn’t about cutting corners. It’s about understanding where tension matters most.

The Evidence: Stretch-Loaded Tension Drives Growth

A growing body of literature supports the idea that muscles respond more favorably to mechanical tension when they are in a stretched state. One standout study by Pedrosa et al. (2023) compared partial reps in the lengthened position to full ROM training for leg extensions. The group performing only the bottom half of the movement, where the quads are under the most stretch, experienced significantly greater hypertrophy than the full ROM group.

Similarly, research on the calf muscles showed that training in the stretched position, heels below the platform in a standing calf raise, led to more growth than training in the shortened position. This aligns with the principle that passive tension, generated when a muscle is elongated under load, contributes heavily to hypertrophic signaling.

Why Shortened Partials Fall Short

Partial reps in the shortened position, where the muscle is fully contracted, don’t produce the same results. The shortened range offers less mechanical tension and reduced force output. Muscles are simply less capable of generating high levels of tension when fully contracted, and the metabolic stress in this range doesn’t appear to compensate for the lack of mechanical load.

In practical terms, doing the top half of a biceps curl or locking out on a leg press doesn’t stimulate the same adaptive response as working through the bottom half. The shortened range may still have value for metabolic fatigue or pump work, but it’s not where the growth stimulus is strongest.

Real-World Applications

Here’s how to apply this concept in training:

Biceps Curls: Focus on the bottom half of the movement. Start from a fully extended elbow and curl to about halfway. This keeps the biceps under tension in their lengthened state, where they are most responsive to load.

Leg Press: Perform partial reps in the lowest portion of the movement, just above the point where your hips begin to shift. This position stretches the quads and glutes, allowing for high mechanical tension without the need to lock out.

Calf Raises: Lower your heels fully below the platform and perform reps only in the bottom range. This emphasizes the stretch in the gastrocnemius and soleus, which has been shown to produce superior growth compared to full ROM or shortened partials.

Hamstring Work: Use Romanian deadlifts with a focus on the bottom range. Lower the bar slowly to maximize the stretch, then come up only halfway. This keeps the hamstrings loaded in their most hypertrophy-prone position.

When to Use Lengthened Partials

To be clear, this is not a recommendation to replace full ROM training altogether. Full ROM remains essential for joint health, balanced development, and overall strength. Lengthened partials are best used as a strategic variation, either at the end of a set when full ROM reps are no longer possible, or during specific hypertrophy-focused blocks where maximizing mechanical tension is the goal.

Think of this as a tool, not a rule. For lifters looking to break plateaus or target lagging muscle groups, this method offers a high-tension alternative without increasing joint stress.

Final Thoughts

The hypertrophy landscape is evolving. Lengthened partials are no longer just a workaround, they are a deliberate, evidence-based strategy for maximizing muscle growth. By understanding where tension is most effective, we can train smarter, not just harder.

The next time you hit the gym, consider where your muscles are under the most stretch. That’s where the magic happens—especially when used thoughtfully and in rotation with other proven methods.