Do You Need to Train 'Ass to Grass' for Muscle Growth?
Squat depth has long been a point of contention in the lifting world, which is where the phrase 'ass-to-grass' was born. Whether you agree or disagree, it's widely accepted that range of motion should be maximised in order to gain as much muscle as possible.
Now researchers set out to compare different range of motions during the leg press. And while it may not exactly be an analysis of squatting, the movement pattern mimics that of getting under the bar, leading us to question whether the old adage of 'ass to grass' (ATG) can really be put to bed.
The Study
The study preprint, available on SportRχiv, investigated whether varying the knee flexion range of motion (ROM) during leg press exercises impacts muscle hypertrophy of the quadriceps in resistance trained participants.
The Methods
The study included 23 participants.
Each participant trained one leg using a fixed knee flexion ROM (slightly reduced ROM at ~100°) and the other leg using their maximum individualised ROM (full ROM at ~154°).
The programme lasted eight weeks, with participants performing unilateral leg presses twice per week. Each workout session consisted of sets performed to failure in the 8-12 rep range.
Quadricep femoris muscle thickness was measured before and after the intervention.
The Results
Muscle Growth: Both ROM conditions led to similar muscle growth adaptations, with muscle thickness increasing by 2.2% to 7.3% across quad regions. Analysis indicated no significant differences between the fixed and maximum ROM conditions.
Volume: The reduced ROM condition allowed participants to lift higher total volume loads compared to the maximum ROM condition.
The Conclusion
The researchers concluded, 'Our findings indicate that both ~100° and maximum individualised knee flexion ROMs in the leg press are similarly effective for inducing quadriceps femoris hypertrophy in resistance-trained individuals after eight weeks of leg press training. These findings support the use of both ROMs as efficient strategies for resistance training.'
What Does This Mean for Us?
The practical implications of this study for our training could include using the leg press with a knee flexion ROM of approximately 100° (this includes the knee being bent a little more than a right angle) for sufficient muscle growth.
The researchers add, 'This ROM also accommodates those with limited ankle dorsiflexion. However, training to full knee flexion is a viable tool, as this approach allows for comparable muscle growth with lower loads.' Meaning, we could potentially load the leg press with more weight when reducing range of motion slightly, and it could be better for those who have less ankle mobility.
Researcher Dr Milo Wolf shared, 'Our findings suggest that knee flexion ROM does not significantly influence quadriceps growth during leg press training, offering flexibility for programming based on personal preference or joint limitations.'
Another study published in the European Journal of Applied Physiology found that full squat training is more effective than half squats for developing lower limb muscles, particularly the adductors and gluteus maximus, while neither squat depth significantly impacts rectus femoris or hamstring muscle volumes.
When comparing these two studies, they both suggest that the importance of ROM may depend on the exercise and target muscles. In machine based exercises like the leg press, ROM beyond 100° does not appear to provide additional muscle growth benefits for the quadriceps. However, in free-weight exercises like squats, greater ROM appears beneficial for certain muscles (adductors and gluteus maximus) and strength development in full-depth squats. Also, it's important to note that when comparing the two exercises, the leg press has an absence of balance demands and a fixed path, resulting in different demands on the body.
The Bottom Line
So is squatting ass-to-grass dead? Maybe, but not necessarily in light of this study. Realistically, squatting ass-to-grass isn't possible biomechanically for all lifters. Instead we should focus on our own individual capabilities. When it comes to ass-to-grass when using the leg press, because it targets different muscles, it is likely to be less necessary.
The bottom line is to still use full range of motion within your capabilities, as this will likely seal the deal when it comes to hypertrophy for a variety of different muscle groups. The study still uses a good range of motion in both conditions, so we should still focus on doing so.
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