It is widely believed that greater gains in muscle size are always achieved after strength training with a full range of motion, compared to after training with a partial range of motion.
While this belief probably originated among strength coaches who were annoyed by seeing their athletes performing quarter squats, it does have some scientific backing.
Some long-term trials have reported greater muscle growth after training with a full range of motion, or after training with a partial range of motion where the muscle reaches a longer length, and is therefore more stretched. The researchers carrying out these studies hypothesized that this would happen because of the potentially additive effects of stretch and contraction on hypertrophy that have been observed in animal models.
However, not every long-term trial has reported greater muscle growth after training with a full range of motion, or with a partial range of motion where the muscle reaches a longer length. A number of recent studies have reported similar hypertrophy after training with various different ranges of motion. Even more surprisingly, some studies have actually reported greater muscle growth after partial range of motion training!
So let us take a careful look at all of the research.
How have researchers compared training with different ranges of motion?
Researchers have assessed the problem of how range of motion affects muscle growth after strength training in several different ways.
In general, there are two groups of studies.
One group of studies has compared full ranges of motion with partial ranges of motion, where the partial range of motion is a part of the full range of motion. The group training with a full range of motion covers all of the range of motion used by the group training with a partial range of motion, and more besides.
Another group of studies has compared different partial ranges of motion (which may or may not overlap slightly). In these studies, one group reaches a shorter (more contracted) muscle length, while the other group reaches a longer (more stretched) muscle length.
#1. Full and partial ranges of motion
Some studies have compared full ranges of motion with partial variations of the same exercise. However, the exact partial ranges of motion used in these studies differ slightly. Some studies use the top part of the full range of motion for the partial range of motion group, while others use the middle.
For example, a couple of studies have compared training with full and partial squats. In these studies, partial squat training involves using the top part of the exercise performed by the full range of motion group. Similarly, another study has compared knee extension training through full (0–100 degrees) and partial (0–60 degrees) ranges of motion.
In these studies, the full range of motion group reaches the same top (contracted muscle) position as the partial range of motion group, but a different bottom (stretched muscle) position.
Other studies have compared training with full and partial ranges of motion, where the partial range of motion is in the middle of the full range of motion exercise. One study compared preacher curl training with a full range of motion (0–130 degrees) and a partial range of motion (50–100 degrees). Another study compared lying triceps extension training with a full range of motion (0–120 degrees) and a partial range of motion (45–90 degrees).
In these studies, the full range of motion group reaches a higher top (contracted muscle) and a lower bottom (stretched muscle) position than the partial range of motion group.
#2. Different partial ranges of motion
Other studies have compared similar partial ranges of motion, where one group trains such that the muscle is quite stretched at the end of the lowering (eccentric) phase, while the other group trains such that the muscle is not as stretched.
For example, one study compared training with a range of knee extension exercises with a partial range of motion that involved reaching either a more stretched position for the quadriceps (40–90 degrees) or a less stretched position (0–50 degrees). Another study compared different triceps extension exercises, where one group trained such that the triceps reached a stretched position (70–150 degrees) and the other group trained such that the muscle reached a contracted position (10–90 degrees).
In these studies, the groups reach different top (contracted muscle) and bottom (stretched muscle) positions from one another, and while one group reaches a more contracted position, the other group reaches a more stretched position.
What do these comparisons tell us?
These studies allow us to assess the effect of range of motion on muscle growth by three different comparisons, depending on the partial ranges of motion that were tested.
The full range of motion group reaches the same top (contracted muscle) position as the partial range of motion group, but a different bottom (stretched muscle) position, for which there are three studies. Together, these studies show that full and partial ranges of motion produce different regional hypertrophy, and while the full range of motion produces greater increases in fiber length, the partial range of motion could produce greater increases in fiber diameter.
The full range of motion group reaches a higher top (contracted muscle) and a lower bottom (stretched muscle) position than the partial range of motion group, for which there are two studies. These studies show that when the partial range of motion used is in the middle of the full range of motion, it produces similar or greater muscle growth.
The groups reach different top (contracted muscle) and bottom (stretched muscle) positions from one another, and while one group reaches a more contracted position, the other group reaches a more stretched position, for which there are two studies. These studies show that when the partial range of motion used reaches a more stretched muscle length, it produces greater increases in fiber length, but the effects on muscle size are unclear.
Overall, the research does not provide unanimous support for the idea that reaching a stretched position is always beneficial for muscle growth. Even if we include those studies reporting greater muscle growth only in some regions as being indicative of greater overall hypertrophy, there are three studies reporting greater hypertrophy after training with a more stretched position, but four studies reporting similar or greater hypertrophy after training with a less stretched position.
In fact, the clearest trend is for greater increases in muscle fiber length after training with full or partial ranges of motion where the muscle reaches a more stretched position, which may be linked to the different regional hypertrophy.
Increases in fiber length seem to be stimulated when the muscle reaches a longer length during an exercise, because this causes the mechanical tension experienced by the muscle fibers to be produced more by passive elements (the structure of the muscle fiber, including titin).
Conversely, the proportionally greater mechanical tension placed on the active elements (the actin-myosin crossbridges) during partial range of motion training could cause greater increases in fiber diameter, which could lead to greater gains in anatomical or physiological cross-sectional area.
What might produce differences between studies?
Since these studies were generally all well-designed and carried out to (comparatively) high methodological standards, it is more likely that any differences between them lies in (1) the ways that the volume or work done was equated between groups,(2) the exercises that were used, or (3) the muscle group that was trained and measured.
#1. Volume or work done
Four of the studies equated volume (sets x reps) between groups, two equated predicted muscle forces, and one equated work done. The single study that equated work done required the partial range of motion group to perform additional sets or reps, indicating that full ranges of motion are more efficient ways to achieve a greater training load.
Moreover, the study that equated work done rather than volume reported greater increases in physiological cross-sectional area after partial range of motion training, suggesting that those studies equating volume and reporting similar or greater muscle growth after training at long muscle lengths may be providing a smaller stimulus in the partial range of motion group because of less work done.
#2. Exercises used
The exercises used in these studies varied in several ways, including (1) the number of exercises used in the training programs, (2) the number of joints used (multi-joint or single-joint), and (3) the strength curves of the exercises. Looking at how the studies differ from one another might help us understand the role of range of motion in hypertrophy.
Number of exercises — All but two of the studies investigating the effects of range of motion have tested single exercises, which makes comparisons between groups fairly reliable. Interestingly, both of these two studies show a beneficial effect of training at longer muscle lengths when using a range of multi-joint lower body exercises, suggesting that increased exercise variation could interact with range of motion.
Number of joints — Three studies assessed multi-joint exercises and these were the three that reported a beneficial effect of training at longer muscle lengths, suggesting that multi-joint exercises could benefit more from a full range of motion. The four studies that reported a similar or superior effect of partial range of motion training all assessed single-joint exercises, of which one assessed the knee extension, two assessed various different triceps extensions, and one assessed the preacher curl.
Strength curves — Not every study used exercises with the same strength curve. Multi-joint lower body exercises generally involve a fairly steep strength curve because of changing external moment arm lengths over the exercise range of motion. This steep strength curve requires the muscles to produce higher forces at the bottom of the exercise than at the top. The preacher curl has a similarly steep strength curve. In contrast, one study used accommodating resistance for the knee extension, thereby creating a flat strength curve, and the triceps exercises probably involved parabolic strength curves, where the exercise required the greatest forces in the middle.
In summary, the studies that reported greater muscle growth after training with a full range of motion, or with a partial range of motion where the muscle reaches a longer length, tended to use a variety of exercises (instead of a single exercise), multi-joint exercises (instead of single-joint exercises), and a steeper strength curve, where the greatest forces are required at the bottom of the lift, corresponding to long muscle lengths.
#3. Muscle group
The muscle groups tested in these studies varied insofar as (1) they belonged to either the upper or the lower body, (2) have different internal moment arm lengths, and therefore different length-tension relationships.
Upper vs. lower body — Three studies assessed changes in the vastus lateralis, one assessed hypertrophy of the whole thigh, two assessed muscle growth in the triceps brachii, and one assessed changes in the biceps brachii. The only studies to report a beneficial effect of training at longer muscle lengths have involved training and measuring thigh (quadriceps) muscles, but beneficial effects of training with a partial range of motion have been reported for both upper and lower body muscle groups.
Internal moment arm lengths (MAL) — The triceps brachii MAL increases with increasing elbow flexion, the biceps brachii MAL peaks with the elbow at 90 degrees, and the quadriceps MAL peaks at 25 degrees from full knee extension. Taking into account other aspects of their muscle architecture, this means that the triceps brachii operates almost entirely on the plateau region of the length-tension relationship (where the active elements of the muscle fibers contribute most to force production), the biceps brachii operates on the ascending limb and plateau regions (where the active elements of the muscle fibers contribute most to force production), and the quadriceps operate for most of the time on the descending limb (where the passive elements of the muscle fibers contribute more to force production). Coincidentally, the only studies to report a beneficial effect of training at longer muscle lengths have involved training and measuring thigh (quadriceps) muscles.
In summary, studies that report greater muscle growth after training with a full range of motion, or with a partial range of motion where the muscle reaches a longer length, tend to test the quadriceps. These muscles could be more susceptible to stretch-mediated muscle growth because they are working on the descending limb of the length-tension relationship for most of the time, meaning that the passive elements of the muscle fibers contribute very substantially to force production.
What does this mean in practice?
By analyzing the studies that have compared exercises with different ranges of motion, and yet have produced different results, we can draw inferences about the factors that might be important for getting the most benefit out of exercises using full ranges of motion, or exercises using a partial range of motion where the muscle reaches a longer length.
Some of these factors (such as greater exercise variety, multi-joint exercises, and lower body muscles) could be coincidental, as it is difficult to find a plausible biological mechanism that could explain their effects.
Two other factors are more promising, however.
Muscles that have peak internal moment arm lengths at short muscle lengths could be more susceptible to stretch-mediated muscle growth, because they are often working on the descending limb of the length-tension relationship for most of their working range of motion. This could explain why only studies measuring the quadriceps have reported any beneficial effect of full ranges of motion, or exercises where muscles are trained at longer lengths.
Exercises involving a steep strength curve, in which the greatest forces are required at the bottom of the lift, corresponding to long muscle lengths, could provide a greater stimulus to the muscle in a stretched position than exercises with flatter strength curves. This might be why the one study assessing the quadriceps that did not find a beneficial effect of using a full range of motion was the only study to use accommodating resistance, which involves a flat strength curve, and was also the only study to test concentric-only exercise, which almost certainly reduced the proportional load on the passive elements of the working muscle fibers.
What is the takeaway?
Reaching a more stretched position in an exercise by using a full range of motion does not always cause more hypertrophy, but it often causes greater increases in fiber length, likely because of the proportionally greater mechanical tension experienced by the passive elements of the fiber.
For a full range of motion to cause greater hypertrophy and not just greater increases in fiber length, the muscle may need to work predominantly on the descending limb of the length-tension relationship, so that the passive elements contribute substantially to total force production for the majority of the lift. A steep exercise strength curve may also help, such that the muscles are loaded very forcefully in the stretched position.