When it comes to lifting, strict form has long been considered the gold standard, with fitness professionals claiming that maintaining controlled movements ensures optimal muscle engagement and minimizes injury risk.
However, some lifters intentionally incorporate cheat reps. Cheat reps involve using momentum, body movement, or “improper form” to complete a lift when strict technique would otherwise lead to failure. This can include swinging the weight or using excessive body drive to lift heavier loads or perform more reps. While some lifters argue that cheat reps can help push past plateaus or provide additional stimulus, they are generally seen as a way to bypass proper muscle engagement and increase injury risk. On the other hand, strict reps emphasize controlled movement, which is often claimed to be crucial for hypertrophy.
Surprisingly though, up until recently, there were no studies directly examining the validity of such claims and more specifically comparing cheat reps to strict reps. While it seems logical to assume that strict reps would be more effective for muscle growth, some have argued that as long as a set is taken to failure, the way you get there might not matter as much as we think.
A recent study (Augustin et al., 2024) directly compared cheat reps vs. strict reps in untrained lifters, focusing on their impact on hypertrophy and strength over an 8-week period. 30 untrained young adults were recruited, with one limb assigned to strict form and the other to external momentum-assisted resistance training.
The intervention consisted of biceps curls and triceps pushdowns performed twice weekly for 8 weeks, with 4 sets of 8-12 repetitions taken to momentary muscular failure. The researchers assessed muscle hypertrophy via ultrasound measurements of the elbow flexors and extensors at both proximal and distal sites, alongside arm circumference measurements using a 3D scanner.
The strict condition required controlled, isolated movements to minimize momentum and ensure that the target muscles (biceps and triceps) performed the majority of the work. For biceps curls, participants maintained an upright posture with no swinging of the torso, hip drive, or shoulder movement. Similarly, for triceps pushdowns, they kept their torso stable and elbows fixed, avoiding any compensatory movements. In contrast, the cheat condition incorporated external momentum to assist the concentric phase of each repetition. For biceps curls, participants were allowed to generate force using hip and torso movement, swinging the weight upwards. For triceps pushdowns, they used leg drive, leaned forward, and allowed elbow flare to assist in moving the weight.
The study found no significant differences in muscle hypertrophy between the strict and cheat conditions. Muscle thickness increased similarly in both conditions at proximal and distal sites of the elbow flexors and extensors, with Bayes Factors ranging from 0.06 to 0.61, indicating strong to moderate evidence against a meaningful difference. One limitation of this study that people online already brought up is that the participants were untrained, meaning they respond more easily to resistance training, which could theoretically mask potential differences between conditions. That said, even in untrained individuals, you’d still expect to see different magnitudes of growth if one method were clearly superior.
So where does this leave us?
There’s still a lot of research needed before we can say anything with absolute confidence about the effects of using momentum, or “cheating,” in resistance training. However, this study suggests that incorporating some external momentum doesn’t seem to negatively impact muscle hypertrophy. That said, despite nearly double the total volume load in the cheat condition, it did not lead to greater hypertrophy, indicating that simply moving more weight through momentum does not necessarily enhance muscle gains.
For those who prioritize strict form, this study reinforces that controlled technique remains effective (duh). On the other hand, those who occasionally use momentum to complete additional reps or lift heavier loads can do so without concern for reduced hypertrophy. However, the potential for increased injury risk with excessive momentum remains a consideration, particularly for joints and connective tissues.
Ultimately, whether you prefer strict reps or occasionally incorporate some momentum, the key takeaway is that muscle growth can occur under both conditions when sets are taken to failure.
