Time Under Tension (TUT) has long been regarded as an important variable in hypertrophy training, with many fitness professionals suggesting that maintaining a TUT of 40 to 60 seconds per set can optimize muscle growth. However, as research evolves, it has become clear that while TUT plays a role in hypertrophy, it is not a simple equation of “longer equals better.” Other key factors such as mechanical tension, load, and effort must be taken into account.
Evaluating TUT in the Context of Hypertrophy
Dr. Brad Schoenfeld, a leading researcher in muscle hypertrophy, emphasizes that while TUT can influence muscle growth, it is not as straightforward as many have believed. For instance, Schoenfeld points out that research into TUT is limited, but one study by Burd et al. suggests that greater TUT (achieved through slow-tempo lifting) led to a delayed increase in muscle protein synthesis compared to faster lifting. However, the study’s design confounded the results since the slow-tempo group trained to volitional failure, while the fast-tempo group did not. This reinforces the idea that effort—specifically training close to failure—may be more critical for muscle growth than TUT alone.
TUT and Mechanical Tension: A Balanced Approach
While TUT can be a useful tool for increasing the duration of mechanical tension, Schoenfeld argues that mechanical tension, rather than the time spent under tension, is the primary driver of hypertrophy. In fact, when sets are performed with submaximal loads and artificially slowed tempos, the recruitment of high-threshold motor units (HTMUs)—which are most responsible for muscle growth—may be compromised. Therefore, focusing on effort and load, ensuring near-failure or failure in each set, may be more effective than simply extending TUT.
Does Longer TUT Equal More Muscle?
Schoenfeld’s research also shows that superslow training, where TUT is exaggerated, has not consistently been shown to produce superior hypertrophy compared to traditional training methods. In fact, when the load is reduced to extend TUT, the benefits of hypertrophy diminish. This highlights that while TUT plays a role, intensity of effort and the load used are crucial factors that cannot be overlooked.
In one of Schoenfeld’s studies, a powerlifting-style workout (7 sets of 3RM) was compared to a bodybuilding-style workout (3 sets of 10RM). Despite the significantly lower TUT in the powerlifting-style sets (~9 seconds per set vs. ~30 seconds in the bodybuilding-style sets), the total TUT for the session was approximately equal due to the higher number of sets. This demonstrates that TUT over an entire training session—not just per set—can have relevance for hypertrophy, but must be balanced with other variables like volume and load.
TUT and Repetition Range: Not All Reps Are Equal
Another important point raised by Schoenfeld is that not all repetitions contribute equally to hypertrophy. In a set of 25RM, the first few reps are relatively easy and do not stimulate significant muscle growth. In contrast, a set of 6RM challenges the muscle from the outset, promoting greater anabolic signaling. Therefore, the relevance of TUT depends on the repetition range and how many of the reps are actually challenging the muscle.
Practical Takeaways: Applying TUT in Your Training
The evidence suggests that while TUT can be a useful tool, it should be applied in context. Here are key ways to use TUT effectively:
- Focus on Effort: Ensure that each set is performed near or to failure, regardless of TUT. As noted in research by Schoenfeld et al., the effort required to achieve near-failure is a more significant driver of hypertrophy than merely prolonging TUT.
- Prioritize Mechanical Tension: Rather than arbitrarily increasing TUT, focus on the load being lifted and the overall mechanical tension generated. Heavier loads with controlled reps engage more muscle fibers than lighter loads performed with an extended tempo. This is supported by studies that show no clear advantage of superslow tempos for hypertrophy when the load is decreased.
- Consider Session-Wide TUT: Total TUT over the course of a training session may be more important than the TUT of individual sets. Ensure that volume and load are sufficient across the workout to stimulate muscle growth. The research suggests that even with shorter TUT per set, an adequate number of sets can produce similar hypertrophy results.
- Tailor TUT to Repetition Range: Keep in mind that the repetition range affects how TUT influences hypertrophy. Lower-rep sets (e.g., 6RM) challenge the muscle from the start, making TUT more effective in these ranges, whereas higher-rep sets (e.g., 25RM) require more reps before hypertrophic stimulation occurs. Evidence from studies highlights that hypertrophy can occur with a wide range of tempos, but focusing on the effort within the target rep range is critical.
- Use a Balanced Tempo: Research shows that a combination of slower eccentric movements and faster concentric movements is often more effective for hypertrophy and strength gains than exclusively slow tempos. This balance helps maximize both muscle tension and neural adaptations, promoting overall growth.
Conclusion
Dr. Brad Schoenfeld’s research emphasizes that while TUT is a relevant variable in hypertrophy training, it should not be the sole focus. Effort, mechanical tension, and load remain the primary drivers of muscle growth, and TUT should be applied within this broader context. A longer TUT may benefit Type I muscle fibers, but the overall training volume, effort, and load must be prioritized for maximum hypertrophic results. Ultimately, TUT is one piece of the puzzle and should be integrated alongside other essential training variables.
References:
Wilk, M., Zajac, A., & Tufano, J. J. (2021). “The influence of movement tempo during resistance training on muscular strength and hypertrophy responses: A review.” Sports Medicine, 51(8), 1629-1650.
Schoenfeld, B. (2020). Science and Development of Muscle Hypertrophy (2nd ed.). Human Kinetics.
Grgic, J., Schoenfeld, B. J., Skrepnik, M., & Davies, T. B. (2018). “Effects of rest interval duration in resistance training on measures of muscular strength: a systematic review.” Sports Medicine, 48(1), 137–151.
Schoenfeld, B. J., Grgic, J., Ogborn, D., & Krieger, J. W. (2017). “Strength and hypertrophy adaptations between low- vs. high-load resistance training: a systematic review and meta-analysis.” Journal of Strength and Conditioning Research, 31(12), 3508–3523.
Schoenfeld, B. J., Ogborn, D., & Krieger, J. W. (2017). “Dose-response relationship between weekly resistance training volume and increases in muscle mass: a systematic review and meta-analysis.” Journal of Sports Sciences, 35(11), 1073–1082.
Burd, N. A., Andrews, R. J., West, D. W. D., Little, J. P., Cochran, A. J. R., Hector, A. J., Cashaback, J. G. A., Gibala, M. J., Potvin, J. R., Baker, S. K., & Phillips, S. M. (2012). “Muscle time under tension during resistance exercise stimulates differential muscle protein sub-fractional synthetic responses in men.” The Journal of Physiology, 590(2), 351-362.
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