Time Under Tension (TuT)… How is it connected to hypertrophy? Although you may hear mixed opinions/statements all over the internet of whether or not it is useless or effective, let’s take a deep dive into some information that will help you develop a better understanding. 

Time under tension can have a direct connection to stimulus & muscle growth. One of the first things I would discuss is mechanical tension & it’s importance. Mechanical tension is the prime driver for hypertrophy. When a muscle is under load for a certain amount of time, fibers experience more strain. More growth can be triggered through mechanotransduction, which is the process where mechanical forces are converted into cellular responses that promote MPS (muscle protein synthesis). According to Pearson et al., https://www.tandfonline.com/doi/abs/10.1080/10408399009527522, new myofibrillar protein must be synthesized and deposited in the muscle cells. It is suggested that adaptation by adding or removing sarcomeres is physiologically determined by the degree of force a muscle can generate that is in turn dependent on the degree of overlap of the thick and thin filaments. 

Article breaking down the concept of force generation & sarcomere length-tension relationship: https://rupress.org/jgp/article-abstract/72/4/565/26891/The-sarcomere-length-tension-relation-in-skeletal

My blog post on mechanical tension & time under tension: https://www.cptlij.com/blog?id=67c9164f15cd4e7a11afb4ba

This repeated exposure to high mechanical load can increase fiber size, strengthen connective tissues, & encourage neuromuscular adaptation. High levels of tension during the eccentric & isometric contractions can trigger the mechanotransduction process will occur. Boost activation for signaling pathways. These articles below support mechanical stress promoting mTOR signaling pathways: 

• https://www.spandidos-publications.com/10.3892/mmr.2019.10808
• https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0083580
• https://www.tandfonline.com/doi/abs/10.4161/cc.5.13.2921

Longer bouts of TuT have been possibly correlated to increase the accumulation of metabolic byproducts like hydrogen ions & lactate. This metabolic stress promotes hypertrophy by increasing cellular swelling and stimulating anabolic pathways.

This excerpt from a peer review article will help you understand why metabolic stress can be important for the stimulation of anabolic pathways: “Numerous studies support an anabolic role of exercise-induced metabolic stress and some have speculated that metabolite accumulation may be more important than high force development in optimizing the hypertrophic response to training. Although metabolic stress does not seem to be an essential component of muscular growth, a large body of evidence shows that it can have a significant hypertrophic effect, either in a primary or secondary manner. This can be noted empirically by examining the moderate intensity training regimes adopted by many bodybuilders, which are intended to heighten metabolic stress while maintaining significant muscular tension.” (Brad, J.S., The mechanisms of muscle hypertrophy and their application to resistance training)

Slow & controlled reps have been considered important for fiber recruitment, but not in the maximal overall recruitment of fiber activation. This is in comparison to heavy loads. The goal is to ensure fatigue sets in & high force is used to engage/activate fast twitch fibers. Lift heavy, & push yourself to or near failure. Reps focused on eccentric control (recruiting high-threshold motor units), reducing joint stress, & aiming to activate target muscles rather than using momentum, ego lifting styles & involving compensatory techniques. 

TuT also plays a huge role in form & biomechanic enhancement. What can slowing a movement down enhance in terms of mechanics?

• Increased motor control.
• Increased coordination.
• Improve muscle awareness or target muscle activation.
• Reduce risk of injury
• Rehabilitation & Pre-habilitation benefits
• If you are an advanced lifter, TUT can be used strategically to reinforce movement patterns or overcome weak points in a lift.
• Beginners need TUT. It is essential for developing proper mechanics before increasing weights.

In simple terms, Slower reps don’t inherently recruit more fibers, but they can enhance tension, metabolic stress, and control, which indirectly contributes to hypertrophy when taken to failure or paired with heavier loads.

My stand. I think everyone could use some form of TuT. But it should be programmed accordingly. I think movements ranging with eccentrics from 2-3 seconds (sometimes more dependent on specific musculature & movements being used) can be a sweet spot to experience the benefits of mechanical tension in correlation with time under tension. Focus on progressive overload!

Supporting articles:

This review examines how different movement tempos during resistance training affect muscular strength and hypertrophy. It discusses the impact of varying repetition durations on muscle activation and growth.

https://pubmed.ncbi.nlm.nih.gov/34043184/

Investigate the effects of different repetition durations on muscle hypertrophy, providing insights into how TUT influences muscle growth.

https://pubmed.ncbi.nlm.nih.gov/25601394/

This study explores how varying TUT during resistance exercises affects muscle protein synthesis, a key factor in hypertrophy.

https://pmc.ncbi.nlm.nih.gov/articles/PMC3285070/

This article explores how resistance training induces neural adaptations, including changes in motor unit recruitment and firing frequency, which are crucial for muscle performance.https://pubmed.ncbi.nlm.nih.gov/12715968/

This study examines how resistance training affects motor unit behavior, including recruitment patterns and firing rates, contributing to strength and hypertrophy gains.

https://pubmed.ncbi.nlm.nih.gov/16794023/