Richard Uzelac Explains Time Under Tension: The Muscle-Building Detail Most Lifters Get Wrong

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Have you ever wondered why lifting heavier weights doesn’t always lead to bigger muscles? We may have overlooked one concept, the Time Under Tension (TUT). What is it? And what does Richard Uzelac, a fitness enthusiast all his life and involved in fitness all his life, say about Time Under Tension?

“First off, let me say train with purpose, embrace the burn, and remember: it’s not just how much you lift, but how long you make your muscles fight. Too little time under tension can stall your progress, while too much can turn your strength workout into an endurance session.” Richard Uzelac, at the age of 45, was a wrestling tournament winner.

Time under tension refers to the total amount of time your muscles are actively working during a set—specifically while lifting, holding, and lowering a load. This time matters more than many people realize.

What Time Under Tension Really Means

Time under tension includes every phase of a repetition, not just how many reps you complete. Each rep has three critical components:

Concentric Phase – This is when you lift the weight, shortening the muscle.
Isometric Phase – This occurs when you briefly hold the weight in place.
Eccentric Phase – This is when you lower the weight, lengthening the muscle under load.

While all three phases contribute to muscle activation, the eccentric phase plays the most important role in muscle growth. Time Under Tension (TUT) refers to the total amount of time your muscles are actively working during a set, including both the lifting (concentric) and lowering (eccentric) phases of each repetition. Rather than focusing only on how much weight is on the bar, TUT shifts attention to how long the muscle is forced to stay engaged, which plays a major role in stimulating muscle growth.

When your muscles remain under tension for too short a period, they may not receive enough stimulus to adapt and grow. On the other hand, keeping your muscles under tension for too long can shift the workout away from strength and hypertrophy and turn it into more of an endurance or cardiovascular challenge.

Why the Eccentric Phase Matters Most, According to Richard Uzelac

The eccentric portion of a lift—lowering the weight under control—is where mechanical tension is highest and where the most muscle damage occurs. This controlled damage is not a bad thing; it’s one of the primary signals your body uses to rebuild muscle stronger and larger.

Rushing through the lowering portion of a lift may allow you to move heavier weights, but it dramatically reduces the stimulus needed for hypertrophy. From a physiological standpoint, speeding through reps simply to increase load does not support muscle growth—it actually works against it.

The Three Key Drivers of Muscle Growth

To understand why Time Under Tension is so important, you need to understand the three primary drivers of hypertrophy:

Mechanical Tension – The force placed on muscle fibers when lifting and lowering weight.
Metabolic Stress – The “burn” and fatigue that build up during a challenging set.
Muscle Damage – Micro-tears in muscle fibers that occur under controlled stress, especially during eccentric movements.

Proper Time Under Tension—particularly during the lowering phase—maximizes all three of these factors. To maximize muscle hypertrophy, your training must strategically balance mechanical tension, metabolic stress, and muscle damage within a structured routine. Mechanical tension is best achieved by performing compound movements, such as squats or lat pulldowns, through a full range of motion while maintaining a controlled tempo—specifically emphasizing a one-second pause during the “deep stretch” phase of the lift.

To trigger muscle damage, you should prioritize the eccentric, or lowering, phase of each repetition; using a slow, three-to-four-second descent on exercises like the Romanian Deadlift forces the muscle fibers to endure controlled micro-tears that signal the body to rebuild stronger tissue.

Finally, you can drive metabolic stress by incorporating high-repetition “finishers” with shorter rest intervals, such as lateral raises or bicep curls, which trap metabolites in the muscle and create the chemical environment necessary for growth.

By consistently applying these three drivers and ensuring progressive overload, you transform a standard workout into a precise physiological stimulus for new muscle mass.

How Long Should Time Under Tension Be?

There’s a sweet spot.

Too little time under tension: You reduce mechanical tension and limit muscle growth.
Too much time under tension: The workout shifts toward cardiovascular endurance rather than hypertrophy.

To maximize muscle growth, your sets should ideally land in a “sweet spot” of 30 to 70 seconds of continuous work. If a set is too short (under 20 seconds), you are primarily building explosive strength and power rather than size, as the muscle isn’t under strain long enough to trigger significant metabolic stress. Conversely, if a set lasts much longer than 70–90 seconds, the intensity typically drops so low that the workout shifts toward cardiovascular endurance rather than hypertrophy. For the best results, aim for a controlled tempo—such as a 3-second lowering phase and a 1-second lift—which naturally keeps your 8–12 rep sets within that optimal 40–60 second window. This balance ensures you maximize mechanical tension and metabolic fatigue without turning your lifting session into a cardio circuit.

Control Beats Momentum

One of the most common mistakes in the gym is rushing through sets to lift heavier weights. While intensity matters, control matters more. Muscle doesn’t respond to ego lifting—it responds to tension, stress, and precise execution.

Slowing down your reps, particularly on the way down, ensures that the muscle—not momentum—is doing the work. This approach not only improves results but also reduces injury risk and improves movement quality.

Richard Uzelac’s TUT Training Takeaway