Have you ever noticed that the first repetition of a deadlift from the floor feels significantly tougher than subsequent reps? Or perhaps you've struggled to press a barbell off your chest from a dead stop, only to find the lift much more manageable if you first lower it from the top? These common experiences in strength training point to fascinating physiological principles at play, primarily involving our muscle's incredible ability to store and release elastic energy.
Let's explore these questions and the science behind them.
The Puzzling Questions
Many lifters instinctively feel these differences, even if they don't know the exact reasons:
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Why is the first repetition of a deadlift from the floor harder than the second repetition?
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Why, if the barbell for the bench press is placed on our chest for the first rep, can't we lift it up, but if we take it from the top (off the rack), lower it down, and then lift it, we can?
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Generally, why is it very difficult if we want to perform the positive (concentric) part of a movement before performing the negative (eccentric) part?
These questions all highlight a core concept: the advantage of initiating a powerful concentric (lifting) movement after an eccentric (lowering) movement.
The Scientific Answer: Muscle Spindles and the Stretch-Shortening Cycle
The key to understanding these phenomena lies within our muscles, specifically with specialized sensory receptors known as muscle spindles.
Inside our muscles, there are fibers called muscle spindles. The function of these spindles is to monitor the degree of muscle stretch.
These tiny, intricate structures are crucial for proprioception (our sense of body position) and for optimizing muscle contraction. They act as "stretch detectors."
When you perform the negative (eccentric) part of the movement and the muscle is stretched, these spindles send a message to the spinal cord, asking it to contract the muscle, and this action helps with the contraction of the positive (concentric) part of the movement.
This mechanism describes what's known as the Stretch-Shortening Cycle (SSC).
Here’s how it works:
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Eccentric Phase (Lowering/Stretching): When a muscle is stretched during the eccentric phase of a movement (e.g., lowering the deadlift bar, lowering the bench press bar to your chest), the muscle spindles detect this stretch.
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Elastic Energy Storage: This stretch causes elastic components within the muscle and connective tissues (like tendons) to store mechanical energy, much like a stretched rubber band.
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Stretch Reflex Activation: Simultaneously, the muscle spindles trigger a protective reflex arc to the spinal cord. This reflex causes the stretched muscle to rapidly contract, acting as a potentiation mechanism.
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Concentric Phase (Lifting/Shortening): When the muscle immediately transitions from the eccentric stretch to the concentric contraction, the stored elastic energy is rapidly released, adding to the force produced by the muscle fibers. The stretch reflex also contributes to a more powerful and efficient contraction.
Connecting the Dots: Why the First Rep is Harder
Now, let's revisit our initial questions with this understanding:
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Deadlift from the Floor: The very first repetition of a deadlift from the floor begins from a "dead stop." There is no preceding eccentric phase to load the muscle spindles or store elastic energy. The lifter has to overcome the inertia of the weight purely through muscular force, without the benefit of the SSC. Subsequent repetitions, even if briefly touching the floor, allow for a slight "bounce" or quick turnaround from eccentric to concentric, engaging the SSC.
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Bench Press from the Chest: Similarly, if the bar is placed on the chest, the muscles are in a relaxed, non-tensioned state. Lifting from this position requires initiating the concentric contraction without any prior stretch or elastic energy contribution. When you lower the bar from the top, you actively engage the eccentric phase, stretching the chest and triceps muscles, activating the muscle spindles, and storing elastic energy. This primes the muscles for a more powerful push upwards.
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Concentric Before Eccentric: Attempting a concentric movement without a preceding eccentric phase (known as a "concentric-only" lift) is inherently more difficult because you completely bypass the benefits of the SSC. You're losing the "free energy" from the elastic recoil and the reflexive potentiation from the muscle spindles.
Conclusion
The "difficulty" of certain lifts, particularly those starting from a dead stop or without a preceding eccentric phase, isn't just a feeling; it's a measurable physiological phenomenon. Understanding the role of muscle spindles and the stretch-shortening cycle helps explain why a controlled eccentric phase is so vital for maximizing force production during the subsequent concentric phase. It's a testament to the sophisticated mechanics of the human body and how our nervous and muscular systems work together to make us stronger and more efficient movers.