You are strongest lowering the weight — why concentric-only work stays a supplement
In short
People handle the heaviest loads during the eccentric phase, when the muscle lengthens under tension. A concentric-only machine can meet up to roughly 680kg (1,500 pounds) of force on the pushing stroke, but it removes the lowering phase and any way to load the stretched position, so it belongs in a programme as low-fatigue accessory volume rather than as the main course. The clearest use cases are people rebuilding after injury or training later in life, and experienced lifters who already own everything else.
The strongest part of a lift is not the push — it is the way down. The same muscle handles more load lengthening under tension (the eccentric) than it does shortening (the concentric). So a machine that resists only the pushing direction trains half the lift no matter how high you crank the resistance.
A recent air-resistance strength machine is the clean example. It packs a leg press, a chest press, and a seated row into one unit, and the pushing stroke can meet up to roughly 680kg (1,500 pounds) of force. The return stroke, though, carries no resistance at all. The flywheel pushes back only as hard as you push into it; it never pulls you.
What disappears when the eccentric does?
- The phase that handles the heaviest load is gone entirely — muscle is strongest while lengthening
- Any way to load the stretched position goes with it, and the stretched position is the expensive part of a hypertrophy stimulus
- Soreness and systemic fatigue vanish too. That is not a flaw; it is the feature that decides what the machine is for
So where does it fit?
Leaving almost no fatigue behind is exactly the use case. Two concrete protocols: set a 10 to 15 minute timer and alternate 15 to 20 single-leg reps per side without rest, holding every rep above 50kg of force; or set a force floor of 80 to 90kg with both legs and keep going until reps drop below the floor back to back. Either way you add unilateral volume without the fatigue that would wreck the deadlifts and lunges later in the week.
The audience splits too. For someone rehabbing or training later in life it is a route back to basic movement patterns and force output without eccentric-driven soreness — and the per-rep force readout makes progress visible. Beginners should skip it; mastering the basic lifts pays far more. For experienced lifters who already own the essentials it becomes a way to train fast, explosive concentric contractions on their own.
Does it move your muscle index?
Not directly. The index starts from your squat, bench press, and deadlift one-rep maxes, and all three include a lowering phase. A big number on a push-only machine does not drag your big-three total up with it. The indirect route is real, though: if the extra weekly volume does not eat into recovery for the main lifts, that volume eventually shows up in the one-rep maxes. Keep accessories in the accessory slot, and do the maths on the big three.
Machines that display large force numbers breed overconfidence. A 680kg readout has nothing to do with a 680kg squat — air resistance pushes back only as hard as you push, so the number is your output at that instant, not the load you handled.
For where a different loading mode sits, see isometric training for strength and size; on splitting the difference between volume and load, volume versus intensity.
Frequently asked questions
Why does the eccentric phase matter?
Muscle handles more load lengthening under tension than it does shortening, and loading the stretched position is the most valuable part of a hypertrophy stimulus. Remove the lowering phase and the training touches only half the lift.
Can you build muscle on a machine with no eccentric?
Concentric-only work does provide a stimulus, but it removes stretched-position and eccentric loading, so it is not enough to build a hypertrophy programme around. It needs bodyweight work such as pushups and pullups plus dumbbell or barbell lifts alongside it.
Who benefits most from concentric-only equipment?
Two groups. People recovering from injury or training later in life, who can train movement patterns and force output for long sessions without eccentric soreness and systemic fatigue; and experienced lifters who already own the basics and want extra volume plus explosive concentric work.
How do you program this kind of machine work?
As accessory volume after the main lifts. Set a 10 to 15 minute timer and alternate 15 to 20 single-leg reps per side while holding every rep above 50kg of force, or set a two-legged force floor of 80 to 90kg and continue until reps fall below it.
Is the force number on the display the same as a one-rep max?
No. Air resistance pushes back only as hard as you push into it, so the readout is your instantaneous output, not the load on the bar. A 680kg reading is unrelated to a squat or deadlift max, and the muscle index is calculated only from big-three one-rep maxes.
Source: Men's Health Fitness