Schwinn 131 User Manual download pdf (Page 18)

Human Performance Systems, Inc.

autilus Application of patented 4-Bar Linkages

Nautilus features the patented 4 bar linkage in all its compound/complex movement

machines. Unlike rotary pattern movements, whose strengths curves can be mimicked

with an elliptical cam, movements such as leg press and low back extension require a

MARKED increase in resistance to compensate for mechanical advantage and gravity.

Why is this so critical in rehab?

Let’s examine a couple machine designs common in the rehabilitation arena.

LOW BACK

Most back extension machines posture a patient in flexion, under load, then require a

patient to move backwards into full extension. Let’s examine this movement:

Resistance (approximately)

100% 75% 50%

full extension torso neutral starting in flexion

In flexion, the patient is required to overcome their own torso weight, the weight of the

lever arm, and whatever weight is chosen on the weight stack…all while attempting to

maintain lordosis and avoid further back trauma. When the patient achieves an upright-

seated position, the gravity load on the torso and lever arm are mitigated, and when the

patient moves beyond the seated posture, he achieves a gravity assist of torso and lever

arm weight. So, most back extension machines can only be loaded with a weight that can

be tolerated at the beginning, weakest point in the ROM, and provides virtually no

resistance in the seated and extended portion of the exercise.

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Schwinn 131 User Manual Page 18