Shock cord

[netwitt]

Greetings all,

Does intentionally shortening the shock cord add more resistance? If anyone does this, how much do you shorten it?

Thanks!

dw

[Citroen]

Greetings all,

Does intentionally shortening the shock cord add more resistance? If anyone does this, how much do you shorten it?

Thanks!

dw

No and don't do it.

Check the machine is clean (drag factor should range from 95 (damper 1) to 210 (damper 10)), use the damper lever to change the "resistance".

[PaulS]

Greetings all,

Does intentionally shortening the shock cord add more resistance? If anyone does this, how much do you shorten it?

Thanks!

dw

It does, but the added resistance will not be accounted for on the Performance monitor (PM).

The only time that shortening the shock cord is desirable is if the handle will not return to the chain guide and remain there with a bit of tension (~ 4-6lbs).

Shortening is quite easy to do, and doing a quick search of the maintanence documents on the C2 site should get you the instructions that you need. Once you've done it one time, which will take 5-10 minutes, you will be able to do it any other time in less than 5 minutes.

[Nosmo]

Greetings all,

Does intentionally shortening the shock cord add more resistance? If anyone does this, how much do you shorten it?

Thanks!

dw

It does, but the added resistance will not be accounted for on the Performance monitor (PM).

Agreed but you get most of the energy back because the cord helps pull you forward. That said, since a tighter cord increases peek power, it is detrimental overall

[PaulS]

Greetings all,

Does intentionally shortening the shock cord add more resistance? If anyone does this, how much do you shorten it?

Thanks!

dw

It does, but the added resistance will not be accounted for on the Performance monitor (PM).

Agreed but you get most of the energy back because the cord helps pull you forward. That said, since a tighter cord increases peek power so it is detrimental overall

It's difficult to think of it as "getting the energy back" in this case, i.e. if you stretch an elastic band and then return to the starting position, did you really "get something back" or did it actually cost you a bit the whole time it was under tension?

Probably not worth worrying about, unless it is made so tight that it becomes hard to stretch, which should be tough to do based on the pulley system that really has the bungee stretching about 1/4 the distance that the handle travels. i.e. "not much", considering a relaxed length of 10 feet for the bungee.

[Nosmo]

Power needed to stretch the cord is about 10 to 20 watts:

Power = force x distance / time.

Assuming:
5 lbs of force = 22.25 Newtons
stroke length of 1.20 meters (47.25 inches)
and 30 strokes per minute (2 seconds)

We get 22.25 N * 1.2 m / 2 s = 13.35 W

I used 5 lbs because Paul gives the range of 4-6lbs above.
I used 1.20 m for the stroke length because that is approximately my stroke length according to the ErgMonitor software that Pauls sells (i'm 5'7"). Really good software BTW. Paul look forward to email comments about the software later this week.

So it looks like this is not insignificant. So if one does not get any of this energy back, loosening the bungee cord as much as possible might be smart.

From a physics point of view, the rower is putting energy in to the shock cord as it is being stretched. Neglecting elastic losses in the cord itself, the shock cord is the returns the energy by pulling the rower forward. It is only costing you energy if you are resisting the return force. If you are pulling your self forward then it saves you energy.

Your rubber band analogy is good--the rubber band does put energy back into your hands, but one has to dissipate that energy when you stop moving at the initial position, resulting in physical fatigue and more calories burned even if on a simplistic level no net work is being done.