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In the video https://www.youtube.com/watch?v=_0GGsBgPic4 they say at 10:49 that you should forget dynamic belaying in trad climbing, because falling more causes more stress on the gear.

Is this correct? In my understand dynamic belaying should reduce stress on bolts, pitons, cams,...

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This is not what they said. They say "falling more causes more stress on the gear" which is correct. The caveat here is that falling is meaning free falling due to additional slack in the system. This is wholly different from a soft catch which does not add slack but distributes the force of the catch over a longer period of time, therefore breaking while "falling more".

Please note one thing on the video:
Unnecessary slack in general is not regarded as something that is helpful for lowering the impact. More slack creates more conversion of potential energy before the rope catches which you then have to shed again through friction. Therefore it is always better to avoid adding energy to the system.
Why do people then think a catch gets softer with more slack? Because the higher impact at the begin helps to overcome the inertia of the belayer. This is especially important when you belay with a locking device and can only give a soft catch by moving with your whole body. With a dynamic device this is different as feeding more rope through the device will give a dynamic catch.

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  • Just a small note: adding slack does not increase gravitational potential energy - the climber ascends to the same height. More slack means more conversion from gravitational potential to kinetic energy, i.e., the final speed before the rope starts stretching increases. It also translates to more rope available to catch, generating more elastic potential energy, but since the kinetic energy is a function of the speed squared and the elastic energy of the stretch distance squared, there is no reduction of impact force due to additional slack.
    – QuantumBrick
    Commented Mar 18, 2020 at 13:15
  • Okay, so summarized: with the same amount of slack, dynamic belaying reduces the stress on the gear. So dynamic belaying should also be used in trad/ ice climbing. Or in other words, for a fixed amount of slack it is possible that for static belaying the pitons, cams fall out, but for dynamic belaying they don't. The other way around is not possible.
    – cerv21
    Commented Mar 18, 2020 at 20:16
  • As long as there is no danger of a groundfall or hitting a ledge (in this case not hitting the ground/ledge is absolute priority) it is always advisable to give a soft catch
    – Manziel
    Commented Mar 19, 2020 at 11:37
  • Everything is clear now! Thanks
    – cerv21
    Commented Mar 19, 2020 at 21:14

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