Japanese term (edited): へたり

This site (http://homepage3.nifty.com/tongermark/bhv2k/bhv2ha.htm) [in あいうえお順 so scroll down quite close to the bottom of the page] gives:

sag, settling, permanent set in fatigue, loss of resilience; spring sag
for へたり,沈下,沈降; ばねのへたり

If 'sag' doesn't seem to fit the context for the clip, how about 'poor recoil,' 'poor rebound' or 'loss of (or poor) resilience.'

Web definitions of 'sag' :
# droop, sink, or settle from or as if from pressure or loss of tautness
wordnet.princeton.edu/perl/webwn

# Sag is the degree to which a shock absorber compresses with the rider sitting motionless on the bike in a normal riding position. Usually, this should be between 15% and 25% of available travel for cross country riding and slightly more for downhill riding. Sag allows the suspension system to extend when it comes to a dip in the trail. If it had no sag and did not extend, the wheel would not follow the dip, which results in decreased traction, especially on bends. ...
www.hkmba.org/en/glossary.php3

熱間成形コイルばねのへたり試験法に関する研究
Title, Study on Sag Test of Hot Coiled Compressive Spring for Suspension. 著者, 熱間成形コイルばねへたり試験法委員会. Author, The committee of for Sag Test ...
wwwsoc.nii.ac.jp/jssr/shuppan/ronbun/j30_10.html

耐へたり性に優れた冷間成形懸架ばね
ページ数, pp.9-12. 種類, 論文. 論文タイトル, 耐へたり性に優れた冷間成形懸架ばね. Title, Cold Formed Coil Spring with High Sag Resistance for Suspension ...
wwwsoc.nii.ac.jp/jssr/shuppan/ronbun/j31_02.html