How has legalizing heel-hook joint-lock techniques affected match dynamics in high-level no-gi Brazilian jiu-jitsu tournaments?

In 2021, heel-hook joint-locks (HHJL), effective and controversial techniques known for forcing opponents to quit, were introduced in Brazilian jiu-jitsu (BJJ) no-gi tournaments. However, the effects of these rule changes on no-gi match dynamics remain unknown. This study aimed to investigate the effects of HHJL legalization on the match dynamics of high-level male BJJ no-gi athletes. One hundred and eighty-five matches were categorized following HHJL legalization (Pre x Post) and into five subdivisions: extra-lightweight, lightweight, middleweight, heavyweight, and absolute. Post-HHJL, the number of matches ending by leg-based submission increased (Pre: 6 x Post: 19, p = 0.02), especially by HHJLs (n = 15). Minor changes were observed in time-motion analysis across combat phases. However, in heavyweight, high-intensity actions (attack-and-defense) decreased after HHJL legalization (median [first and third interquartiles]; Pre: 98s [59-112s] x Post: 47s [29-96s], p = 0.02). Moreover, total points scored were reduced in extra-lightweight (Pre: 7 [4-10] x Post: 0 [0-8], p = 0.02) and heavyweight (Pre: 8 [2-11] x Post: 2 [0-6], p = 0.01) after HHJL, while the number of applied techniques during matches were reduced in middleweight (Pre: 7 [5-8] x Post: 3 [2-6.5], p = 0.01) and heavyweight (Pre: 7 [5-10] x Post: 5 [3-7], p = 0.03), respectively. Total match duration did not change after HHJL legalization. HHJL legalization increased the occurrences of leg-based submissions. However, only minor changes were observed in the time structure of BJJ no-gi matches, with heterogeneous effects across weight divisions.