As general rule, the strong beat in Latin music is at beat 1. But in the CD "Rhythm of Results" of Ton Greten (http://www.dsi-london.com/site/?action=prod_page&pid=9163&cat_id=13&type=18&sub_id) he said that the strong beat in Rumba is in beat 4 (it is syncopated!!!). I also do not know why Walter Laid said in his book that Rumba has beat 4 strong)

Therefore what is the exact music of International Rumba (used in WDC and WDSF contests)? Rumba with strong beat in beat 1 or Rumba with strong beat in beat 4? If they use beat 4 strong, what is the reason?

Can anyone know it clearly? And how about music rhythm of Chacha in WDC & WDSF?

Dance Lover. There is a musical accent in the Cha Cha on beat 1.
In the Rumba. It is possible with some that the Rumbas they dance to are not true Rumbas. The predominent percussive accent is on beat 4 in a Rumba.

You mean that the true Rumba has strong accent on beat 4. But can you let me know it is syncopated (strong beat at 2 and 4) or it is normal with extra beat in 4 (strong beat at 1,3,4)?
Do you have any information about strong beat at 2 in Rumba except Walter Laird book?
Thank in advance

Why ?.. because if you study "latin " rhythm, you would know that "4" is the stressed note in Cuban Son, which along with Clave, is the foundation for ALL latin rhythms.

The European "ear " has concentrated on the down beat forever ( it seems ) .

Cuban Son music and Clave is played in 8-beats cycle ( 1, & after 2,4,,6,7) and have no relation to international Rumba played in 4-beat cycle with step on 2,3,4. If you know the history of the int. rumba dance, you will see it is different to Cuban rumba

The Q was " WHY " the 4 was dominant..

and, I was probably dancing and teaching indigenous ( and BR )latin rhythms, before you were born ( IN the States with latinos )also trained with Laird in the 40s, and, DO you know Intern. Rumbas origins, and its antecedent ? and its NOT danzon.

ALL indigenous latin, in the Rumba genre ( an umbrella term ) is Son and Clave driven.

If you have a dis agreement with this, then may I suggest you take your posit to Salsa Forums, where there has just been a discussion on this very topic,( Son ) by NY latin musicians.

In 1947 Mr. Pierre visited Havana, modified the Cuban Rumba which is played with 6 or 7 steps in a phrase (2 bars) of 8 beats. This Cuban Rumba is played with the Clave and Conga.. The modified Rumba (now is the int Rumba) is played only 3 steps in a bar of 4 beats. It is very different, can you dance int Rumba with the Clave?