I define "Body Rhythm" as the physical movement (rhythm) of the body as compared to the physical movement (rhythm) of the legs. I can't think of any ballroom dance where the rhythm of the body and legs are the same. Most dancers tend to think of only having one rhythm when in fact there are basically two rhythms (the "body" and the "legs"). The reality of it is that most dancers are not aware that there may be more than one rhythm when ballroom dancing.
Each ballroom dancer is composed of two physical parts (the "body" and the "legs"). The definitions of "body" and "legs" are different between the Smooth/Standard dancer and the Rhythm/Latin dancer. The Smooth/Standard dancer's "legs" are from the hip sockets and down. The Rhythm/Latin dancer's "legs" start at the bottom of the ribcage and go down. The Rhythm/Latin "legs" include the hips and the soft area below the ribcage. The body is everything else except the "legs". (Reference previous article: "Ballroom Dancers Have Two Bodies" dated 09/07).
We have all seen the "Pump Handle" dancer. This is where the dancer's body tilts on the left foot weight change then tilts back to the other side on the right foot weight change. This action results from trying to maintain the same rhythm in the body and the legs. The leader's left arm goes up and down like a "pump handle". We also have seen the "River Dancer". The body of the River Dancer is kept very still and the legs (from the hip sockets down) create the rhythm. Although the River Dancer is a non-partnership dancer, it clearly illustrates the differences in the rhythms between the body and the legs. It is obvious that we do not want our Ballroom Dancing to look like either of the above.
Let's take a look at American Style Tango from the leaders' point of view. The rhythm difference between the "body" and the "legs" is very evident in this dance. Tango is also known as "the dance of stops". It is the "body" that is moving and stopping and the legs have a more continuous pulsing movement. Let's analyze just two forward steps. The "body" remains still as the left "leg" moves forward. Once the left "leg" is in the forward position, the "body" is moved on to it. The "body" now remains still until the right "leg" moves from behind the "body" forward to the front of the "body". The "body" is then moved on to the right "leg". To complete the two steps, the "body" remains still as the left "leg" closes from behind to under the "body". As we have just described, the "body" has a stopping type of rhythm and the "legs" have a more continuous moving rhythm.
Now let's take a quick look at some Smooth/Standard dances. In Waltz, the "body" moves horizontal then goes up and down. In Foxtrot, the "body" moves continuously horizontally. In Tango, the "body" moves horizontally then stops, moves horizontally then stops, etc. The "legs" are doing whatever is needed to develop the correct body movement.
When dancing Rhythm/Latin, the "body" (from the bottom of the ribcage up) is still while the "legs" (from the bottom of the ribcage down) executes Latin/Cuban motion and the rhythm of the particular dance. The two different rhythms are very obvious in Rhythm/Latin as well.
One of our goals in ballroom dancing (four-legged movement) is to keep the body still, but as described above, this doesn't exclude the body from having rhythm. Allowing the "body" to be still doesn't mean that the "body" isn't working. The "body" is working with what I call "quiet power". Just being aware that there is "body" and "leg" rhythms will change your dancing.