In my opinion, Slow Foxtrot, at the higher levels of dancing is the most difficult of all the Ballroom dances. It may also be the most enjoyable to dance. The difficulty is maintaining a constant and even body movement and at the same time executing the smooth "Slow, Quick, Quick" musical rhythm through the legs. There is no other feeling quite like a well danced Slow Foxtrot.
The Slow Foxtrot at the Silver and above levels is a very different dance than the Slow Foxtrot at the lower levels. The goal of Slow Foxtrot is to have a smooth, level, soft, powerful and controlled movement of the partnership (Singularity). The body of the partnership (from the hip sockets and up) has very little rise and fall and it has a constant horizontal movement. Slow Foxtrot feels as if you are just gliding across the floor.
The Slow Foxtrot body has basically no rhythm and the legs have a "Slow, Quick, Quick" timing. The "Slow" is 2 beats of music and the "Quick" is 1 beat of music. The feet and legs have to move in such a manner as to maintain a constant movement of the body. The body has a different speed than the feet and legs. The body movement is continuous and smooth and the feet and legs have more of a "Slow, Quick, Quick" gliding feeling.
To achieve the even body movement, the "Slow" step (two beats) needs to be twice the length of the "Quick" step (one beat). This causes to the body to travel the same distance for each beat whether it is the two beats for the "Slow" or the one beat for the "Quick". For example: If the "Quick" step is one foot in length for one beat, then the "Slow" step would be two feet in length for two beats. If you do the math, you will discover that the body moves one foot for each beat whether it is a "Slow" or a "Quick". This results in the body movement being constant.
Now that the body is moving at a constant rate, it must also move smoothly. Keeping the feet in continual contact with the floor and having soft knees produces a level body movement. The weight change transitions are barely noticeable resulting in a very smooth horizontal movement. Good dance shoes and a good floor are also important ingredients to smooth movements. The challenge of Slow Foxtrot is the transition between the second "Quick" step to the "Slow" step. The leg speed changes but the body speed doesn't. The way the ankles are used is the key to solving this problem. The ankles are used to reduce the speed of "Quick" steps and transition to the "Slow" step.
In Slow Waltz the body, legs and ankles are used for "Rise" (lifting). Just the ankles are used to create a soft and controlled "Fall" (lowering). The strong but yet soft ankle action is controlling the vertical movement. A similar action happens in Slow Foxtrot except that the ankles are controlling the horizontal movement instead of the vertical movement.
In Slow Waltz, the body weight is directly over the legs on the "Rise" and the "Fall". This allows the ankles to control the vertical up and down movement. In Slow Foxtrot, the leg needs to be in front of the body weight's direction of movement in order to be able to control the horizontal forward and backward movement. The second "Quick" step must be out in front of the body movement in order to strongly and softly control the horizontal change of weight to start the "Slow" step. This action creates a very strong, soft and smooth horizontal movement.
Slow Foxtrot requires strong feet and ankles. A good exercise to strengthen the feet and ankles is to place a length of 2x4 on the floor. Stand on it with just the balls of the feet with the heels hanging over the edge. Now, relax your ankles and allow the heels to lower and touch the floor. Lift through the ankles and rise on the balls of the feet. This stretches the back of the legs as you lower and strengthens the feet and ankles as you rise. The knees need to be soft (slightly bent) to maintain your balance while doing this exercise.
It takes some serious training and skill by both partners (Singularity) to dance a good Slow Foxtrot. The time and effort expended is well worth it and the rewards are enormous. There is nothing quite like the feeling of a SMOOOTH SLOW FOXTROT.