Active Isolated Flexibility.

Active Isolated Flexibility Tezoro Productions. DVD, 108 mins. $49.95. Active-Isolated Strength Program. DVD, 62 rains. $49.95.

In the last decade, our knowledge about strength training and flexibility has grown by leaps and bounds. Today, countless dance schools offer Pilates and body conditioning, while teachers such as Michele Assaf have designed workouts to strengthen and stretch dancers' bodies. Assaf, a choreographer and instructor at New York City's Broadway Dance Center, worked with the Whartons, a father-and-son team who train and rehabilitate athletes, to create the approach for dancers that's documented in these DVDs. Her Active Isolated Flexibility (AIF) DVD advocates a unique rhythm: Each stretch is held for two seconds (about the length of an exhale) and then released for an inhale, or roughly two seconds. The Wharton men say the rhythm keeps blood and oxygen flowing through the body. By stretching and releasing, you work through a muscle's reciprocal inhibition and thereby stretch more deeply and effectively.

While it's interesting to see the crossover between athletes' and dancers' training systems, the DVDs, like any "virtual" class, lack the vital teacher's eyes (and corrections) that ensure proper form. Some exercises are presented in positions that may compromise proper alignment. On the Active-Isolated Strength DVD, the Whartons teach arm exercises while kneeling down and resting the upper arm on the seat of a folding chair to isolate the lower arm that hangs through the space in the back of the chair. It's an awkward position that can allow the back to slump. Perhaps the best way to experience these DVDs is to take a class from Assaf first and to keep her corrections in mind as you follow the DVDs. See www.Liveat BroadwayDanceCenter.com.