"Isometric contraction" refers to a type of muscle contraction where the length of the muscle doesn't change. It occurs when the muscle tenses up or contracts, but doesn't produce any movement. Full definition
Rather than being a flowing or vinyasa style of yoga, the Bikram series is more static as the body is moved into and held in a particular position resulting in isometric contraction of the involved muscles. (womenshealthandfitness.com.au)
Huang, L. «Effects of Quadriceps Functional Exercise with Isometric Contraction in the Treatment of Knee Osteoarthritis.» (feelgoodknees.com)
Yoga stimulates the bone with isometric contraction at almost every conceivable angle for long periods of time. (yogauonline.com)