Plank

1. The plank (also called a front hold, hover, or abdominal bridge) is an isometric core strength exercise that involves maintaining a difficult position for extended periods of time. The most common plank is the front plank which is held in a push-up position with the body's weight borne on forearms, elbows, and toes.

Many variations exist such as the side plank and the reverse plank.[1][2] The plank is commonly practiced in pilates and yoga, and by those training for boxing and other sports.

2. The Planck constant (denoted h, also called Planck's constant) is a physical constant that is the quantum of action in quantum mechanics. Published in 1900, it originally described the proportionality constantbetween the energy, E, of a charged atomic oscillator in the wall of a black body, and the frequency, ν, of its associated electromagnetic wave. Its relevance is now integral to the field of quantum mechanics, describing the relationship between energy and frequency, known as the Planck–Einstein relation: