Final answer:
PNF stretching is the technique that combines passive stretch with isometric and concentric muscle actions. It uses isotonic and isometric contractions to enhance flexibility and strength, and involves periods of stretching, muscle contraction, and relaxation.
Step-by-step explanation:
PNF Stretching and Muscle Contractions
The flexibility training technique that combines passive stretching with isometric and concentric muscle actions is known as PNF stretching, or Proprioceptive Neuromuscular Facilitation stretching. This technique involves a series of movements that incorporate both isotonic (concentric and eccentric) and isometric muscle contractions to enhance flexibility and strength.
In isotonic contractions, the muscle length changes through the movement, which can be either concentric as seen when a muscle shortens to move a load or eccentric when a muscle lengthens while releasing a load. During PNF stretching, initially, a passive stretch is applied to a muscle group, and then the muscle is contracted isometrically against the resistance. This is typically followed by a period where the muscle relaxes and another passive stretch is applied, which should be deeper due to the preceding isometric contraction.
For example, when performing a PNF stretching routine for the biceps brachii, an individual may first extend the arm to passively stretch the biceps, then contract the muscle without moving the arm (isometric), and finally move the arm to deepen the stretch or contract the muscle as the arm moves, engaging in a concentric contraction.