Active Isolated Stretching (AIS) is a highly specific, dynamic method of flexibility and mobility training. Developed by Aaron Mattes, this technique departs from traditional approaches by incorporating active muscle contraction and precise timing. AIS focuses on moving the body through its full range of motion in a controlled manner. It is used for injury rehabilitation, performance enhancement, and restoring lost range of motion.
Defining Active Isolated Stretching
Active Isolated Stretching is defined by three foundational components: active movement, isolation of a muscle group, and a brief, controlled hold. The “active” component means the person uses their own muscle strength to move the limb. For example, to stretch the hamstring, the individual actively contracts the quadriceps to lift the leg into position, rather than passively pulling the limb.
The “isolated” element focuses on targeting one specific muscle group at a time. This specificity allows for a more direct lengthening of the tissue compared to general, multi-joint movements. The technique is performed in sets of repetitions, similar to strength training, with each repetition aiming to slightly increase the range of motion.
The most characteristic element of AIS is the short, controlled hold, lasting no more than 1.5 to 2 seconds. At the point of maximum active stretch, a light external assist, such as a rope or hand, gently moves the limb a few degrees further. This momentary assistance pushes the boundary of the stretch before immediately returning to the starting position. The rhythmic action of stretching and releasing also promotes local blood flow, which aids tissue recovery.
The Underlying Physiological Mechanism
The effectiveness of AIS relies on manipulating two neurological principles. The first is reciprocal inhibition, which governs muscle action around a joint. When the agonist muscle group contracts, the nervous system automatically signals the opposing muscle group, the antagonist, to relax.
This neural signaling ensures smooth, coordinated movement by preventing the antagonist muscle from fighting the agonist’s action. By actively contracting the muscle opposite the one being stretched, AIS leverages this reflex to achieve greater lengthening in the target muscle. The relaxation signal allows the stretched muscle to temporarily reduce tension and extend further.
The second mechanism involves avoiding the protective stretch reflex, also known as the myotatic reflex. This reflex is an involuntary contraction triggered by muscle spindles, which monitor the speed and extent of lengthening. If a muscle is stretched too forcefully or held too long, the muscle spindles signal the central nervous system to contract the muscle to prevent tearing.
The brief, 2-second hold used in AIS is precisely timed to stay below the threshold that activates this protective reflex. By immediately releasing the stretch before the reflex engages, the technique allows the muscle to lengthen progressively. This enables deeper stretching over multiple repetitions without triggering the body’s natural defense mechanism.
Comparison to Other Stretching Methods
Active Isolated Stretching is often contrasted with common stretching forms based on methodology and timing. Static stretching involves holding a stretch for an extended period, typically 30 seconds or longer. This prolonged, passive hold increases the risk of triggering the myotatic reflex, which causes the muscle to tighten and limits flexibility gains.
Holding a static stretch before exercise can temporarily decrease muscular strength and power output. AIS, conversely, uses an active contraction and a very short hold, making it a dynamic movement often incorporated into a warm-up routine. The active nature of AIS also stimulates blood flow, while prolonged static holds can restrict circulation.
Dynamic stretching, while also active and movement-based, differs from AIS in execution. Dynamic stretching typically involves continuous, multi-joint movements that rely on momentum, such as leg swings. These movements prepare the body for activity by taking joints through their functional range of motion. AIS is a more controlled and isolated movement, focusing on maximizing the length of a single muscle group with specific, repetitive actions.