Isometric Contraction
Isometric Muscle Contraction: A type of muscle contraction in which activation of motor units and the production of force does not result in joint motion or a change in muscle length. This occurs when the force produced by the muscle is equal to the external resistance. Functionally, isometric contractions can be thought of as actions that stabilize or maintain the position of a joint or body segment in opposition to an external load.
- Etymology: The word is formed from two parts: "iso" (equal) and "metric" (measure). That is, the force produced by the muscle is equal to the external load.
Key Characteristics:
- Muscle fibers shorten while generating tension.
- Produces acceleration in opposition to the external resistance (e.g., lifting a weight).
Contraction Types:
- Shortening Contraction: Concentric contraction
- Same-length Contraction: Isometric contraction
- Lengthening Contraction: Eccentric contraction
Additional Resources:
- Related Course: Lesson 3: Joint Actions
- Related Course: Acute Variables: Repetition Tempo
- Related Article: The Best Weight Lifting Tempo: Maximum Velocity Concentrics
Examples of Isometric Contractions:
- Biceps Curl (Shoulder): When performing a bicep curl, if the arm remains still, the deltoid is performing an isometric contraction.
- Squat (Trunk): During a squat, the lower extremity moves, but the trunk muscles have to maintain an isometric contraction.
- Push-Up (Trunk): During a push-up, the upper extremity moves, but the trunk muscles have to maintain an isometric contraction.
- Seated Row (Erector Spinae): During a seated row, the arms and scapula move, but the erector spinae have to perform an isometric contraction to keep the torso upright.
- Core Exercises : Core exercises like planks, side-planks , quadrupeds , and chop patterns all challenge the core/trunk muscles to maintain an isometric contraction against resistance from various directions.
An Example of "Isometric Contraction" Used in Practice:
- Cited from the course Acute Variables: Repetition Tempo , and the article The Best Weight Lifting Tempo: Maximum Velocity Concentrics .
Tempo Notation and Recommendations
Repetition (rep) tempos are generally notated in the following format "(3:1:2)". The numbers are seconds (sec.) unless otherwise indicated. Each number corresponds to a phase of contraction in the following order: "eccentric: isometric: concentric." For Example, a pull-up with a 4:1:2 tempo would be performed with the following cadence: 2 seconds on the way up, 1-second hold at the top, and 4 seconds on the way down.
- Slow Tempo: 5 sec. or more per rep (e.g. 3:1:2)
- Moderate Tempo: 2 - 4 sec. per rep (e.g. 2:1:1)
- Fast tempo: 2 sec. or less per rep (e.g. 1:0:1)
- Maximum Voluntary Concentric Tempo (MaxV): A maximum velocity concentric contraction that does not include a quick pre-stretch, the intent to throw an object, or the intent to leave the ground (e.g. the fastest concentric contraction that can be achieved during a bench press or squat). These tempos are as fast as the load can be lifted, but are distinct from the explosive tempos used during power exercises.
- Explosive: A maximal velocity rep that includes a quick pre-stretch, shortest possible amortization phase (isometric), and the intent to release an object or leave the ground during the concentric contraction.
- +: indicates "or longer"
Brookbush Institute's Evidence-based Tempo Recommendations:
- Activation Exercises: 2-4: 2-4: MaxV or explosive
- Endurance: 2+: 0-2: MaxV or longer
- Hypertrophy: 2+: 0-2: MaxV or longer
- Functional Strength: 2+: 0-2: MaxV
- Max Strength: lifter's preference: 0: MaxV (load)
- Power: Explosive: 0: Explosive (speed) - Explosive tempos include a quick pre-stretch, the shortest amortization phase possible, and a concentric contraction with the intent to release an object or leave the ground.