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The eccentric phase of this isometric exercise
11%
411/3648
The concentric phase of this isometric exercise
4%
132/3648
The eccentric phase of this isokinetic exercise
18%
646/3648
The concentric phase of this isotonic exercise
391/3648
The eccentric phase of this isotonic exercise
56%
2033/3648
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The patient sustained a distal biceps rupture while doing a dumbbell biceps curl. Distal biceps ruptures, as well as other tendon avulsions, most commonly occur during the eccentric phase of exercise. A biceps curl is an isotonic exercise. In isotonic exercises, the muscle delivers constant force through the range of motion and is at constant tension. The muscle shortens in the concentric phase (elbow flexes in a biceps curl), and lengthens in the eccentric phase (elbow extends). Distal biceps ruptures occur most commonly in the eccentric phase of loading. O'Driscoll et al. evaluated the hook test in 45 patients undergoing surgical exploration for distal biceps injuries. They found that sensitivity and specificity was both 100% for the hook test, compared with 92% and 85% respectively, for MRI. They recommend the hook test as a reliable physical exam test for both complete ruptures (abnormal test) and partial ruptures (painful hook test). Illustration A shows the hook test. The elbow is flexed to 90° and the forearm fully supinated. With an intact biceps tendon, a finger can in inserted under the lateral edge of the biceps tendon between the biceps tendon and underlying brachialis from anterolateral to posteromedial. With a biceps tendon avulsion, there is absence of a cord-like structure (abnormal test). Incorrect Answers: Answers 1 and 2: In an isometric exercise, a muscle contracts against with constant length and there is no appreciable joint motion. An example of isometric exercises is pushing against an immovable object. Muscle length and tension remains constant. Answer 3: In an isokinetic exercise (a type of strengthening protocol), muscles contract at a constant velocity, but resistance varies depending on force exerted through the range of motion. Special machines are necessary for this exercise. Answer 4: Distal biceps ruptures most commonly occur during the eccentric (not concentric) phase.
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