The stretch‐shortening cycle (SSC) revisited: residual force enhancement contributes to increased performance during fast SSCs of human m. adductor pollicis

• Published in: Physiological reports Vol. 3; no. 5; pp. e12401 - n/a
• Main Authors: Seiberl, Wolfgang, Power, Geoffrey A., Herzog, Walter, Hahn, Daniel
• Format: Journal Article
• Language: English
• Published: United States BlackWell Publishing Ltd 01.05.2015
• Subjects: Concentric; eccentric; electrical stimulation; force depression; force enhancement; force redevelopment; muscle; Original Research; potentiation; thumb; force depression; electrical stimulation; force enhancement; potentiation; thumb; force redevelopment; muscle; eccentric; Concentric
• ISSN: 2051-817X; 2051-817X
• DOI: 10.14814/phy2.12401

The stretch‐shortening cycle (SSC) occurs in most everyday movements, and is thought to provoke a performance enhancement of the musculoskeletal system. However, mechanisms of this performance enhancement remain a matter of debate. One proposed mechanism is associated with a stretch‐induced increase in steady‐state force, referred to as residual force enhancement (RFE). As yet, direct evidence relating RFE to increased force/work during SSCs is missing. Therefore, forces of electrically stimulated m. adductor pollicis (n = 14 subjects) were measured during and after pure stretch, pure shortening, and stretch‐shortening contractions with varying shortening amplitudes. Active stretch (30°, ω = 161 ± 6°s−1) caused significant RFE (16%, P < 0.01), whereas active shortening (10°, 20°, and 30°; ω = 103 ± 3°s−1, 152 ± 5°s−1, and 170 ± 5°s−1) resulted in significant force depression (9–15%, P < 0.01). In contrast, after SSCs (that is when active stretch preceded active shortening) no force depression was found. Indeed for our specific case in which the shortening amplitude was only 1/3 of the lengthening amplitude, there was a remnant RFE (10%, P < 0.01) following the active shortening. This result indicates that the RFE generated during lengthening affected force depression when active lengthening was followed by active shortening. As conventional explanations, such as the storage and release of elastic energy, cannot explain the enhanced steady‐state force after SSCs, it appears that the stretch‐induced RFE is not immediately abolished during shortening and contributes to the increased force and work during SSCs. Mechanisms underlying muscular performance enhancement in stretch‐shortening cycles (SSC) still are a matter of debate. Measuring thumb adduction force during and after pure stretch, pure shortening, and stretch‐shortening contractions we found a remnant increased force following the active shortening. As conventional explanations, such as the storage and release of elastic energy, cannot explain the enhanced steady‐state force after SSCs, it appears that mechanisms associated with stretch‐induced residual force enhancement contribute to the increased performance during SSCs.