The force‐velocity relationship of human adductor pollicis muscle during stretch and the effects of fatigue

Abstract

1. We have examined the force-velocity characteristics of tetanically activated human adductor pollicis working in vivo, in the fresh and fatigued states. 2. The increase in force in response to stretch was divided into two major components. The first, steady, component persisted after the stretch and is concluded not to be a function of active cycling cross-bridges because it was not affected by either the velocity of the stretch or the level of muscle activation. 3. The origin of the second, transient, component of the increased force seen during stretch is consistent with cross-bridge activity since it increased with increasing velocity of stretch and was proportional to the level of activation. 4. It is likely that both components of the stretch response make a significant contribution to muscle performance when acting to resist a force. For the fastest stretch used, the contributions of cross-bridge and non-cross-bridge mechanisms were equal. For the slowest stretch, lasting 10 s and over the same distance, the force response was attributed almost entirely to non-cross-bridge mechanisms. 5. As a result of acute fatigue (50% isometric force loss) there were only small reductions in the non-cross-bridge component of the force response to stretch, while the cross-bridge component decreased in absolute terms. 6. The transient component of the stretch response increased as a result of fatigue, relative to the isometric force, while the force during shortening decreased. The results are consistent with a decrease in cross-bridge turnover in fatigued muscle. Keywords:

Characterization of the passive component of force enhancement following active stretching of skeletal muscle

“…The idea that force enhancement has the properties of a passive 'elastic' element has been proposed, but not directly demonstrated before (Edman et al, 1982;Noble, 1992;Edman and Tsuchiya, 1996;DeRuiter et al, 2000). The molecular spring titin has been suggested to fill this role, and although we do not have direct evidence for a possible contribution of titin to the passive force enhancement observed here, titin's properties and structural arrangement appear consistent with the results found in this study.…”

“…Abbott and Aubert, 1952;Edman et al, 1978Edman et al, , 1982Edman and Tsuchiya, 1996;Linari et al, 2000;Morgan et al, 2000;DeRuiter et al, 2000). However, the mechanisms underlying force enhancement following active stretch are not known.…”

The torque–velocity relationship in large human muscles: Maximum voluntary versus electrically stimulated behaviour

“…For the stimulation condition T ecc /T 0 ranged between 1.4 − 1.8. The lower end of this range is similar to values reported in previous in vivo stimulation studies for the quadriceps (Dudley et al, 1990;Westing et al, 1991) soleus (Pinniger et al, 2000) and adductor pollicis (De Ruiter et al, 2000;Lee and Herzog, 2002). While the upper end is similar to values found in previous in vivo stimulation studies for the first dorsal interosseus (Cook and McDonagh, 1995) and in vitro studies for mouse and frog muscle fibres (Katz, 1939;Délèze, 1961;Edmann, 1988;Lombardi and Piazzesi, 1990;Krylow and Sandercock, 1997).…”

Variation in isometric force after active shortening and lengthening and their mechanisms: a review

“…However, these arguments are refuted by studies showing that the phenomenon also occurs, albeit to a lesser extent, in the ascending limb of the LTC. Even in the presence of a control mechanism to stabilize and maintain uniformity, structural integrity and regulate sarcomere length, FD has been observed, also revealing a reduction in muscle passive tension (6,7,21,32,33,34,38,39,40).…”

“…It is proposed that the phenomenon of FD would associated to the descending limb and to the peak of the SLT (35,36,37), but recent evidence suggests that this would happen too, even on a smaller scale, the ascending limb of the LTC (21,32,38,39).…”