Force enhancement following muscle stretch of electrically stimulated and voluntarily activated human adductor pollicis

Abstract

For electrically stimulated muscles, it has been observed that maximal muscle force during and after stretch is substantially greater than the corresponding isometric force. However, this observation has not been made for human voluntary contractions. We investigated the effects of active muscle stretch on muscle force production for in vivo human adductor pollicis (n= 12) during maximal voluntary contractions and electrically induced contractions. Peak forces during stretch, steady‐state isometric forces following stretch, and passive forces following muscle deactivation were compared to the corresponding isometric forces obtained at optimal muscle length. Contractions with different stretch magnitudes (10, 20, and 30 deg at a constant speed of 10 deg s−1) and different speeds (10, 20, and 60 deg s−1 over a range of 30 deg) were performed in triplicate in a random order, balanced design. We found three novel results: (i) there was steady‐state force enhancement following stretch in voluntarily contracted muscles; (ii) some force enhancement persisted following relaxation of the muscle and (iii) force enhancement, for some stretch conditions, exceeded the maximum isometric force at optimal muscle length. We conclude from these results that voluntary muscle contraction produces similar force enhancement to that observed in the past with electrically stimulated preparations. Therefore, steady‐state force enhancement may play a role in everyday movements. Furthermore, these results suggest that non‐uniformities in sarcomere length do not, at least not exclusively, account for the force enhancement following active muscle stretch, and that the stretch magnitude‐dependent passive force enhancement observed here may be responsible for the enhancement of force above the isometric reference force at optimal muscle length.

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).…”

Modulation of passive force in single skeletal muscle fibres

“…Recent evidence shows that the PEVK segments of titin bind Ca 2C with high affinity (Tatsumi et al 2001), and that increasing Ca 2C concentration enhances force produced by titin at a given sarcomere length (Labeit et al 2003), suggesting a link between Ca 2C -induced activation and force produced by titin. In studies conducted in our laboratory with singlemuscle fibres (Rassier et al 2003;Rassier & Herzog 2004a,b), whole muscles (Herzog & Leonard 2002;Herzog et al 2003) and human muscles (Lee & Herzog 2002), we observed that passive force is increased when activated muscles are stretched along the descending limb of the force-length relationship, when compared with the passive forces following passive stretches or isometric contractions at the corresponding lengths. We refer to this phenomenon as passive force enhancement (Herzog & Leonard 2002;Herzog et al 2003;Rassier et al 2003;Rassier & Herzog 2004a,b).…”

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

“…As in FD, the occurrence of FE initially was linked only to the lower limb and the peak of the LTC (22,23,24). However, new findings indicate that FE is also observed with reasonable stability in the ascending limb of the LCT (39,80,81,82).…”

“…This association is independent of the coupling of new cross bridges actin -myosin that remains after ceased the stimulus (7,17,22,28,33,97).…”

“…stimulation combined with maximum voluntary dynamic contractions (5). Furthermore, devices have relied on complex servo motors coupled to force transducers that bear little resemblance to human movement pattern (2,11,14,15,16,17,18,19,20,21,22,23,24,25,26).…”