Isometric and concentric performance of electrically stimulated ankle plantar flexor muscles in intact rat

Abstract

summaryThe relationship between muscle force and ankle position during isometric and pre-loaded slow concentric contractions (angular velocity, 0·52 rad s¢; range of motion, 1·22 rad) and the recovery of isometric force following concentric contractions at different velocities were determined for electrically stimulated plantar flexor muscles in intact rats. Pre-loaded refers to the isometric contraction which immediately precedes the concentric contraction. Ankle position was controlled by a dynamometer and force was recorded under the sole of the foot. The peak isometric force (19·2 N) was nearly constant at all ankle positions (range of motion, 1·57 rad). The muscle length and distal fibre length of gastrocnemius medialis at ankle positions between 0·79 rad and 2·01 rad were increased by 12·6% and 20·3%, respectively. During slow concentric contractions, the force progressively decreased (23·1 ± 2·1%); the force decreased by only 6·3 ± 0·9% during sustained isometric contractions of similar duration (3400 ms). The recovery of isometric force following concentric contractions with similar stimulation frequencies (80 Hz) was velocity dependent (i.e. more rapid at higher velocities). It is concluded that pre-loaded slow concentric contractions of the plantar flexor muscles in intact rats do not follow the same relationship as that of isometric force and ankle position. Our results in intact rats show that the force output of electrically stimulated ankle plantar flexor muscles measured under the sole of the foot can be used to study the physiological properties of skeletal muscle working in situ.

Ageing, but not yet senescent, rats exhibit reduced muscle quality and sarcoplasmic reticulum function

“…Overall, the observed force values were similar to those previously reported for the entire plantarflexor group (Wexler et al 1997, Willems & Stauber 1999, and contractile force was reduced in the muscles of the old rats. The age-related differences in both peak force and muscle quality increased with increasing frequencies of stimulation (Fig.…”

The effect of number of lengthening contractions on rat isometric force production at different frequencies of nerve stimulation

“…Details on the dissection procedure for nerve cuff placement, necessary for electrical stimulation of the tibial nerve of the left hind limb, positioning of the rats and use of the dynamometer have been described elsewhere (Cutlip et al. 1997, Willems & Stauber 1999). Force production of the plantar flexor muscles was induced by electrical stimulation of the tibial nerve and was recorded as a reaction force under the sole of the foot (Willems et al.…”

“…In all groups, before and after 1 h of rest following the repeated LC, force–frequency measurements were performed at an ankle position of 90°. A knee and ankle position of 90° coincides with optimum length of the plantar flexor muscles (Willems & Stauber 1999).…”

High force reaching task induces widespread inflammation, increased spinal cord neurochemicals and neuropathic pain

“…These latter studies have found tactile allodynia, reduced nerve conduction velocity, endoneurial macrophage infiltration, spinal cord neuroplasticity and augmented neuronal excitation, as well as spinal cord inflammatory responses after peripheral nerve injury. In addition to the effects on peripheral nerve, several laboratories, including our own, have documented the effects of repetitive motion on musculoskeletal tissues, including inflammatory cell infiltrates, tendinopathy, degenerative changes and tissue necrosis (Soslowsky et al, 1996;Willems and Stauber, 1999;Barbe et al, 2003;Barr et al, 2003;Geronilla et al, 2003;Diao et al, 2005;Nakama et al, 2005;Perry et al, 2005;Baker et al, 2007;Sommerich et al, 2007). …”