In?￠????situ measurements of tensile forces in the tibialis anterior tendon of the rat in concentric, isometric, and resisted co?￠????contractions

摘要

Tensile?￠????force transmitted by the tibialis anterior (TA) tendon of 11 anesthetized adult male Wistar rats (body?￠????mass: 360.6???????±????66.3????g) was measured in?￠????situ within the intact biomechanical system of the hind?￠????limb using a novel miniature in?￠????line load?￠????cell. The aim was to demonstrate the dependence of the loading?￠????profile experienced by the muscle, on stimulation?￠????frequency and the resistance to shortening in a group of control?￠????animals. Data from these acute?￠????experiments shows the type of loading achievable by means of implantable electrical stimulators activating agonists or agonist/antagonist groups of muscles during programmed resistance?￠????training in freely moving healthy subjects. Force?￠????responses to electrical stimulation of the common peroneal nerve for single pulses and short bursts were measured in unloaded and isometric contractions. A less time?￠????consuming approach to measure the force?￠????frequency relationship was investigated by applying single bursts containing a series of escalating stimulus?￠????frequencies. We also measured the range of loading attainable by programmed co?￠????contraction of the TA?￠????muscle with the plantar?￠????flexor muscles for various combinations of stimulation?￠????frequencies. The maximal average peak?￠????force of single twitches was 179% higher for isometric than for unloaded twitches. Average maximal isometric tetanic?￠????force per gramme muscle?￠????mass was 16.5???????±????3.0????N????g ?￠????1 , which agrees well with other studies. The standard and time?￠????saving approaches to measure the force?￠????frequency relationship gave similar results. Plantar?￠????flexor co?￠????activation produced greatly increased tension in the TA?￠????tendon, similar to isometric contractions. Our results suggest that unloaded contractions may not be adequate for studies of resistance?￠????training. Plantar?￠????flexor co?￠????contractions produced considerably higher force?￠????levels that may be better suited to investigate the physiology and cell?￠????biology of resistance?￠????training in rodents.