In situ measurements of skeletal muscle power output using new capacitive strain gauge

Experiments are described in which a fatigue index is determined for the la tissimus dorsi muscle of sheep in situ, using capacitive strain gauges. Par allel experiments for invasive and non-invasive measurements are conducted, measuring global contraction and relaxation rates and shortening duration for paced muscle. The results show that, above one pulse per burst (5 V, 10 0 mu s pulsewidth), contraction rates (62 +/- 17 mm s(-1)) and relaxation r ates (50 +/- 7 mm s(-1)) are constant for unloaded muscle. For one animal, fatigue testing with a 2.5 kg load at six pulses per burst shows shortening rates increasing to a maximum (80 mm s(-1)) after 30 s and reducing to 5 m m s(-1) after 150s. The decrease in shortening amplitude is used as a fatig ue index, log displacement against time. Power output is load dependent, me asuring 4.7 W kg(-1) with a 2.5 kg load. There is good agreement between th e invasive and non-invasive measurements, thus providing a method for monit oring changes in muscle parameters non-invasively during future pacing tran sformation.