Force–frequency and force–length properties in skeletal muscle following unilateral focal ischaemic insult in a rat model
Article first published online: 9 MAY 2009
© 2009 The Authors. Journal compilation © 2009 Scandinavian Physiological Society
Volume 197, Issue 3, pages 227–239, November 2009
How to Cite
Dormer, G. N., Teskey, G. C. and MacIntosh, B. R. (2009), Force–frequency and force–length properties in skeletal muscle following unilateral focal ischaemic insult in a rat model. Acta Physiologica, 197: 227–239. doi: 10.1111/j.1748-1716.2009.02001.x
- Issue published online: 7 OCT 2009
- Article first published online: 9 MAY 2009
- Received 5 May 2008, revision requested 29 June 2008, final revision received 28 March 2009, accepted 6 May 2009
- cerebrovascular attack;
- length dependence of force;
- muscular fatigue;
- tetanic fade
Aim: Our purpose was to quantify skeletal muscle properties following unilateral focal ischaemic insult (stroke) in a rat model.
Methods: Male rats were divided into two groups: stroke and 2 weeks recovery (n = 8) and control group (n = 7). Stroke was induced in the area of the motor neocortex containing hind limb corticospinal neurones. Contractile properties of the medial gastrocnemius muscle were measured in situ in both limbs. Force–length and force–frequency properties were measured before and 35 min after 5 min fatiguing stimulation.
Results: Stroke resulted in bilateral tetanic fade during 200 Hz stimulation. When normalized to 100 Hz contractions, force at 200 Hz was 95.4 ± 0.9% for the paretic muscles, 96.7 ± 1.7% for non-paretic muscles and 102.2 ± 1.0% for muscles of control rats (P = 0.006). Prior to fatiguing contractions, there was no difference in the length dependence of force. During repetitive contractions, active force fell significantly to 19 ± 4 and 25 ± 5% of initial force in paretic and non-paretic muscles of animals with a stroke respectively. In control animals active force fell to 37 ± 5%. During repetitive contractions, fusion index increased in muscles of stroke animals to 1.0 ± 0 but in control animals it was 0.95 ± 0.02. There was selective force depression at short lengths for fatigued paretic muscle (significant difference at muscle lengths less than reference length −2 mm).
Conclusion: The tetanic fade at high stimulation frequencies indicates that there may be activation failure following focal ischaemic insult. The greater magnitude of fatigue and selective depression at short lengths following repetitive contractions should be investigated further.