Twitch kinetics of motor units and muscle fibers from young adult rats and mice
| Experimental preparation | n | Time of peak | Half-relaxation time | FDHM |
| ms | ms | ms | ||
| A. Motor units in anesthetized ratsa (normal sarcomere length; 35-36°C) | ||||
| 1. Soleus muscle (slow-twitch units) | 34 | 38 ± 4 | 57 ± 8 | — |
| 2. EDL muscle (fast-twitch units) | 48 | 11 ± 1 | 11 ± 2 | — |
| B. Singly dissected mouse fibersb (normal sarcomere length; 20-21°C) | ||||
| 1. Soleus fibers (slow-twitch) | 12 | 96 ± 7.5 | 130 ± 14 | — |
| 2. EDL fibers (fast-twitch) | 11 | 33 ± 6.1 | 62 ± 12 | — |
| C. Small bundles of mouse fibersc(long sarcomere length; 16°C) | ||||
| 1. Soleus fibers (slow-twitch) | 14 | 173 ± 9 | 708 ± 73 | 843 ± 80 |
| 2. EDL fibers (fast-twitch) | 16 | 52 ± 2 | 162 ± 11 | 197 ± 12 |
| Experimental preparation | n | Time of peak | Half-relaxation time | FDHM |
| ms | ms | ms | ||
| A. Motor units in anesthetized ratsa (normal sarcomere length; 35-36°C) | ||||
| 1. Soleus muscle (slow-twitch units) | 34 | 38 ± 4 | 57 ± 8 | — |
| 2. EDL muscle (fast-twitch units) | 48 | 11 ± 1 | 11 ± 2 | — |
| B. Singly dissected mouse fibersb (normal sarcomere length; 20-21°C) | ||||
| 1. Soleus fibers (slow-twitch) | 12 | 96 ± 7.5 | 130 ± 14 | — |
| 2. EDL fibers (fast-twitch) | 11 | 33 ± 6.1 | 62 ± 12 | — |
| C. Small bundles of mouse fibersc(long sarcomere length; 16°C) | ||||
| 1. Soleus fibers (slow-twitch) | 14 | 173 ± 9 | 708 ± 73 | 843 ± 80 |
| 2. EDL fibers (fast-twitch) | 16 | 52 ± 2 | 162 ± 11 | 197 ± 12 |
n is the number of motor units (A) or experiments (B and C). Time of peak is the time between the external stimulus and the peak of the twitch tension response, half-relaxation time is the time between the peak and half-decay of tension, and FDHM is the time between the half-rise and half-decay of tension. In A and B, the sarcomere length was set to give the maximum tension response. In C, average sarcomere length was 3.7 µm (range, 3.3–3.9 µm).
Close, 1967.
González et al., 2000.
Hollingworth et al., 1996, 2008, 2012; and Baylor and Hollingworth, 2003.