Table 3. Stretch activation kinetics and maximal isometric tension of MHC-based fibre types from Xenopus iliofibularis muscle.
| Type X1 (n = 56) | Type X1 + 2 (n = 19) | Type X2 (n = 16) | Type X2 + 3 (n = 17) | Type X3 (n = 16) | Type X3 + 4 (n = 7) | Type X4 (n = 17) | Type XT + 1 (n = 27) | |
|---|---|---|---|---|---|---|---|---|
| t2 (ms) | 20.4 ± 5.4 | 33.8 ± 14.6 | 38.9 ± 9.6 | 65.8 ± 18.9 | 77.0 ± 15.3 | 275.0 ± 62.6 | 292.5 ± 106.5 | 871.2 ± 265.9 |
| (26.5) | (43.2) | (23.7) | (28.7) | (19.9) | (22.8) | (36.4) | (30.5) | |
| t3 (ms) | 57.8 ± 10.8 | 87.0 ± 21.3 | 108.8 ± 18.1 | 195.6 ± 58.1 | 224.2 ± 47.3 | 733.6 ± 115.1 | 797.1 ± 96.8 | 2868.5 ± 999.2 |
| (18.7) | (24.5) | (16.6) | (29.7) | (21.1) | (15.7) | (12.1) | (34.7) | |
| T0 | 411 ± 61 | 377 ± 62 | 358 ± 32 | 362 ± 44 | 360 ± 41 | 343 ± 36 | 325 ± 32 | 261 ± 23 |
| (mN mm−2) | (14.8) | (16.4) | (8.9) | (12.2) | (11.4) | (10.5) | (9.8) | (8.8) |
T0, maximal isometric tension. The results are given as means ± s.d.; the number in parentheses represents the coefficient of variation. Maximal isometric tension was calculated by relating maximal Ca2+-activated force to the cross-sectional area of the fibres determined in relaxation solution. t2, time from the beginning of the stretch to the onset of delayed force increase; t3, time from the beginning of the stretch to the peak of the delayed force increase. X1 versus all types, P < 0.01, and XT + 1 versus all types, P < 0.01 (ANOVA with Student-Neuman-Keuls post hoc test); for t2: within all types, P < 0.01, except X2 + 3 versus X3 and X3 + 4 versus X4, P > 0.1 (two-tailed Student's t test); for t3: within all types, P < 0.01, except X2 + 3 versus X3 and X3 + 4 versus X4, P > 0.2 (two-tailed Student's t test).