Table 2.
Activation threshold (pCa10), Ca2 + sensitivity (pCa50) and pCa-force slope (Hill coefficient, h) of myosin heavy chain (MHC) I, I/IIA, IIA and IIAX single muscle fibers from young and older adults.
| n | N | pCa10 | pCa50 | h | ||||
|---|---|---|---|---|---|---|---|---|
| MHC | Y/O | Y/O | Y | O | Y | O | Y | O |
| I | 45/50 | 11/10 | 6.01 ± 0.02 | 5.90 ± 0.02 ** | 5.73 ± 0.01 a | 5.59 ± 0.02 ** a | 3.49 ± 0.13 a | 3.46 ± 0.13a |
| I/IIA | 7/5 | 3/5 | 5.96 ± 0.02 | 5.88 ± 0.03 | 5.71 ± 0.02 ab | 5.59 ± 0.02 ** a | 3.82 ± 0.10 ab | 3.43 ± 0.27a |
| IIA | 42/38 | 11/10 | 6.01 ± 0.01 | 5.90 ± 0.01 ** | 5.76 ± 0.01 bc | 5.69 ± 0.01 ** b | 4.09 ± 0.15 b | 4.65 ± 0.16 * b |
| IIAX | 7/4 | 5/2 | 6.03 ± 0.02 | 5.92 ± 0.03 * | 5.78 ± 0.02 c | 5.73 ± 0.04 b | 3.55 ± 0.12 ab | 5.47 ± 0.13 ** b |
Data are presented as mean ± SE.
Values correspond to the pCa-normalized specific force curves.
n indicates the number of fibers assessed and N indicates the number of subjects.
Y = young; O = older.
Significantly different from Young group at * = p < 0.05; ** = p < 0.01.
Where fiber type effects were observed, different letters identify pairwise differences (p < 0.05) between fiber types within an age group.