Table 2.
ktr and VO at maximal and submaximal Ca2+ levels
| Young | Old | P Value | Men | Women | P Value | |
|---|---|---|---|---|---|---|
| Slow MHC I | ||||||
| n (N) | 83 (15) | 155 (19) | 135 (20) | 103 (14) | ||
| ktr pCa 4.5, /s | 2.12 ± 0.37 | 2.09 ± 0.41 | 0.564 | 2.06 ± 0.41 | 2.15 ± 0.38 | 0.193 |
| ktr pCa50, /s | 0.58 ± 0.17 | 0.55 ± 0.15 | 0.793 | 0.57 ± 0.16 | 0.56 ± 0.15 | 0.862 |
| % Change | −72 ± 9 | −73 ± 9 | 0.803 | −72 ± 11 | −74 ± 6 | 0.257 |
| n (N) | 73 (14) | 131 (19) | 116 (19) | 88 (14) | ||
| VO pCa 4.5, fl/s | 1.14 ± 0.31 | 1.07 ± 0.29 | 0.377 | 1.12 ± 0.35 | 1.06 ± 0.21 | 0.368 |
| VO pCa50, fl/s | 0.45 ± 0.18 | 0.38 ± 0.14 | 0.138 | 0.41 ± 0.17 | 0.41 ± 0.14 | 0.578 |
| % Change | −61 ± 9 | −64 ± 8 | 0.240 | −64 ± 9 | −62 ± 8 | 0.516 |
| Fast MHC IIa | ||||||
| n (N) | 80 (17) | 131 (18) | 113 (20) | 98 (15) | ||
| ktr pCa 4.5, /s | 6.59 ± 1.35 | 7.04 ± 1.57 | 0.252 | 6.69 ± 1.54 | 7.07 ± 1.44 | 0.250 |
| ktr pCa50, /s | 1.60 ± 0.45 | 1.66 ± 0.51 | 0.622 | 1.69 ± 0.55 | 1.59 ± 0.40 | 0.199 |
| % Change | −75 ± 7 | −76 ± 7 | 0.535 | −74 ± 8 | −77 ± 6 | 0.033 |
| n (N) | 58 (15) | 91 (18) | 81 (19) | 68 (14) | ||
| VO pCa 4.5, fl/s | 3.20 ± 1.07 | 3.38 ± 1.09 | 0.563 | 3.46 ± 1.11 | 3.13 ± 1.02 | 0.235 |
| VO pCa50, fl/s | 0.97 ± 0.58 | 0.97 ± 0.44 | 0.839 | 1.03 ± 0.55 | 0.89 ± 0.41 | 0.354 |
| % Change | −72 ± 9 | −71 ± 9 | 0.923 | −71 ± 10 | −72 ± 8 | 0.736 |
Data are presented as means ± SD. The number of fibers (n) and number of subjects (N) are reported for each group and fiber type. Sexes are combined when comparing age groups, and ages are combined when comparing between sexes. ktr, rate of force development; VO, unloaded shortening velocity. Boldfaced P values highlight statistical significance at P < 0.05.