Table 2.
Cross-sectional area (CSA), specific tension (ST), stiffness and maximum velocity of unloaded shortening (V0) in skinned single muscle fibres expressing different MyHC isoforms in HRT using and non-using co-twins
| Type I | Type I/IIa | Type IIa | Type IIax | Type IIx | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| HRT non-users | HRT users | HRT non-users | HRT users | HRT non-users | HRT users | HRT non-users | HRT users | HRT non-users | HRT users | |
| (N= 6) | (N= 6) | (N= 4) | (N= 6) | (N= 6) | (N= 6) | (N= 4) | (N= 6) | (N= 2) | (N= 1) | |
| CSA (μm2) | 2550 ± 110 | 2460 ± 140 | 2630 ± 450 | 1860 ± 190 | 2240 ± 170 | 2260 ± 130 | 1850 ± 120 | 1560 ± 280 | 2050 ± 100 | 1320 |
| (n= 97) | (n= 79) | (n= 13) | (n= 16) | (n= 39) | (n= 50) | (n= 10) | (n= 17) | (n= 3) | (n= 2) | |
| ST (N cm−2) | 28.5 ± 2 | 36.4 ± 2.7* | 30.1 ± 5.3 | 39.1 ± 4 | 31.2 ± 2.2 | 38.2 ± 1.3* | 29.3 ± 3 | 31.8 ± 4.8 | 23 ± 2.3 | 30.8 |
| (n= 71) | (n= 48) | (n= 9) | (n= 11) | (n= 25) | (n= 39) | (n= 9) | (n= 15) | (n= 3) | (n= 2) | |
| Stiffness (N cm−2) | 2550 ± 40 | 2870 ± 170 | 2450 ± 900 | 2880 ± 460 | 2140 ± 130 | 2500 ± 70* | 2200 ± 270 | 2050 ± 230 | ||
| (n= 71) | (n= 48) | (n= 7) | (n= 8) | (n= 20) | (n= 32) | (n= 8) | (n= 6) | |||
| V0 (ML[LJ29] s−1) | 1 ± 0.1 | 0.90 ± 0.1 | 1.6 ± 0.6 | 1.8 ± 0.3 | 2.1 ± 0.3 | 2.3 ± 0.2 | 2.5 ± 0.2 | 2.7 ± 0.1 | 2.3 ± 0.1 | 2.5 |
| (n= 59) | (n= 46) | (n= 8) | (n= 10) | (n= 20) | (n= 32) | (n= 7) | (n= 12) | (n= 3) | (n= 2) | |
*
Significant difference from non-user group (P < 0.05) according to paired t test. Values are mean ± SEM. Statistical analysis has been restricted to muscle fibres expressing type I or type IIa MyHC isoform, because of small sample size in fibres expressing other isoforms or combinations of isoforms. (N= number of subjects; n= number of fibres).