Table 2.
Latissimus Dorsi Muscle Morphological Characteristics and In Vitro Isometric Force Parameters
| |
|
1 month postinjury |
2 months postinjury |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Uninjured | NR | TEMR-1SP | TEMR-1SPD | TEMR-2SPD | NR | TEMR-1SP | TEMR-1SPD | TEMR-2SPD | Analysis of variance (p) | |
| Sample size | 22 | 5 | 6 | 7 | 8 | 4 | 6 | 7 | 8 | |
| Muscle characteristics | ||||||||||
| Wet weight (mg) | 90.3±3.7 | 102.4±11.8 | 166.1±10.1a,b | 154.8±14.1a,b | 162.0±14.6a,b | 86.6±11.5 | 152.0±14.3a,b | 151.6±23.5a,b | 152.8±17.0a,b | <0.001 |
| Lo (mm) | 34.9±0.8 | 33.3±1.7 | 33.8±1.4 | 36.2±1.5 | 34.9±1.4 | 32.6±0.8 | 31.0±2.2 | 31.9±1.3 | 32.1±0.6 | 0.099 |
| Isometric force parameters | ||||||||||
| Ptmeas, mN | 46.8±3.5 | 16.1±2.6a | 31.6±2.7a,b | 19.8±3.2a | 24.1±5.4a | 10.6±2.4a | 21.9±4.9a | 20.0±2.9a | 39.0±4.3b,e | <0.001 |
| P80Hzmeas, mN | 212.2±8.9 | 61.0±8.3a | 125.5±9.6a,b | 95.6±13.2a | 138.8±14.6a,b | 54.2±9.9a | 102.0±16.4a,b | 104.9±10.7a,b | 135.5±17.1a,b | <0.001 |
| Pomeas, mN | 374.4±12.1 | 93.1±17.3a | 196.9±13.0a,b | 144.4±21.9a | 203.2±19.7a,b,d | 123.3±19.1a,e | 197.2±24.0a,b | 200.1±16.3a,b,e | 259.3±19.3a,b,c,d,e | <0.001 |
| EC50, Hz | 78.7±1.6 | 68.7±4.4a | 76.2±3.6 | 68.4±4.4a | 68.5±3.6a | 87.0±3.3e | 81.9±2.3 | 81.8±1.5e | 85.3±4.2e | <0.001 |
| n Coefficient | 4.1±0.2 | 3.6±0.2 | 4.6±0.6 | 3.6±0.4 | 4.4±0.5 | 4.4±0.3 | 6.1±1.4 | 4.2±0.5 | 4.5±0.3 | 0.127 |
| Specific Pomeas, N cm2 | 15.6±0.7 | 3.2±0.5a | 4.2±0.2a | 3.4±0.7a | 4.9±0.7a | 5.1±1.0a | 4.5±0.8a | 4.7±0.3a | 6.4±1.0a | <0.001 |
| Caffeine, mN | 112.5±6.3 | – | – | – | – | 41.3±3.7a | 83.7±10.8a,b | 67.3±5.4a,b | 86.6±5.5a,b | <0.001 |
Values are mean±standard error. LD muscle sample sizes are for measured electrical stimulation force parameters. Lo is the optimal muscle length coinciding with peak twitch force. Measured isometric twitch (Pt), titanic force at 80 Hz (P80Hz), and peak titanic (Po) force were elicted using direct electrical stimulation (0.2 ms pulse width; 30 V). EC50 is the stimulation frequency at which half of the rise in amplitude of force occurred. The n coefficient is the slope of the linear portion of the force–frequency curves depicted in Fig. 3. Absolute Po was normalized by physiological cross-sectional area to determine specific force. Following force–frequency testing a subset of muscles performed an isometric caffeine (50 mM) contracture test. Denotations indicate statistically significantly different group means (p<0.05): aUninjured; bnot repaired at same postinjury time; cTEMR-1SP at same postinjury time; dTEMR-1SPD at same postinjury time; e1 month for same experimental group.
LD, latissimus dorsi.