Table 1.
Measurements included in the study
| Measurement | Abbreviation | Definition |
|---|---|---|
| Thoraco-lumbar spine length (mm) | TLS | The maximum distance between the tips of the spinous processes of T1 and the last lumbar vertebra |
| Proximal tendon length (mm) | TP | Measured as the maximum distance between the proximal tendon attachment to bone and the proximal tendon attachment to the myotendinous junction (Fig.1) |
| Distal tendon length (mm) | TD | Measured as the maximum distance between the distal tendon attachment to bone and the distal tendon attachment to the myotendinous junction (Fig.1) |
| Total tendon length | TL | Σ (TP + TD) |
| Tendon-to-fiber length ratio | – | TL/(NLf + TL) |
| Muscle belly length (mm) | Lb | Measured as the maximum length along the long axis of each muscle segment |
| Muscle weight (g) | MWt | Wet weights of each thoracic and lumbar segment of iliocostalis, longissimus and multifidus |
| Normalized fiber length (mm) | NLf | Average linear distance between the proximal and distal myotendinous junctions of a fasciculus, normalized by standard sarcomere length |
| Surface pinnation angle (°) | θ | Measured as the surface angle of a fiber relative to the muscle’s line of action, divided by NLf (Fig.2) |
| Physiological cross-sectional area (cm2) | PCSA | Muscle mass × cos (pinnation angle)/NLf × 1.0564 (gm/cm3) |
| Potential maximum whole-muscle excursion | h | NLf [cos θ – √(cos2 θ + n2 – 1)] |