Back extension vs Machine back extension
FR : Back extension ↔ Extension lombaire machine
Swapping Back extension (Machine) for Machine back extension (Machine) retains 100% overlap; expect externally braced cam track. Compare exact 17-muscle fractional recruitment before swapping equipment mid-session.
Weighted Muscle Overlap
100%
Sum of min(coef A, coef B)
Primary Equipment
Machine → Machine
Same rep/load measurement family
Load Transfer Protocol
Target RPE 7.5–8.5
Never assume 1:1 kg across leverages
Side-by-Side 17-Muscle Recruitment Delta
How primary mover (1.0× set) and synergist (0.5× set) allocation changes when swapping Back extension for Machine back extension.
| Muscle Group | Back extension | Machine back extension | Leverage Shift |
|---|---|---|---|
| Hamstrings | Primary (45%) | Primary (45%) | Matched |
| Glutes (Gluteus Maximus / Medius) | Primary (35%) | Primary (35%) | Matched |
| Lower Back (Spinal Erectors) | Secondary (20%) | Secondary (20%) | Matched |
Load & Volume Conversion: Back extension → Machine back extension
Worked weight heuristic: a 115 kg set on Back extension (Machine) maps roughly to 115 kg on Machine back extension (Machine; 5 kg jumps, curve: cam-matched resistance across sticking points). Calibrate set 1 at RPE 8 so e1RM history for Back extension remains unskewed. Zero anatomical muscles are dropped between Back extension and Machine back extension; 1:1 weekly set volume carries straight across.
Supporting Sports-Science Literature
| Study Title | Lead Author & Year | Verified Link |
|---|---|---|
| Influence of joint position on electromyographic and torque generation during maximal voluntary isometric contractions of the hamstrings and gluteus maximus muscles. | Worrell (2001) | PubMed 11767248 ↗ |
| Progressive overload without progressing load? The effects of load or repetition progression on muscular adaptations. | Plotkin (2022) | PubMed 36199287 ↗ |
| Muscle metabolism during intense, heavy-resistance exercise. | Tesch (1986) | PubMed 3758035 ↗ |