Muscle Activation
Every exercise in HyperIron has percentage-based muscle activation values that determine how sets count toward your per-muscle volume.
How it works
Each exercise defines which muscles it targets and how much:
| Exercise | Chest | Triceps | Front Delts |
|---|---|---|---|
| Bench Press | 100% | 60% | 40% |
| Incline DB Press | 90% | 50% | 60% |
| Tricep Pushdown | 0% | 100% | 0% |
When you log a set, HyperIron applies these percentages to calculate effective sets per muscle:
4 sets of Bench Press =
4.0 effective chest sets (4 × 100%)
2.4 effective triceps sets (4 × 60%)
1.6 effective front delt sets (4 × 40%)
Why percentages instead of "primary/secondary"?
A simple primary/secondary label doesn't capture the real differences between exercises:
- Bench press hits triceps significantly (~60%), while a chest fly barely involves them (~10%)
- Both would be labeled "primary: chest, secondary: triceps" but their triceps contribution is vastly different
Percentage-based tracking gives you accurate volume numbers per muscle group, so you can see exactly how much stimulus each muscle is getting across your program.
Where muscle volume appears
Calendar & Stats
The Calendar shows effective sets per muscle for any day, week, or month. You can see exactly how much chest, back, quads, etc. you're training.
Planned vs Actual
When you have an active program, HyperIron shows your planned volume (from target sets × muscle percentages) alongside actual volume (from logged sets). This tells you if you're on track.
Example: Full push day
| Exercise | Sets | Chest | Triceps | Front Delts |
|---|---|---|---|---|
| Bench Press (100/60/40) | 4 | 4.0 | 2.4 | 1.6 |
| Incline DB Press (90/50/60) | 3 | 2.7 | 1.5 | 1.8 |
| Cable Fly (100/0/10) | 3 | 3.0 | 0 | 0.3 |
| Tricep Pushdown (0/100/0) | 3 | 0 | 3.0 | 0 |
| Lateral Raise (0/0/100) | 3 | 0 | 0 | 3.0 |
| Day Total | 16 | 9.7 | 6.9 | 6.7 |
Even though you did 16 total sets, each muscle received a different effective volume. Chest got 9.7 effective sets, triceps got 6.9, and front delts got 6.7.
Adjusting activations
If you disagree with the default activations for a library exercise — say you feel your bench press is more triceps-dominant due to your grip width — you can create a custom exercise with adjusted percentages.