Low index
Bilateral Builder
The parts beat the pair by a wide margin. The limbs are individually capable but do not fire together. Train bilateral strength, power and two-leg takeoff timing.
Free coach's guide
Bilateral Deficit
Test one leg, then the other, then both. Add the two singles. The two-leg number almost always comes in lower, and that gap is information rather than error. Testing only the bilateral jump hides the limb that fails first.
The gap, on one athlete
The parts beat the pair.
This is not a measurement error and it is not the athlete dogging it. It is a real, repeatable phenomenon with a name, and once you have seen it on a few athletes you cannot unsee it.
Left + Right29″
>
Two-Leg Jump22″
Bilateral index = two-leg jump ÷ (left + right) × 100. Neither leg alone beats the two-leg jump. Only their sum does, and this athlete lands at 76%, right in the typical range. Illustrative example, not normative data.
The standards
What the index should be.
Male in blue, female in pink. Typical is highlighted. These are Plyomat testing standards drawn from trained athletes ages 11 to 19, and they are protocol dependent, which the guide explains in full.
| Low | Below avg | Typical | Above avg | High | |
|---|---|---|---|---|---|
| Male | 68% | 72% | 78% | 83% | 88% |
| Female | 59% | 62% | 74% | 80% | 95% |
Reading the number
The lower the index, the stronger each leg.
This is the part that trips most people up, so it is worth seeing directly. Hold the two-leg jump at 22 inches and change nothing but the single legs. As each leg gets stronger, the index falls.
| Each leg | Left + right | Index | Single legs |
|---|---|---|---|
| 11.0″ | 22.0″ | 100% | Weakesteach leg only half the pair |
| 12.5″ | 25.0″ | 88% | Weak |
| 14.1″ | 28.2″ | 78% | Averagetypical male |
| 14.9″ | 29.7″ | 74% | Averagetypical female |
| 16.9″ | 33.8″ | 65% | Strongesteach leg nearly matches the pair |
Which is why the lower female typical is not a sign of weaker legs. Female youth athletes carry the larger deficit, not the weaker single legs. Their legs sit closer to what the pair can do, which points at two-leg takeoff timing rather than per-limb strength. A population tendency, not a diagnosis.
Reading the athlete
Three athletes, three plans.
Typical
Balanced Base
The deficit sits in the normal range and the pair and parts are proportionate. No corrective priority. Keep a mixed programme and train toward the sport.
High index
Single-Leg Builder
The two-leg jump nearly matches the summed singles, so the pair is carrying the athlete. Build per-limb strength and screen closely for asymmetry.
The 13-page coach's guide
Everything above, plus the parts that do not fit on a chart: the testing protocol, the mechanics, the research, and what to program for each athlete type.
- The standards by sex, and how the group actually distributes
- The testing protocol, including the free-leg rule that changes the number
- Why transfer depends on the metric, not a 50% rule of thumb
- Single-leg versus double-leg mechanics, with the research
- What to program for each of the three athlete types
- Full reference list, peer reviewed
01 The deficit, measured
02 What one leg is actually worth
03 The standards and the distribution
04 Testing protocol
05 Arms free or hands on hips
06 Single leg vs double leg mechanics
07 The three athlete types
08 Which test tells you more
09 Training considerations
10 What the field says
11 Summary and references
Questions
Bilateral deficit FAQ
What is the bilateral deficit?
It is the difference between what an athlete produces with both limbs together and what those same limbs produce one at a time, added up. When both legs fire at once, the combined output usually comes in under the sum of each leg working alone.
What is a normal bilateral index?
On our protocol, around 78% for male athletes and 74% for female athletes. The number is protocol dependent, so compare an athlete to their own history under one fixed protocol rather than to a published figure collected under different rules.
Is this the same as asymmetry?
No. The deficit compares both legs together against the sum of each alone. Asymmetry compares left against right. An athlete can be close to balanced left to right and still show a real deficit, so keep them in separate columns.
Does the testing protocol change the result?
Substantially. Letting the free leg swing adds real height to a single-leg jump. A 2026 force-plate study that pinned the non-stance limb reported a very different ratio. Pick one protocol, write it down, and hold it across retests. The guide covers this in full.
Measure the leg that fails first.
Plyomat times every contact to a thousandth of a second and computes the bilateral index for you, on the floor, rep by rep.
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